导电水凝胶

Myocardial ischemia‐reperfusion injury (MIRI) is a leading cause of complications and high mortality associated with acute myocardial infarction. Injectable hydrogel emerges as a promising biomaterial for myocardial repair due to their ability to mimic the mechanical and electrophysiological properties of heart tissue. In this study, an injectable conductive hydrogel is developed that responds to the weakly acidic microenvironment of ischemic injury, enabling the intelligent release of metformin and exosomes to enhance cardiac repair following MIRI. This multifunctional hydrogel demonstrates self‐healing properties, shear‐thinning injectability, electrical conductivity, and an elastic modulus comparable to natural myocardium, alongside excellent biocompatibility. At the cellular level, the hydrogel system exhibits significant antioxidant, anti‐apoptotic, improvement of electrophysiological characteristics, mitochondrial protection and angiogenic effects, with transcriptome sequencing revealing the effective activation of the PI3K/AKT, VEGF, and AMPK signaling pathways. In vivo studies further confirm that the hydrogel treatment reduces infarct size, cardiac fibrosis and incidence of arrhythmia, while improving ventricular ejection fraction and facilitating the restoration of cardiac function after MIRI. In conclusion, an injectable pH‐responsive conductive hydrogel is presented that enables the intelligent delivery of metformin and exosomes, offering a promising and novel therapeutic approach for enhancing cardiac repair and treating MIRI.

Functional conductive hydrogels with customizable shapes and structures facilitate seamless integration between biological and electronic interfaces. However, the current capacity to adjust the properties of conductive gels is constrained, frequently requiring complex post‐processing methods to ensure gel formation and achieve a balance between mechanical and electrical properties. This significantly limits the flexibility in fabricating gel‐based sensing interfaces. In this study, a 3D‐printable, photo‐crosslinked, carbon‐based conductive nanocomposite hydrogel (FPCH) comprising poly(ether) F127 diacrylate (F127DA), Single‐Walled carbon nanotubes (SWCNT), and poly(3,4‐ethylenedioxythiophene)‐polystyrene sulfonic acid (PEDOT:PSS) is developed. By optimizing the proportion of conductive fillers, the hydrogel achieves tunable modulus (as low as 90 kPa), high stretchability (up to 520% strain), conductivity (440 S m−1), and 3D printability. The conductive gel can be rapidly cured on demand via UV‐induced crosslinking and demonstrates good biocompatibility. It functions not only as a “skin electronic tattoo” for multimodal applications, such as strain and humidity sensing and thermal compensation but also effectively stimulates the sciatic nerve in vivo at low voltage. Furthermore, electrodes fabricated using 3D printing technology offer conformal contact with brain tissue and enable real‐time monitoring of electrophysiological signals, providing a versatile bioelectronic sensing interface for multi‐modal applications adaptable for both the in vivo and in vitro environments.

Conductive hydrogels as promising candidate materials for flexible strain sensors have gained considerable attentions. However, it is still a great challenge to construct hydrogel with multifunctional performance via natural polymer. Herein, a novel multifunctional conductive hydrogel based on methylcellulose and cellulose nanocrystal was prepared via a facile and low-cost strategy. Methylcellulose (MC) was introduced to not only guarantee the stability of tannic acid coated cellulose nanocrystal (TA@CNCs) in LiCl solution, but also improve anti-freezing ability. The obtained hydrogel exhibited high transparency (98 % at 800 nm), good stretchability (663.1 %), low temperature tolerance (-23.9 °C), superior conductivity (2.89 S/m) and excellent UV shielding behavior. Flexible strain sensor assembled by the prepared hydrogels can be used to detect human body motions include subtle and large motions, and exhibited good sensitivity and stability over a wide temperature range. Multiple flexible hydrogels can also be assembled into a 3D sensor array to detect the distribution and magnitude of spatial pressure. Therefore, the hydrogels prepared via natural polymers will have broad application prospects in wearable devices, electronic skin and multifunctional sensor components.

Wounds at joints are difficult to treat and tend to recover more slowly due to the frequent motions. When using traditional hydrogel dressings, they are easy to crack and undergo bacterial infection, difficult to match and monitor the irregular wounds. Integrating multiple functions within a hydrogel dressing to achieve intelligent wound monitoring and healing remains a significant challenge. In this research, a multifunctional hydrogel is developed based on polysaccharide biopolymer, poly(vinyl alcohol), and hydroxylated graphene through dynamic borate ester bonding and supramolecular interaction. The prepared hydrogel not only exhibits rapid self‐healing (within 60 s), injectable, conductive and motion monitoring properties, but also realizes in situ bacterial sensing and killing functions. It shows excellent bacterial sensitivity (within 15 min) and killing ability via the changes of electrical signals and photothermal therapy, avoiding the emergence of drug‐resistant bacteria. In vivo experiments prove that the hydrogel can promote wound healing effectively. In addition, it displays great electromechanical performance to achieve real‐time monitoring and prevent re‐tearing of the wound at human joints. The injectable pH‐responsive hydrogel with good biocompatibility demonstrates considerable potential as multifunctional bioelectronic dressing for the detection, treatment, management, and healing of infected joint wounds.

Advanced conductive hydrogels demonstrate substantial potential for wearable devices. Nevertheless, the transformative advance in soft electronics raises harsh requirements on the hydrogel candidates, such as rapid and on‐site fabrication, mechanical flexibility, high sensitivity, and wide use temperature. Here, this problem is overcome by incorporating a dual catalytic system based on lignin‐modified MXene‐Fe3+ into commercial hydrogels. This system 1) can form a composite hydrogel in a time scale of min at ambient condition without the supply of external energy, 2) incorporates multiple enhanced strategies into polymer chains, and 3) constructs well‐organized hybrid conductive network. The fabricated hydrogel displays an improved and balanced overall performance, including high ductility (2139%), moderate electrical conductivity, and strong temperature tolerance (−70–50 °C). Combined with the great merits of above performance, the hydrogel‐based sensor with good sensing (maximum GF: 2.8), stable repeatability (200% for 200 cycles), and wide work window of 0%–947%, thereby disclosing promising application in physiological movements, such as motion recognition and breathing state detection. Sensationally, even in complex or harsh surroundings, the sensors also produce stable and reliable signal output. Together, the strategy provides a new mentality of designing hydrogel materials for booming and advanced wearable electronics.

Integrating superior mechanical performance, anisotropic conductivity, and biocompatibility into conductive hydrogels as all‐in‐one human‐machine interaction device remains challenging. Herein, by mimicking the anisotropic structures of human muscles, a robust anisotropic conductive hydrogel is developed by initially aligning polyvinyl alcohol with polypyrrole decorated cellulose nanofibrils to form an anisotropically oriented polymer networks, followed by post‐crosslinking with tannic acid (TA). Introducing TA into hydrogel network permanently secures its hierarchically anisotropic structure through multiple hydrogen bonds, thus endowing the hydrogel with exceptional mechanical properties (tensile strength of 11.41 MPa, toughness of 12.44 MJ m−3), anisotropic adhesive property, and direction‐dependent conductivity. With these attributes, a hydrogel strain sensor with excellent multidirectional sensitivity is developed, enabling stable monitoring of multi‐degrees of freedom joint movements in the human body and facilitating the control of a multiaxial virtual robot manipulator. Moreover, the in vitro/vivo tests demonstrate exceptional biocompatibility and anti‐biofouling properties of the as‐prepared hydrogel sensor, maintaining stable electronic response signals for over 14 days after successful implantation into the Achilles tendon of mice. Overall, this study presents a promising approach for designing conductive hydrogels with superior mechanical properties and anisotropic functionality for emerging applications in both in vitro and in vivo human‐machine interface materials.

Electroceuticals, through the selective modulation of peripheral nerves near target organs, are promising for treating refractory diseases. However, the small sizes and the delicate nature of these nerves present challenges in simplifying the fixation and stabilizing the electrical-coupling interface for neural electrodes. Herein, we construct a robust neural interface for fine peripheral nerves using an injectable bio-adhesive hydrogel bioelectronics. By incorporating a multifunctional molecular regulator during network formation, we optimize the injectability and conductivity of the hydrogel through fine-tuning reaction kinetics and multi-scale interactions within the conductive network. Meanwhile, the mechanical and electrical stability of the hydrogel is achieved without compromising its injectability. Minimal tissue damage along with low and stable impedance of the injectable neural interface enables chronic vagus neuromodulation for myocardial infarction therapy in the male rat model. Our highly-stable, injectable, conductive hydrogel bioelectronics are readily available to target challenging anatomical locations, paving the way for future precision bioelectronic medicine. Electroceuticals could treat refractory diseases by the selective modulation of peripheral nerves but their utility is hindered by the small sizes and the delicate nature of the nerves. Here, the authors address these issues by developing an injectable, stable, and conductive hydrogel that allows a safer and more effective treatment during chronic neuromodulation of delicate peripheral nerves.

Pursuing high-performance conductive hydrogels is still hot topic in development of advanced flexible wearable devices. Herein, a tough, self-healing, adhesive double network (DN) conductive hydrogel (named as OSA-(Gelatin/PAM)-Ca, O-(G/P)-Ca) was prepared by bridging gelatin and polyacrylamide network with functionalized polysaccharide (oxidized sodium alginate, OSA) through Schiff base reaction. Thanks to the presence of multiple interactions (Schiff base bond, hydrogen bond, and metal coordination) within the network, the prepared hydrogel showed outstanding mechanical properties (tensile strain of 2800 % and stress of 630 kPa), high conductivity (0.72 S/m), repeatable adhesion performance and excellent self-healing ability (83.6 %/79.0 % of the original tensile strain/stress after self-healing). Moreover, the hydrogel-based sensor exhibited high strain sensitivity (GF = 3.66) and fast response time (<0.5 s), which can be used to monitor a wide range of human physiological signals. Based on this, excellent compression sensitivity (GF = 0.41 kPa-1 in the range of 90-120 kPa), a three-dimensional (3D) array of flexible sensor was designed to monitor the intensity of pressure and spatial force distribution. In addition, a gel-based wearable sensor was accurately classified and recognized ten types of gestures, achieving an accuracy rate of >96.33 % both before and after self-healing under three machine learning models (the decision tree, SVM, and KNN). This paper provides a simple method to prepare tough and self-healing conductive hydrogel as flexible multifunctional sensor devices for versatile applications in fields such as healthcare monitoring, human-computer interaction, and artificial intelligence.

As a soft material with biocompatibility and stimulation response, ionic conductive hydrogel‐based wearable strain sensors show great potential across a wide spectrum of engineering disciplines, but their mechanical toughness is limited in practical applications. In this study, freeze‐thawing techniques were utilized to fabricate double‐network hydrogels of poly(vinyl alcohol)/polyacrylamide (PVA/PAM) with both covalent and physical cross‐linking networks. These double‐network hydrogels demonstrate excellent mechanical performance, with an elongation at break of 2253% and tensile strength of 268.2 kPa. Simultaneously, they also display a high sensitivity (Gage factor, GF = 2.32 at 0%–200% strain), achieve a rapid response time of 368 ms without the addition of extra conductive fillers or ions, stable signal transmission even after multiple cycles, and fast response to human motion detection.

Hydrogel‐based electronics have inherent similarities to biological tissues and hold potential for wearable applications. However, low conductivity, poor stretchability, nonpersonalizability, and uncontrollable dehydration during use limit their further development. In this study, projection stereolithography 3D printing high‐conductive hydrogel for flexible passive wireless sensing is reported. The prepared photocurable silver‐based hydrogel is rapidly planarized into antenna shapes on substrates using surface projection stereolithography. After partial dehydration, silver flakes within the circuits form sufficient conductive pathways to achieve high conductivity (387 S cm−1). By sealing the circuits to prevent further dehydration, the resistance remains stable when tensile strain is less than 100% for at least 30 days. Besides, the sealing materials provide versatile functionalities, such as stretchability and shape memory property. Customized flexible radio frequency identification tags are fabricated by integrating with commercial chips to complete the accurate recognition of eye movement, realizing passive wireless sensing.

The intricate muscle arrangement structure endows the biological tissues with unique mechanical properties. Inspired by that, a mechanically robust and multifunctional anisotropic Polyacrylamide/Sodium alginate/Zirconium ion/Carbon dots (PAM/SA/Zr4+/CDs, PSZC) hydrogel is developed through the synergistic effect of mechanical‐assisted stretching, Zr4+ metal‐coordination and CDs embedding. The resulting hydrogel exhibited an impressive tensile strength of 2.56 MPa and exceptional toughness of 10.10 MJ m−3 along the stretching direction, attributing to the oriented alignment of PAM and SA molecular chains induced by mechanical‐assisted stretching and metal‐coordination. The dense network structure endowed the PSZC hydrogel with excellent anti‐swelling performance, achieving a swelling ratio of only 1.7% after being stored in water for 30 days. The presence of Zr4+ conferred remarkable electrical conductivity of 2.15 S m−1 to the PSZC hydrogel. Furthermore, the integration of carbon dots imparted the PSZC hydrogel fluorescence properties, rendering it visual sensing capabilities. Overall, a straightforward strategy is proposed for fabricating a mechanically robust and multifunctional hydrogel suitable for underwater sensing and visual sensing, offering valuable insights for the development of high‐performance underwater sensors.

Conductive hydrogels with high performance and frost resistance are essential for flexible electronics, electronic skin, and soft robots. Nonetheless, the preparation of hydrogel-based flexible strain sensors with rapid response, wide strain detection range, and high sensitivity remains a considerable challenge. Furthermore, the inevitable freezing and evaporation of water in sub-zero temperatures and dry environments lead to the loss of flexibility and conductivity in hydrogels, which seriously limits their practical application. In this work, ionic liquids (ILs) and MXene are introduced into gelatin/polyacrylamide (PAM) precursor solution, and a PAM/gelatin/ILs/MXene/glycerol (PGIMG) hydrogel-based flexible strain sensor with MXene co-ILs ion-electron composite conductive network is prepared by combining the electrohydrodynamic (EHD) printing method and in-situ photopolymerization. The introduction of ILs provides an ionic conductive channel for the hydrogel. The introduction of MXene nanosheets forms an interpenetrating network with gelatin and PAM, which not only provides a conductive channel, but also improves the mechanical and sensing properties of the hydrogel-based flexible strain sensor. The prepared PGIMG hydrogel with the MXene co-ILs ion-electron composite conductive network demonstrates a tensile strength of 0.21 MPa at 602.82 % strain, the conductivity of 1.636 × 10-3 S/cm, high sensitivity (Gauge Factor, GF = 4.17), a wide strain detection range (1-600 %), and the response/recovery times (73 ms and 74 ms). In addition, glycerol endows the hydrogel with excellent freezing (-60 °C) and water retention properties. The application of the hydrogel-based flexible strain sensor in the field of human motion detection and information transmission shows the great potential of wearable devices, electronic skin, and information encryption transmission.

No abstract available

The development of a strong and tough conductive hydrogel capable of meeting the strict requirements of the electrode of a hydrogel-based triboelectric nanogenerator (H-TENG) remains an enormous challenge. Herein, a robust conductive polyvinyl alcohol (PVA) hydrogel is designed via a three-step method: (1) grafting with 3,4-dihydroxy benzaldehyde, (2) metal complexation using ferric chloride (FeCl3) and (3) salting-out using sodium citrate. The hydrogel contains robust crystalline PVA domains and reversible/high-density non-covalent interactions, such as hydrogen bonding, π-π interactions and Fe3+-catechol complexations. Benefiting from the crystalline domains, the hydrogel can resist external forces to the hydrogel network; meanwhile, the reversible/high-density of non-covalent interactions can impart gradual and persistent energy dissipation during deformation. The hydrogel possesses multiple cross-linked networks, with 6.47 MPa tensile stress, 1000 % strain, 35.24 MJ/m3 toughness and 37.59 kJ/m2 fracture energy. Furthermore, the inter-connected porous hydrogel has an ideal structure for ionic-conducing channels. The hydrogel is assembled into an H-TENG, which can generate open circuit voltage of ∼ 150 V, short-circuit current of ∼ 3.0 μA, with superb damage immunity. Subsequently, road traffic monitoring systems are innovatively developed and demonstrated by using the H-TENG. This study provides a novel strategy to prepare superiorly strong and tough hydrogels that can meet the high demand for H-TENGs.

Large mechanical hysteresis, stemming from the inherent viscoelasticity of the hydrogel networks, seriously affected its service life and application scope. Herein, we introduced a synergistic approach combining MXene nanoconfinement and bridging effect to produce hydrogels with low mechanical hysteresis. The introduced MXene was able to provide an effective nanoconfined effect on the polymerization of acrylamide monomers. By synergizing with the bridging effect-facilitated by strong interactions between chitosan-grafted polyacrylamide and solvent molecules to accelerate stress transfer-we successfully developed a MXene-reinforced conductive hydrogel with mechanical hysteresis as low as 3.17 %. Additionally, the strong electrostatic interactions between the chitosan and MXene further affiliate the dispersion of MXene within the hydrogel. The resulting MXene-reinforced conductive hydrogel demonstrated remarkable temperature sensitivity (TCR = -1.42 %/°C), making it suitable to be used as a health monitoring device. These findings opened up new perspectives for the further expansion of MXene and beyond.

Peripheral nerve injury often leads to the loss of neurological functions due to the slow regeneration rate and inefficient functional reconstruction. Current clinical treatments using nerve guidance conduits (NGCs) still face challenges in providing a biomimetic microenvironment to promote nerve repair. Herein, decellularized extracellular matrix (dECM) is obtained from porcine Achilles tendon and crosslinked with 3‐amino‐4‐methoxybenzoic acid grafted gelatin (PAMB‐G) to obtain conductive hydrogels. Then, a novel nerve guidance conduit is developed by assembling poly(vinyl alcohol) (PVA) conduit and conductive ECM@PAMB‐G hydrogel. This bioengineered ECM@PAMB‐G/PVA conduit demonstrated excellent cytocompatibility, electrical conductivity, mechanical properties, and biodegradability. In vitro experiments confirmed that the ECM@PAMB‐G hydrogel significantly promotes the proliferation and migration of PC12 cells and primary Schwann cells, as well as the growth of dorsal root ganglion (DRG) axons. Furthermore, in vivo studies in a rat sciatic nerve model exhibited improvements in axonal regeneration, Schwann cell migration, myelin sheath formation, and functional recovery mediated by the ECM@PAMB‐G/PVA conduit. This work demonstrates the synergistic effects of extracellular matrix and electrical cues in enhancing peripheral nerve regeneration. The ECM@PAMB‐G/PVA nerve guidance conduit shows potential as an alternative to autografts for supporting peripheral nerve reconstruction.

Conductive hydrogels have attracted intensive attention in the field of flexible electronics due to their excellent biocompatibility, suitable Young's modulus, and outstanding electrical conductivity. However, the inherent water-rich feature and...

Conductive hydrogels have been widely applied in human-computer interaction, tactile sensing, and sustainable green energy harvesting. Herein, a double cross-linked network composite hydrogel (MWCNTs/CNWs/PAM/SA) by constructing dual enhancers acting together with PAM/SA was constructed. By systematically optimizing the compositions, the hydrogel displayed features advantages of good mechanical adaptability, high conductivity sensitivity (GF = 5.65, 53 ms), low hysteresis (<11 %), and shape memory of water molecules and temperature. The nanocellulose crystals (CNWs) were bent and entangled with the backbone of the polyacrylamide/ sodium alginate (PAM/SA) hydrogel network, which effectively transferred the external mechanical forces to the entire physical and chemical cross-linking domains. Multi-walled carbon nanotubes (MWCNTs) were filled into the cross-linking network of the hydrogel to enhance the conductivity of the hydrogel effectively. Notably, hydrogels are designed as flexible tactile sensors that can accurately recognize and monitor electrical signals from different gesture movements and temperature changes. It was also assembled as a friction nanogenerator (TENG) that continuously generates a stable open circuit voltage (28 V) for self-powered small electronic devices. This research provides a new prospect for designing nanocellulose and MWCNTs reinforced conductive hydrogels via a facile method.

Mixed ion-electron conductive (MIEC) bioelectronics has emerged as a state-of-the-art type of bioelectronics for bioelectrical signal monitoring. However, existing MIEC bioelectronics is limited by delamination and transmission defects in bioelectrical signals. Herein, a topological MXene network enhanced MIEC hydrogel bioelectronics that simultaneously exhibits both electrical and mechanical property enhancement while maintaining adhesion and biocompatibility, providing an ideal MIEC bioelectronics for electrophysiological signal monitoring, is introduced. Compared with nontopology hydrogel bioelectronics, the MXene topology increases the dynamic stability of bioelectronics by a factor of 8.4 and the electrical signal by a factor of 10.1 and reduces the energy dissipation by a factor of 20.2. Besides, the topology-enhanced hydrogel bioelectronics exhibits low impedance (<25 Ω) at physiologically relevant frequencies and negligible impedance fluctuation after 5000 stretch cycles. The creation of multichannel bioelectronics with high-fidelity muscle action mapping and gait recognition was made possible by achieving such performance.

Myocardial infarction (MI) results in an impaired heart function. Conductive hydrogel patch-based therapy has been considered as a promising strategy for cardiac repair after MI. In our study, we fabricated a three-dimensional (3D) printed conductive hydrogel patch made of fibrinogen scaffolds and mesenchymal stem cells (MSCs) combined with graphene oxide (GO) flakes (MSC@GO), capitalizing on GO's excellent mechanical property and electrical conductivity. The MSC@GO hydrogel patch can be attached to the epicardium via adhesion to provide strong electrical integration with infarcted hearts, as well as mechanical and regeneration support for the infarcted area, thereby up-regulating the expression of connexin 43 (Cx43) and resulting in effective MI repair in vivo. In addition, MI also triggers apoptosis and damage of cardiomyocytes (CMs), hindering the normal repair of the infarcted heart. GO flakes exhibit a protective effect against the apoptosis of implanted MSCs. In the mouse model of MI, MSC@GO hydrogel patch implantation supported cardiac repair by reducing cell apoptosis, promoting gap connexin protein Cx43 expression, and then boosting cardiac function. Together, this study demonstrated that the conductive hydrogel patch has versatile conductivity and mechanical support function and could therefore be a promising candidate for heart repair.

Conductive gel interface materials are widely employed as reliable agents for electroencephalogram (EEG) recording. However, prolonged EEG recording poses challenges in maintaining stable and efficient capture due to inevitable evaporation in hydrogels, which restricts sustained high conductivity. This study introduces a novel ion‐electron dual‐mode conductive hydrogel synthesized through a cost‐effective and streamlined process. By embedding graphite nanoparticles into ionic hyaluronic acid (HAGN), the hydrogel maintains higher conductivity for over 72 h, outperforming commercial gels. Additionally, it exhibits superior low skin contact impedance, considerable electrochemical capability, and excellent tensile and adhesion performance in both dry and wet conditions. The biocompatibility of the HAGN hydrogel, verified through in vitro cell viability assays and in vivo skin irritation tests, underscores its suitability for prolonged skin contact without eliciting adverse reactions. Furthermore, in vivo EEG tests confirm the HAGN hydrogel's capability to provide high‐fidelity signal acquisition across multiple EEG protocols. The HAGN hydrogel proves to be an effective interface for prolonged high‐quality EEG recording, facilitating high‐performance capture and classification of evoked potentials, thereby providing a reliable conductive medium for EEG‐based systems.

The dramatic growth of smart wearable electronics has generated a demand for conductive hydrogels due to their tunability, stimulus responsiveness, and multimodal sensing capabilities. However, the substantial trade-off between mechanical and electrical properties hinders their multifunctionality. Here, we report a double-network hydrogel composite that features a conductive "highway" constructed using magnetic-field-aligned nickel nanowires and liquid metal. The liquid metal fills the gaps between the aligned nickel nanowires. Such interconnected structures can form efficient conductive paths at low filler content, resulting in high conductivity (1.11 × 104 S/m) and mechanical compliance (Young's modulus, 89 kPa; toughness, 721 kJ/m3). When used as a wearable sensor, the hydrogel displays a high sensitivity and fast response for wireless motion detection and human-machine interaction. Furthermore, by exploiting its outstanding conductivity and electrical heating capacity, the hydrogel integrates electromagnetic shielding and thermal management functionalities. Owing to these all-around properties, our design offers a broader platform for expanding hydrogel applications.

Deep eutectic solvents (DES) have been regarded as green solvents in the biorefinery of lignocellulosic biomass, but long duration time has severely limited efficiency. The microwave-assisted DES pretreatment along with enzymatic hydrolysis and high-pressure homogenization process was proposed to produce lignin-containing cellulose nanofibrils (LCNF) from corncob. Benefiting from microwave-assisted DES pretreatment, the duration time was greatly shortened; meanwhile the effects of different kinds of DES on the resultant LCNF were investigated. The results showed that, the microwave-assisted DES fabricated LCNF (M-LCNF) was successfully obtained, exhibiting good nano size, thermal stability, colloidal stability, and fluorescence. M-LCNF was further introduced into phytic acid (PA) enhanced poly(acrylamide-co-acrylic acid) (P(AM-co-AA)) network and constructed composite conductive hydrogels (PLP). The obtained hydrogels exhibited good mechanical strength, UV blocking ability, fluorescence, and conductivity. A simple battery assembled with the resultant PLP as electrolyte had an out voltage of 2.41 V. The composite conductive hydrogel showed good sensing performance towards different stimuli (e.g., stretching and compression) and human motions in real time. It is expected that this research would provide an alternative way for green fabrication of LCNF and potential application of LCNF in flexible sensors.

Spinal cord injury (SCI) represents a severe neurological condition often coupled with a drastic secondary inflammatory response, which further exacerbates the damage in most cases. Due to their unique electrical and mechanical compatibilities with the spinal cord, the utilization of conductive hydrogels through injection for SCI repair, particularly in scenarios involving non‐uniform and large gaps, has emerged as a promising approach. Herein, leveraging the acidic microenvironment characteristic of acute SCI sites, an injectable conductive hydrogel with pH‐responsive immunoregulation is engineered for SCI repair. Based on the dynamic Schiff base chemistry and covalent photo‐crosslinking, this composite hydrogel, composed of gelatin methacryloyl, oxidized dextran, and MoS2, exhibits adjustable mechanical and conductive properties, enabling a customized match with the natural spinal cord's attributes. Additionally, the incorporation of Wnt5a and its selective release in acidic conditions prompt the immediate suppression of inflammatory factors and enhances neural differentiation and regeneration. In the 2‐mm hemisection mouse SCI model, the optimized conductive hydrogel can effectively bridge the injury gap, establish nerve connections and signal, mitigate inflammatory response, and promoted recovery of mobility. This novel injectable conductive hydrogel system offers a promising advance in therapeutic materials for SCI repair.

The utilization of hydrogels in soft electronics has led to significant progress in the field of wearable and implantable devices. However, challenges persist in hydrogel electronics, including the delicate equilibrium between stretchability and electrical conductivity, intricacies in miniaturization, and susceptibility to dehydration. Here, a lignin‐polyacrylamide (Ag‐LPA) hydrogel composite endowed with anti‐freeze, self‐adhesive, exceptional water retention properties, and high stretchability (1072%) is presented. Notably, this composite demonstrated impressive electrical conductivity at room temperature (47.924 S cm−1) and extremely cold temperatures (42.507 S cm−1). It is further proposed for microfluidic‐assisted hydrogel patches (MAHPs) to facilitate customizable designs of the Ag‐LPA hydrogel composite. This approach enhances water retention and offers versatility in packaging materials, making it a promising choice for enduring soft electronics applications. As a proof‐of‐concept, soft electronics across diverse applications and dimensions, encompassing healthcare monitoring, environmental temperature sensing, and 3D‐spring pressure monitoring electronics are successfully developed. The scenery of an extremely cold environment is further extended. The conductivity of the embedded Ag‐LPA hydrogel composite unveils the potential of MAHPs in polar rescue missions. It is envisioned that MAHPs will impact the development of sophisticated and tailored soft electronics, thereby forging new frontiers in engineering applications.

Benefiting from the tissue-like mechanical properties, conductive hydrogels have emerged as a promising candidate for manufacturing wearable electronics. However, the high water content within hydrogels will inevitably freeze at subzero temperature, causing a degradation or loss of functionality, which severely prevent their practical application in wearable electronics. Herein, an anti-freezing hydrogel integrating high conductivity, superior stretchability, and robust adhesion was fabricated by dissolving choline chloride and gallium in gelatin/guar gum network using borax as the cross-linker. Based on the synergistic effect of dynamic borate ester bonds and hydrogen bonds, the hydrogel exhibited rapid self-healing property and excellent fatigue resistance. Profiting from these fascinating characteristics, the hydrogel was assembled as strain sensor to precisely detect various human activities with high strain sensitivity and fast response time. Meanwhile, the hydrogel was demonstrated high sensitivity and rapid response to temperature, which can be used as thermal sensor to monitor temperature. Moreover, the conductive hydrogel was encapsulated into supercapacitors with high areal capacitance and favorable cycle stability. Importantly, the flexible sensor and supercapacitors still maintain stable sensing performance and good electrochemical performance even at subzero temperature. Therefore, our work broaden hydrogels application in intelligent wearable devices and energy storage in extreme environments.

Conductive hydrogel is considered a promising wearable sensor material. Developing flexible conductive hydrogel sensors with stretchability, adhesion, and stability remains challenging. In this study, a transparent, self‐adhesive, antifreeze, anti‐UV, stretchable, conductive, and reusable hydrogel with polyacrylamide/glycerol/gelatin/tannic acid/Fe3+ (PGGT‐Fe3+) structure is successfully constructed through a simple one‐pot polymerization method. The PGGT‐Fe3+ hydrogel is composed of dual networks of polyacrylamide and gelatin for organic cross‐linking, using water/glycerol as the dispersion medium, and incorporates a viscous substance: tannic acid, and a conductive substance: metal ions (Fe3+). Due to the introduction of the abundant amino, carboxylic acid, and hydroxyl functional groups on gelatin and tannic acid, the PGGT‐Fe3+ hydrogel exhibits excellent and repeatable adhesion capabilities on various surfaces (including glass, metal, plastic, and pigskin) with maximum adhesion strength of 98 kPa when attached to pigskin. Furthermore, based on the stable conductive network and high conductivity, the hydrogel not only exhibits strain sensitivity, fast response, and stability but also can stably collect epidermal bio signals. In conclusion, this work provides a new approach to the design and development of next‐generation multifunctional conductive hydrogels and opens up vast possibilities for their applications in the flexible electronics field.

Wearable electronics based on conductive hydrogels (CHs) offer remarkable flexibility, conductivity, and versatility. However, the flexibility, adhesiveness, and conductivity of traditional CHs deteriorate when they freeze, thereby limiting their utility in challenging environments. In this work, we introduce a PHEA-NaSS/G hydrogel that can be conveniently fabricated into a freeze-resistant conductive hydrogel by weakening the hydrogen bonds between water molecules. This is achieved through the synergistic interaction between the charged polar end group (-SO3-) and the glycerol-water binary solvent system. The conductive hydrogel is simultaneously endowed with tunable mechanical properties and conductive pathways by the modulation caused by varying material compositions. Due to the uniform interconnectivity of the network structure resulting from strong intermolecular interactions and the enhancement effect of charged polar end-groups, the resulting hydrogel exhibits 174 kPa tensile strength, 2105 % tensile strain, and excellent sensing ability (GF = 2.86, response time: 121 ms), and the sensor is well suited for repeatable and stable monitoring of human motion. Additionally, using the Full Convolutional Network (FCN) algorithm, the sensor can be used to recognize English letter handwriting with an accuracy of 96.4 %. This hydrogel strain sensor provides a simple method for creating multi-functional electronic devices, with significant potential in the fields of multifunctional electronics such as soft robotics, health monitoring, and human-computer interaction.

The rapid development of wearable electronic devices and virtual reality technology has revived interest in flexible sensing and control devices. Here, we report an ionic hydrogel (PTSM) prepared from polypropylene amine (PAM), tannic acid (TA), sodium alginate (SA), and MXene. Based on the multiple weak H-bonds, this hydrogel exhibits excellent stretchability (strain >4600%), adhesion, and self-healing. The introduction of MXene nanosheets endows the hydrogel sensor with a high gauge factor (GF) of 6.6. Meanwhile, it also enables triboelectric nanogenerators (PTSM-TENGs) fabricated from silicone rubber-encapsulated hydrogels to have excellent energy harvesting efficiency, with an instantaneous output power density of 54.24 mW/m2. We build a glove-based human-computer interaction (HMI) system using PTSM-TENGs. The multidimensional signal features of PTSM-TENG are extracted and analyzed by the HMI system, and the functions of gesture visualization and robot hand control are realized. In addition, triboelectric signals can be used for object recognition with the help of machine learning techniques. The glove based on PTSM-TENG achieves the classification and recognition of five objects through contact, with an accuracy rate of 98.7%. Therefore, strain sensors and triboelectric nanogenerators based on hydrogels have broad application prospects in man-machine interface, intelligent recognition systems, auxiliary control systems, and other fields due to their excellent stretchable and high self-healing performance.

To achieve the green and sustainable development of environment, biocompatible hydrogels with exceptional ionic conductivity and flexibility are highly desired for intelligent and wearable sensors. However, it remains a great challenge to obtain biopolymer hydrogel-based sensors with high transparency, excellent mechanical properties, and good adhesion ability simultaneously. Herein, starch/polyacrylamide double-network hydrogel is achieved to endow the multifunctionality of traditional hydrogel sensor. Specifically, the resultant hydrogel sensor exhibits wide strain detection range of 2580 %, fast response time of 120 ms, high conductivity of 31.9 mS·m-1, superior sensitivity, remarkable fatigue resistance of 1350 cycles. In addition, multiple hydrogen bonding endows starch/polyacrylamide hydrogel with high mechanical properties and high transparency. Owing to these merits, the hydrogel sensor is capable of discriminating different human motions. Notably, the ionic conducting hydrogels could be employed as single-electrode TENGs for energy harvesting. The multifunctionality and biocompatibility of starch-based hydrogel sensor may offer an inspiration for the future development of next-generation sustainable and wearable electronics.

No abstract available

Conducting polymer hydrogels offer promising electrical interfaces with biological tissues for electrophysiological signal recording, sensing, and stimulation due to their favorable electrical properties, biocompatibility, and stability. Among them, Poly (3,4-ethylenedioxythiophene): Polystyrene sulfonate (PEDOT:PSS) is widely used as a conductive filler, forming a network of conjugated nanofibers within the hydrogel matrix. This structure enables robust electronic conductivity while preserving ionic transport and biocompatibility in physiological environments. However, the mechanical integrity of these hydrogels is often compromised by micellar microstructures in aqueous colloidal dispersions. The absence of interconnected conducting polymer nanofibers to maintain mechanical integrity during swelling hinders the mechanical properties of hydrogels. Here, three modification strategies were explored to enhance the flexibility and stretchability: constructing an interpenetrating network, phase separation induced by ionic compounds, and pure conductive hydrogels formed through polar solvent additives and dry-annealing. These strategies synergistically enhance conductivity and flexibility by controlling interchain entanglement and redesigning the distribution of conjugated crystal regions and soft regions. The resulting hydrogels exhibit excellent conductivity (1.99–5.25 S/m), softness (elastic modulus as low as 280 Pa), and elasticity (tensile properties up to 800 %). When used as epidermal or implantable bioelectrodes, they provided a soft interface, ensuring longer-lasting and more stable electromyogram, electrocardiogram, and electroencephalogram signals compared to commercial gel electrodes, with a signal-to-noise ratio of up to 20.0 dB. Therefore, the conducting polymer hydrogels developed in this study leverage the synergy between conductivity and flexibility, paving the way for further transformative applications in bioelectronics.

No abstract available

Because of their distinct electrochemical and mechanical properties, conducting polymer hydrogels have been widely exploited as soft, wet, and conducting coatings for conventional metallic electrodes, providing mechanically compliant interfaces and mitigating foreign body responses. However, the long‐term viability of these hydrogel coatings is hindered by concerns regarding fatigue crack propagation and/or delamination caused by repetitive volumetric expansion/shrinkage during long‐term electrical interfacing. This study reports a general yet reliable approach to achieving a fatigue‐resistant conducting polymer hydrogel coating on conventional metallic bioelectrodes by engineering nanocrystalline domains at the interface between the hydrogel and metallic substrates. It demonstrates the efficacy of this robust, biocompatible, and fatigue‐resistant conducting hydrogel coating in cardiac pacing, showcasing its ability to effectively reduce the pacing threshold voltage and enhance the long‐term reliability of electric stimulation. This study findings highlight the potential of its approach as a promising design and fabrication strategy for the next generation of seamless bioelectronic interfaces.

Electrical bioadhesive interface (EBI), especially conducting polymer hydrogel (CPH)-based EBI, exhibits promising potential applications in various fields, including biomedical devices, neural interfaces, and wearable devices. However, current fabrication techniques of CPH-based EBI mostly focus on conventional methods such as direct casting, injection, and molding, which remains a lingering challenge for further pushing them toward customized practical bioelectronic applications and commercialization. Herein, 3D printable high-performance CPH-based EBI precursor inks are developed through composite engineering of PEDOT:PSS and adhesive ionic macromolecular dopants within tough hydrogel matrices (PVA). Such inks allow the facile fabrication of high-resolution and programmable patterned EBI through 3D printing. Upon successive freeze-thawing, the as-printed PEDOT:PSS-based EBI simultaneously exhibits high conductivity of 1.2 S m-1 , low interfacial impedance of 20 Ω, high stretchability of 349%, superior toughness of 109 kJ m-3 , and satisfactory adhesion to various materials. Enabled by these advantageous properties and excellent printability, the facile and continuous manufacturing of EBI-based skin electrodes is further demonstrated via 3D printing, and the fabricated electrodes display excellent ECG and EMG signal recording capability superior to commercial products. This work may provide a new avenue for rational design and fabrication of next-generation EBI for soft bioelectronics, further advancing seamless human-machine integration.

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With the increasing demand for portable electronic devices, it is urgent to develop a flexible energy storage system with high performance and good stability. In this paper, a new kind of poly(vinyl alcohol)–polypyrrole–acidified carbon nanotube (PVA–PPy–CNT‐COOH) conductive composite hydrogel was prepared using a freezing–thawing method for fabricating flexible symmetric solid‐state supercapacitors. The PVA–PPy–CNT‐COOH conductive composite hydrogel has a unique three‐dimensional interpenetrating network structure and functional components, endowing the prepared hydrogel with softness, elasticity, compressibility and formability. Furthermore, the influence of feed mode and feeding ratio on hydrogel preparation was explored. According to the optimal experimental process, a flexible symmetric solid‐state supercapacitor with high energy storage capacity and stability was fabricated using PVA–PPy–CNT‐COOH as the electrode. The capacitance change of the supercapacitor was almost negligible when subjected to 50% strain. Even at 70% strain, the retention rate of volume specific capacitance was still about 88%. This study not only provides a preparation method for a new electrode material but also develops a new type of high‐performance and stable flexible symmetric solid‐state supercapacitor, which has potential application prospects in flexible energy devices. © 2025 Society of Chemical Industry.

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Implantable neural microelectrodes are recognized as a bridge for information exchange between inner organisms and outer devices. Combined with novel modulation technologies such as optogenetics, it offers a highly precise methodology for the dissection of brain functions. However, achieving chronically effective and stable microelectrodes to explore the electrophysiological characteristics of specific neurons in free-behaving animals continually poses great challenges. To resolve this, poly(3,4-ethylenedioxythiophene)/poly(styrenesulfonate)/poly(vinyl alcohol) (PEDOT/PSS/PVA) interpenetrating conducting polymer networks (ICPN) are fabricated via a hydrogel scaffold precoating and electrochemical polymerization process to improve the performance of neural microelectrodes. The ICPN films exhibit robust interfacial adhesion, a significantly lower electrochemical impedance, superior mechanical properties, and improved electrochemical stability compared to the pure poly(3,4-ethylenedioxythiophene)/poly(styrenesulfonate)(PEDOT/PSS) films, which may be attributed to the three-dimensional (3D) porous microstructure of the ICPN. Hippocampal neurons and rat pheochromocytoma cells (PC12 cells) adhesion on ICPN and neurite outgrowth are observed, indicating enhanced biocompatibility. Furthermore, alleviated tissue response at the electrode-neural tissue interface and improved recording signal quality are confirmed by histological and electrophysiological studies, respectively. Owing to these merits, optogenetic modulations and electrophysiological recordings are performed in vivo, and an anxiolytic effect of hippocampal glutamatergic neurons on behavior is shown. This study demonstrates the effectiveness and advantages of ICPN-modified neural implants for in vivo applications.

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Recent advances in drug delivery have made it possible to release bioactive agents from neural implants specifically to local tissues. Conducting polymer coatings have been explored as a delivery platform in bioelectronics, however, their utility is restricted by their limited loading capacity and stability. This study presents the fabrication of a stable conducting polymer hydrogel (CPH), comprising the hydrogel gelatin methacrylate (GelMA), and conducting polymer polypyrrole (PPy) for the electrically controlled delivery of glutamate (Glu). The hybrid GelMA/PPy/Glu can be photolithographically patterned and covalently bonded to an electrode. Fourier-transform infrared (FTIR) analysis confirmed the interpenetrating nature of PPy through the GelMA hydrogels. Electrochemical polymerisation of PPy/Glu through the GelMA hydrogels resulted in a significant increase in the charge storage capacity as determined by cyclic voltammetry (CV). Long-term electrochemical and mechanical stability was demonstrated over 1000 CV cycles and extracts of the materials were cytocompatible with SH-SY5Y neuroblastoma cell lines. Release of Glu from the CPH was responsive to electrical stimulation with almost five times the amount of Glu released upon constant reduction (-0.6 V) compared to when no stimulus was applied. Notably, GelMA/PPy/Glu was able to deliver almost 14 times higher amounts of Glu compared to conventional PPy/Glu films. The described CPH coatings are well suited in implantable drug delivery applications and compared to conducting polymer films can deliver higher quantities of drug in response to mild electrical stimulus.

The lithium-sulfur (Li-S) system is a promising material for the next-generation of high energy density batteries with application extending from electrical vehicles to portable devices and aeronautics. Despite progress, the energy density of current Li-S technologies is still below that of conventional intercalation-type cathode materials due to limited stability and utilization efficiency at high sulfur loading. Here, we present a conducting polymer hydrogel integrated highly performing free-standing three-dimensional (3D) monolithic electrode architecture for Li-S batteries with superior electrochemical stability and energy density. The electrode layout consists of a highly conductive three-dimensional network of N,P codoped carbon with well-dispersed metal-organic framework nanodomains of ZIF-67 and HKUST-1. The hierarchical monolithic 3D carbon networks provide an excellent environment for charge and electrolyte transport as well as mechanical and chemical stability. The electrically integrated MOF nanodomains significantly enhance the sulfur loading and retention capabilities by inhibiting the release of lithium polysulfide specificities as well as improving the charge transfer efficiency at the electrolyte interface. Our optimal 3D carbon-HKUST-1 electrode architecture achieves a very high areal capacity of >16 mAh cm-2 and volumetric capacity ( CV) of 1230.8 mAh cm-3 with capacity retention of 82% at 0.2C for over 300 cycles, providing an attractive candidate material for future high-energy density Li-S batteries.

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A rapid, sensitive and low-fouling sensor for application to detect clinical biomarkers directly in biological media is highly desirable. Herein, we report a versatile strategy to prepare polyaniline (PANI) based conducting polymer hydrogel through the assembly of PANI and phytic acid (PA) by dynamic boronate bond. PANI/PA, a conductive hydrogel with high specific area and multiple pore structures have demonstrated excellent antifouling ability and electrochemical property. The electrochemical biosensors for microRNA can be developed by the immobilization of DNA probes onto PANI/PA interface (microRNA24 is used as a model case), and redox currents of PANI were utilized as the sensing signals to assay DNA/RNA hybridization reaction. Owing to the typical characteristics of PANI/PA hydrogel, the biosensor has shown excellent sensing performances with wide linear range (1.0 fM-1.0 pM), low sensing limit (0.34 fM) and efficient ability to detect microRNA mismatches. Given the facile processability, excellent stability and good antifouling property of the PANI/PA hydrogel, the proposed hydrogel-based biosensor may find broad applications in clinical diagnostics and biomedical devices.

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In this study, the release of fluorescein from a photo‐crosslinked conducting polymer hydrogel made from a hydrogel precursor poly(dimethylacrylamide‐co‐4‐methacryloyloxy benzophenone (5%)‐co‐4‐styrenesulfonate (2.5%)) (PDMAAp) and the conducting polymer poly(3,4‐ethylenedioxythiophene) (PEDOT) is investigated. Fluorescein, here used as a model for a drug, is actively released through application of an electrical trigger signal. The detected quantity is more than six times higher in comparison to that released from a conventional PEDOT/polysterene sulfonate (PSS) system. Release profiles, drug dose, and timing can be tailored by the application of different trigger signals and pretreatments. To demonstrate that the novel drug release system can be used for a drug relevant for local delivery to a neural interface, experiments are furthermore performed with the anti‐inflammatory drug dexamethasone (Dex). The conducting polymer hydrogel facilitates the active release of Dex, in comparison to the previously used PEDOT/Dex. It is suggested that PEDOT/PDMAAp is an interesting alternative for conducting polymer based drug release systems, with the potential to offer more volume for storage, yet retaining the excellent electrochemical properties known for PEDOT electrodes.

This study presents a new conducting polymer hydrogel (CPH) system, consisting of the synthetic hydrogel P(DMAA-co-5%MABP-co-2,5%SSNa) and the conducting polymer (CP) poly(3,4-ethylenedioxythiophene) (PEDOT), intended as coating material for neural interfaces. The composite material can be covalently attached to the surface electrode, can be patterned by a photolithographic process to influence selected electrode sites only and forms an interpenetrating network. The hybrid material was characterized using cyclic voltammetry (CV), impedance spectroscopy (EIS) and X-ray photoelectron spectroscopy (XPS), which confirmed a homogeneous distribution of PEDOT throughout all CPH layers. The CPH exhibited a 2,5 times higher charge storage capacity (CSC) and a reduced impedance when compared to the bare hydrogel. Electrochemical stability was proven over at least 1000 redox cycles. Non-toxicity was confirmed using an elution toxicity test together with a neuroblastoma cell-line. The described material shows great promise for surface modification of neural probes making it possible to combine the beneficial properties of the hydrogel with the excellent electronic properties necessary for high quality neural microelectrodes. STATEMENT OF SIGNIFICANCE Conductive polymer hydrogels have emerged as a promising new class of materials to functionalize electrode surfaces for enhanced neural interfaces and drug delivery. Common weaknesses of such systems are delamination from the connection surface, and the lack of suitable patterning methods for confining the gel to the selected electrode site. Various studies have reported on conductive polymer hydrogels addressing one of these challenges. In this study we present a new composite material which offers, for the first time, the unique combination of properties: it can be covalently attached to the substrate, forms an interpenetrating network, shows excellent electrical properties and can be patterned via UV-irradiation through a structured mask.

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We present a reliable approach for producing high-performance ion-conducting gel polymer electrolytes (GPEs) based on the sodium chloride (NaCl)-integrated dual network hydrogel of poly (vinyl alcohol)/sodium alginate (PVA/SA) using a binary solvent system of ethylene glycol (EG) and water, providing exceptional ionic conductivity, mechanical strength, and self-healing properties. Different GPEs were produced via the freezing-thawing method using different v/v% of EG and water (named PVA/SA/EG). The best PVA/SA/EG GPE provided a maximum ionic conductivity of 25 mS cm-1, astonishing mechanical strength of 0.42 MPa, exceptional stretchability of 462 %, and remarkable self-healing properties. The binary solvent system- and water-based GPEs were utilized in the construction of symmetric supercapacitors (SSCs) using carbon cloth electrodes and their electrochemical performance were compared. At a current density of 0.5 mA cm-2, the SSC prepared using the best PVA/SA/EG GPE demonstrated a high specific capacity of 577.21 mF cm-2, maintained 94.5 % capacitance after 5000 cycles at 1 mA cm-2, and provided an energy density of 80.14 mWh cm-2 while operating at a power density of 293.3 mW cm-2. The flexible SSC prepared based on this GPE demonstrated outstanding flexibility, while no significant decline in capacitive performance and ionic conductivity was detected when it was bent.

Objectives Normal and chronic wound healing is a global challenge. Electrotherapy has emerged as a novel and efficient technique for treating such wounds in recent decades. Hydrogel applied to the wound to uniformly distribute the electric current is an important component in wound healing electrotherapy. This study reports the development and wound healing efficacy testing of vitamin D entrapped polyaniline (PANI)-chitosan composite hydrogel for electrotherapy. Materials and Methods To determine the morphological and physicochemical properties, techniques like scanning electron microscopy (SEM); differential scanning calorimetry; X-ray diffraction; fourier-transform infrared spectroscopy were used. Moreover, pH, conductance, viscosity, and porosity were measured to optimize and characterize the vitamin D entrapped PANI-chitosan composite hydrogel. The biodegradation was studied using lysozyme, whereas the water uptake ability was studied using phosphate buffer. Ethanolic phosphate buffer was used to perform the vitamin D entrapment and release study. Cell adhesion, proliferation, and electrical stimulation experiments were conducted by seeding dental pulp stem cells (DPSC) into the scaffolds and performing (3-[4,5-dimethylthiazol-2-yl]-2,5 diphenyl tetrazolium bromide) assay; SEM images were taken to corroborated the proliferation results. The wound healing efficacy of electrotherapy and the developed hydrogel were studied on excision wound healing model in rats, and the scarfree wound healing was further validated by histopathology analysis. Results The composition of the developed hydrogel was optimized to include 1% w/v PANI and 2% w/v of chitosan composite. This hydrogel showed 1455 μA conduction, 98.97% entrapment efficiency and 99.12% release of vitamin D in 48 hrs. The optimized hydrogel formulation showed neutral pH of 6.96 and had 2198 CP viscosity at 26°C. The hydrogel showed 652.4% swelling index and 100% degradation in 4 weeks. The in vitro cell culture studies performed on hydrogel scaffolds using DPSC and electric stimulation strongly suggested that electrical stimulation enhances the cell proliferation in a three-dimensional (3D) scaffold environment. The in vivo excision wound healing studies also supported the in vitro results suggesting that electrical stimulation of the wound in the presence of the conducting hydrogel and growth factors like vitamin D heals the wound much faster (within 12 days) compared to non-treated control wounds (requires 21 days for complete healing). Conclusion The results strongly suggested that the developed PANI-chitosan composite conducting hydrogel acts effectively as an electric current carrier to distribute the current uniformly across the wound surface. It also acted as a drug delivery vehicle for delivering vitamin D to the wound. The hydrogel provided a moist environment, a 3D matrix for free migration of the cells, and antimicrobial activity due to chitosan, all of which contributed to the electrotherapy's faster wound healing mechanism, confirmed through the in vitro and in vivo experiments.

Strain sensors are essential for accurately capturing intricate motions across various applications. However, achieving both high mechanical strength and stability in strain sensors remains challenging. Herein, we present a novel and high-performance strain sensor using an amino-ended hyperbranched polyamide (HBPN) as a cross-linker to construct a strong and tough conducting polymer hydrogel composed of polyvinyl alcohol (PVA) and poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS). The terminal amino groups in HBPN create non-covalent cross-links within the network, resulting in a robust structure. Notably, the unique hyperbranched topology of HBPN significantly enhances the hydrogel's properties, providing superior strength and toughness compared to its non-hyperbranched counterparts. Specifically, the distinctive macromolecular structure and abundant hydrogen bonding in the HBPN-PVA-PEDOT:PSS conducting polymer hydrogel result in exceptional toughness (991.53 kJ m-3), which is five times higher than that of the PVA-PEDOT:PSS hydrogel without HBPN. Additionally, the HBPN cross-linker enhances the sensitivity of the conducting polymer hydrogel, making it more responsive than linear analogs when used as a strain sensor. The resulting sensors adapt dynamically to human motion, demonstrating excellent detection capabilities. This work showcases a promising approach for developing cost-effective, sustainable, flexible, and high-performance wearable devices.

Spatiotemporal controlled drug delivery minimizes side-effects and enables therapies that require specific dosing patterns. Conjugated polymers (CP) can be used for electrically controlled drug delivery; however so far, most demonstrations were limited to molecules up to 500 Da. Larger molecules could be incorporated only during the CP polymerization and thus limited to a single delivery. This work harnesses the record volume changes of a glycolated polythiophene p(g3T2) for controlled drug delivery. p(g3T2) undergoes reversible volumetric changes of up to 300% during electrochemical doping, forming pores in the nm-size range, resulting in a conducting hydrogel. p(g3T2)-coated 3D carbon sponges enable controlled loading and release of molecules spanning molecular weights of 800-6000 Da, from simple dyes up to the hormone insulin. Molecules are loaded as a combination of electrostatic interactions with the charged polymer backbone and physical entrapment in the porous matrix. Smaller molecules leak out of the polymer while larger ones could not be loaded effectively. Finally, this work shows the temporally patterned release of molecules with molecular weight of 1300 Da and multiple reloading and release cycles without affecting the on/off ratio.

A stretchable electrically conductive hydrogel was developed by combining the use of a unique salt with both oxidizing and salting-out abilities and directional freezing to polymerize a conducting polymer into a hierarchically structured hydrogel.

Polymeric nanocomposites were obtained by the formation of a thermosensitive hydrogel matrix around conducting polymer (CP) nanoparticles. The CP is able to absorb electromagnetic radiation which is converted into heat and induces the phase transition of the surrounding hydrogel. The method chosen to form the hydrogel is the free radical polymerization of a copolymer (N-isopropylacrylamide (NIPAM) and 2-acrylamide-2-methylpropano sulfonic acid (AMPS), PNIPAM-co-2% AMPS) in the presence of bisacrylamide as the crosslinker. The nanoparticles are polypyrrole nanospheres (PPy NP), polyaniline nanofibers (PANI NF), and polyaniline nanospheres (PANI NP). The morphology of the composites was studied using SEM microscopy and the percentage composition of each material was evaluated by thermogravimetric analysis (TGA). The swelling equilibrium capacity and rate are clearly affected by the nanoparticle shape and nature. However, the nanocomposites LCST are similar to that of the matrix. Upon RF irradiation, the three nanocomposites increase the temperature and reach the LCST after 320 seconds of irradiation (320 kJ). Upon MW application, the local temperature reaches the LCST after only 30 s (21 kJ), resulting in a MW more effective than RF to drive the transition. These results demonstrate that the proposed materials are useful as a remotely driven actuator.

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The mechanical mismatch between microelectrode of brain–machine interfaces (BMIs) and soft brain tissue during electrophysiological investigations leads to inflammation, glial scarring, and compromising performance. Herein, a nanostructured, stimuli‐responsive, conductive, and semi‐interpenetrating polymer network hydrogel‐based coated BMIs probe is introduced. The system interface is composed of a cross‐linkable poly(N‐isopropylacrylamide)‐based copolymer and regioregular poly[3‐(6‐methoxyhexyl)thiophene] fabricated via electrospinning and integrated into a neural probe. The coating's nanofibrous architecture offers a rapid swelling response and faster shape recovery compared to bulk hydrogels. Moreover, the smart coating becomes more conductive at physiological temperatures, which improves signal transmission efficiency and enhances its stability during chronic use. Indeed, detecting acute neuronal deep brain signals in a mouse model demonstrates that the developed probe can record high‐quality signals and action potentials, favorably modulating impedance and capacitance. Evaluation of in vivo neuronal activity and biocompatibility in chronic configuration shows the successful recording of deep brain signals and a lack of substantial inflammatory response in the long‐term. The development of conducting fibrous hydrogel bio‐interface demonstrates its potential to overcome the limitations of current neural probes, highlighting its promising properties as a candidate for long‐term, high‐quality detection of neuronal activities for deep brain applications such as BMIs.

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Conducting polymer hydrogels with inherent flexibility, ionic conductivity and environment friendliness are promising materials in the fields of energy storage. However, a trade-off between mechanical and electrochemical properties has limited the development of flexible/stretchable conducting polymer hydrogel electrodes, owing to the intrinsic conflict among mechanical and electrical phases. Here, we report a reliable design to enable conducting polymer with both exceptional mechanical and electrical/electrochemical performance through the construction of bi-continuous conducting polymer crosslinked network. The resultant bi-continuous conducting polymer hydrogels (BCPH) demonstrate significantly improved mechanical and electrochemical properties compared to the conventional conducting polymer hydrogel (CPH) electrode. BCPH presents a high specific capacitance of 715 F g-1 at 0.5 A/g, a high mechanical strength (∼1 MPa) and a large stretchability (∼300%). Enabled by such intrinsically deformability and electrochemical properties, we further demonstrate its utility in flexible solid-state supercapacitor (FSSC), which exhibits an outstanding specific capacitance of 760 mF cm-2 at 2 mA cm-2, excellent electrochemical stability with 81% capacitance retention after 5000 charge/discharge cycles, and superior bending cycle stability. This simple and scalable strategy provides a platform for the fabrication of high-performance conducting hydrogel electrodes for various wearable electronic equipment.

The poor cycling stability of faradaic materials owing to volume expansion and stress concentration during faradaic processes limits their use in large-scale electrochemical deionization (ECDI) applications. Herein, we developed a "soft-hard" interface by introducing conducting polymer hydrogels (CPHs), that is, polyvinyl alcohol/polypyrrole (PVA/PPy), to support the uniform distribution of Prussian blue analogues (e.g., copper hexacyanoferrate (CuHCF)). In this design, the soft buffer layer of the hydrogel effectively alleviates the stress concentration of CuHCF during the ion-intercalation process, and the conductive skeleton of the hydrogel provides charge-transfer pathways for the electrochemical process. Notably, the engineered CuHCF@PVA/PPy demonstrates an excellent salt-adsorption capacity of 22.7 mg g-1 at 10 mA g-1, fast salt-removal rate of 1.68 mg g-1 min-1 at 100 mA g-1, and low energy consumption of 0.49 kW h kg-1. More importantly, the material could maintain cycling stability with 90% capacity retention after 100 cycles, which is in good agreement with in situ X-ray diffraction tests and finite element simulations. This study provides a simple strategy to construct three-dimensional conductive polymer hydrogel structures to improve the desalination capacity and cycling stability of faradaic materials with universality and scalability, which promotes the development of high-performance electrodes for ECDI.

The present work highlights the synthesis and characterization of conducting polymer (CP)-based composite hydrogels with gelatin (GL-B) for their application as drug delivery vehicles. The spectral, morphological, and rheological properties of the synthesized hydrogels were explored, and morphological studies confirmed formation of an intense interpenetrating network. Rheological measurements showed variation in the flow behavior with the type of conducting polymer. The hydrogels showed a slow drug release rate of about 10 h due to the presence of the conducting polymer. The release kinetics were fitted in various mathematical models and were best fit in first order for PNA-, POPD-, and PANI-based GL-B hydrogels, and the PVDF/GL-B hydrogel was best fit in the zero-order models. The drug release was found to follow the order: POPD/GL-B > PANI/GL-B > PVDF/GL-B.

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Electrically modulated delivery of proteins provides an avenue to target local tissues specifically and tune the dose to the application. This approach prolongs and enhances activity at the target site whilst reducing off-target effects associated with systemic drug delivery. The work presented here explores an electrically active composite material comprising of a biocompatible hydrogel, gelatin methacryloyl (GelMA) and a conducting polymer, poly(3,4-ethylenedioxythiophene), generating a conducting polymer hydrogel. In this paper, the key characteristics of electroactivity, mechanical properties and morphology are characterized using electrochemistry techniques, atomic force and scanning electron microscopy. Cytocompatibility is established through exposure of human cells to the materials. By applying different electrical-stimuli, the short-term release profiles of a model protein can be controlled over 4 hours, demonstrating tunable delivery patterns. This is followed by extended-release studies over 21 days which reveal a bimodal delivery mechanism influenced by both GelMA degradation and electrical stimulation events. This data demonstrates an electroactive and cytocompatible material suitable for the delivery of protein payloads over 3 weeks. This material is well suited for use as a treatment delivery platform in tissue engineering applications where targeted and spatio-temporal controlled delivery of therapeutic proteins is required. STATEMENT OF SIGNIFICANCE: Growth factor use in tissue engineering typically requires sustained and tunable delivery to generate optimal outcomes. While conducting polymer hydrogels (CPH) have been explored for the electrically responsive release of small bioactives, we report, for the first time, a CPH capable of releasing a protein payload in response to electrical stimulus. The composite material combines the benefits of soft hydrogels acting as a drug reservoir and redox-active properties from the conducting polymer enabling electrical responsiveness. The CPH is able to sustain protein delivery over 3 weeks, with electrical stimulus used to modulate release. The described material is well suited as a treatment delivery platform to deliver large quantities of proteins in applications where spatio-temporal delivery patterns are paramount.

Conducting polymer hydrogels have emerged as promising materials to fabricate highly sensitive strain sensors. However, due to weak bindings between conducting polymer and gel network, they usually suffer from limited stretchability and large hysteresis, failing to achieve wide-range strain sensing. Herein, we combine hydroxypropyl methyl cellulose (HPMC), poly (3,4-ethylenedioxythiophene):poly (styrene sulfonic acid) (PEDOT: PSS) with chemically cross-linked polyacrylamide (PAM) to prepare a conducting polymer hydrogel for strain sensors. Owing to abundant hydrogen bonds between HPMC, PEDOT:PSS and PAM chains, this conducting polymer hydrogel exhibits high tensile strength (166 kPa), ultra-stretchability (>1600 %) and low hysteresis (<10 % at 1000 % cyclic tensile strain). The resultant hydrogel strain sensor shows ultra-high sensitivity, wide strain sensing ranges of 2-1600 %, and excellent durability and reproducibility. Finally, this strain sensor can be used as wearable sensor to monitor vigorous human movement and fine physiological activity, and services as bioelectrodes for electrocardiograph and electromyography monitoring. This work provides new horizons to design conducting polymer hydrogels for advanced sensing devices.

Conductive hydrogels are promising materials with mixed ionic‐electronic conduction to interface living tissue (ionic signal transmission) with medical devices (electronic signal transmission). The hydrogel form factor also uniquely bridges the wet/soft biological environment with the dry/hard environment of electronics. The synthesis of hydrogels for bioelectronics requires scalable, biocompatible fillers with high electronic conductivity and compatibility with common aqueous hydrogel formulations/resins. Despite significant advances in the processing of carbon nanomaterials, fillers that satisfy all these requirements are lacking. Herein, intrinsically dispersible acid‐crystalized PEDOT:PSS nanoparticles (ncrys‐PEDOTX) are reported which are processed through a facile and scalable nonsolvent induced phase separation method from commercial PEDOT:PSS without complex instrumentation. The particles feature conductivities of up to 410 S cm−1, and when compared to other common conductive fillers, display remarkable dispersibility, enabling homogeneous incorporation at relatively high loadings within diverse aqueous biomaterial solutions without additives or surfactants. The aqueous dispersibility of the ncrys‐PEDOTX particles also allows simple incorporation into resins designed for microstereolithography without sonication or surfactant optimization; complex biomedical structures with fine features (< 150 µm) are printed with up to 10% particle loading . The ncrys‐PEDOTX particles overcome the challenges of traditional conductive fillers, providing a scalable, biocompatible, plug‐and‐play platform for soft organic bioelectronic materials.

Conductive hydrogels have demonstrated great potential in flexible wearable sensors due to their excellent flexibility and conductivity. Nevertheless, traditional hydrogels suffer from limitations such as weak mechanical properties, inadequate fatigue resistance, and lack of recyclability, which have hindered their practical applications. In this study, a polyvinyl alcohol/polyacrylamide/κ-carrageenan-Ca2+/K+ (PPK-Ca2+/K+) composite hydrogel was developed by constructing a dynamic network structure involving hydrogen bonds, electrostatic interactions, and synergistic co-crosslinking of Ca2+/K+. The resulting ionic conductive hydrogel exhibited remarkable stretchability (~ 414 %), high tensile strength (1190 kPa), and excellent fatigue resistance. Benefiting from the negatively charged κ-carrageenan and the ion transport co-regulation by Ca2+/K+, the hydrogel achieved a high ionic conductivity of 7.26 mS/cm. Moreover, owing to the thermoreversible properties of κ-carrageenan and PVA, the hydrogel material could be recycled through high-temperature remolding processes. The flexible sensor assembled with PPK-Ca2+/K+ hydrogel demonstrated high sensitivity, a broad detection range (0-400 %), and rapid response time (152 ms), enabling precise monitoring of various human activities, ranging from large joint movements to subtle muscle contractions. The proposed fabrication strategy for robust, fatigue-resistant, self-healing, and recyclable conductive hydrogel provides new insights for developing high-performance wearable sensors and electronic skin.

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Flexible wearable devices have achieved remarkable applications in health monitoring because of the advantages of multisignal collecting and real-time wireless transmission of information. However, the integration of bulky sensing elements and rigid metal circuit components in traditional wearable devices may lead to a mechanical and signal-conducting mismatch between wearable devices and biological tissues, thus restricting their wide applications in the human body. The excellent mechanical properties, conductivity, and high tissue resemblance of conductive hydrogel contribute to its application in flexible electronic sensors to monitor human health. In this work, a dual-network, temperature-responsive ionic conductive hydrogel with excellent stretchability, fast temperature responsiveness, and good conductivity was developed by introducing a polyvinylpyrrolidone (PVP)/ tannic acid (TA)/ Fe3+ cross-linked network into the N,N-methylene diacrylamide (MBAA) cross-linked poly(N-isopropylacrylamide-co-acrylamide) (P(NIPAAm-co-AM)) network. Furthermore, the introduction of the PVP/TA/Fe3+ cross-linked network endowed the hydrogel with excellent stretchability and conductivity. By adjusting the molar ratio of TA and Fe3+ to 3:5, a hydrogel with a maximal stretching ratio of 720% and sensitive strain response (GF = 3.61) was achieved, showing a promising application in wearable strain sensors to monitor both large and fine human motions. Moreover, by introducing PNIPAAm with a lower critical solution temperature (LCST), the hydrogel may be used to monitor the environmental temperature through the temperature-conductivity responsiveness, which can be applied as a wearable temperature sensor to detect fever or tissue hyperthermia in the human body.

Ionic conductive hydrogels have broad application prospects in the field of stretchable and flexible electronic products. Among them, salt ion conductive hydrogel has the advantages of high conductivity, simple preparation and low cost, but salt ions are easy to diffuse into the water environment through concentration gradient, and the evaporation of water will lead to salting out. A core-shell strategy is designed, in which the hydrophobic conductive network of polyaniline (PANI) is in situ constructed as a waterproof shell outside the freezing cross-linking and salting out polyvinyl alcohol (PVA) ionic conductive hydrogel (PVA-salt-PANI). This shell effectively locks in water and ions inside, suppressing salt precipitation and ion loss. The obtained PVA-salt-PANI hydrogel has excellent electrical conductivity (5.31 S m-1), good viscoelasticity, temperature resistance, frost resistance (-40°C unfrozen) and self-regeneration ability. Due to the synergistic effect between the dual network polymer chains, it has excellent fracture strain (1784.01%) and tensile strength (10.17 MPa). The environmental stability and versatility of PVA-salt-PANI hydrogel enable it to be used as a human motion sensor, and its waterproof property can reliably sense even in underwater environments. This work provides a novel design strategy for multifunctional sensors that operate reliably under harsh conditions.

Hydrogels with excellent flexibility and conductivity have attracted intensive attention in wearable human monitoring and energy harvesting devices. However, hydrogels containing plenty of water inevitably freeze at subzero temperatures, which deteriorates flexibility and conductivity and limits their practical applications. Herein, an anti-freezing ionic conductive hydrogel is developed by introducing Na+ into the gellan gum/hydrophobically associated polyacrylamide double network. The optimized anti-freezing hydrogel AICH3 achieves outstanding mechanical properties (fracture stress 1.1 MPa and fracture strain 1700%), remarkable conductivity (2.2 S/m), and impressive strain sensitivity (GF = 7.4) at −20 °C. Benefiting from excellent flexibility, conductivity and strain sensitivity, the assembled AICH3-based strain sensor can accurately sense the bending movement of the bionic finger at −20 °C. In addition, the AICH3 can also be used as a stretchable electrode of a triboelectric nanogenerator (TENG), and the assembled AICH3-based TENG can effectively harvest energy and power electronic devices at −20 °C. The comprehensive mechanical and conductive properties of AICH3 at subzero temperatures might be attributed to the multifunctionality of Na+, which not only promotes the fabrication of physically crosslinked gellan gum/hydrophobically associated polyacrylamide double network but also suppresses the formation of ice crystals.

As soft material ionic conductors, ionically conductive hydrogels are of great significance for the development of flexible electronics. However, it is still a great challenge to effectively design functional hydrogel structures to address various practical application scenarios (such as low temperature environments) and expand their application range (such as transparent display devices). In this paper, an anti-bacterial and ionically conductive TEMPO-oxidized cellulose nanofiber/polyvinyl alcohol/quaternary ammonium chitosan/Al3+ (CPQA-EH) hydrogel (conductivity of 7.50 ms cm-1) with high transparency (93.7%) is constructed by a simple method of solution mixing and immersion. An organic solvent is used to induce in situ phase separation and multiple interactions between molecular chains to promote crystallization. The hydrogel network structure is regulated step by step, and nanofibrils are induced in situ to form a nano-fishnet structure. The CPQA-EH ionically conductive hydrogel with a nanofibrous network exhibits excellent tensile strength (1341.86 kPa) and toughness (6992.53 kJ m-3). Meanwhile, it shows low-temperature sensing ability even at -80 °C (freezing point of -122.08 °C). The flexible sensor based on the CPQA-EH conductive hydrogel can sensitively recognize external stimuli (strain/pressure). It shows stable detection of the movement of human joints and vocalization, and the hydrogel with high transparency can also be used as a display device to recognize writing signals.

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Electrochromic materials, prized for their energy efficiency and environmental adaptability, have drawn significant research attention toward energy conservation and sustainability. Conversely, traditional photocured gels face challenges such as high equipment requirements, toxic photoinitiators, and intricate preparation processes. In response, this research develops a facile method for preparing photocured conductive hydrogels, employing tungsten trioxide (WO3) and molybdenum trioxide (MoO3) as non‐toxic photoinitiators, such as reliance on UV equipment and toxic photoinitiators. WO3 and MoO3 synergistically enhance the photo‐response and curing speed, enabling rapid solidification into a conductive hydrogel under sunlight within 3 min. The resulting hydrogel demonstrates remarkable mechanical properties, including 400% elongation, self‐healing capabilities (restored conductivity within 5 min), and good water–retention, showcasing excellent performance in flexible electrochromic devices and stress sensors. The present study delves into the gel's curing mechanism, electrical and mechanical properties, and self‐healing capability, inspiring future applications in electronic devices, flexible circuits, and smart materials.

The lignocellulosic skeleton is obtained through delignification and alkali treatment, which not only preserves the inherent anisotropy of wood but also introduces naturally occurring ion channels. The resulting cellulose skeleton is integrated with a poly(vinyl alcohol)/polyacrylamide double network to fabricate a wood‐derived double‐network hydrogel. To ensure ionic conductivity while maintaining excellent mechanical properties, a sodium sulfate ion solution and glycerol were incorporated into the system, achieving a conductivity of up to 2.20 S m−1, a tensile strength of 2.06 MPa, and a tensile strain of 13.6%. This wood‐based conductive hydrogel is employed as an electrolyte in supercapacitors. The specific capacitance values of the supercapacitor at different scan rates. Furthermore, this hydrogel can be used to fabricate flexible sensors. Such sensors exhibit stable periodic signals under different bending angles, and are particularly stable and sensitive at a 60° bend, making them suitable for simulating dynamic movements. This study leverages the hierarchical porosity of wood and a dual‐network design to develop a mechanically robust and conductive hydrogel. The material holds great potential for applications in energy storage and flexible electronic devices, offering a promising strategy for the development of high‐performance systems.

Self‐healing ionic conductive hydrogels have shown significant potential in applications like wearable electronics, soft robotics, and prosthetics because of their high strain sensitivity and mechanical and electrical recovery after damage. Despite the enormous interest in these materials, conventional fabrication techniques hamper their use in advanced devices since only limited geometries can be obtained, preventing proper conformability to the complexity of human or robotic bodies. Here, a photocurable hydrogel with excellent sensitivity to mechanical deformations based on a semi‐interpenetrating polymeric network is reported, which holds remarkable mechanical properties (ultimate tensile strain of 550%) and spontaneous self‐healing capabilities, with complete recovery of its strain sensitivity after damages. Furthermore, the developed material can be processed by digital light processing 3D printing technology to fabricate complex‐shaped strain sensors, increasing mechanical stress sensitivity with respect to simple sensor geometries, reaching an exceptional pressure detection limit below 1 Pa. Additionally, the hydrogel is used as an electrolyte in the fabrication of a laser‐induced graphene‐based supercapacitor, then incorporated into a 3D‐printed sensor to create a self‐powered, fully integrated device. These findings demonstrate that by using 3D printing, it is possible to produce multifunctional, self‐powered sensors, appropriately shaped depending on the various applications, without the use of bulky batteries.

Recent advancements in wearable electronic technology demand advanced power sources to be flexible, deformable, durable, and sustainable. An ionic-solution-modified conductive hydrogel-based triboelectric nanogenerator (TENG) has advantages in wearable devices. However, fabricating a conductive hydrogel with better mechanical and electrical properties is still a challenge. Herein, a simple approach is developed to insert ion-rich pores inside the hydrogel, followed by ionic solution soaking. The suggested ionic conductive hydrogel is obtained by cross-linking the polyvinyl alcohol (PVA) hydrogel and carboxymethyl cellulose sodium salt (CMC), followed by soaking in the ionic solution. Furthermore, a flexible and shape-adaptable single-electrode TENG (S-TENG) is fabricated by combinations of ionic-solution-modified dual-cross-linked CMC/PVA hydrogel and silicone rubber. Additionally, the effects of the CMC concentration, type of ionic solution, and concentration of optimized ionic solutions on the hydrogel properties and S-TENG output performance are studied systematically. The well-dispersed CMC- and PVA-based hydrogel provides ion-rich pores with high ion migration, leading to enhanced conductivity. The fabricated S-TENG delivers maximum output performance in terms of voltage, current, and charge density of ∼584 V, 25 μA, and 120 μC/m2, respectively. The rectified S-TENG-generated energy is used to charge capacitors and to power a portable electronic display. In addition to energy harvesting, the S-TENG is successfully demonstrated as a touch sensor that can automatically control the light and the speaker based on human motions. This investigation provides a deep insight into the influence of the hydrogel on the device performance and gives a guidance for designing and fabrication of highly flexible and stretchable TENGs.

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Flexible sensors are garnering substantial interests for various promising applications, including medical electronics, environmental monitoring, and wearable devices. Developing a flexible sensor with high compliance, high sensitivity, and high reliability through the construction of a novel composite conductive hydrogel based on the synergistic enhancement effect of conductive polymers and metal ions is a remarkable achievement. Herein, an electronic/ionic‐conductive double network hydrogel (polypyrrole (PPy)/carboxymethyl cellulose (CMC)‐Al3+/polyvinyl alcohol (PVA)) with soft compliance, highly conductivity, and stability is presented. Moreover, owing to the synergistic reinforcement effect of the relatively immobilized “islands” of PPy particles and large amounts of movable “bridges” of aluminum ions (Al3+) within the double network hydrogel, the as‐optimized PPy/CMC‐Al3+/PVA composite gels exhibit excellent conductivity (σ = 3.47 ± 0.25 S m−1) and mechanical properties (E = 18.53 ± 0.67 kPa). Furthermore, it has been developed as strain sensors with relatively high linear sensitivity (gauge factor = 2.58) within a broad linearity range (0–400%). It can also be served as a monitoring devices for subtle physiological signals emanating from various parts of the human body. The robust sensor has great potential to be developed as wearable electronic devices and applied in healthcare monitoring fields.

Wearable devices impose stringent demands on sensor materials, structural processes, material costs, wearability, and operational performance. This study developed an innovative sandwich-structured flexible piezoelectric sensor fabricated using ionic conductive hydrogel and PVDF film. The fabrication process involved the preparation of ionic conductive PVA/gelatin double-network hydrogel (CPGH) through a freeze-thaw cycle and saltwater immersion process. The sandwich structure was developed using a CPGH and PVDF film, which effectively enhanced the deformation capacity of the PVDF film, stress concentration, and internal polarization intensity. Test results indicated that the proposed sensor can generate linear output and has higher sensitivity, short response times, robust stability, and reliability. The sensor can be used to monitor the bending angle of finger joints, displaying an impressive linear fit with a coefficient of determination ( ${R} ^{{2}}$ ) of 0.97538 within the range of 30° to 135°. Furthermore, the sensor has potential in other applications, which involve distinguishing different human gait patterns.

Benefiting from the good electromechanical performance, ionic conductive hydrogel can easily convert the deformation into electrical signals, showing great potential in wearable electronic devices. However, due to the high water content, icing and water evaporation problems seriously limit their development. Although additives can ease these disadvantages, the accompanying performance degradation and complex preparation processes couldn't meet application needs. In this work, a convenient method was provided to prepare ionic conductive hydrogels with sensitive electromechanical performance, harsh environmental tolerance, and long-term stability without additives. Based on the hydratability between metal ions and water molecules resulting in spatial condensation of the hydrogel framework, the hydrogel exhibits good flexibility and ionic conductivity (70.3 mS/cm). Furthermore, the metal salt can bind with water molecules to reduce the vapor pressure, thus endowing the hydrogel with good freezing resistance (-40 °C) and long-term stability over a wide temperature range (-20 °C-50 °C). Based on these unique advantages, the hydrogel shows good sensitivity. Even in a harsh environment, it still maintained excellent stability (-20 °C-50 °C, GF = 2.2, R2 > 0.99). Assembled with a Wi-Fi device, the hydrogel sensor demonstrates good health activity and physiological state detection performance, demonstrating great potential for wearable medical devices.

Conductive hydrogels have been considered ideal candidate materials for fabricating human-motion sensors due to their combination properties of electronic and tissue-like soft nature and the similar functions of human skin with mechanical and sensory properties. However, the perfect integration of multiple functionalities such as environmentally tolerant, stretchable, self-adhesive, self-healing, transparent, high sensitivity, and rapid response in one system (all-in-one) is still a significant challenge. Herein, a novel ionic conductive hydrogel platform with excellent comprehensive performance through multiple dynamic interactions was prepared by employing [BMIm]BF4/glycerol/water ternary solvent system. The dynamic hydrogen bonds, coordination bonds, and electrostatic interaction within the network endows the hydrogel excellent mechanical performance. The synchronous effect of ionic liquids and glycerol realized the high ionic conductivity, transparency, environmentally tolerance, and long-term stability. Sensors based on this hydrogel have a relatively high sensitivity, a fast response time, and a wide linear sensing range in monitoring human movements. It can also serve as electronic skin, like human skin, for touchscreen pen and writing. Thus, the all-in-one hydrogel was concluded to hold considerable promise for constructing the next generation of hydrogel platforms for human-motion sensors.

Ionic conductive hydrogels have attracted great attention due to their good flexibility and conductivity in flexible electronic devices. However, because of the icing and water loss problems, the compatibility issue between the mechanical properties and conductivity of hydrogel electrolytes over a wide temperature range remains extremely challenging to achieve. Although, antifreezing/water-retaining additives could alleviate these problems, the reduced performance and complex preparation methods seriously limit their development. In this work, a simple strategy without additives was provided to prepare an ionic conductive cellulose hydrogel (ICH) in one step through molten salt hydrate. The hydrogel featured controllable mechanical properties (0.19 MPa - 0.67 MPa), high ionic conductivity (78.96 mS/cm), excellent freezing resistance (-80 °C). More importantly, due to the existing metal salts component, the ICH exhibited long-term stability in water-retention ability (75.6 %, after 90 days) and ionic conductivity (85 %, after 90 days) over a wide working temperature range (-80 °C to 40 °C). Benefiting from these advantages, the ICH exhibited excellent electromechanical performance in human movement detection and movement direction identification, indicating a promising apply for flexible electronic device.

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Wearable devices made of ionic conductive hydrogels have drawn great attention within the scientific community, but there has been a crucial issue in making multimodal sensors as most of the existing hydrogel based sensors could only detect one kind of signal. in this study, we presented a new 3D printable hydrogel (named as GSA-PNIPAM@Fe3+/AS) made of a semi-interpenetrating polymer network which was synthesized by photocuring a three-component mixture of gelatin, sodium alginate, and N-isopropylacrylamide followed by soaking it successively in sodium ferric ethylenediaminetetraacetate and ammonium sulfate solutions. Using the Hofmeister effect, we reduced the hydration layer around the gelatin which helped form a triple-helix structure and led to a closely cross-linked, swell-resistant network so the resulting hydrogel had excellent properties such as a toughness of 661 kJ m-3, a compressive modulus of 30 MPa, an ionic conductivity of 1.78 S m-1, and long-lasting resistance to swelling over a long time and after being submerged in water for 12 days, the equilibrium swelling ratio reached a plateau at 80%. moreover, the hydrogel showed outstanding responsiveness within a wide temperature range from -10 to 50 °C. sensors made from this hydrogel could accurately record multidimensional human movement both on land and underwater, keep monitoring body temperature all the time, and distinguish underwater Morse code signals for aquatic communication. This research clarified a flexible method for creating multimodal wearable sensors intended to work in various difficult environments thus increasing the usefulness of flexible electronic devices.

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In this paper, ternary DES (choline chloride, glycerol, Lewis acid) was used to pretreat lignocellulose, and the DES solution with dissolved lignin was utilized as the medium of hydrogel to prepare DES-based polyacrylic acid/polyvinyl alcohol (PAA/PVA) double network hydrogels with great mechanical properties, self-adhesion, and high electrochemical sensitivity. The entanglement of PAA with PVA chains, the covalent linkage between Al3+ and PAA chains and the metal phenol network (MPN) formed by Al3+ and lignin improved the mechanical properties of the hydrogels, enabling the prepared hydrogels to achieve a tensile strain of 400 % and an elongation at break of 150 kPa. Secondly, the introduction of DES solution endowed the hydrogel with excellent electrical sensing ability and anti-freezing property, so that the hydrogel still maintains good flexibility and ionic conductivity at -20 °C. It was also found that the above hydrogel can achieve a high gauge factor of 4.19 as a flexible sensor, which provides scientific ideas for the application of the pretreated DES solution in the field of flexible wearable.

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In the past two decades, ionic conductive hydrogel has attracted tremendous research interests for their intrinsic characteristics in the field of flexible sensor. However, synchronous achievement of high mechanical strength, satisfied ionic conductivity, and broad adhesion to various substrates is still a challenge. Herein, a novel zwitterionic composite hydrogel that displayed excited strechability (up to 900%), satisfied strength (about 30 kPa), high ionic conductivity (1.2 mS cm-1 ), and adhesion to polar and nonpolar materials is fabricated though the combination of waterborne polyurethanes (PU) and poly(sulfobetaine zwitterion-co-acrylamide) (SAm). Especially, this facile strategy demonstrates that PU has a synergistic effect on enhancing mechanical strength and ionic conductivity for ionic conductive hydrogel. Moreover, the hydrogel-based strain/stress sensor shows high sensitivity, wide sensing range, great stability, and accuracy for human body movements detecting and voice recognition. This novel ionic conductive hydrogel has promoted the development of wearable devices.

Fabrication of stretchable chemical sensors becomes increasingly attractive for emerging wearable applications in environmental monitoring and health care. Here, for the first time, chemically derived ionic conductive polyacrylamide/carrageenan double-network (DN) hydrogels are exploited to fabricate ultrastretchable and transparent NO2 and NH3 sensors with high sensitivity (78.5 ppm-1) and low theoretical limit of detection (1.2 ppb) in NO2 detection. The hydrogels can withstand various rigorous mechanical deformations, including up to 1200% strain, large-range flexion, and twist. The drastic mechanical deformations do not degrade the gas-sensing performance. A facile solvent replacement strategy is devised to partially replace water with glycerol (Gly) molecules in the solvent of hydrogel, generating the water-Gly binary hydrogel with 1.68 times boosted sensitivity to NO2 and significantly enhanced stability. The DN-Gly NO2 sensor can maintain its sensitivity for as long as 9 months. The high sensitivity is attributed to the abundant oxygenated functional groups in the well-designed polymer chains and solvent. A gas-blocking mechanism is proposed to understand the positive resistance shift of the gas sensors. This work sheds light on utilizing ionic conductive hydrogels as novel channel materials to design highly deformable and sensitive gas sensors.

Conductive hydrogels are polymers that respond to mechanical stimuli and have been widely used in wearable sensors and soft machines. Myriads applications posed high-performance requirements for hydrogels: compliance, stretchability, and high sensitivity. However, sensors based on flexible polymers often struggle to achieve a highly sensitive response. We propose a highly sensitive hydrogel strain sensor based on the Kirigami structure. The structure solves the problem of low stretchability caused by the high stiffness of double-network hydrogel. It greatly improves the stretchability of the strain sensor by customizing the cutting of a high-toughness PAAM-PAA double-network hydrogel. We further analyze the deformation and sensing characteristics through simulation and experiments and successfully apply them to monitor human motion.

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This paper reports a novel high-deformable and transparent triboelectric hydrogel sensor (THS) with anti-freezing and anti-drying properties for physiology sensing and motion monitoring. It is the first time to fabricate the micro-pyramidal structure on hydrogel's surface for a highly sensitive self-powered sensor. Excellent mechanical and electrical performances can be obtained due to deformable and conductive ionic hydrogel with anti-freezing and anti-drying properties. It shows no significant variations of output signals after being stored at −20°С for seven days and 60°С for 1-day compared with placed at room temperature. Besides, combined with the same processing method of the triboelectric PDMS layer, THS shows an instant response to physiological movement, including breathing with a mask, finger bending and sitting/squatting down. This work provides an insightful method for hydrogel in the application of the physiological sensors field.

High hydraulic pressure in air-cathode microbial fuel cells (MFCs) can lead to severe cathodic water leakage and power reduction, thereby hindering the practical applications of MFCs. In this study, an alternative air cathode without a diffusion layer was developed using a cross-linked hydrogel, oxidized konjac glucomannan/2-hydroxypropytrimethyl ammonium chloride chitosan (OKH), for ion bridging. The cathode was placed horizontally to avoid hydraulic pressure on its surface. Ion transportation was sustained with a minimal OKH hydrogel loading of 10 mg/cm2. A maximum power density of 1.0 ± 0.04 W/m2 was achieved, which was only slightly lower than the 1.28 ± 0.02 W/m2 of common air cathodes. Moreover, the cost of the OKH hydrogel is only $0.12/m2, which can reduce ~85% of the cathode cost without using the advanced polyvinylidene fluoride diffusion layer. Therefore, the development of this new diffusion-layer-free air cathode using conductive ionic hydrogel provides a low-cost strategy for stable MFC operation, thereby demonstrating great potential for practical applications of MFC technology.

This paper reported a double-network (DN) ion-conducting hydrogel membrane sensor for humidity sensing. Lithium bromide was introduced into the hydrogel by the simple immersion method to improve the antifreezing, anti-drying ability and moisture sensitivity of the hydrogel. Also, this sensor exhibited deformability (withstand 100% tensile strain), high transmittance in the visible light range (above 89%), and a wide relative humidity (RH) detection range (22-98%). The sensitivity of the membrane humidity sensor prepared in this paper was greatly improved compared to the bulk hydrogel sensor. For example, the sensor's response at 98% relative humidity was increasing 16,280 times. It was found that the response has an exponential relationship with relative humidity. Also, this humidity sensor based on a hydrogel membrane can detect changes in the relative humidity of the environment caused by human breathing and finger contact.

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In this study, we successfully prepared a composite hydrogel that integrates the superior conductivity of carbon nanotubes (CNTs) with the elasticity of hydrogels. This was achieved by depositing a layer of hydroxylated CNTs onto a polyacrylamide (PAM) hydrogel. The PAM hydrogel was immersed in a CNT dispersion at 50°C and subjected to ultrasonic treatment for 30 min, followed by a 50% dehydration process to achieve densification. This process enabled the adsorption of CNTs onto the PAM hydrogel surface, forming robust physical entanglements and hydrogen bonds with the PAM polymer chains. Consequently, this significantly strengthened the interfacial adhesion between the CNTs and the hydrogel, yielding a more durable and resilient composite material. Impressively, the adhesion strength between the CNT layer and the PAM‐CNT composite hydrogel surface reached a remarkable 61.75 J/m2, contributing to its good electrical conductivity (1.284 ± 0.034 S/m), stability, and mechanical properties. Additionally, our study explores the application of the composite material in wearable devices by quantifying its response to pressure, bending, and stretching through resistance change measurements. The findings indicate that this research introduces a new method for preparing conductive hydrogels and offers valuable insights for their use in electronics, biomedicine, and various other related domains.

In this study successfully prepared AG@MXene/CC composite electrodes by employing a thermosolvation-ultrasonication technique combined with an impregnation method. This approach uniformly dispersed MXene, known for its high electrochemical properties, onto the surface of carbon cloth (CC) through biomass-derived AG hydrogels featuring a three-dimensional network structure. The hydrogen bonding and van der Waals forces between AG and MXene were harnessed to enhance material interactions, thereby improving electron transfer efficiency and electrocatalytic activity. Experimental results demonstrated that the composite electrode could achieve up to 96.16 % degradation rate of tigecycline (TGC) within 30 min under optimal conditions. Furthermore, this study delved into the reaction mechanism of the electrocatalytic system, clarifying the key roles of H* and H2O2 generated at the cathode, as well as ·OH and active chlorine species on the anode's surface during the TGC degradation process. A synergistic catalytic mechanism for the cathode and anode was proposed. The intermediates that may be formed during TGC degradation were analyzed and their toxicity was evaluated, confirming the high biosafety of the treated wastewater. This work not only offers new insights for designing efficient and stable electrocatalysts but also broadens the application scope of the green material AG in the electrocatalytic degradation of antibiotics.

Tough hydrogels show great potential applied in flexible electronics, sensors and soft robotics, but it remains challenging to combine high strength, toughness and stability. Here, we report the use of carbon dots (CDs) to induce the formation of crystalline domains, to give materials with favourable properties. The CDs act as nanoscale nucleation-sites within polyvinyl alcohol hydrogels, forming dense crystalline domains that serve as physical crosslinking sites. These domains enable a “pinning effect” that enhances energy dissipation and restricts crack propagation. The resulting hydrogels exhibit strong mechanical performance, including tensile strength up to 156 MPa and toughness of 225 MJ m-3, while also maintaining good swelling resistance. This strategy is generalizable across different types of CDs and polymer systems. In addition, the hydrogels demonstrate stable conductivity under water, making them suitable for applications in underwater motion sensing and flexible supercapacitors. This work provides a scalable approach to engineer robust, multifunctional hydrogels. Tough hydrogels have potential in a range of applications, but achieving the required balance of properties can be challenging. Here, the authors report the use of carbon dots to induce the formation of crystalline domains in hydrogels, to give materials with favourable properties.

Although flexible double layer capacitors based on hydrogels overcome the drawbacks of commercial double layer capacitors such as low safety and non-deformability, it is still considered as attractive challenges to achieve high conductivity for hydrogel electrolytes as well as high operating voltages for hydrogel flexible supercapacitors. In this paper, ion migration channels were engineered by immobilizing positive and negative charges on polymer skeleton and dispersing cellulose nanofibers in the polymerized polyelectrolyte network, providing ultra-high ionic conductivity (103 mS cm-1). In addition, K3[Fe(CN)6] was introduced through a soaking method, leading to redox reactions on the surface of carbon electrode during charging and discharging, supporting a relatively wide voltage window (1.8 V). Moreover, the specific capacitance at high current remained 55 % of the specific capacitance at low current, indicating excellent rate performance. In addition, the device displayed high cycling stability (80.05 % after 10,000 cycles). Notably, we successfully light up the red LED with only one device. Accordingly, this work provides a feasible design concept for the development of cellulose nanofibers (CNF) hydrogel-based solid-state electrolyte with high conductivity for flexible supercapacitors with wide potential window and high energy density.

The recycling of agricultural residues into functional nanomaterials offers a sustainable pathway for next-generation electronics and energy devices. In this study, sugarcane bagasse was valorized to synthesize aluminum/copper-doped carbon dots (Al/Cu-CDs) embedded in a magnetite-graphene oxide (Fe3O4-GO) reinforced carboxymethyl cellulose–2-acrylamido-2-methyl-1-propanesulfonic acid (CMC-AMPS) hydrogel by a sustainable, in situ one-pot microwave-assisted approach. The sequential doping of Al and Cu ions in the carbon dots enables precise tuning of electronic structure, leading to significantly enhanced electrical conductivity, permittivity, and charge storage capacity compared to undoped analogs. Physicochemical characterizations, including FTIR, TEM, and UV-vis spectroscopy, confirm uniform nanoparticle distribution, and nanoscale features, with particle sizes in the range of 2.8–5.4 nm for Cu-CDs and 5.0–5.4 nm for Al/Cu-CDs. The resulting composite exhibits enhanced multifunctionality, combining magnetic, conductive, and biocompatible properties. Electrical measurements revealed a four-decade increase in conductivity and permittivity upon aluminum doping, alongside reduced impedance, indicating superior charge mobility. These findings demonstrate that the sustainable Al/Cu–Fe3O4/GO-CMC-AMPS nanocomposite is a promising candidate for applications in energy storage, supercapacitors, and biosensing applications.

This research investigates the transformative impact of incorporating unmodified multi‐walled carbon nanotubes (um‐MWCNTs) on properties of guar gum (GG)‐based hydrogel. The study focuses on the enhancement of thermal stability, mechanical strength, and electrical properties of hydrogel composite. Thermal analysis reveals a significant increase in residual weight remaining at 430°C from 3% to 10% with the addition of 0.2 wt% um‐MWCNTs to GG hydrogel. Viscoelastic properties of hydrogel composite investigated by rheology analysis observed that enhancements in storage modulus from 0.2 to 2.2 MPa indicative of enhanced structural integrity. Moreover, electrical conductivity exhibits a substantial increase with the addition of nanotubes, indicating the potential applicability of the composite in electronic and sensing applications. This research showcases the potential of GG/um‐MWCNT composites for diverse applications in biomedicine, sensors, and advanced materials. Distribution of um‐MWCNTs into guar‐gum matrix to obtain maximum benefits. Inclusion of um‐MWCNTs improves the rheological properties of GG/um‐MWCNTs composites. Rheological properties can be tuned with um‐MWCNT content. MWCNTs improved thermal stability of the GG hydrogel. MWCNTs improved electrical conductivity of the GG hydrogel.

Electronic conductive hydrogels have prompted immense research interest as flexible sensing materials. However, establishing a continuous electronic conductive network within a hydrogel is still highly challenging. Herein, we develop a new strategy to establish a continuous corrugated carbon network within a hydrogel by embedding carbonized crepe paper into the hydrogel with its corrugations perpendicular to the stretching direction using a casting technique. The corrugated carbon network within the as-prepared composite hydrogel serves as a rigid conductive network to simultaneously improve the tensile strength and conductivity of the composite hydrogel. The composite hydrogel also generates a crack structure when it is stretched, enabling the composite hydrogel to show ultrahigh sensitivity (gauge factor = 59.7 and 114 at strain ranges of 0-60 and 60-100%, respectively). The composite hydrogel also shows an ultralow detection limit of 0.1%, an ultrafast response/recovery time of 75/95 ms, and good stability and durability (5000 cycles at 10% strain) when used as a resistive strain sensing material. Moreover, the good stretchability, adhesiveness, and self-healing ability of the hydrogel were also effectively retained after the corrugated carbon network was introduced into the hydrogel. Because of its outstanding sensing performance, the composite hydrogel has potential applications in sensing various human activities, including accurately recording subtle variations in wrist pulse waves and small-/large-scale complex human activities. Our work provides a new approach to develop economical, environmentally friendly, and reliable electronic conductive hydrogels with ultrahigh sensing performance for the future development of electronic skin and wearable devices.

A carbon nanotube-doped octapeptide self-assembled hydrogel (FEK/C) and a hydrogel-based polycaprolactone PCL composite scaffold (FEK/C3-S) were developed for cartilage and subchondral bone repair. The composite scaffold demonstrated modulated microstructure, mechanical properties, and conductivity by adjusting CNT concentration. In vitro evaluations showed enhanced cell proliferation, adhesion, and migration of articular cartilage cells, osteoblasts, and bone marrow mesenchymal stem cells. The composite scaffold exhibited good biocompatibility, low haemolysis rate, and high protein absorption capacity. It also promoted osteogenesis and chondrogenesis, with increased mineralization, alkaline phosphatase (ALP) activity, and glycosaminoglycan (GAG) secretion. The composite scaffold facilitated accelerated cartilage and subchondral bone regeneration in a rabbit knee joint defect model. Histological analysis revealed improved cartilage tissue formation and increased subchondral bone density. Notably, the FEK/C3-S composite scaffold exhibited the most significant cartilage and subchondral bone formation. The FEK/C3-S composite scaffold holds great promise for cartilage and subchondral bone repair. It offers enhanced mechanical support, conductivity, and bioactivity, leading to improved tissue regeneration. These findings contribute to the advancement of regenerative strategies for challenging musculoskeletal tissue defects.

Soft, conductive, and stretchable sensors are highly desirable in many applications, including artificial skin, biomonitoring patches, and so on. Recently, a combination of good electrical and mechanical properties was regarded as the most important evaluation criterion for judging whether hydrogel sensors are suitable for practical applications. Herein, we demonstrate a novel carboxylated carbon nanotube (MWCNT-COOH)-embedded P(AM/LMA)/SiO2@PANI hydrogel. The hydrogel benefits from a double-network structure (hydrogen bond cross-linking and hydrophobic connectivity network) due to the role of MWCNT-COOH and SiO2@PANI as cross-linkers, thus resulting in tough composite hydrogels. The obtained P(AM/LMA)/SiO2@PANI/MWCNT-COOH hydrogels exhibited high tensile strength (1939 kPa), super stretchability (3948.37%), and excellent strain sensitivity (gauge factor = 11.566 at 100-1100% strain). Obviously, MWCNT-COOH not only improved the electrical conductivity but also enhanced the mechanical properties of the hydrogel. Therefore, the integration of MWCNT-COOH and SiO2@PANI-based hydrogel strain sensors will display broad application in sophisticated intelligence, soft robotics, bionic prosthetics, personal health care, and other fields using inexpensive, green, and easily available biomass.

In the era of big data, developing next-generation self-powered continuous energy harvesting systems is of great importance. Taking advantage of fallen leaves’ specific structural advantage gifted by nature, we propose a facile approach to convert fallen leaves into energy harvesters from ubiquitous moisture, based on surface treatments and asymmetric coating of hygroscopic iron hydrogels. Upon moisture absorption, a water gradient is established between areas with/without hydrogel coating, and maintained due to gel-like behaviors and leaf veins for water retention and diffusion restriction, thus forming electrical double layers over the leaf surface and showing capacitance-like behavior for energy charging and discharging. Besides, the specific leaf cell structures with small grooves enabled uniform carbon coatings instead of aggregations, and high electrical conductivity, resulting in 49 μA/cm2 and 497 μW/cm3 electrical output, achieving competitive performance with the state-of-art and potential for lower environmental impact compared to other types of energy harvesters. In this work, authors convert fallen leaves into energy harvesters using hygroscopic iron hydrogel, achieving continuous power generation from moisture. The device delivers high current density and power output with potential for lower environmental impact compared to alternative harvesters.

The operating temperature of hydrogels, especially at low temperatures, is crucial due to their wide applicability in soft robots, sensors, and electronic skin. Hydrogels are often used at room temperature, but their performance may deteriorate at low temperatures. Therefore, it is crucial to develop hydrogels that can be used at low temperatures to expand their range of use. Herein, we have proposed a simple one-pot method to prepare a frost-resistant (-70 °C) and conductive hydrogel consisting of a glycerol (Gly)-water binary solvent. We have added tannic acid (TA)-coated carboxymethylated cellulose nanofibrils (CMCNFs) to poly (vinyl alcohol) (PVA) as a functional filler to improve the hydrogel's mechanical properties. The introduction of sulfonated carbon nanotubes (SCNT) has provided the hydrogel with high conductivity (0.1 S/m), strain sensitivity (gauge factor of 3.76), and cyclic stability (1600 cycles). Due to the strong hydrogen bonding and physical entanglement effects between the components, the hydrogel exhibied excellent tensile properties (297 %), high toughness (0.44 MJ/m3), and a high Young's modulus (1.25 MPa). These characteristics ensure that the hydrogel is well suited for low-temperature environments, health monitoring, and wearable devices.

Shortages of organs and damaged tissues for transplantation have prompted improvements in biomaterials within the field of tissue engineering (TE). The rise of hybrid hydrogels as electro-conductive biomaterials offers promise in numerous challenging biomedical applications. In this work, hybrid printable biomaterials comprised of alginate and gelatin hydrogel systems filled with carbon nanofibers (CNFs) were developed to create electroconductive and printable 3-D scaffolds. Importantly, the preparation method allows the formation of hydrogels with homogenously dispersed CNFs. These hybrid composite hydrogels were evaluated in terms of mechanical, chemical and cellular response. They display excellent mechanical performance, which is augmented by the CNFs, with Young's moduli and conductivity reaching 534.7 ± 2.7 kPa and 4.1 × 10-4 ± 2 × 10-5 S/cm respectively. CNF incorporation enhances shear-thinning behaviour, allowing ease of 3-D printing. In-vitro studies indicate improved cellular proliferation compared to controls. These conductive hydrogels have the potential to be used in a myriad of TE strategies, particularly for those focused on the incorporation of electroconductive components for applications such as cardiac or neuronal TE strategies.

It is often assumed that carbon nanotubes (CNTs) stimulate neuronal differentiation by transferring electrical signals and enhancing neuronal excitability. Given this, CNT–hydrogel composites are regarded as potential materials able to combine high electrical conductivity with biocompatibility, and therefore promote nerve regeneration. However, whether CNT–hydrogel composites actually influence neuronal differentiation and maturation, and how they do so remain elusive. In this study, CNT–hydrogel composites are prepared by in situ polymerization of poly(ethylene glycol) around a preformed CNT meshwork. It is demonstrated that the composites facilitate long‐term survival and differentiation of pheochromocytoma 12 cells. Adult neural stem cells cultured on the composites show an increased neuron‐to‐astrocyte ratio and higher synaptic connectivity. Moreover, primary hippocampal neurons cultured on composites maintain morphological synaptic features as well as their neuronal network activity evaluated by spontaneous calcium oscillations, which are comparable to neurons cultured under control conditions. These results indicate that the composites are promising materials that could indeed facilitate neuronal differentiation while maintaining neuronal homeostasis.

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Developing conductive hydrogels has led to significant advancements in bioelectronics, especially in the realms of neural interfacing and neuromodulation. Despite this progress, the synthesis of hydrogels that simultaneously exhibit superior mechanical stretchability, robust bioadhesion, and high conductivity remains a significant challenge. Traditional approaches often resort to high filler concentrations to achieve adequate electrical conductivity, which detrimentally affects the hydrogel's mechanical integrity and biocompatibility. In this study, we present a multifunctional conductive hydrogel, designated as PAACP, which is engineered from a polyacrylamide-poly(acrylic acid) (PAM-PAA) matrix and enhanced with polydopamine-modified carbon nanotubes (CNT-PDA). This composition ensures an exceptional conductivity of 9.52 S/m with a remarkably low carbon nanotube content of merely 0.33 wt %. The hydrogel exhibits excellent mechanical properties, including low tensile modulus (∼100 kPa), high stretchability (∼1000%), and high toughness (7.33 kJ m-2). Moreover, the synergistic action of catechol and NHS ester functional groups provides strong tissue adhesive strength (107.14 kPa), ensuring stable bioelectronic-neural interfaces. As a cuff electrode, it enables suture-free implantation and bidirectional electrical communication with the sciatic nerve, which is essential for neuromodulation. Leveraging these capabilities, our hydrogel is integrated into a closed-loop system for sciatic nerve repair, significantly enhancing real-time feedback driven nerve regeneration and accelerating functional recovery. This work offers a strategy for dynamic, personalized neuromodulation in nerve repair and clinical applications.

Flexible wearable electronic devices based on hydrophobic, conductive hydrogels have attracted widespread attention in the field of underwater sensing. However, traditional homogeneous hydrogels tend to compromise their conductivity and sensing performance when achieving hydrophobicity, and the high complexity of marine environments further reduces their sensing performance and service life. Here, we develop a seawater-resistant conductive hydrogel with ultrahigh sensitivity and self-healing ability by the introduction of a skin-like heterogeneous structure, consisting of a hydrophobic outer layer that protects against seawater and a conductive internal layer that senses. Based on a heterogeneous structure obtained through surface hydrophobic modification of confined nitrogen-alkylation reaction, the conductive hydrogel simultaneously achieves satisfying seawater resistance (contact angle of 123.2°), high ionic conductivity (2.86 S m-1), and excellent sensing sensitivity in seawater (GF = 6.15), harmonizing the contradiction between water resistance and sensing of traditional hydrophobic hydrogels. In addition, abundant hydrogen-bonding and dipole-dipole interactions endow the heterogeneous hydrogel with an outstanding self-healing ability, exhibiting high-efficiency self-healing behavior in seawater. Underwater strain sensors constructed with the heterogeneous hydrogel can be used for detecting human motion in simulated seawater environments and real-time signal transmission, showcasing their great potential as wearable electronic devices in the marine sensing field.

The development of self‐healing conductive hydrogels is critical in electroactive nerve tissue engineering. Typical conductive materials such as polypyrrole (PPy) are commonly used to fabricate artificial nerve conduits. Moreover, the field of tissue engineering has advanced toward the use of products such as hyaluronic acid (HA) hydrogels. Although HA‐modified PPy films are prepared for various biological applications, the cell–matrix interaction mechanisms remain poorly understood; furthermore, there are no reports on HA‐modified PPy‐injectable self‐healing hydrogels for peripheral nerve repair. Therefore, in this study, a self‐healing electroconductive hydrogel (HASPy) from HA, cystamine (Cys), and pyrrole‐1‐propionic acid (Py‐COOH), with injectability, biodegradability, biocompatibility, and nerve‐regenerative capacity is constructed. The hydrogel directly targets interleukin 17 receptor A (IL‐17RA) and promotes the expression of genes and proteins relevant to Schwann cell myelination mainly by activating the interleukin 17 (IL‐17) signaling pathway. The hydrogel is injected directly into the rat sciatic nerve‐crush injury sites to investigate its capacity for nerve regeneration in vivo and is found to promote functional recovery and remyelination. This study may help in understanding the mechanism of cell–matrix interactions and provide new insights into the potential use of HASPy hydrogel as an advanced scaffold for neural regeneration.

Chronic diabetic wounds remain a globally recognized clinical challenge. They occur due to high concentrations of reactive oxygen species and vascular function disorders. A promising strategy for diabetic wound healing is the delivery of exosomes, comprising bioactive dressings. Metformin activates the vascular endothelial growth factor pathway, thereby improving angiogenesis in hyperglycemic states. However, multifunctional hydrogels loaded with drugs and bioactive substances synergistically promote wound repair has been rarely reported, and the mechanism of their combinatorial effect of exosome and metformin in wound healing remains unclear. Here, we engineered dual-loaded hydrogels possessing tissue adhesive, antioxidant, self-healing and electrical conductivity properties, wherein 4-armed SH-PEG cross-links with Ag+, which minimizes damage to the loaded goods and investigated their mechanism of promotion effect for wound repair. Multiwalled carbon nanotubes exhibiting good conductivity were also incorporated into the hydrogels to generate hydrogen bonds with the thiol group, creating a stable three-dimensional structure for exosome and metformin loading. The diabetic wound model of the present study suggests that the PEG/Ag/CNT-M + E hydrogel promotes wound healing by triggering cell proliferation and angiogenesis and relieving peritraumatic inflammation and vascular injury. The mechanism of the dual-loaded hydrogel involves reducing the level of reactive oxygen species by interfering with mitochondrial fission, thereby protecting F-actin homeostasis and alleviating microvascular dysfunction. Hence, we propose a drug–bioactive substance combination therapy and provide a potential mechanism for developing vascular function-associated strategies for treating chronic diabetic wounds.

Wearable electronic devices based on conductive hydrogels have gained attention for applications in health monitoring, electronic skin, and human-computer interaction. However, limited functionality hinders the development of conventional hydrogels. Herein, a multifunctional poly(acrylic acid)/carboxymethyl cellulose/polydopamine-ethylene glycol (PAA/CMC/PDA-EG) hydrogel is developed via free radical polymerization initiated by a PDA-Fe3+ redox system and dynamic metal coordination. The hydrogel exhibits excellent mechanical properties (tensile strength, 71 kPa; elongation, 872%), strong adhesion, self-healing ability, and environmental tolerance (nonfreezing at -15 °C). It functions as a strain sensor with a wide working range (0-500%) and high sensitivity (GF = 10.49), suitable for human motion detection. As an electrode in a triboelectric nanogenerator (TENG), the hydrogel delivers stable electrical output (open-circuit voltage: 100 V), powering small electronics and enabling signal transmission. This work provides a reference for the development of multifunctional hydrogel-based flexible electronics and self-powered devices.

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The development of cost-effective, eco-friendly conductive hydrogels with excellent mechanical properties, self-healing capabilities, and non-toxicity holds immense significance in the realm of biosensors. The biosensors demonstrate promising applications in the fields of biomedical engineering and human motion detection. A unique double-network hydrogel was prepared through physical-chemical crosslinking using chitosan (CS), polyacrylic acid (AA), and sodium alginate (SA) as raw materials. The prepared double-network hydrogels exhibited exceptional mechanical properties, as well as self-healing and conductive capabilities. Polyacrylic acid as the first layer network, while chitosan and sodium alginate were incorporated to establish the second layer network through electrostatic interactions, thereby imparting self-healing and self-recovery properties. The hydrogel was subsequently immersed in the salt solution to induce network winding. The mechanical robustness of the hydrogel was significantly enhanced through synergistic coordination of covalent and non-covalent interactions. When the concentration of sodium alginate was 20 g/L, the double-network hydrogel exhibits enhanced mechanical properties, with a tensile fracture stress of up to 1.31 MPa and a strength of 4.17 MPa under 80% compressive deformation. Furthermore, the recovery rate of this double-network hydrogel reached an impressive 89.63% within a span of 30 min. After 24 h without any external forces, the self-healing rate reached 26.11%, demonstrating remarkable capabilities in terms of self-recovery and self-healing. Furthermore, this hydrogel exhibited consistent conductivity properties and was capable of detecting human finger movements. Hence, this study presents a novel approach for designing and synthesizing environmentally friendly conductive hydrogels for biosensors.

In the realm of health monitoring, wearable electronic devices that utilize conductive hydrogels have garnered considerable attention. Nonetheless, the formidable challenge persists in streamlining the intricate preparation process and formulating a conductive hydrogel that seamlessly integrates diverse functionalities. In this study, we propose a strategy to fabricate multifunctional wearable hydrogel-based strain sensors (ε-PL/AMC-Al) in an ultrafast manner. Amide-modified chitin (AMC) was synthesized homogeneously, thereafter, Al3+ ions and ε-Polylysine (ε-PL) were introduced to interact with AMC through physical cross-linking techniques to form a three-dimensional network. Favorable mechanical and self-healing properties were achieved through the presence of multiple noncovalent interactions. The incorporation of ε-PL imparted antibacterial properties to the hydrogel sensor, thereby safeguarding it against bacterial contamination. Importantly, the incorporation of Al3+ not only facilitated the gelation process but also imparted electrical conductivity to the hydrogel, enabling it to function as a strain sensor. Notably, the adhesive property of the ε-PL/AMC-Al hydrogel ensured intimate contact, thereby allowing it to accurately monitor and differentiate between both gross and subtle human body movements without compromising its long-term stability. Based on its straightforward manufacturing process and versatility, the as-prepared hydrogel sensor exhibits significant potential for a diverse array of large-scale applications, including wearable electronic devices.

Conductive hydrogels are promising for flexible electronics, yet integrating high conductivity, mechanical robustness, biocompatibility, and environmental stability for flexible supercapacitors (FSCs) and wearable epidermal sensors remains challenging. Herein, a self-healing hydrogel with multiple energy dissipation pathways was constructed using synergistic dynamic borate ester bonds, Schiff base bonds, and hydrogen bonds. Incorporating polydopamine-coated MXene (MP) enhanced the mechanical strength, conductivity, and antibacterial/antioxidant properties. FSCs with the hydrogel electrolyte exhibited excellent electrochemical performance with a specific capacitance of 373.41 mF/cm2, an energy density of 74.67 μWh/cm2, a capacitance retention of 82.43% after 5000 cycles, and high deformation tolerance. As a strain sensor, it effectively detected both large and subtle human motions, including physiological microexpressions and pulse beats due to its high sensitivity (gauge factor = 1.73) and repeatability. Importantly, its notable degradability owing to the inherent degradability of the chitosan framework and the reversible dissociation of dynamic bonds addresses environmental concerns from traditional electronics.

Hydrogel based stress‐strain sensors have been given significant attention due to their potential in developing wearable electronic devices and health‐monitoring systems, owing to their intrinsic softness and mechanical flexibility. Hence, this study aims to develop a hydrogel with self‐healing properties, conductivity, and good mechanical performance, which is essential for accurate data analysis and measurements. A composite hydrogel based on polyvinyl pyrrolidine (PVP) and sunitinib malate (SUM) was successfully prepared. The PVP/SUM hydrogel formed H‐bonds and dipole‐dipole bonds, which exhibited good mechanical properties, rapid self‐healing, and sensing properties. It showed mechanical elongation up to 190 mm. Furthermore, PVP/SUM hydrogel developed a conductive network within the hydrogel, improving its conductivity from 3.28 × 10−5 S/cm. The hydrogel's sensing test showed quick response times when used as a soft human motion sensor, effectively enabling real‐time monitoring of both large‐scale and delicate human physiological stress activities, including joint movements in the neck, wrist, elbow, and forefinger.

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To date, conductive hydrogels as an alternative to traditional rigid metallic conductors have attracted much attention in the field of flexible wearable electronic devices due to their inherent characteristics. Herein, a conductive bacterial cellulose (BC) nanocomposite hydrophobic-association (HA) hydrogel with highly stretchable, strong, self-healing, and notch-insensitive was fabricated by introducing the hydrophobic association. The obtained BCNC HA hydrogel shows excellent mechanical properties (~ 2400 % of stress and ~ 0.35 MPa of mechanical strength), superior notch-insensitive property with a fracture energy of ~38 KJ.m-2, and good self-healing property (healing efficiency of ~97 %). In addition, the hydrogel exhibits excellent ionic conductivity of ~1.90 S.m-1 and high sensing sensitivity toward tensile deformation. The wearable strain sensor based on this material is assembled can detect both large-scale motions and subtle body motions in real time, which show excellent durability (1000 cycles with the strain of 30 %). Thus, the BCNC HA hydrogels have promising potential in various wearable flexible electronic devices for artificial intelligence and human-machine interface applications in the future.

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Conductive hydrogels are widely used in electronic skin and wearable sensors. Their inherent self-adhesion, exceptional sensitivity, and remarkable toughness guarantee the consistent and reliable operation of flexible motion sensors. However, creating chitosan-based conductive hydrogels with all these properties remains challenging. In this study, a triple-network hydrogel was synthesized by incorporating poly (vinyl alcohol) (PVA), chitosan quaternary ammonium salt (QCS) and poly(N-(2-Hydroxyethyl) acrylamide)-Co-Sodium acrylate copolymer (P(HEAA-Co-AANa)). Lithium chloride (LiCl) is introduced to enhance conductivity. The optimized hydrogel shows good conductivity (0.77 S/m), high tensile strain (~2113 %) and strong mechanical properties (463 kPa). The assembled sensors have high sensitivity, and enable precisely monitoring human motions. This study offers a simple, eco-friendly way to develop high-performance chitosan-based conductive hydrogels.

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Self-healing, self-adhesive, and stretchable bio-based conductive hydrogels exhibit properties similar to those of biological tissues, making them an urgent requirement for emerging wearable devices. The primary challenge lies in devising straightforward strategies to accomplish all the aforementioned performances and achieve equilibrium among them. This study used the natural compound thioctic acid (TA) and modified cellulose to prepare conductive hydrogels with stretchability, healing, and self-adhesion through a simple one-step strategy. Metastable poly(TA) was obtained through ring-opening polymerization of lithiated TA, followed by the introduction of dopamine-grafted cellulose nanofibers (DCNF) to stabilize poly(TA) and prepare PTALi/DCNF hydrogels with the aforementioned properties. The hydrogels demonstrated remarkable conductivity, attributed to the existence of Li + ions, with a maximum conductivity of 17.36 mS/cm. The self-healing capacity of the hydrogels was achieved owing to the presence of disulfide bond in TA. The introduction of DCNF can effectively stabilize poly(TA), endow the hydrogel with self-adhesion ability, improve the mechanical properties, and further enhance the formability of hydrogels. Generally, bio-based PTALi/DCNF hydrogels with stretchability, self-healing, self-adhesion, and conductivity are obtained through a simple strategy and used as a sensor with a wide response range and high sensitivity. Hydrogels have significant potential for application in wearable electronic devices, electronic skins, and soft robots.

Constructing natural polymers such as cellulose, chitin, and chitosan into hydrogels with excellent stretchability and self-healing properties can greatly expand their applications but remains very challenging. Generally, the polysaccharide-based hydrogels have suffered from the trade-off between stiffness of the polysaccharide and stretchability due to the inherent nature. Thus, polysaccharide-based hydrogels (polysaccharides act as the matrix) with self-healing properties and excellent stretchability are scarcely reported. Here, a solvent-assisted strategy was developed to construct MXene-mediated cellulose conductive hydrogels with excellent stretchability (∼5300%) and self-healability. MXene (an emerging two-dimensional nanomaterial) was introduced as emerging noncovalent cross-linking sites between the solvated cellulose chains in a benzyltrimethylammonium hydroxide aqueous solution. The electrostatic interaction between the cellulose chains and terminal functional groups (O, OH, F) of MXene led to cross-linking of the cellulose chains by MXene to form a hydrogel. Due to the excellent properties of the cellulose-MXene conductive hydrogel, the work not only enabled their strong potential in both fields of electronic skins and energy storage but provided fresh ideas for some other stubborn polymers such as chitin to prepare hydrogels with excellent properties.

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Flexible and wearable hydrogel strain sensors have attracted tremendous attention for applications in human motion and physiological signal monitoring. However, it is still a great challenge to develop a hydrogel strain sensor with certain mechanical properties and tensile deformation capabilities, which can be in conformal contact with the target organ and also have self-healing properties, self-adhesive capability, biocompatibility, antibacterial properties, high strain sensitivity, and stable electrical performance. In this paper, an ionic conductive hydrogel (named PBST) is rationally designed by proportionally mixing polyvinyl alcohol (PVA), borax, silk fibroin (SF), and tannic acid (TA). SF can not only be a reinforcement to introduce an energy dissipation mechanism into the dynamically cross-linked hydrogel network to stabilize the non-Newtonian behavior of PVA and borax but it can also act as a cross-linking agent to combine with TA to reduce the dissociation of TA on the hydrogel network, improving the mechanical properties and viscoelasticity of the hydrogel. The combination of SF and TA can improve the self-healing ability of the hydrogel and realize the adjustable viscoelasticity of the hydrogel without sacrificing other properties. The obtained hydrogel has excellent stretchability (strain > 1000%) and shows good conformal contact with human skin. When the hydrogel is damaged by external strain, it can rapidly self-repair (mechanical and electrical properties) without external stimuli. It shows adhesiveness and repeatable adhesiveness to different materials (steel, wood, PTFE, glass, iron, and cotton fabric) and biological tissues (pigskin) and is easy to peel off without residue. The obtained PBST conductive hydrogel also has a wide strain-sensing range (>650%) and reliable stability. The hydrogel adhered to the skin surface can monitor large strain movements such as in finger joints, wrist joints, knee joints, and so on and detect swallowing, smiling, facial bulging and calming, and other micro-deformation behaviors. It can also distinguish physical signals such as light smile, big laugh, fast and slow breathing, and deep and shallow breathing. Therefore, the PBST conductive hydrogel material with multiple synergistic functions has great potential as a flexible wearable strain sensor. The PBST hydrogel has antibacterial properties and good biocompatibility at the same time, which provides a safety guarantee for it as a flexible wearable strain sensor. This work is expected to provide a new way for people to develop ideal wearable strain sensors.

With rapid advancements in health and human-computer interaction, wearable electronic skins (e-skins) designed for application on the human body provide a platform for real-time detection of physiological signals. Wearable strain sensors, integral functional units within e-skins, can be integrated with Internet of Things (IoT) technology to broaden the applications for human body monitoring. A significant challenge lies in the reliance of most existing wearable strain sensors on rigid external power supplies, limiting their practical flexibility. In this study, we present an innovative strategy to fabricate glutaraldehyde (GA)-poly(vinyl alcohol) (PVA)/cellulose nanocrystals (CNC)/Poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) conductive hydrogels through multiple hydrogen bonding systems. Combining the advantageous rheological properties of the precursor solution and the high specific surface area after freeze-thaw cycling, we have created a self-powered sensing system prepared by large-area printing using direct ink writing (DIW) printing. The resulting conductive hydrogel exhibits commendable mechanical properties (411 KPa), impressive stretchability (580 %), and robust self-healing capabilities (>98.3 %). The strain sensor, derived from the conductive hydrogel, demonstrates a gauge factor (GF) of 2.5 within a stretching range of 0-580 %. Additionally, the resultant supercapacitor displays a peak energy density of 0.131 mWh/cm3 at a power density of 3.6 mW/cm3. Benefiting from its elevated strain response and remarkable power density features, this self-powered strain sensing system enables the real-time monitoring of human joint motion. The incorporation of a 5G transmission module enhances its capabilities for remote data monitoring, thereby contributing to the progress of wireless tracking technologies for self-powered electronic skin.

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Recently, a great deal of research has focused on the study of self-healing hydrogels possessing electronic conductivity due to their wide applicability for use in biosensors, bioelectronics, and energy storage. The low solubility, poor biocompatibility, and lack of effective stimuli-responsive properties of their sp2 carbon-rich hybrid organic polymers, however, have proven challenging for their use in electroconductive self-healing hydrogel fabrication. In this study, we developed stimuli-responsive electrochemical wireless hydrogel biosensors using ureidopyriminone-conjugated gelatin (Gel-UPy) hydrogels that incorporate diselenide-containing carbon dots (dsCD) for cancer detection. The cleavage of diselenide groups of the dsCD within the hydrogels by glutathione (GSH) or reactive oxygen species (ROS) initiates the formation of hydrogen bonds that affect the self-healing ability, conductivity, and adhesiveness of the Gel-UPy/dsCD hydrogels. The Gel-UPy/dsCD hydrogels demonstrate more rapid healing under tumor conditions (MDA-MB-231) compared to that observed under physiological conditions (MDCK). Additionally, the cleavage of diselenide bonds affects the electrochemical signals due to the degradation of dsCD. The hydrogels also exhibit excellent adhesiveness and in vivo cancer detection ability after exposure to a high concentration of GSH or ROS, and this is comparable to results observed in a low concentration environment. Based on the combined self-healing, conductivity, and adhesiveness properties of the Gel-UPy/dsCD, this hydrogel exhibits promise for use in biomedical applications, particularly those that involve cancer detection, due to its selectivity and sensitivity under tumor conditions.

Stretchable, self-healing and conductive hydrogels have attracted much attention for wearable strain sensors, which are highly required in health monitoring, human-machine interaction and robotics. However, the integration of high stretchability, self-healing capacity and enhanced mechanical performance into one single conductive hydrogel is still challenging. In this work, a type of stretchable, self-healing and conductive composite hydrogels are fabricated by uniformly dispersing TEMPO-oxidized cellulose nanofibers (TOCNFs)-graphene (GN) nanocomposites into polyacrylic acid (PAA) hydrogel through an in-situ free radical polymerization. The resulting hydrogels demonstrate a stretchability (∼850 %), viscoelasticity (storage modulus of 32 kPa), mechanical strength (compression strength of 2.54 MPa, tensile strength of 0.32 MPa), electrical conductivity (∼ 2.5 S m-1) and healing efficiency of 96.7 % within 12 h. The hydrogel-based strain sensor shows a high sensitivity with a gauge factor of 5.8, showing great potential in the field of self-healing wearable electronics.

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Hydrogel sensors attained increasing attention due to their excellent mechanical and sensing properties. However, it is still a big challenge to fabricate hydrogel sensors with multifunctional properties of transparent, high stretchability, self-adhesive and self-healing ability. In this study, chitosan as a natural polymer has been employed to construct a polyacrylamide-chitosan-Al3+ (PAM-CS-Al3+) double network (DN) hydrogel with high transparency (>90 % at 800 nm), good electrical conductivity (up to 5.01 S/m) and excellent mechanical properties (strain and toughness as high as 1040 % and 730 kJ/m3). Moreover, the dynamic ionic and hydrogen bond interaction between PAM and CS endowed the PAM-CS-Al3+ hydrogel good self-healing ability. In addition, the hydrogel possesses good self-adhesive ability on different substrates, including glass, wood, metal, plastic, paper, polytetrafluoroethylene (PTFE) and rubber. Most importantly, the prepared hydrogel could be assembled into transparent, flexible, self-adhesive, self-healing and high sensitive strain/pressure sensor for monitoring human body movement. This work may pave the way for fabricating the multifunctional chitosan-based hydrogels which has potential application in the fields of wearable sensor and soft electronic devices.

Conductive hydrogels (CHs) are ideal electrolyte materials for the preparation of flexible supercapacitors (FSCs) due to their excellent electrochemical properties, mechanical properties, and deformation restorability. However, most of the reported CHs are prepared by the chemical crosslinking of synthetic polymers and thus usually display the disadvantages of poor self-healing abilities and nonadaptability at environmental temperatures, which greatly limits their application. To overcome these problems, in the present work, we constructed a sodium alginate-borax/gelatin double-network conductive hydrogel (CH) by a dynamic crosslinking between sodium alginate (SA) and borax via borate bonds and hydrogen bonding between amino acids in gelatin and SA chains. The CH displays an excellent elongation of 305.7% and fast self-healing behavior in 60 s. Furthermore, a phase-change material (PCM), Na2SO4·10H2O, was introduced into the CH, which, combined with the nucleation effect of borax, improved the ionic conductivity and temperature adaptability of the CH. The flexible supercapacitor (FSC) assembled with the obtained CH as the electrolyte exhibits a high specific capacitance of 185.3 F·g-1 at a current density of 0.25 A·g-1 and good stability with 84% capacitance retention after 10 000 cycles and excellent temperature tolerance with a resistance variation of 2.11 Ω in the temperature range of -20-60 °C. This green CH shows great application potential as an electrolyte for FSCs, and the preparation method can be potentially expanded to the fabrication of self-repairing FSCs with good temperature adaptabilities.

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The application of conductive hydrogels in flexible wearable devices has garnered significant attention. In this study, a self-healing, anti-freezing, and fire-resistant hydrogel strain sensor is successfully synthesized by incorporating sustainable natural biological materials, viz. Tremella polysaccharide and silk fiber, into a polyvinyl alcohol matrix with borax cross-linking. The resulting hydrogel exhibits excellent transparency, thermoplasticity, and remarkable mechanical properties, including a notable elongation (1107.3 %) and high self-healing rate (91.11 %) within 5 min, attributed to the dynamic cross-linking effect of hydrogen bonds and borax. A strain sensor based on the prepared hydrogel sensor can be used to accurately monitor diverse human movements, while maintaining exceptional sensing stability and durability under repeated strain cycles. Additionally, a hydrogel touch component is designed that can successfully interact with intelligent electronic devices, encompassing functions like clicking, writing, and drawing. These inherent advantages make the prepared hydrogel a promising candidate for applications in human health monitoring and intelligent electronic device interaction.

The synthesis of multifunctional conductive hydrogel has attracted extensive attention worldwide due to their integrated properties of stretchability, self-adhesion, self-healing, and high sensitivity, while it is still a challenge. Although various kinds of polysaccharides and their derivatives are used to achieve the aforementioned objective, there are few researches about hydrogel design introducing sulfated polysaccharide from Enteromorpha prolifera (SPE), which is rich in hydroxyl, sulfate, and carboxyl groups providing amounts of reaction sites for hydrogel synthesis. Herein, conductive hydrogel (PAA-Al3+-SPE3) reinforced by SPE was designed by simple one pot hot polymerization method. This hydrogel demonstrated charming extension ratio (up to 4027.40 %), strain stress (up to 59.94 kPa), compressive strength (19.71 Mpa), and high conductivity sensibility (GF 6.76, 300 % - 700 %). Additionally, PAA-Al3+-SPE3 showed good self-healing property (repaired autonomously after 60 s) and satisfied self-adhesion (31.11 kPa) due to the reversible hydrogen bonds and metal coordination interactions. Furthermore, the PAA-Al3+-SPE3 hydrogel showed great real-time sensing performance to monitor various motions. These findings suggest the potential of PAA-Al3+-SPE3 hydrogel as an affordable and reliable conductive sensing material. Meantime, the first utilization of SPE to construct flexible wearable sensors offers new route for the high-value application of Enteromorpha prolifera.

Addressing the diverse environmental demands for electronic material performance, the design of a multifunctional ionic conductive hydrogel with mechanical flexibility, anti-freezing capability, and antibacterial characteristics represents an optimal solution. Leveraging the Dead Sea effect and the strong hydrogen bonding, this study exploits the CaCl2 and the abundant hydroxyl groups in phytic acid (PA) to induce chain entanglements, thereby constructing a complex, multi-crosslinked network. Furthermore, PA and ternary solvent systems (CaCl2/Glycerol/H2O) synergistically impart excellent mechanical strength, toughness (with tensile strength of 8.93 MPa, elongation at break of 859.93%, and toughness of 39.92 MJ m-3), high electrical conductivity, antifreeze capability, antibacterial properties, and high strain sensitivity (gauge factor up to 2.10) to the hydrogels. Remarkably, the hydrogel structure maintains stability even after undergoing 6000 loading-unloading cycles, demonstrating its outstanding fatigue resistance. Upon receiving external stimuli, the hydrogel exhibits a response time of 126 ms, making it ideal for the dynamic monitoring of human motion signals. This study offers novel insight into the potential application of ionic conductive hydrogels as flexible sensors in challenging environments.

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In recent years, hydrogel has become favorable choice for sensor substrate materials due to its decent flexibility and biocompatibility. Ideal hydrogels with self-healing property are considered to extend the service life of hydrogel-based sensors. And the durability of hydrogel is also largely dependent on environmental stability, especially in high humidity and underwater environments. Herein, CS/Vanillin-P(AA-co-HEMA)/SBMA hydrogels with self-healing behavior under diverse environmental conditions could be fabricated with chitosan (CS), vanillin, acrylic acid (AA), 2-hydroxyethyl methacrylate (HEMA) and [2-(Methacryloyloxy)ethyl]dimethyl-(3-sulfopropyl)ammonium hydroxide (SBMA). Owing to the formation of Schiff base bonds, electrostatic interactions and hydrogen bonds and the hydrophilic-hydrophobic chain segments balance, CS/Vanillin-P(AA-co-HEMA)/SBMA hydrogel demonstrated decent anti-swelling performance and excellent mechanical properties in amphibiotic environment. Moreover, CS/Vanillin-P(AA-co-HEMA)/SBMA hydrogel exhibited self-healing property in a wide range of environments including corn oil, seawater and low-temperature condition, which held great significance for broadening the application scope of hydrogel. In addition, the hydrogel displayed adhesion property, which could be attributed to carboxyl, hydroxyl, amino, quaternary ammonium and sulfonic acid groups of the hydrogel. As a result, CS/Vanillin-P(AA-co-HEMA)/SBMA hydrogel could adhere to the surface of substrates through Schiff base bonds, metal coordination bonds, electrostatic interactions and hydrogen bonds. Meanwhile, CS/Vanillin-P(AA-co-HEMA)/SBMA hydrogel also exhibited outstanding electrical conductivity due to the introduction of SBMA. Therefore, the prepared multifunctional hydrogel was employed as hydrogel-based wearable strain sensor, which could sensitively detect various human movements, especially in underwater environments. It could be anticipated that the designed hydrogel holds significant potential in the domain of wearable strain sensors.

Ion-conductive-hydrogel strain sensors demonstrate broad application prospects in the fields of flexible sensing and bioelectric signal monitoring due to their excellent skin conformability and efficient signal transmission characteristics. However, traditional preparation methods face significant challenges in enhancing adhesion strength, conductivity, and mechanical stability. To address this issue, this study employed a freeze–thaw cycling method, using polyvinyl alcohol (PVA) as the matrix material, tannic acid (TA) as the adhesion reinforcement material, and lithium chloride (LiCl) as the conductive medium, successfully developing an ion-conductive hydrogel with superior comprehensive performance. Experimental data confirm that the PVA-TA-0.5/LiCl-1 hydrogel achieves optimal levels of adhesion strength (2.32 kPa on pigskin) and conductivity (0.64 S/m), while also exhibiting good tensile strength (0.1 MPa). Therefore, this hydrogel shows great potential for use in strain sensors, demonstrating excellent sensitivity (GF = 1.15), reliable operational stability, as the ΔR/R0 signal remains virtually unchanged after 2500 cycles of stretching, and outstanding strain sensing and electromyographic signal acquisition capabilities, fully highlighting its practical value in the fields of flexible sensing and bioelectric monitoring.

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A novel double-network conductive hydrogel based on lithium acetate/gelatin/polyacrylamide (PAAM) was synthesized by heating-cooling and subsequent γ-ray radiation-induced polymerization and cross-linking. Owing to the hydrogen bonding interaction between lithium acetate, physical cross-linked gelatin, and chemical cross-linked PAAM, the resultant hydrogel exhibited high tensile strength (1260 kPa), high ionic conductivity (35.2 mS cm-1), notch-insensitivity (tensile strength 415 kPa, elongation at break 872% with transverse notch), and extensive strain monitoring range (0.15-800%) under optimum conditions. The lithium acetate/gelatin/polyacrylamide hydrogel strain sensor attached to the skin can sensitively monitor the subtle movements of the human body. The strain sensor based on the resultant hydrogel with transverse notch can still work for 1200 cycles, due to that the covalent-cross-linked PAAm chain bridges the cracks and stabilizes the deformation, while the physical-cross-linked gelatin was unzipped to make the blunting of notch. The conductive hydrogel with high-sensitivity and high stability is expected to be used as materials for the preparation of flexible strain sensors in the future.

As a smart wearable sensor device, the mildew of the biocompatible hydrogel limits its application. In this paper, silver nanoparticles were prepared by solid-state reduction of hydroxyethyl cellulose and compounded into a chemically cross-linked hydrogel as an antibacterial, flexible strain sensor. Because the high surface energy of silver nanoparticles can quench free radicals, we designed three initiators to synthesize hydrogels: ammonium persulfate (APS), 2,2'-Azobis(2-methylpropionitrile) (AIBN) and 2,2'-azobis(2-methylpropionamidine) dihydrochloride (AIBA). Impressively, silver nanoparticles composite hydrogel could only be successfully fabricated and triggered by the AIBN. The mechanical property of the composite hydrogel (0.12 MPa at 704.33 % strain) was significantly improved because of dynamic crosslinking point by HEC. Finally, the composite hydrogels are applied to the field of antibacterial strain sensor and the highest Gauge Factor (GF) reached 4.07. This article proposes a novel, green and simple strategy for preparing silver nanoparticles and compounding them into a hydrogel system for antibacterial strain sensor.

The limited strength and stability of conductive hydrogels greatly impede their practical applications in wearable devices. Therefore, a conductive double‐network hydrogel with high strength, high toughness, and high stability was prepared by one‐pot method in this paper. The rigid and flexible skeletons as well as the three‐dimensional dense honeycomb lattice network structure endow the hydrogel with good strength. The reversible cross‐linking synergistic effect between the rigid bacterial cellulose chains scaffolding uniformly dispersed Ti3C2 MXene nanosheets and the flexible acrylic acid chains doped with propylene glycol presents the hydrogel with excellent stability and elongation at break (862%). Consequently, a strain sensor based on the prepared hydrogel exhibits high sensitivity (GF = 1.28), rapid response (150 ms), and superior stability (over 2000 cycles) within a very wide strain range (5%–620%). Various strain signals generated by human activities are successfully detected by the presented strain sensor, which promises its broad applications in health monitoring.

Conductive hydrogels possess excellent flexibility, conductivity, and sensing properties, making them important carrier materials for flexible strain sensors. They show promising application prospects in fields such as human motion detection and artificial intelligence. This paper introduces polyaniline (PANI) and glycerol (GL) into the magnesium acrylate (AMgA) monomer and prepares the polymagnesium acrylate/glycerol/polyaniline (PAMgA/GL/PANI) hydrogel by free radical polymerization method. When the addition of PANI is 9 wt.%, the PAMgA/GL/PANI hydrogel exhibits good mechanical properties, with a tensile strength of 0.385 MPa, an elongation at break of up to 505%, a compressive strength of 1.04 MPa, and its room temperature conductivity is 1.437 S m−1. Even after freezing at −20 °C, its conductivity can still reach 1.254 S m−1. When the tensile deformation of this conductive hydrogel reaches 500%, the gauge factor (GF) reaches 10.33. In addition, the PAMgA/GL/PANI hydrogel also has good self‐healing, adhesion, and moisture retention. These excellent characteristics make it suitable as a flexible strain sensor that can not only accurately monitor human joint movements and subtle physiological signals but also serve as an encrypted information transmission medium.

Conductive hydrogels for smart wearable devices have attracted increasing attention due to their excellent flexibility, versatility, and outstanding biocompatibility. In order to prepare high-performance conductive hydrogels that can be applied to strain sensing, polyacrylamide was introduced into the polyvinyl alcohol (PVA)-borax hydrogel to construct a double-network hydrogel (DNH), and Ti3C2Tx MXene and polydopamine were introduced into improve conductivity, realizing the preparation of MXene/polydopamine/PVA/polyacrylamide DNH (MXene-DNH). The effects of different mass ratios of PVA and acrylamide on the mechanical properties and electrical properties of hydrogels are systematically investigated. Among them, the MXene-DNH with the mass ratio of PVA: acrylamide =1:3.5 exhibits excellent mechanical and electrical performance, with elongation at break of 1420%, tensile strength of 249 kPa, and toughness of 1397.1 kJ/m3, electrical conductivity of 0.661 mS/cm. Moreover, the MXene-DNH can be used as strain sensor, and the sensor exhibits great sensing performance and possesses a wide strain working range (0%–965%), good sensitivity (0.38 in the 0%–100% strain range), and low hysteresis. Finally, the flexible strain sensor was applied to monitor multiple joint motions and recognize gestures, demonstrating it has broad application potential in the fields of portable wearable electronics and human-computer interaction.

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Many disabled people are not suitable for the control of the current mainstream manual joystick-controlled wheelchair, so the study of new control methods can provide convenience for these people, including bioelectrical signal control, voice control, and visual control, but these control methods have peripheral equipment complex or susceptible to environmental noise interference, in contrast. These problems can be solved effectively by using a wearable flexible sensor to recognize human movement signal. To collect and identify the strain signal characteristics of the moving neck muscles, based on the principle of flexible piezoresistive sensor, we designed and produced a K-carrageenan at polydimethylsiloxane (PDMS) flexible sensor, designed a series of experiments to explore the conductive properties, mechanical properties, and air permeability of the sensor, and also designed the peripheral acquisition circuit and signal processing algorithm. Finally, the empirical mode decomposition (EMD)-long short-term memory (LSTM) algorithm is used to classify the signal and explore the feasibility of fitting the signal to the human neck to control the wheelchair. The results show that the maximum tensile rate of the sensor designed by us is as high as 180%, and the air permeability is also improved slightly. After 1000 cycles of stretching, the sensor still has good performance and can effectively collect human neck action signals. Through the field test, the accuracy of this system is up to 95%, which provides a new idea for wheelchair control.

Hydrogel-based wearable devices have attracted tremendous interest due to their potential applications in electronic skins, soft robotics, and sensors. However, it is still a challenge for hydrogel-based wearable devices to be integrated with high conductivity, a self-healing ability, remoldability, self-adhesiveness, good mechanical strength and high stretchability, good biocompatibility, and stimulus-responsiveness. Herein, multifunctional conductive composite hydrogels were fabricated by a simple one-pot method based on poly(vinyl alcohol) (PVA), sodium alginate (SA), and tannic acid (TA) using borax as a cross-linker. The composite hydrogel network was built by borate ester bonds and hydrogen bonds. The obtained hydrogel exhibited pH- and sugar-responsiveness, high stretchability (780% strain), and fast self-healing performance with healing efficiency (HE) as high as 93.56% without any external stimulus. Additionally, the hydrogel displayed considerable conductive behavior and stable changes of resistance with high sensitivity (gauge factor (GF) = 15.98 at a strain of 780%). The hydrogel was further applied as a strain sensor for monitoring large and tiny human motions with durable stability. Significantly, the healed hydrogel also showed good sensing behavior. This work broadens the avenue for the design and preparation of biocompatible polymer-based hydrogels to promote the application of hydrogel sensors with comfortable wearing feel and high sensitivity.

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As a classic flexible material, hydrogels show great potential in wearable electronic devices. The application of strain sensors prepared using them in human health monitoring and humanoid robotics is developing rapidly. However, it is still a challenge to fabricate a high-toughness, large-tensile-deformation, strain-sensitive. and human-skin-fit hydrogel with the integration of excellent mechanical properties and high electrical conductivity. In this study, a flexible sensor using a highly strain-sensitive skin-like hydrogel with acrylamide and sodium alginate was designed using liquid metallic gallium as a "reactive" conductive filler. The sensor had a low elastic modulus (30 kPa) similar to that of skin, a high-toughness (2.25 MJ m-3), self-stiffness, a large tensile deformation (1400%), recoverability, and excellent fatigue resistance. Moreover, the addition of gallium might enhance the electrical conductivity (1.9 S m-1) of the hydrogel while maintaining high transparency, and the flexible sensor device constructed from it showed high sensitivity to strain (gauge factor = 4.08) and pressure (gauge factor = 0.455 kPa-1). As a result, the hydrogel sensor could monitor various human motions, including large-scale joint bending and tiny facial expression, breathing, voice recognition, and handwriting. Furthermore, it might even be used for human-computer communication.

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Polyaniline (PANi) hydrogels often exhibit highly mechanical and electrochemical properties, which have received extensive attention in the fields of batteries, supercapacitors, and sensors. However, the shortcomings such as hydrophobicity and easy aggregation of PANi frequently result in deterioration of mechanical and electrochemical performance of PANi hydrogels. Here, a bifunctional natural product, glycyrrhizic acid (GL), is utilized to prepare the homogeneous conductive PANi hydrogel, because GL not only can assemble into supramolecular hydrogel as the biocompatible matrix but also can salinize aniline monomers to facilitate the polymerization in situ to form uniformly dispersed PANi within GL matrix. Accordingly, the resulting GL/PANi hydrogel shows the Tyndall effect caused by the nanoclusters entangled by nanofibers and exhibits an improved storage modulus G' (3.2 kPa) and loss modulus G″ (0.9 kPa), as well as the expected conductivity (0.17 S·m-1). In addition, the GL/PANi hydrogel is further reinforced by blending poly(vinyl alcohol) (PVA) for the required strength and stretchability as a flexible strain sensor. The results reveal that the obtained PVA/GL/PANi hydrogel has a fracture stress of 693 kPa at an elongation of 329%, with a fracture toughness of 82 MJ·m-3 and Young's modulus of 47.9 kPa. Its gauge factor (GF) is measured to be 2.5 at lower strain (<130%) and up to 4.3 at larger strain (>130%). This good sensitivity and sensing stability make the PVA/GL/PANi hydrogel effectively monitor relevant human motion detections. Our work provides an innovative strategy to manufacture the homogeneous conductive PANi hydrogel for high-performance soft electronic devices.

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Achieving the integration of multiple properties in a single hydrogel system faces significant challenges. This research presents a simple approach to developing a multifunctional conductive hydrogel with high stretchability (>740 %), electrical conductivity, frost resistance and self-adhesiveness. It serves as a wearable, flexible electronic material, it remains functional even in low-temperature environments. The hydrogel is synthesized by incorporating a uniformly mixed solution of carboxymethyl cellulose (CMC) and aminated carbon nanotubes (NH2-CNTs) into a polyacrylamide (PAM)/gelatin dual-network hydrogel. By adjusting the CMC mass fraction, the optimal composite hydrogel is obtained within a specified gradient. After cross-linking modification with a calcium chloride (CaCl2) solution, enhances its mechanical properties, resulting in a final hydrogel with excellent stretchability (strain = 749 %), strong adhesion, frost resistance, moisture retention, and conductivity. Additionally, this research explores the hydrogel's potential for anti-counterfeiting and salt ion monitoring by analyzing changes in mechanical properties and transparency. The hydrogel exhibits high sensitivity to external strains and effectively monitors human signals such as finger bending, head movement, and speech, even at low temperatures. This research provides new insights into flexible electronic skin, wearable sensors and human-computer interaction, expanding the potential applications of multifunctional conductive hydrogels.

Gait abnormalities have been widely investigated in the diagnosis and treatment of neurodegenerative diseases. However, it is still a great challenge to achieve a comfortable, convenient, sensitive and high-pressure resistant flexible gait detection sensor for real-time health monitoring. In this work, a polyaniline (PANI)@(polyacrylic acid (PAA)-polyvinyl alcohol (PVA)) (PANI@(PVA-PAA)) ternary network hydrogel with a uniaxially oriented porous featured structure was successfully prepared using a simple freeze-thaw method and in situ polymerization. The PANI@(PVA-PAA) hydrogel shows excellent compressive mechanical properties (423.44 kPa), favorable conductivity (2.02 S m-1) and remarkable durability (500 loading-unloading cycle), and can sensitively detect the effect of pressure with a fast response time (200 ms). The PANI@(PVA-PAA) hydrogel assembled into a flexible sensor can effectively identify the movement state of the shoulder, knee and even the sole of the plantar for gait detection. The uniaxially oriented porous structure enables the hydrogel-based sensor to have a high rate of change in the longitudinal direction and can effectively distinguish various gaits. The construction of a hydrogen bond between PANI and the PVA-PAA hydrogel ensures the uniform distribution of PANI in the hydrogel to form a ternary network structure, which improves the pressure resistance and conductivity of the PANI@(PVA-PAA) hydrogel. Thus, PANI@(PVA-PAA) hydrogel flexible sensor for gait detection can not only effectively monitor some serious diseases but also detect some unscientific exercise in people's daily life.

Conductive hydrogels show extensive applications in flexible electronics and biomedical areas, but it is a challenge to simultaneously achieve high mechanical properties, satisfied electrical conductivity, good biocompatibility, self-recovery and anti-freezing properties through a simple preparation method. Herein, chitin nanocrystals (ChNCs) were employed to encapsulate liquid metal nanoparticles (LMNPs) to ensure the dispersion stability of LMNPs in a hydrogel system composed of polyacrylamide (PAM) and polyvinyl alcohol (PVA). The synergistic effect of ChNCs-stabilized LMNPs imparts remarkable conductivity to the hydrogel, making it an effective strain sensor for human motion. With 1 % LMNPs, the composite hydrogel stretches up to 2100 %, showing excellent stretchability. Under 10 cycles of 200 % strain, hysteresis loop curves overlap, indicating outstanding fatigue resistance. The hydrogel exhibits remarkable self-recovery, enduring 1400 % deformation without rupture. In addition, its effective antifreeze properties result from immersion in a glycerol-water solvent. Even at -20 °C and 60 °C, the hydrogel maintains stable, reproducible resistance changes at 150 % tensile strain. Therefore, the high-performance conductive hydrogel containing ChNCs stabilized LM has promising applications in flexible wearable sensing devices.

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Conductive hydrogels have emerged as excellent candidates for the design and construction of flexible wearable sensors and have attracted great attention in the field of wearable sensors. However, there are still serious challenges to integrating high stretchability, self-healing, self-adhesion, excellent sensing properties, and good biocompatibility into hydrogel wearable devices through easy and green strategies. In this paper, multifunctional conductive hydrogels (PCGB) with good biocompatibility, high tensile (1694 % strain), self-adhesive, and self-healing properties were fabricated by incorporating boric acid (BA) and glucose (Glu) simultaneously into polyacrylic acid (PAA) and chitosan (CS) polymer networks using a simple one-pot polymerization method. Furthermore, the hydrogel strain sensor constructed from the PCGB assembly had great sensing property including high sensitivity (GF = 5.7), durability and stability (5000 cycles). The hydrogel strain sensor was applied to the detection of human motion, which exhibited accurate detection behavior for both large-scale motions and small activities. A strategy to design and fabricate multifunctional conductive hydrogels integrating high stretchability, self-healing, self-adhesion and good biocompatibility was provided, and the multifunctional conductive hydrogels broadened the application of hydrogel-based wearable sensor.

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With the accelerated integration of flexible electronic technology and modern information technology, the demand for multifunctional flexible devices is becoming increasingly urgent. Hydrogel, as an excellent flexible material, is receiving widespread attention and in-depth research from researchers. In this study, a multifunctional ionic hydrogel was successfully prepared by introducing bacterial cellulose (BC), tannic acid (TA), and LiCl into the P(AM-co-AA) polymer network. This hydrogel exhibits excellent mechanical properties (3208.3 %), good conductivity (4.15 S/m), and outstanding self-adhesiveness. Flexible strain sensors and flexible supercapacitors based on PBTL hydrogel were fabricated, exhibiting advantages such as a wide detection range (0-3000 %), high sensitivity (GF = 6.93), high areal capacitance (133.6 mF/cm2), and good stability. It demonstrates excellent application potential in wearable motion detection and energy storage fields. Furthermore, a smart glove was developed using a 5-unit PBTL sensor, which, combined with VR technology, enables wireless gesture control of a hexapod robot. This system provides a high-quality solution for achieving more advanced interactive tasks in complex environments.

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A piezoresistive hydrogel sensor composed of bacterial cellulose and MXene nanosheets shows real-time stress sensing abilities at different amplitudes of human motions and maintains its sensing ability underwater.

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In neural biointerfacing technologies, mitigating the mismatch in mechanical and impedance attributes between neural tissues and bioelectronics remains a central challenge for achieving high‐efficacy neuromodulation. Here, full‐hydrogel bioelectronics that demonstrate superior mechanical compliance and impedance matching with 3D peripheral nerves, allowing for low‐voltage vagus nerve stimulation, are reported. By precisely tuning the dimensional parameters through 3D printing, the hydrogel bioelectronics, initially in a 2D planar form in a dehydrated state, can curl spontaneously around nerves and form a seamless interface. During the hydration process, instant, and tough bioadhesion is achieved through a dry crosslinking mechanism, enabling a mechanically robust nerve‐electrode interface to resist dynamic yet vigorous deformations of the peripheral nerve systems. The as‐formed nerve‐electrode interface significantly mitigates the impedance mismatch, in favor of electrical stimulation at a threshold voltage of 10 mV, one order of magnitude lower than that of conventional metallic electrodes. The use of the hydrogel bioelectronics for successful stroke rehabilitation through low‐voltage vagus nerve stimulation in a rat model is also demonstrated.

Over the past decade, conductive hydrogels have received great attention as tissue-interfacing electrodes due to their soft and tissue-like mechanical properties. However, a trade-off between robust tissue-like mechanical properties and good electrical properties has prevented the fabrication of a tough, highly conductive hydrogel and limited its use in bioelectronics. Here, we report a synthetic method for the realization of highly conductive and mechanically tough hydrogels with tissue-like modulus. We employed a template-directed assembly method, enabling the arrangement of a disorder-free, highly-conductive nanofibrous conductive network inside a highly stretchable, hydrated network. The resultant hydrogel exhibits ideal electrical and mechanical properties as a tissue-interfacing material. Furthermore, it can provide tough adhesion (800 J/m^2) with diverse dynamic wet tissue after chemical activation. This hydrogel enables suture-free and adhesive-free, high-performance hydrogel bioelectronics. We successfully demonstrated ultra-low voltage neuromodulation and high-quality epicardial electrocardiogram (ECG) signal recording based on in vivo animal models. This template-directed assembly method provides a platform for hydrogel interfaces for various bioelectronic applications. Conductive hydrogels have potential as tissue-interfacing electrodes, but it is challenging to achieve both robust mechanical properties and good electrical properties. Here, the authors report a synthetic method for developing highly conductive and mechanically tough hydrogels, with a tissue-like modulus, for electrocardiogram signal recording.

Epidermal electrophysiological signals, including ECG, EMG, and EEG, provide valuable health information. Real-time and accurate recording of these signals is vital for clinical diagnosis, monitoring, and therapy. A critical aspect of this process is the seamless integration of electronic devices in direct contact with biological tissues. Herein, we proposed a high-performance conductive composite hydrogel to build an electrical bio-adhesive interface for epidermal electrophysiological monitoring. Such hydrogel allows the facile fabrication of one-step UV crosslinking, which exhibits high stretchability of ~280%, great conformability, exceptional adhesion to skin and other non-biological materials, and stable conductivity. Enabled by these advantageous properties, the prepared hydrogel demonstrates excellent ECG and EMG signal recording capability, providing a new avenue for strategic development and manufacturing of advanced bio-adhesive interfaces for soft bioelectronics, further advancing seamless human-machine integration.

Stretchable bioelectronics has notably contributed to the advancement of continuous health monitoring and point-of-care type health care. However, microscale nonconformal contact and locally dehydrated interface limit performance, especially in dynamic environments. Therefore, hydrogels can be a promising interfacial material for the stretchable bioelectronics due to their unique advantages including tissue-like softness, water-rich property, and biocompatibility. However, there are still practical challenges in terms of their electrical performance, material homogeneity, and monolithic integration with stretchable devices. Here, we report the synthesis of a homogeneously conductive polyacrylamide hydrogel with an exceptionally low impedance (~21 ohms) and a reasonably high conductivity (~24 S/cm) by incorporating polyaniline-decorated poly(3,4-ethylenedioxythiophene:polystyrene). We also establish robust adhesion (interfacial toughness: ~296.7 J/m2) and reliable integration between the conductive hydrogel and the stretchable device through on-device polymerization as well as covalent and hydrogen bonding. These strategies enable the fabrication of a stretchable multichannel sensor array for the high-quality on-skin impedance and pH measurements under in vitro and in vivo circumstances.

Seamless integration with biological tissues and environmental adaptability are essential for continuous health monitoring, yet conventional bioelectronics often suffer from mechanical mismatch, poor adhesion, and limited stability. Here, we develop a self-adhesive and environmentally resilient ionic hydrogel (PHS-PA) with exceptional conductivity, flexibility, and durability. Constructed from a dual network of polyvinyl alcohol (PVA) and zwitterionic poly(SBMA-co-HEMA), physically cross-linked by phytic acid (PA), PHS-PA exhibits strong tissue adhesion, high ionic conductivity (10.6 S/m), anti-freezing capacity, low water loss, and intrinsic antibacterial activity. Its relatively low piezoresistive sensitivity under small deformations, along with superior conformability and stable skin-electrode interfaces, makes it ideal as soft electrodes for reliable electrocardiogram (ECG) monitoring. Moreover, its wide strain/pressure detection range (0-400 %, 0-10 kPa) enables effective tracking of large-scale motions such as gait. This study presents a versatile hydrogel platform for next-generation wearable bioelectronics, enabling reliable real-time health monitoring even in harsh environments.

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Conventional Silver/Silver Chloride (Ag/AgCl) electrodes remain the clinical standard for electrophysiological monitoring but are hindered by poor skin conformity, mechanical rigidity, and signal degradation, particularly under motion or sweat. Here, two hydrogel-based alternatives are presented and benchmarked using a wireless commercial platform: a porous poly(3,4-ethylenedioxythiophene):polystyrene sulfonate scaffold infused with hydrogel (PPSCF), and an all-hydrogel, crosslinker-free electrode (PPHG) synthesizes via a scalable, one-pot process. PPHG demonstrates intrinsic stretchability, self-adhesion, and biocompatibility, forming stable, low-impedance contacts with skin. Electrochemical measurements reveal that PPHG maintains a capacitive interface with reduced resistive losses, low loss tangent, high dielectric constant, and fast relaxation dynamics, features that enable intrinsic signal smoothing and noise suppression. In a cohort of 39 participants, PPHG electrodes outperform Ag/AgCl in electrocardiography (ECG), showing reduced motion artifacts, higher signal-to-noise ratios, and clear preservation of P-, R-, and T-waves. Electroencephalography (EEG) recordings demonstrate enhanced alpha-delta separation, while electrooculography (EOG) and electromyography (EMG) signals exhibit greater amplitude and sharper features. Machine learning analysis of ECG signals reveals a 2.2-fold improvement in inter-lead classification accuracy. These findings position PPHG as a soft, adhesive, and sustainable alternative for high-fidelity, multimodal bioelectronic interfaces, with strong potential for wearables and clinical monitoring systems.

ABSTRACT Emerging demand in soft bioelectronic systems poses critical challenges in stiffness control and end-to-end connections due to the huge modulus difference in various components. Here, a bidirectional electrical interface of hydrogel and metal electrodes to bridge soft skin/tissue and data collection circuits is enabled by coordination interactions. The dual-mode chelation including internal chelation and surface chelation effectively configures the cross-linking structure of hydrogel, as well as enhances the binding interface of metal–hydrogel complex surfaces. Internally, strong chelation competes with esterification, yielding tissue-like softness of hydrogel with an ultra-low modulus of ∼339.9 Pa. Externally, the hydrogel passivates the combined metal surfaces, promoting the formation of interlocked structures between metal oxide nanoislands, achieving a high binding strength of ∼1.95 MPa without compromising electrical conductivity. The stable electrical interconnections via hybrid interfacial bonding enable high signal-to-noise ratio signal recordings from the skin, neural surfaces and brain, maintaining reliable performance, even under mechanical disturbances. This work provides an effective strategy for achieving mechanically and electrically robust hybrid bioelectronic interfaces, advancing their applications in capturing both in vitro and in vivo electrical signals.

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Multifunctional bioelectronic systems are crucial for next-generation medical applications, enabling real-time sensing, targeted stimulation, and effective biological integration. In this work, we present a novel approach integrating conjugated polymer (CP) nanoparticles (NPs), made of poly(3-hexylthiophene, (P3HT) blended with [6], [6] phenyl-C61-butyric acid methyl ester (PCBM), into polyethylene oxide (PEO) hydrogels to develop a bioelectronic interface for biophotonic applications. We demonstrate that this composite material exhibits adequate electrochemical performance, providing, a photo-induced stable and reproducible photocurrent response (current density ranging from 13 to $25 \text{nA} / \text{cm}^{2}$). This work enhances CPNPs potential for bio-sensing/stimulation applications and introduces PEO|P3HT:PCBM-NPs composites as promising candidates for applications in neural interfacing, photo-biosensing, and regenerative medicine.

To meet the stringent requirements of wearable and flexible electronics for functionality and comfort, it is urgent to develop green conductive, self-adhesive, and stretchable functional hydrogels. The chelates of transition metal ions and lignosulfonate sodium (LS) can impart multi-functionality to the hydrogel and significantly improve the hydrogel's gelation speed. However, the presence of metal ions may weaken the adhesiveness of hydrogels by shielding the functional adhesive groups. Here, an oxidative metal ions-free lignin-catalyzed multifunctional polyacrylic acid (PAA) hydrogel is proposed. LS itself can undergo a redox reaction with the initiator to generate many free radicals, thereby catalyzing the rapid polymerization of polymer monomers at room temperature and subsequent gelation. Furthermore, LS can easily improve the hydrogels' softness (compressive modulus: ∼7 kPa) and stretchability (maximum ∼2700 %). Interestingly, LS can simultaneously promote the hydrogel's conductivity, adhesion, and UV blocking. Notably, the hydrogel integrating these advantageous features is suitable as non-invasive electronics in the human epidermis. We explored its ability to act as adhesive bioelectrodes to collect electrooculographic signals in patients with physical and language impairments. Bioelectrodes can recognize the patient's eye movements. The displayed electrical signal can be output in 6 languages after being encoded. This provides a valuable case for LS-doped functional hydrogels in the medical field.

Hydrogels offer tissue-like softness, stretchability, fracture toughness, ionic conductivity, and compatibility with biological tissues, which make them promising candidates for fabricating flexible bioelectronics. A soft hydrogel film offers an ideal interface to directly bridge thin-film electronics with the soft tissues. However, it remains difficult to fabricate a soft hydrogel film with an ultrathin configuration and excellent mechanical strength. Here we report a biological tissue-inspired ultrasoft microfiber composite ultrathin (< 5 μm) hydrogel film, which is currently the thinnest hydrogel film as far as we know. The embedded microfibers endow the composite hydrogel with prominent mechanical strength (tensile stress ~ 6 MPa) and anti-tearing property. Moreover, our microfiber composite hydrogel offers the capability of tunable mechanical properties in a broad range, allowing for matching the modulus of most biological tissues and organs. The incorporation of glycerol and salt ions imparts the microfiber composite hydrogel with high ionic conductivity and prominent anti-dehydration behavior. Such microfiber composite hydrogels are promising for constructing attaching-type flexible bioelectronics to monitor biosignals. Highlights A novel strategy was developed to construct ultrathin microfiber composite hydrogel films (< 5 μm) by embedding an electrospun fiber network into a hydrogel. The microfiber composite hydrogel offers tunable modulus in a broad range (from ~ 5 kPa to tens of MPa), which matches the modulus of most biological tissues and organs. The ultrathin configuration and ultrasoft nature allow the microfiber composite hydrogel seamlessly attaching to various rough surfaces.

Developing bioelectronics that retains their long‐term functionalities in the human body during daily activities is a current critical issue. To accomplish this, robust tissue adaptability and biointerfacing of bioelectronics should be achieved. Hydrogels have emerged as promising materials for bioelectronics that can softly adapt to and interface with tissues. However, hydrogels lack toughness, requisite electrical properties, and fabrication methodologies. Additionally, the water‐swellable property of hydrogels weakens their mechanical properties. In this work, an intrinsically nonswellable multifunctional hydrogel exhibiting tissue‐like moduli ranging from 10 to 100 kPa, toughness (400–873 J m−3), stretchability (≈1000% strain), and rapid self‐healing ability (within 5 min), is developed. The incorporation of carboxyl‐ and hydroxyl‐functionalized carbon nanotubes (fCNTs) ensures high conductivity of the hydrogel (≈40 S m−1), which can be maintained and recovered even after stretching or rupture. After a simple chemical modification, the hydrogel shows tissue‐adhesive properties (≈50 kPa) against the target tissues. Moreover, the hydrogel can be 3D printed with a high resolution (≈100 µm) through heat treatment owing to its shear‐thinning capacity, endowing it with fabrication versatility. The hydrogel is successfully applied to underwater electromyography (EMG) detection and ex vivo bladder expansion monitoring, demonstrating its potential for practical bioelectronics.

Carbon aerogels with exceptional electrical properties are considered promising materials for bioelectronics in signal detection and electrical stimulation. To address the mechanical incompatibilities of carbon aerogels with bio‐interfaces, particularly for dynamic tissues and organs, the incorporation of hydrogels is an effective strategy. However, achieving excellent electrical performance in carbon aerogel‐hydrogel hybrids remains a significant challenge. Two key factors contribute to this difficulty: 1) unrestricted hydrogel infiltration during preparation can lead to complete encapsulation of the conductive aerogel, and 2) the high swelling behavior of hydrogels can cause disconnection of the aerogel. Herein, a stretchable, highly conductive bioelectronic interface is achieved by forming an interlocking network between hierarchical porous carbon aerogel (PA) with polyvinyl alcohol (PVA) hydrogel. Partial exposure of the PA due to confined infiltration of PVA into the porous structure maintains the electrical performance, while the non‐swellable PVA ensures mechanical stretchability and stability. The hybrid demonstrates excellent conductivity (370 S·m−1), high charge storage capacity (1.66 mC cm−2), remarkable stretchability (250%), and long‐term stability over three months, enabling effective signal recording and electrical stimulation. For the first time, carbon aerogel‐hydrogel hybrids enable cardiac pacing both ex vivo and in vivo in rat heart models. Compared to conventional platinum electrodes, the PA‐PVA electrodes require lower pacing voltages, suggesting potential advantages in power efficiency and reduced tissue damage. The electrodes can be integrated with a wireless implantable device for in vivo synchronous electrocardiogram monitoring and cardiac pacing, underscoring their potential for arrhythmia management.

Traditional temporary cardiac pacemakers (TCPs), which employ transcutaneous leads and external wired power systems are battery-dependent and generally non-absorbable with rigidity, thereby necessitating surgical retrieval after therapy and resulting in potentially severe complications. Wireless and bioresorbable transient pacemakers have, hence, emerged recently, though hitting a bottleneck of unfavorable tissue-device bonding interface subject to mismatched mechanical modulus, low adhesive strength, inferior electrical performances, and infection risks. Here, to address such crux, we develop a multifunctional interface hydrogel (MIH) with superior electrical performance to facilitate efficient electrical exchange, comparable mechanical strength to natural heart tissue, robust adhesion property to enable stable device-tissue fixation (tensile strength: ∼30 kPa, shear strength of ∼30 kPa, and peel-off strength: ∼85 kPa), and good bactericidal effect to suppress bacterial growth. Through delicate integration of this versatile MIH with a leadless, battery-free, wireless, and transient pacemaker, the entire system exhibits stable and conformal adhesion to the beating heart while enabling precise and constant electrical stimulation to modulate the cardiac rhythm. It is envisioned that this versatile MIH and the proposed integration framework will have immense potential in overcoming key limitations of traditional TCPs, and may inspire the design of novel bioelectronic-tissue interfaces for next-generation implantable medical devices.

A tissue-like skin-device interface was prepared by using ultrathin functionalized hydrogels for wearable bioelectronics. Hydrogels consist of a cross-linked porous polymer network and water molecules occupying the interspace between the polymer chains. Therefore, hydrogels are soft and moisturized, with mechanical structures and physical properties similar to those of human tissue. Such hydrogels have a potential to turn the microscale gap between wearable devices and human skin into a tissue-like space. Here, we present material and device strategies to form a tissue-like, quasi-solid interface between wearable bioelectronics and human skin. The key material is an ultrathin type of functionalized hydrogel that shows unusual features of high mass-permeability and low impedance. The functionalized hydrogel acted as a liquid electrolyte on the skin and formed an extremely conformal and low-impedance interface for wearable electrochemical biosensors and electrical stimulators. Furthermore, its porous structure and ultrathin thickness facilitated the efficient transport of target molecules through the interface. Therefore, this functionalized hydrogel can maximize the performance of various wearable bioelectronics.

Hydrogel bioelectronics that can interface biological tissues and flexible electronics is at the core of the growing field of healthcare monitoring, smart drug systems, and wearable and implantable devices. Here, a simple strategy is demonstrated to prototype all‐hydrogel bioelectronics with embedded arbitrary conductive networks using tough hydrogels and liquid metal. Due to their excellent stretchability, the resultant all‐hydrogel bioelectronics exhibits stable electrochemical properties at large tensile stretch and various modes of deformation. The potential of fabricated all‐hydrogel bioelectronics is demonstrated as wearable strain sensors, cardiac patches, and near‐field communication (NFC) devices for monitoring various physiological conditions wirelessly. The presented simple platform paves the way of implantable hydrogel electronics for Internet‐of‐Things and tissue–machine interfacing applications.

Optoelectronic biointerfaces have made a significant impact on modern science and technology from understanding the mechanisms of the neurotransmission to the recovery of the vision for blinds. They are based on the cell interfaces made of organic or inorganic materials such as silicon, graphene, oxides, quantum dots, and π‐conjugated polymers, which are dry and stiff unlike a cell/tissue environment. On the other side, wet and soft hydrogels have recently been started to attract significant attention for bioelectronics because of its high‐level tissue‐matching biomechanics and biocompatibility. However, it is challenging to obtain optimal opto‐bioelectronic devices by using hydrogels requiring device, heterojunction, and hydrogel engineering. Here, an optoelectronic biointerface integrated with a poly(3,4‐ethylenedioxythiophene):poly(styrene sulfonate), PEDOT:PSS, hydrogel that simultaneously achieves efficient, flexible, stable, biocompatible, and safe photostimulation of cells is demonstrated. Besides their interfacial tissue‐like biomechanics, ≈34 kPa, and high‐level biocompatibility, hydrogel‐integration facilitates increase in charge injection amounts sevenfolds with an improved responsivity of 156 mA W−1, stability under mechanical bending , and functional lifetime over three years. Finally, these devices enable stimulation of individual hippocampal neurons and photocontrol of beating frequency of cardiac myocytes via safe charge‐balanced capacitive currents. Therefore, hydrogel‐enabled optoelectronic biointerfaces hold great promise for next‐generation wireless neural and cardiac implants.

Living conductive hydrogels that unite biological activity with robust electrogenic performance are emerging as transformative platforms for adaptive bioelectronics, yet most lose electrical functionality after mechanical damage or extended use. Here, we introduce an electrogenic living hydrogel embedding Bacillus subtilis spores─metabolically dormant, environmentally resilient, and capable of germinating into electrogenic bacteria─within a dual self-healing framework. The primary mechanism exploits hydrogen-bonded poly(3,4-ethylenedioxythiophene):polystyrenesulfonate-poly(vinyl alcohol) (PEDOT:PSS-PVA) networks to restore mechanical integrity, while a secondary, conductivity-specific mechanism is activated by rupture of carbon nanotube (CNT)-loaded cellulose acetate microcapsules at the fracture interface, re-establishing percolation pathways. Germination triggers extracellular electron transfer (EET) by B. subtilis, synergistically boosting conductivity beyond the undamaged state and reducing internal resistances. As a proof-of-concept, the hydrogel served as the anode in a paper-based microbial fuel cell (MFC), achieving a maximum power density of 1.5 μW cm-2 and an open-circuit voltage of 0.38 V─comparable to state-of-the-art paper MFCs. By integrating mechanically resilient matrices, microcapsule-mediated conductivity restoration, and biologically triggered electroactivity, this platform establishes a paradigm for self-repairing, high-performance living electronics with broad potential in biosensing, energy harvesting, and soft bioelectronic systems.

Microelectrode arrays (MEAs) are pivotal brain-machine interface devices that facilitate in situ and real-time detection of neurophysiological signals and neurotransmitter data within the brain. These capabilities are essential for understanding neural system functions, treating brain disorders, and developing advanced brain-machine interfaces. To enhance the performance of MEAs, this study developed a crosslinked hydrogel coating of calcium alginate (CA) and chitosan (CS) loaded with the anti-inflammatory drug dexamethasone sodium phosphate (DSP). By modifying the MEAs with this hydrogel and various conductive nanomaterials, including platinum nanoparticles (PtNPs) and poly (3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT: PSS), the electrical properties and biocompatibility of the electrodes were optimized. The hydrogel coating matches the mechanical properties of brain tissue more effectively and, by actively releasing anti-inflammatory drugs, significantly reduces post-implantation tissue inflammation, extends the electrodes' lifespan, and enhances the quality of neural activity detection. Additionally, this modification ensures high sensitivity and specificity in the detection of dopamine (DA), displaying high-quality dual-mode neural activity during in vivo testing and revealing significant functional differences between neuron types under various physiological states (anesthetized and awake). Overall, this study showcases the significant application value of bioactive hydrogels as excellent nanobiointerfaces and drug delivery carriers for long-term neural monitoring. This approach has the potential to enhance the functionality and acceptance of brain-machine interface devices in medical practice and has profound implications for future neuroscience research and the development of strategies for treating neurological diseases.

A hydrogel with tissue-like softness and ideal biocompatibility has emerged as a promising candidate for bioelectronics, especially in bidirectional bioelectrical transduction and communication. Conformal standardized hydrogel biointerfaces are in urgent demand to bridge electronic devices and irregular tissue surfaces. Herein, we presented a shape-adaptative electroactive hydrogel with tissue-adapted conductivity (≈1.03 S/m) by precisely regulating molecular chains and polymer networks of multisource gelatin at the molecular scale. Local amine-carboxylate electrostatic domains formed by ion interactions between gelatin and sodium citrate significantly enhance the physiological adaptability and regulate the biodegradation period. Benefiting from the reversible fluid-gel transition property, the hydrogel can be in situ gelatinized and establish a dynamic compliance bioelectronic interface with tissues by chemical bonding and the physical topological effect. Further, the mechanical-electrical coupling capacity of the hydrogel interface allows for bioelectrical conduction function reconstruction and electrical stimulation therapy after mechanical bridging at tissue defects to boost tissue regeneration and sensory restoration.

Hydrogel based electrodes have been applied in the field of bioelectronics, which is of great significance for constructing a robust human-computer interface. However, achieving both reliable conductivity and tissue matching mechanical properties remains challenging. Here, we report a synergistic strategy for constructing a hydrogel electrode for bioelectronic interface with tissue modulus and high conductivity by bacterial cellulose (BC) template induced growth polypyrrole (PPy) electrical percolation network combining a polymethacryloyloxyethyl trimethyl ammonium chloride (PDMC) hydrophilic network. This strategy balances the modulus and conductivity of the bioelectrode, makes up for the adverse effect of the conductive filler on the mechanical properties of the hydrogel, and constructs an effective conductive pathway. The electrical percolation of the hydrogel can be achieved at a low permeability threshold, and the flexibility (E = 288 kPa) of the hydrogel electrode with high conductivity (135.75 S/m) can be obtained. Moreover, the hydrogel electrode has low interface impedance and superior charge storage and injection capability, which allows higher signal-to-noise ratio of recording epidermal electrophysiological signals than that of commercial electrodes. The conductive, flexible and biocompatible hydrogel prepared here provides a new way to construct reliable bioelectronic devices.

Hydrogel-based electrodes and optical guides are promising tools for neural bioelectronics, offering tissue-like compliance, hydration capacity, and customizable functionalities. However, integrating multiple hydrogel modalities into a single device remains challenging due to material compatibility, cross-modal interference, and interfacial integration issues. In this work, an integrated hydrogel optical fiber electronics (iHOFE) platform is reported, including a step-index optical core, a conductive hydrogel layer, and a tissue-matched insulating sheath. By engineering the robust interface between each layer through chemical bonding and topological entanglement, a multilayer architecture capable of concurrent electrical and optical operation under dynamic mechanical deformation is created, thus high-fidelity electrophysiological recording and optogenetic modulation within the same region. The efficacy of the iHOFE is validated via two-month hippocampal implantation, demonstrating recording and manipulation of neural activity. This platform marks a significant advancement in developing multifunctional neural bioelectronics for interrogating and manipulating deep neural circuits compared to existing technologies.

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Hydrogels are emerging as stretchable electromagnetic interference (EMI) shielding materials because of their tissue-like mechanical properties and water-rich porous cellular structures. However, achieving high-performance hydrogel shields remains a challenge because enhancing conductivity often results in a compromise in deformation adoptability. This work proposes a treatment strategy involving sulfuric acid/titanium carbide MXene, which can simultaneously enhance the conductivity and stretchability of poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS)/poly(vinyl alcohol) (PVA) double-network hydrogels. Multiple spectroscopic characterizations reveal that sulfuric acid promotes the linear conformation transition of the PEDOT molecular chain, while MXene increases charge delocalization and hydrogen bond cross-linking sites. The hydrogels, synthesized with a combined content of 0.6 wt % of MXene and PEDOT:PSS, exhibit an average X-band EMI SE of 41 dB. This performance is sustained at 94.5%, even following stretching and release at a strain of 200%. Interestingly, the EMI SE is found to linearly increase, reaching a value of 99 dB as the frequency is increased to 26.5 GHz. This increase is attributed to the enhanced water molecular polarization process, as supported by theoretical calculations of the impedance and attenuation constant. This work introduces a post-treatment technique that optimizes double-network hydrogels, providing deep insights into their EMI shielding mechanism and enabling high-performance EMI shielding with an ultralow conductive filler content.

Moisture-electric generators (MEGs) can utilize water vapor in the air to provide energy. In recent years, hydrogel-based MEGs have gradually become a research direction of great importance due to the excellent electrical conductivity and mechanical properties of hydrogels. However, most hydrogels have poor anti-freezing properties, which greatly limits the application of MEGs. In this work, PVA/AG/AMPS/PA-LiCl (PAAP-L) hydrogels were successfully synthesized via one-pot and immersion methods using polyvinyl alcohol (PVA), agarose (AG), 2-acrylamido-2-methyl-1-propanesulfonic acid (AMPS), phytic acid (PA), and LiCl. The hydrogel exhibits excellent anti-freezing and moisture-retaining properties, with a freezing point as low as -66.58 °C and a high conductivity of 7.61 S/m, enabling it to serve as a strain sensor for detecting human movement. More importantly, a MEG was successfully developed based on this hydrogel, which quickly generated an open-circuit voltage of up to 622 mV within 6 s of exposure to humid air. In addition, the hydrogel successfully addressed the limitation of its inability to function as a self-powered respiratory monitor under low-temperature conditions, enabling it to sensitively monitor human respiratory patterns. The PAAP-L hydrogel in this study broadens the application scope in the fields of green energy and self-powered respiratory monitor sensors.

The hydrogel sensors with outstanding tensile strength, high sensitivity, broad sensing range and excellent stability are highly desired for flexible electronics. Here, a double network piezoresistive flexible hydrogel sensor equipped with a convex structure was fabricated using the template method, which consists of CMCNTs-PAM/SA-Ca2+ convex array and ultra-high-conductivity liquid metal droplets (LMs). Such a novel hybrid architecture enables the prepared piezoresistive sensor to have high sensitivity (GF up to 32.42), fast response time (209 ms), good cyclic stability (ultra 2000 cyclic tensile), and excellent strength. Due to its good comprehensive monitoring performance, the double network hydrogel sensor can be used for human activity monitoring, providing a tremendous potential in electronic wearable devices.

The increasing demand for durable and high-performance energy storage systems, particularly for flexible and extreme-environment applications, drives innovation in solid-state electrolytes. Zinc-air batteries (ZABs) offer high energy density and intrinsic safety yet suffer from zinc dendrite growth and interfacial degradation in alkaline environments. Zinc dendrite growth remains a critical barrier for zinc-air batteries. Herein, we develop a double-network hydrogel electrolyte integrating bacterial cellulose (BC)-reinforced polyacrylamide (PAM) for mechanical robustness and quaternized Poly[3-(Methacryloylamino) propyl] trimethylammonium chloride (PMPTC) for ion conduction. The BC nanofibers form a percolating hydrogen-bond network that enables efficient proton hopping (Grotthuss mechanism), while the quaternary ammonium groups of PMPTC create continuous hydrophilic channels for vehicular ion transport. This unique combination enables synergistic Vehicular-Grotthuss conduction, achieving ultra-high ionic conductivity of 269.47 mS·cm-1. Additionally, the polarized functional groups in both components help guide zincate ions (Zn (OH)42-) toward stable (002) plane deposition, effectively suppressing dendrite formation in ZABs. This design achieves exceptional water retention and enables ZABs operating over a wide temperature range. They exhibit a peak power density of 89.76 mW·cm-2 at room temperature, along with extended cycling stability. Multi-scale simulations confirm homogenized ion flux for uniform plating. This work establishes a paradigm for dendrite-suppressed, temperature-resilient zinc-air batteries.

The development of aqueous zinc-ion batteries (AZIBs) has attracted attention owing to their excellent safety and electrochemical performances; however, the practical application is still limited by the poor temperature tolerance of water. Therefore, hydrogel electrolytes with superb conductivity and mechanical properties over a wide temperature range are highly desirable to assemble an all-climate AZIB. Herein, a hydrogel electrolyte with excellent comprehensive performance was successfully fabricated by constructing double-network (DN) hydrogels and introducing a certain concentration of salt solution. Surprisingly, the electrolyte exhibited an impressive ionic conductivity (23 mS cm-1 at -30 °C) and tensile strength (107 KPa at -60 °C) due to the interactions of internal networks. The prepared Zn-MnO2 battery showed excellent rate performance and specific capacity (251.9 mAh g-1 at room temperature) within a wide operating temperature range (-30 to 60 °C). Remarkably, the battery could work normally even under 85% compressive strain or 135° bending. It is believed that the flexible Zn-MnO2 battery with a wide operating temperature based on the DN hydrogel electrolyte holds enormous potential as a reliable power source for flexible wearable electronic devices.

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In the present work, a new strategy is proposed to simultaneously enhance the toughness and electrochemical performance of the hydrogel with conductive microgel to form microgel-reinforced double network hydrogel. In this hydrogel, the conductive microgel is cross-linked to form the first network, which can dissipate energy to improve mechanical performance and stabilize the conductive network to improve the electrochemical performance. These hydrogels show excellent mechanical properties and good conductivity. When these hydrogels are assembled to all-gel-state intrinsically flexible and stretchable supercapacitor, they deliver outstanding capacitance. The strategy put forward here can extend the application scope of the hydrogel with multifunction.

The application of adhesive conductive hydrogel materials in flexible sensors has been extensively studied. However, existing adhesive hydrogel sensor materials have problems such as poor adhesion, low conductivity, and difficulty in balancing mechanical and adhesive properties, which limit their practical applications. In this study, we propose a simple and economical method to fabricate double‐network hydrogels for flexible strain sensors by dissolving acrylamide (AM), chitosan (CS), polyethylene glycol (PEG) and gelatin (Gel) in a mixed solvent of deionized water and a food‐grade phosphate. The prepared AM/CS/PEG/Gel (ACPG) hydrogel exhibits excellent toughness (maximum stress of 154 kPa, maximum elongation of 2256%), self‐adhesiveness (maximum adhesion strength to wood of 17.2 kPa), and high conductivity (2.33 S/m). Compared with similar adhesive hydrogels, the conductivity of ACPG hydrogel is significantly improved. Therefore, ACPG hydrogel can be used as an ideal material for flexible sensors, and has broad application potential in wearable devices and human‐computer interaction.

Sodium carboxymethyl cellulose showed great potential in wearable intelligent electronic devices due to its low price and good biocompatibility. This research aimed to develop a novel conductive hydrogel with stretchable, self-healing, self-adhesive, antibacterial, 3D printable properties, for the development of multifunctional flexible electronic materials based on sodium carboxymethyl cellulose. A multifunctional conductive hydrogel based on sodium carboxymethyl cellulose (SCMC) was synthesized by simple polymerization of SCMC, acrylic acid (AA) and alkaline calcium bentonite (AC-Bt). The multifunctional hydrogels (PAA-SCMC) possess excellent mechanical property (stress: 0.25 MPa; strain: 1675.0 %), Young's modulus (75.6 kPa), and conductivity (2.25 S/m). The multifunctional PAA-SCMC hydrogels serve as strain sensors (Gauge Factor (GF) = 12.68), temperature sensors (temperature coefficient of resistance (TCR) = -0.887 % °C at 20 °C-60 °C), sweat sensors, and pressure sensors. Importantly, the obtained hydrogels exhibited exceptional self-healing capability, self-adhesive properties, antimicrobial properties and 3D printability. The printed hydrogel has good mechanical properties, conductivity and antibacterial properties. Moreover, the hydrogel sensor possessed prominent sensitivity and cyclic stability to accurately monitor human motion, emotional changes, physiological signals in real time, and a hydrogel-based flexible touch keyboard was also fabricated to recognize writing trajectories. Overall, this study provided novel insights into the simple and efficient synthesis and sustainable manufacturing of environmentally friendly multifunctional flexible electronic skin sensors.

Flexible electronic devices, such as supercapacitors (SCs), place high demands on the mechanical properties, ionic conductivity, and electrochemical stability of electrolytes. Hydrogels, which combine flexibility and the advantages of both solid and liquid electrolytes, will meet the demand. Here, we report the synthesis of novel poly(ionic liquid)/polyacrylamide double-network (DN) (PIL/PAM DN) hydrogel electrolytes containing different metal salts via a two-step γ-radiation method. The resultant Li2SO4-1.0/PIL/PAM DN hydrogel electrolyte possesses excellent mechanical properties (tensile strength of 3.64 MPa, elongation at break of 446%) and high ionic conductivity (24.1 mS·cm-1). The corresponding flexible SC based on the Li2SO4-1.0/PIL/PAM DN hydrogel electrolyte (SC-Li2SO4) presents improved ion diffusion, ideal electrochemical double-layer capacitor behavior, good rate capability, and excellent cyclic stability. Moreover, symmetric SC-Li2SO4 achieves a wide operating voltage range of up to 1.5 V, with a maximum energy density of 26.0 W h·kg-1 and a capacitance retention of 94.1% after 10,000 galvanostatic charge-discharge cycles, owing to the deactivation of free water molecules by the synergistic effect of PIL, PAM, and SO42-. Above all, the capacitance of SC-Li2SO4 is well-maintained after overcharge, overdischarge, short circuit, extreme temperature, compression, and bending tests, indicating its high security and flexibility. This work reveals the enormous application potential of PIL-based conductive hydrogel electrolytes for flexible electronic devices.

Abstract Hydrogels have attracted extensive attention for their promising applications as flexible sensors. Developing conductive hydrogels with excellent mechanical properties still remains a significant challenge. Herein, double-network (DN) hydrogels composed of poly(vinyl alcohol) (PVA) and poly(ionic liquids) (PILs) are prepared through repetitive freezing/thawing process. The hydrogels are further treated with Fe3+ ions to enhance the mechanical properties due to the complexation between carboxyl groups and Fe3+ ions. The influence of the amount of PILs and concentration of Fe3+ on mechanical properties and conductivity is investigated. The optimal DN hydrogel P(VMCA-AA)1/PVA-Fe3+4 shows excellent mechanical properties, whose tensile strength, elongation at break, and toughness are 2.2 MPa, 350%, and 3.5 MJ m−3, respectively. P(VMCA-AA)1/PVA-Fe3+4 also displays a good conductivity of 1.04 S m−1. Moreover, the hydrogel demonstrates a high sensing sensitivity with a gauge factor (GF) of 3.36, indicating its application potential as a flexible sensor. Graphical Abstract

Stretchable conductive hydrogels have garnered considerable recognition due to their uses in strain sensors, electronic skins, soft robotics, and actuators. However, many hydrogels have poor mechanical properties limiting widespread implementation. While the development of ultrastretchable and mechanically robust hydrogels remains a challenge, the fabrication of these materials with customized designs is also highly desirable. Herein, a direct‐ink write 3D printable double‐network (DN) hydrogel is reported by integrating a physically cross‐linked κ‐carrageenan and a chemically cross‐linked poly(acrylamide‐co‐hydroxyethyl acrylate‐co‐Pluronic F127‐bisurethane methacrylate) with an ionically cross‐linked coordination between κ‐carrageenan and Fe3+ ions in water–glycerol binary solvent. The DN hydrogel demonstrates excellent stretchability (1770% strain), remarkable toughness (6.24 MJ m−3), high ionic conductivity (1.55 S m−1), biocompatibility, and nondrying behavior. A variety of 3D printed constructs including auxetic structures are fabricated and used as a strain sensor. The sensor exhibited real‐time electrical response to strain to detect human motions demonstrating the practicality of this system. These 3D printable DN hydrogels show great potential for on‐demand fabrication of flexible health‐monitoring devices.

Stretchable conductive hydrogel fibers are crucial for flexible electronics, yet their continuous manufacturing and mechanical adaptability remain challenging, which hinders widespread application. In this work, coordination networks of sodium alginate and slide-ring topological networks have been combined to improve the spinnability and mechanical properties of double-network hydrogel fibers for wearable sensors. The coordination of crosslinked networks of sodium alginate with calcium ions not only helps in the in situ formation of spinning processes with tunable mechanical properties but also results in excellent conductivity of the hydrogel fibers. A slide-ring topological network has been introduced through a polymerizable pseudorotaxane between acrylated β-cyclodextrin and long-chain bile acid guest photopolymerized with acrylamide, improving tensile properties of the polymer. The hybrid crosslinked double-network ensures that the fibers have high dynamic mechanical stability with negligible hysteresis and creep. The fabricated hydrogel fibers show excellent ion conductivity (0.64 S m-1, 20 °C), transparency, and stretchability (>3000%). Accordingly, strain sensors made from hydrogel fibers accurately capture high-frequency (2 Hz) and high-speed (1.6 cm s-1) motion, exhibit little drift for 300 stretch-release cycles, and detect repetitive human body movements. This double-network slide-ring topological hydrogel fiber system may provide inspiration for the design of textile-based stretchable electronic devices.

Conducting polymer hydrogels are promising materials in soft bioelectronics because of their tissue‐like mechanical properties and the capability of electrical interaction with tissues. However, it is challenging to balance electrical conductivity and mechanical stretchability: pure conducting polymer hydrogels are highly conductive, but they are brittle; while incorporating the conducting network with a soft network to form a double network can improve the stretchability, its electrical conductivity significantly decreases. Here, the problem is addressed by concentrating a poorly crosslinked precursor hydrogel with a high content ratio of the conducting polymer to achieve a densified double‐network hydrogel (5.5 wt% conducting polymer), exhibiting both high electrical conductivity (≈10 S cm–1) and a large fracture strain (≈150%), in addition to high biocompatibility, tissue‐like softness, low swelling ratio, and desired electrochemical properties for bioelectronics. A surface grafting method is further used to form an adhesive layer on the conducting hydrogel, enabling robust and rapid bonding on the tissues. Furthermore, the proposed hydrogel is applied to show high‐quality physiological signal recording and reliable, low‐voltage electrical stimulation based on an in vivo rat model. This method provides an ideal strategy for rapid and reliable tissue‐device integration with high‐quality electrical communications.

Conductive hydrogels usually suffer from weak mechanical properties and are easily destroyed, resulting in limited applications in flexible electronics. Concurrently, adding conductive additives to the hydrogel solution increases the probability of agglomeration and uneven dispersion issues. In this study, the biocompatible natural polymer chitosan was used as the network substrate. The rigid network employed was the Cit3-ion crosslinked chitosan (CS) network, and the MBA chemically crosslinked polyacrylamide (PAM) network was used as the flexible network. Tannic acid-reduced graphene oxide (TA-rGO), which has excellent conductivity and dispersibility, is used as a conductive filler. Thus, a CS/TA-rGO/PAM double network conductive hydrogel with excellent performance, high toughness, high conductivity, and superior sensing sensitivity was prepared. The prepared CS/TA-rGO/PAM double network conductive hydrogels have strong tensile properties (strain and toughness as high as 2009 % and 1045 kJ/cm3), excellent sensing sensitivity (GF value was 4.01), a wider strain detection range, high cycling stability and durability, good biocompatibility, and antimicrobial properties. The hydrogel can be assembled into flexible wearable devices that can not only dynamically detect human movements, such as joint bending, facial expression changes, swallowing, and saying, but also recognize handwriting and enable human-computer interaction.

Double-network (DN) hydrogels have emerged as promising candidates for flexible supercapacitor applications due to their exceptional mechanical toughness and flexibility. However, their practical use has been limited by poor electrolyte retention and low ionic conductivity, which hinder capacitive performance. In this study, we present a novel DN hydrogel modified through the self-assembly of metal nanoparticles to address these limitations. The hydrogel was synthesized via a combination of physical and chemical cross-linking, followed by in situ reduction of incorporated metal ions to form nanoparticles within the network. The resulting nanocomposite hydrogel exhibited enhanced electrolyte swelling capacity and improved ionic conductivity and maintained robust mechanical flexibility. A flexible supercapacitor (FSC) was fabricated using this modified DN hydrogel as both the electrode and solid-state electrolyte, with activated carbon nanosheets (ACNSs) derived from banana leaves serving as the active material. The ACNSs adhered effectively to the hydrogel matrix with the aid of a polyvinylidene fluoride (PVDF) binder. Electrochemical performance was evaluated in a symmetric two-electrode configuration using 0.5 M sodium sulfate aqueous solution as the supporting electrolyte. The device achieved a high areal specific capacitance (Csp) of 1361 mF cm-2, an energy density (E) of 23 mWh cm-2, and a power density (P) of 700 mW cm-2. Furthermore, the FSC demonstrated excellent cyclic stability, retaining 94% of its initial Coulombic efficiency after 500 cycles. These findings highlight the potential of metal nanoparticle-enriched DN hydrogels as multifunctional materials for next-generation integrated supercapacitors.

As typical soft materials, hydrogels have demonstrated great potential for the fabrication of flexible sensors due to their highly compatible elastic modulus with human skin, prominent flexibility, and biocompatible three-dimensional network structure. However, the practical application of wearable hydrogel sensors is significantly constrained because of weak adhesion, limited stretchability, and poor self-healing properties of traditional hydrogels. Herein, a multifunctional sodium hyaluronate (SH)/borax (B)/gelatin (G) double-cross-linked conductive hydrogel (SBG) was designed and constructed through a simple one-pot blending strategy with SH and gelatin as the gel matrix and borax as the dynamic cross-linker. The obtained SBG hydrogels exhibited a moderate tensile strength of 25.3 kPa at a large elongation of 760%, high interfacial toughness (106.5 kJ m-3), strong adhesion (28 kPa to paper), and satisfactory conductivity (224.5 mS/m). In particular, the dynamic cross-linking between SH, gelatin, and borax via borate ester bonds and hydrogen bonds between SH and gelatin chain endowed the SBG hydrogels with good fatigue resistance (>300 cycles), rapid self-healing performance (HE (healing efficiency) ∼97.03%), and excellent repeatable adhesion. The flexible wearable sensor assembled with SBG hydrogels demonstrated desirable strain sensing performance with a competitive gauge factor and exceptional stability, which enabled it to detect and distinguish various multiscale human motions and physiological signals. Furthermore, the flexible sensor is capable of precisely perceiving temperature variation with a high thermal sensitivity (1.685% °C-1). As a result, the wearable sensor displayed dual sensory performance for temperature and strain deformation. It is envisioned that the integration of strain sensors and thermal sensors provide a novel and convenient strategy for the next generation of multisensory wearable electronics and lay a solid foundation for their application in electronic skin and soft actuators.

Hydrogel-based strain sensors have garnered significant attention for their potential for human health monitoring. However, its practical application has been hindered by water loss, freezing, and structural impairment during long-term motion monitoring. Here, a strain sensor based on double-network (DN) hydrogel of polyacrylamide (PAAm)/carboxymethylcellulose (CMC) was developed in a ternary solvent system of lithium chloride (LiCl)/ethylene glycol (EG)/H2O through a facile one-pot radical polymerization strategy. The incorporation of EG effectively mitigated the hydration of lithium salts by generating stable ion clusters with Li+ and stronger hydrogen bonds within the polymer matrix. The sensor demonstrated excellent mechanical properties, including a stretchability of 1858 %, toughness of 1.80 MJ/m3, and recoverability of 102 %. Furthermore, the LiCl/EG/H2O ternary system resulted in high conductivity, excellent anti-freezing performance, and superior sensing stability. In addition, the sensor exhibited remarkable sensitivity, enabling the monitoring of human movements ranging from subtle to significant deformations, including throat motion and bending of the elbow, wrist, finger, and lower limb. This study presents a viable approach for constructing hydrogel-based strain sensors with exceptional sensing stability for long-term tracking of human motions.

Flexible sensors have attracted great attention due to their wide applications in various fields such as motion monitoring and medical health. It is reasonable to develop a sensor with good flexibility, sensitivity, and biocompatibility for wearable device applications. In this study, a double-network hydrogel was obtained by blending poly(vinyl alcohol) (PVA) with poly(ethylene glycol) diacrylate (PEGDA), which combines the flexibility of the PVA network and the fast photocuring ability of PEGDA. Subsequently, polydopamine-coated carbon nanotubes were used as conductive fillers of the PVA-PEG hydrogel matrix to prepare a flexible sensor that exhibits an effective mechanical response and significant stability in mechanics and conductivity. More importantly, the resistance of the sensor is very sensitive to pressure and thermal changes due to the optimized conductive network in the hydrogel. A motion monitoring test showed that the flexible sensor not only responds quickly to the motion of different joints but also keeps the output signal stable after many cycles. In addition, the excellent cell affinity of the hybrid hydrogel also encourages its application in health monitoring and motion sensors.

Conductive hydrogel, as a promising candidate material, is ideal for multifunctional strain sensors due to its similarity to biological tissues. It offers good wearability and high-precision information acquisition. However, fabricating conductive hydrogel-based strain sensors with both superior mechanical and conductive properties remains challenging. In this study, a compressive and conductive strain sensor based on multi-dynamic interactions is fabricated through a simple strategy. The strategy exploits hydrogen bonding and ionic ligand bonding by using nanocellulose reinforced poly(acrylic acid) hydrogels impregnated with the Fe3+ solution to prepare a double-network hydrogel. The prepared PAA/CNF–Fe3+ double-network hydrogel exhibited excellent properties, including extraordinary performance compressive stress (2.96 MPa) and remarkable electrical conductivity (6.34 S/m). With these advantages, the PAA/CNF–Fe3+ double network hydrogel was developed to be an attractive strain flexible sensor with cyclic stability (150 cycles) and good strain sensitivity (GF = 2.87). In addition, the PAA/CNF–Fe3+ hydrogel flexible sensor can be used as an electronic skin to accurately discriminate subtle and large body movements. Given the simple strategy, double network structure, and satisfactory functionality, the PAA/CNF–Fe3+ hydrogel provides a new sustainable and multifunctional development strategy that can be applied in the field of strain sensors and medical detection.

Ionic conductive hydrogels have recently attracted tremendous attention in flexible wearable strain sensors. However, achieving a combination of good mechanical properties, strong adhesion to various material surfaces, and remarkable ionic conductivity in a single ionic conductive hydrogel remains a challenge. Herein, new poly(acrylamide-co-sulfobetaine methacrylate)/chitosan/phytic acid (ASCP) ionic conductive hydrogels with double networks were prepared through free radical polymerization. The versatile functional groups from chitosan and phytic acid gave the hydrogels universal adhesion capabilities with a maximum adhesion strength of 18.7 kPa to paper. The obtained ASCP conductive hydrogels exhibited a large elongation of 675 % and a moderate tensile strength 52.8 kPa due to the synergy of chemical cross-linking and physical interactions. Phytic acid as the conductive component conferred the hydrogels with excellent ionic conductivity of 10.3 S m-1. Moreover, the incorporation of chitosan and phytic acid imparted the hydrogels with enhanced anti-drying capability, as evidenced by a residual mass ratio of 58.3 % after 10 days, and exhibited favorable anti-swelling behavior, with an equilibrium swelling ratio of 115 % in water after 4 days. The described ionic conductive hydrogels were assembled into wearable strain sensors to detect various human joint movements. This work offers a straightforward strategy to design multifunctional conductive hydrogels which envision prospective applications in wearable sensors and other flexible electronic devices.

Novel double-network (DN) ion-conducting hydrogel (ICH) based on a poly(ionic liquid)/MXene/poly(vinyl alcohol) system (named PMP DN ICH) was synthesized using freeze–thawing and ionizing radiation technology. The PMP DN ICH possesses a multiple cross-linking mechanism and exhibits outstanding ionic conductivity (63.89 mS cm−1), excellent temperature resistance (−60–80 °C) and decent mechanical performance. The well-designed PMP DN ICH shows considerable potential in wearable sensing, energy storage, and energy harvesting. Novel double-network (DN) ion-conducting hydrogel (ICH) based on a poly(ionic liquid)/MXene/poly(vinyl alcohol) system (named PMP DN ICH) was synthesized using freeze–thawing and ionizing radiation technology. The PMP DN ICH possesses a multiple cross-linking mechanism and exhibits outstanding ionic conductivity (63.89 mS cm−1), excellent temperature resistance (−60–80 °C) and decent mechanical performance. The well-designed PMP DN ICH shows considerable potential in wearable sensing, energy storage, and energy harvesting. High-performance ion-conducting hydrogels (ICHs) are vital for developing flexible electronic devices. However, the robustness and ion-conducting behavior of ICHs deteriorate at extreme temperatures, hampering their use in soft electronics. To resolve these issues, a method involving freeze–thawing and ionizing radiation technology is reported herein for synthesizing a novel double-network (DN) ICH based on a poly(ionic liquid)/MXene/poly(vinyl alcohol) (PMP DN ICH) system. The well-designed ICH exhibits outstanding ionic conductivity (63.89 mS cm−1 at 25 °C), excellent temperature resistance (− 60–80 °C), prolonged stability (30 d at ambient temperature), high oxidation resistance, remarkable antibacterial activity, decent mechanical performance, and adhesion. Additionally, the ICH performs effectively in a flexible wireless strain sensor, thermal sensor, all-solid-state supercapacitor, and single-electrode triboelectric nanogenerator, thereby highlighting its viability in constructing soft electronic devices. The highly integrated gel structure endows these flexible electronic devices with stable, reliable signal output performance. In particular, the all-solid-state supercapacitor containing the PMP DN ICH electrolyte exhibits a high areal specific capacitance of 253.38 mF cm−2 (current density, 1 mA cm−2) and excellent environmental adaptability. This study paves the way for the design and fabrication of high-performance multifunctional/flexible ICHs for wearable sensing, energy-storage, and energy-harvesting applications.

No abstract available

Benefiting from the unique properties such as flexibility, bio-tissue-like mechanical compliance and adjustable conductivity, conductive hydrogels have demonstrated great application prospects in the field of wearable sensors. However, synthetic polymer-based conductive hydrogels are poorly biocompatible, and their overuse can exacerbate resource depletion. Herein, a biobased conductive hydrogel with double-network structure was prepared for stretchable strain sensors by synergistic interaction of carboxymethyl chitosan, carboxylated cellulose nanofibers, calcium chloride and ionic liquid. Owing to the reinforcing effect by nanofibers and the construction of double-network, the conductive hydrogel showed good mechanical properties with elongation at break of 406.7 % and tensile strength of 248.9 kPa, and the corresponding Young's modulus and toughness were 69.2 kPa and 527.6 kJ/m3, respectively. Moreover, the conductive hydrogel exhibited excellent conductivity and freezing resistance, its ionic conductivity and freezing point reached 1.073 mS/cm and -12.32 °C, respectively. Meanwhile, the conductive hydrogel showed remarkable cell compatibility, skin-friendliness and biodegradability. In addition, the conductive hydrogel-based stretchable strain sensor possessed good comprehensive sensing performance and was able to accurately recognize joint flexion and subtle changes of human body. The strategy to prepare biobased and high-performance conductive hydrogel in this work will promote the sustainable development and application of flexible electronics.

Conductive hydrogels have potential applications in wearable strain sensors. However, the diverse operating environments impose higher demands on their conductivity, freeze resistance, mechanical properties, self-healing capabilities, and adhesion. In this work, glycerol (GL), an antifreeze agent, and polyaniline (PANI), a conductive polymer, were introduced into a polyacrylic acid sodium (PAAS) hydrogel system. Using a one-pot method, a double-network PAAS/GL/PANI conductive hydrogel was fabricated. The incorporation of GL significantly enhanced the hydrogel’s freeze resistance and moisture retention, allowing it to maintain good flexibility even at − 23 °C. PANI improved both the electrical conductivity and gauge factor (GF) of the hydrogel. When the PANI content was 7.5 wt%, the PAAS/GL/PANI conductive hydrogel exhibited outstanding antifreeze properties, electrical conductivity, mechanical strength, adhesion, self-healing ability, and fatigue resistance. The wearable strain sensor based on the PAAS/GL/PANI (7.5 wt%) conductive hydrogel is able to accurately monitor joint movements and detect subtle physiological signals. Preparation of PAAS/GL/PANI conductive hydrogels and demonstration of their multifunctional applications Preparation of PAAS/GL/PANI conductive hydrogels and demonstration of their multifunctional applications

A conductive hydrogel with double network structure was prepared by embedding Ag nanoparticles onto polyvinylpyrrolidone through in situ reduction, and subsequently crosslinking the mixture with polyvinyl alcohol and sodium lignosulfonate. This unique architecture imparted the hydrogel with good mechanical properties and fatigue resistance. Notably, the hydrogel exhibited remarkable antibacterial efficacy, achieving inhibition rates of 99.9 % against E. coli and 95.8 % against S. aureus. Furthermore, the conductive network, formed through the synergistic interaction of free ions and AgNPs, significantly enhanced both the conductivity and durability of the hydrogel sensor. The results demonstrated that the sensor maintained stable sensitivity even after 1000 cycles of stretching at 3 % and 30 % strain. In practical applications, this hydrogel sensor was successfully employed for real-time monitoring of various human body parts, including fingers, elbows, knees and facial expressions, underscoring its significant potential in the fields of flexible electronics and wearable sensing technologies.

As one of the promising alternatives of lithium-ion batteries, zinc-ion batteries (ZIBs) have received growing interest from researchers due to their good safety, eco-friendliness, and low cost. Nevertheless, aqueous ZIBs are still a step away from practical applications due to the nonuniform deposition of Zn and parasitic side reactions, which cause capacity fading and even short circuit. To tackle these problems, here we introduce a single-Zn-ion conducting hydrogel electrolyte (SIHE), P(ICZn-AAm), synthesized with iota carrageenan (IC) and acrylamide (AAm). The SIHE manifests single Zn2+ conductivity via the abundant sulfates fixed on the IC polymer backbone, delivering a high Zn2+ transference number of 0.93. It also exhibits outstanding ionic conductivity of 2.15 × 10-3 S cm-1 at room temperature. The enhanced compatibility at the electrode-electrolyte interface was verified by the stable Zn striping/plating performance along with a homogenous and smooth Zn deposition layer. It is also found that the passivation of the Zn anode can be effectively prohibited due to the lack of free anions in the electrolyte. The practical performance of the SIHE is further investigated with Zn-V2O5 batteries, which showed a stable capacity of 271.6 mA h g-1 over 150 cycles at 2 C and 127.5 mA h g-1 over 500 cycles at 5 C.

Due to their stretchability, conductivity, and good biocompatibility, hydrogels have been recognized as potential materials for flexible sensors. However, it is still challenging for hydrogels to meet the conductivity, mechanical strength, and freeze-resistant requirements in practice. In this study, a chitosan-poly (acrylic acid-co-acrylamide) double network (DN) hydrogel was prepared by immersing the chitosan-poly (acrylic acid-co-acrylamide) composite hydrogel into Fe2(SO4)3 solution. Due to the formation of an energy-dissipative chitosan physical network, the DN hydrogel possessed excellent tensile and compression properties. Moreover, the incorporation of the inorganic salt endowed the DN hydrogel with excellent conductivity and freeze-resistance. The strain sensor prepared using this DN hydrogel displayed remarkable sensitivity and reliability in detecting stretching and bending deformations. In addition, this DN hydrogel sensor also worked well at a lower temperature (−20 °C). The highly mechanical, conductive, and freeze-resistant DN hydrogel revealed a promising application in the field of wearable devices.

Hydrogel-based flexible electronic devices are essential in future healthcare and biomedical applications, such as human motion monitoring, advanced diagnostics, physiotherapy, etc. As a satisfactory flexible electronic material, the hydrogel should be conductive, ductile, self-healing, and adhesive. Herein, we demonstrated a unique design of mechanically resilient and conductive hydrogel with double network structure. The Ca2+ crosslinked alginate as the first dense network and the ionic pair crosslinked polyzwitterion as the second loose network. With the synthetic effect of these two networks, this hydrogel showed excellent mechanical properties, such as superior stretchability (1,375%) and high toughness (0.57 MJ/m3). At the same time, the abundant ionic groups of the polyzwitterion network endowed our hydrogel with excellent conductivity (0.25 S/m). Moreover, due to the dynamic property of these two networks, our hydrogel also performed good self-healing performance. Besides, our experimental results indicated that this hydrogel also had high optical transmittance (92.2%) and adhesive characteristics. Based on these outstanding properties, we further explored the utilization of this hydrogel as a flexible wearable strain sensor. The data strongly proved its enduring accuracy and sensitivity to detect human motions, including large joint flexion (such as finger, elbow, and knee), foot planter pressure measurement, and local muscle movement (such as eyebrow and mouth). Therefore, we believed that this hydrogel had great potential applications in wearable health monitoring, intelligent robot, human-machine interface, and other related fields.