Gema 水凝胶

Gelatin methacryloyl (GelMA) hydrogels have been widely used for various biomedical applications due to their suitable biological properties and tunable physical characteristics. Three dimensional (3D) GelMA hydrogels closely resemble some essential properties of native extracellular matrix (ECM) due to the presence of cell-attaching and matrix metalloproteinase responsive peptide motifs, which allow cells to proliferate and spread in GelMA-based scaffolds. GelMA is also versatile from a processing perspective. It crosslinks when exposed to light irradiation to form hydrogels with tunable mechanical properties which mimic the native ECM. It can also be microfabricated using different methodologies including micromolding, photomasking, bioprinting, self-assembly, and microfluidic techniques to generate constructs with controlled architectures. Hybrid hydrogel systems can also be formed by mixing GelMA with nanoparticles such as carbon nanotubes and graphene oxide, and other polymers to form networks with desired combined properties and characteristics for specific biological applications. Recent research has demonstrated the proficiency of GelMA-based hydrogels in a wide range of applications including engineering of bone, cartilage, cardiac, and vascular tissues, among others. Other applications of GelMA hydrogels, besides tissue engineering, include fundamental single-single cell research, cell signaling, drug and gene delivery, and bio-sensing.

… of 3D tumor models utilizing GelMA hydrogel, including the preparation procedures, tumor … for the advancement of GelMA hydrogels. It is anticipated that GelMA hydrogels will find …

Increasing data reveals that gelatin that has been methacrylated is involved in a variety of physiologic processes that are important for therapeutic interventions. Gelatin methacryloyl (GelMA) hydrogel is a highly attractive hydrogels-based bioink because of its good biocompatibility, low cost, and photo-cross-linking structure that is useful for cell survivability and cell monitoring. Methacrylated gelatin (GelMA) has established itself as a typical hydrogel composition with extensive biomedical applications. Recent advances in GelMA have focused on integrating them with bioactive and functional nanomaterials, with the goal of improving GelMA's physical, chemical, and biological properties. GelMA's ability to modify characteristics due to the synthesis technique also makes it a good choice for soft and hard tissues. GelMA has been established to become an independent or supplementary technology for musculoskeletal problems. Here, we systematically review mechanism-of-action, therapeutic uses, and challenges and future direction of GelMA in musculoskeletal disorders. We give an overview of GelMA nanocomposite for different applications in musculoskeletal disorders, such as osteoarthritis, intervertebral disc degeneration, bone regeneration, tendon disorders and so on.

Regeneration of corneal stroma has always been a challenge due to its sophisticated structure and keratocyte-fibroblast transformation. In this study, we fabricate grid poly (ε-caprolactone)-poly (ethylene glycol) microfibrous scaffold and infuse the scaffold with gelatin methacrylate (GelMA) hydrogel to obtain a 3 D fiber hydrogel construct; the fiber spacing is adjusted to fabricate optimal construct that simulates the stromal structure with properties most similar to the native cornea. The topological structure (3 D fiber hydrogel, 3 D GelMA hydrogel, and 2 D culture dish) and chemical factors (serum, ascorbic acid, insulin, and β-FGF) are examined to study their effects on the differentiation of limbal stromal stem cells to keratocytes or fibroblasts and the phenotype maintenance, in vitro and in vivo tissue regeneration. The results demonstrate that fiber hydrogel and serum-free media synergize to provide an optimal environment for the maintenance of keratocyte phenotype and the regeneration of damaged corneal stroma. Regeneration of corneal stroma has been a challenge due to its sophisticated structure and the easy transformation of the keratocyte. Here, the authors use a hydrogel reinforced with orthogonally aligned fibres and serum free medium to maintain keratocyte phenotype for the in vivo stromal regeneration.

Photocrosslinked gelatin methacryloyl (GelMA) hydrogels have attracted great concern in the biomedical field because of their good biocompatibility and tunable physicochemical properties. Herein, different approaches to synthesize GelMA were introduced, especially, the typical method using UV light to crosslink the gelatin-methacrylic anhydride (MA) precursor was introduced in detail. In addition, the traditional and cutting-edge technologies to characterize the properties of GelMA hydrogels and GelMA prepolymer were also overviewed and compared. Furthermore, the applications of GelMA hydrogels in cell culture and tissue engineering especially in the load-bearing tissue (bone and cartilage) were summarized, followed by concluding remarks.

Gelatin-based hydrogel, which mimics the natural dermal extracellular matrix, is a promising tissue engineering material. However, insufficient and uncontrollable mechanical and degradation properties remain the major obstacles for its application in medical bone regeneration material. Herein, we develop a facile but efficient strategy for a novel hydrogel as guided bone regeneration (GBR) material. In this study, methacrylic anhydride (MA) has been used to modify gelatin to obtain photo-crosslinkable methacrylated gelatin (GelMA). Moreover, the GelMA/PEGDA hydrogel was prepared by photo-crosslinking GelMA and PEGDA with photoinitiator I2959 under UV treatment. Compared with the GelMA hydrogel, the GelMA/PEGDA hydrogel exhibits several times stronger mechanical properties than pure GelMA hydrogel. The GelMA/PEGDA hydrogel shows a suitable degradation rate of more than 4 weeks, which is beneficial to implant in body. In vitro cell culture showed that osteoblast can adhere and proliferate on the surface of the hydrogel, indicating that the GelMA/PEGDA hydrogel had good cell viability and biocompatibility. Furthermore, by changing the quantities of GelMA, I2959, and PEGDA, the gelation time can be controlled easily to meet the requirement of its applications. In short, this study demonstrated that PEGDA enhanced the performance and extended the applications of GelMA hydrogels, turning the GelMA/PEGDA hydrogel into an excellent GBR material.

Purpose Non-healing or slow healing chronic wounds are among serious complications of diabetes that eventually result in amputation of limbs and increased morbidities and mortalities. Chronic diabetic wounds show reduced blood vessel formation (lack of angiogenesis), inadequate cell proliferation and poor cell migration near wounds. In this paper, we report the development of a hydrogel-based novel wound dressing material loaded with reduced graphene oxide (rGO) to promote cell proliferation, cell migration and angiogenesis for wound healing applications. Methods Gelatin-methacryloyl (GelMA) based hydrogels loaded with different concentrations of rGO were fabricated by UV crosslinking. Morphological and physical characterizations (porosity, degradation, and swelling) of rGO incorporated GelMA hydrogel was performed. In vitro cell proliferation, cell viability and cell migration potential of the hydrogels were analyzed by MTT assay, live/dead staining, and wound healing scratch assay respectively. Finally, in vivo chicken embryo angiogenesis (CEO) testing was performed to evaluate the angiogenic potential of the prepared hydrogel. Results The experimental results showed that the developed hydrogel possessed enough porosity and exudate-absorbing capacity. The biocompatibility of prepared hydrogel on three different cell lines (3T3 fibroblasts, EA.hy926 endothelial cells, and HaCaT keratinocytes) was confirmed by in vitro cell culture studies (live/dead assay). The GelMA hydrogel containing 0.002% w/w rGO considerably increased the proliferation and migration of cells as evident from MTT assay and wound healing scratch assay. Furthermore, rGO impregnated GelMA hydrogel significantly enhanced the angiogenesis in the chick embryo model. Conclusion The positive effect of 0.002% w/w rGO impregnated GelMA hydrogels on angiogenesis, cell migration and cell proliferation suggests that these formulations could be used as a functional wound healing material for the healing of chronic wounds.

… In this regard, applications employing GelMA hydrogels are currently limited by the low … of GelMA. Therefore, this review focuses on modifications made to GelMA hydrogels to make …

Photocrosslinkable materials have been frequently used for constructing soft and biomimetic hydrogels for tissue engineering. Although, ultraviolet (UV) light is commonly used for photocrosslinking such materials, its use has been associated with several biosafety concerns such as DNA damage, accelerated aging of tissues, and cancer. Here we report an injectable visible light crosslinked gelatin-based hydrogel for myocardium regeneration. Mechanical characterization revealed that the compressive moduli of the engineered hydrogels could be tuned in the range of 5–56 kPa, by changing the concentrations of the co-initiator and co-monomer in the precursor formulation. In addition, the average pore sizes (26–103 μm) and swelling ratio (7–13%) were also shown to be tunable by varying the hydrogel formulation. In vitro studies showed that visible light crosslinked GelMA hydrogels supported the growth and function of primary cardiomyocytes (CMs). In addition, the engineered materials were shown to be biocompatible in vivo, and could be successfully delivered to the heart after myocardial infarction in an animal model to promote tissue healing. The developed visible light crosslinked hydrogel could be used for the repair of various soft tissues such as the myocardium, and for the treatment of cardiovascular diseases with enhanced therapeutic functionality.

Gelatin methacryloyl (GelMA), a photocurable hydrogel, is widely used in 3D culture, particularly in 3D bioprinting, due to its high biocompatibility, tunable physicochemical properties, and excellent formability. However, as the properties and performances of GelMA vary under different synthetic conditions, there is a lack of standardization, leading to conflicting results. In this study, a uniform standard is established to understand and enhance GelMA applications. First, the basic concept of GelMA and the density of the molecular network (DMN) are defined. Second, two properties, degrees of substitution and ratio of solid content, as the main measurable parameters determining the DMN are used. Third, the mechanisms and relationships between DMN and its performance in various applications in terms of porosity, viscosity, formability, mechanical strength, swelling, biodegradation, and cytocompatibility are theoretically explained. The main questions that are answered: what does performance mean, why is it important, how to optimize the basic parameters to improve the performance, and how to characterize it reasonably and accurately? Finally, it is hoped that this knowledge will eliminate the need for researchers to conduct tedious and repetitive pre‐experiments, enable easy communication for achievements between groups under the same standard, and fully explore the potential of the GelMA hydrogel.

Bioprinting technology promotes innovation of fabricating tissue engineered constructs. Dental pulp stem cells (DPSCs) have significant advantages over classical bone mesenchymal stem cells (BMSCs) and are a promising seed cell candidate for bone engineering bioprinting. However, current reports about bioprinted DPSCs for bone regeneration are incomprehensive. The objective of this study was to investigate the osteogenic potential of DPSCs in methacrylate gelatin (GelMA) hydrogels bioprinted scaffolds in vitro and in vivo. Firstly, we successfully bioprinted GelMA with different concentrations embedded with or without DPSCs. Printability, physical features and biological properties of the bioprinted constructs were evaluated. Then, osteogenic differentiation levels of DPSCs in bioprinted constructs with various concentrated GelMA were compared. Finally, effects of bioprinted constructs on cranial bone regeneration were evaluated in vivo. The results of our study demonstrated that 10% GelMA had higher compression modulus, smaller pores, lower swelling and degradation rate than 3% GelMA. Twenty-eight days after printing, DPSCs in three groups of bioprinted structures still maintained high cell activities (>90%). Moreover, DPSCs in 10% GelMA showed an upregulated expression of osteogenic markers and a highly activated ephrinB2/EphB4 signaling, a signaling involved in bone homeostasis. In vivo experiments showed that DPSCs survived at a higher rate in 10% GelMA, and more new bones were observed in DPSC-laden 10% GelMA group, compared with GelMA of other concentrations. In conclusion, bioprinted DPSC-laden 10% GelMA might be more appropriate for bone regeneration application, in contrast to GelMA with other concentrations.

… GelMA hydrogel (A-GelMA S1 ). To obtain stage-2-autoclaved GelMA hydrogels (A-GelMA S2 ), untreated GelMA powder was used to cast untreated GelMA hydrogel, which was then …

Tissue engineering aims to replace missing or damaged tissues and restore their functions. Three-dimensional (3D) printing has been gaining more attention because it enables the researchers to design and produce cell loaded constructs with predetermined shapes, sizes, and interior architecture. In the present study, a 3D bioprinted corneal stroma equivalent was designed to substitute for the native tissue. Reproducible outer and inner organization of the stroma was obtained by optimizing printing conditions such as the nozzle speed in the x-y direction and the spindle speed. 3D printed GelMA hydrogels were highly stable in PBS during three weeks of incubation (8% weight loss). Live-Dead cell viability assay showed 98% cell viability on day 21 indicating that printing conditions were suitable for keratocyte printing. Mechanical properties of the cell loaded 3D printed hydrogels increased 2-fold during this incubation period and approached those of the native cornea (ca. 20 kPa vs. 27 kPa, respectively). Expression of collagens types I and V, and proteoglycan (decorin) in keratocytes indicates maintenance of the phenotype in the hydrogels. Transparency of cell-loaded and cell-free hydrogels was over 80% (at 700 nm) during the three week culture period and comparable to that of the native cornea (85%) at the same wavelength. Thus, GelMA hydrogels bioprinted with keratocytes mimic the biological and physical properties of the corneal stroma with their excellent transparency, adequate mechanical strength, and high cell viability.

Periodontitis is a chronic inflammatory disease caused by plaque that leads to alveolar bone resorption. In the treatment of periodontitis, it is necessary to reduce the bacterial load and promote alveolar bone regeneration. In this study, zeolitic imidazolate framework-8 (ZIF-8) is used in the treatment of periodontitis, and an injectable photopolymerizable ZIF-8/gelatin methacryloyl (GelMA) composite hydrogel (GelMA-Z) is constructed. We confirm that ZIF-8 nanoparticles are successfully loaded into GelMA, which demonstrates fluidity and photopolymerizability. GelMA-Z continuously releases Zn2+ and shows good cytocompatibility. In vitro, GelMA-Z can effectively upregulate the expression of osteogenesis-related genes and proteins, increase alkaline phosphatase activity, promote extracellular matrix mineralization by rat bone mesenchymal stem cells, and exert an obvious antibacterial effect against Porphyromonas gingivalis. In vivo, GelMA-Z reduces the bacterial load, relieves inflammation and promotes alveolar bone regeneration in a rat model. The above results show that GelMA-Z has potential prospects in the treatment of periodontitis. STATEMENT OF SIGNIFICANCE: : Various methods have been explored for the treatment of periodontitis. However, current regiments have difficulty achieving ideal alveolar bone regeneration. In this study, we constructed a zeolitic imidazolate framework-8 (ZIF-8)/gelatin methacryloyl (GelMA) composite hydrogel (GelMA-Z). (1) The injectable and photopolymerizable GelMA-Z showed biocompatibility in vitro and in vivo. (2) GelMA-Z continually released zinc ions to promote the osteogenic differentiation of bone mesenchymal stem cells and kill bacteria in vitro. (3) In a rat model, the GelMA-Z pregel solution was used to fill the periodontal pocket and then crosslinked by UV exposure. GelMA-Z can stably remain in the periodontal pocket to reduce the bacterial load, relieve inflammation and promote alveolar bone regeneration. In conclusion, GelMA-Z has great potential for use in the treatment of periodontitis, especially in promoting alveolar bone regeneration.

Gelatin-methacryloyl (GelMA) is a semi-synthetic hydrogel which consists of gelatin derivatized with methacrylamide and methacrylate groups. These hydrogels provide cells with an optimal biological environment (e.g., RGD motifs for adhesion) and can be quickly photo-crosslinked, which provides shape fidelity and stability at physiological temperature. In the present work, we demonstrated how GelMA hydrogels can be synthesized with a specific degree of functionalization (DoF) and adjusted to the intended application as a three-dimensional (3D) cell culture platform. The focus of this work lays on producing hydrogel scaffolds which provide a cell promoting microenvironment for human adipose tissue-derived mesenchymal stem cells (hAD-MSCs) and are conductive to their adhesion, spreading, and proliferation. The control of mechanical GelMA properties by variation of concentration, DoF, and ultraviolet (UV) polymerization conditions is described. Moreover, hAD-MSC cell viability and morphology in GelMA of different stiffness was evaluated and compared. Polymerized hydrogels with and without cells could be digested in order to release encapsulated cells without loss of viability. We also demonstrated how hydrogel viscosity can be increased by the use of biocompatible additives, in order to enable the extrusion bioprinting of these materials. Taken together, we demonstrated how GelMA hydrogels can be used as a versatile tool for 3D cell cultivation.

Osteochondral regeneration is an orchestrated process of inflammatory immunity, host cell response, and implant degradation in tissue engineering. Here, the effects of a platelet-rich plasma (PRP)-gelatin methacryloyl (GelMA) hydrogel scaffold fabricated using the digital micro-mirror device (DMD) technique for osteochondral repair were investigated in a rabbit model. GelMA hydrogels with different PRP concentrations were fabricated, and their roles in bone marrow mesenchymal stem cells (BMSCs) and macrophage polarization in vitro were investigated. The incorporation of 20% PRP into the hydrogel showed optimal effects on the proliferation, migration, and osteogenic and chondrogenic differentiation of BMSCs. The 20% PRP-GelMA (v/v) hydrogel also promoted M2 polarization with high expression of Arg1 and CD206. Compared to the 20% PRP group, the 50% PRP group showed similar biological roles in BMSCs but less extent of osteogenesis. In the vivo study, the 20% PRP-GelMA composite was used for osteochondral reconstruction and showed more cartilage and subchondral bone regeneration than that observed using the pure GelMA hydrogel. The PRP-GelMA group exhibited more M2 macrophage infiltration and less M1 macrophage presentation at three time points as compared to the nontreatment group. The expression of Arg1 in the PRP-GelMA group increased significantly at 6 weeks but decreased to a lower level at 12 weeks, while CD163 showed sustained high expression until 18 weeks. Our findings demonstrated that the 3D-printed PRP-GelMA composite could promote osteochondral repair through immune regulation by M2 polarization and could be a potential candidate for osteochondral tissue engineering. STATEMENT OF SIGNIFICANCE: : PRP-GelMA hydrogels promoted the migration and osteogenic and chondrogenic differentiation of BMSCs. PRP-GelMA hydrogels participated in immune regulation and M1-to-M2 transition of macrophages. PRP-GelMA hydrogels coordinated and promoted several overlapping osteochondral repair events, including dynamic immune regulation, chemotaxis of MSCs, and osteochondral differentiation. PRP-GelMA hydrogels showed superior cartilage and subchondral bone repair properties.

Applicability of hydrogels as drug delivery systems is on the rise due to their highly tunable degree of polymeric crosslinking to attain varying rates of payload release. Sustaining the release of therapeutic payloads at certain physiological sites has been the need of the hour to treat disorders such as peritoneal or pleural malignancies. These disorders can be targeted via intracavitary administration of hydrogels, providing localized therapy. In this study, a gelatin methacrylate (GelMa) hydrogel with tunable physicochemical traits is developed and characterized. A hydrogel-based depot system was curated using GelMa as backbone, a photo-initiator (lithium phenyl-2,4,6-trimethylbenzoylphosphinate) and a chemical crosslinker (N,N-methylenebisacrylamide). Hydrogels were optimized using a 23 factorial design, by testing for their gelling time, injectability, viscosity change, elasticity, bio-adhesion, swelling-index, in vitro degradation, in vitro release, and biocompatibility. Gelling time for hydrogel formulations was found to be <60 seconds with gelling being achieved in as fast as 24 seconds. Bio-adhesion studies revealed that formulations with higher concentrations of both crosslinkers had more adhesion to guinea pig lung tissues. Hydrogels with higher swelling showcased a more sustained release. Biocompatibility studies for hydrogel formulations was done by evaluating formulation performance in MTT, live/dead, and apoptosis assays performed using non-malignant Human embryonic kidney cells (HEK-293). The optimized hydrogel formulations were biocompatible, yielding >90% cellular viability over 72 hours. This delivery system prototype may be used to deliver potent chemotherapeutics locally, reducing off target effects and improving therapeutic benefits.

Medication-related osteonecrosis of the Jaw (MRONJ) is a rare but severe side effect in patients treated with medications such as Bisphosphonates (BPs). Its pathophysiological mechanism needs to be more precise. Establishing preventive measures and treatment standards is necessary. This study aimed to develop a composite hydrogel scaffold constituted by methacrylated gelatin (GelMA), methacrylated heparin (HepMA) and PRF, and investigate its potential application value in the prevention of MRONJ. GelMA, HepMA, and PRF were prepared using specific ratios for hydrogel scaffolds. Through mechanical properties and biocompatibility analysis, the release rate of growth factors and the ability to promote bone differentiation in vitro were evaluated. To explore the healing-enhancing effects of hydrogels in vivo, the composite hydrogel scaffold was implanted to the MRONJ rat model. Micro-computed tomography (Micro-CT) and histological examination were conducted to evaluate the bone morphology and tissue regeneration. The Hep/GelMA-PRF hydrogel improved the degradation rate and swelling rate. It was also used to control the release rate of growth factors effectively. In vitro, the Hep/GelMA-PRF hydrogel was biocompatible and capable of reversing the inhibitory effect of zoledronic acid (ZOL) on the osteogenic differentiation of MC3T3-E1s. In vivo, the micro-CT analysis and histological evaluation demonstrated that the Hep/GelMA-PRF group exhibited the best tissue reconstruction. Moreover, compared to the ZOL group, the expression of osteogenesis proteins, including osteocalcin (OCN), type collagen I (Col I), and bone morphogenetic protein-2 (BMP-2) in the Hep/GelMA-PRF group were all significantly upregulated (P < 0.05). The Hep/GelMA-PRF hydrogel scaffold could effectively control the release rate of growth factors, induce osteogenic differentiation, reduce inflammation, and keep a stable microenvironment for tissue repair. It has potential application value in the prevention of MRONJ.

Compared with systemic administration methods like injection and oral administration, traditional transdermal drug delivery has the advantages of rapid onset of activity and low side effects. However, hydrophilic drugs and bioactive substances are often unsuitable for traditional transdermal drug delivery.

Currently, the clinical treatment of critical bone defects attributed to various causes remains a great challenge, and repairing these defects with synthetic bone substitutes is the most common strategy. In general, tissue engineering materials that mimic the structural, mechanical and biological properties of natural bone have been extensively applied to fill bone defects and promote in situ bone regeneration. Hydrogels with extracellular matrix (ECM)-like properties are common tissue engineering materials, among which methacrylate-based gelatin (GelMA) hydrogels are widely used because of their tunable mechanical properties, excellent photocrosslinking capability and good biocompatibility. Owing to their lack of osteogenic activity, however, GelMA hydrogels are combined with other types of materials with osteogenic activities to improve the osteogenic capability of the current composites. There are three main aspects to consider when enhancing the bone regenerative performance of composite materials: osteoconductivity, vascularization and osteoinduction. Bioceramics, bioglass, biomimetic scaffolds, inorganic ions, bionic periosteum, growth factors and two-dimensional (2D) nanomaterials have been applied in various combinations to achieve enhanced osteogenic and bone regeneration activities. Three-dimensional (3D)-bioprinted scaffolds are a popular research topic in bone tissue engineering (BTE), and printed and customized scaffolds are suitable for restoring large irregular bone defects due to their shape and structural tunability, enhanced mechanical properties, and good biocompatibility. Herein, the recent progress in research on GelMA-based composite hydrogel scaffolds as multifunctional platforms for restoring critical bone defects in plastic or orthopedic clinics is systematically reviewed and summarized. These strategies pave the way for the design of biomimetic bone substitutes for effective bone reconstruction with good biosafety. Graphical Abstract This review provides novel insights into the development and current trends of research on GelMA-based hydrogels as effective bone tissue engineering (BTE) scaffolds for correcting bone defects, and these contents are summarized and emphasized from various perspectives (osteoconductivity, vascularization, osteoinduction and 3D-bioprinting). In addition, advantages and deficiencies of GelMA-based bone substitutes used for bone regeneration are put forward, and corresponding improvement measures are presented prior to their clinical application in near future (created with BioRender.com).

Bio-fabrication is an emerging area that involves the creation of tissue constructs with a hierarchical architecture. The essential requirements for fabricating a tissue construct are cells, biomaterial and bioactive molecules....

Gelatin methacryloyl (GelMA) hydrogels are promising materials for tissue engineering applications due to their biocompatibility and tunable properties. However, the time-consuming process of preparing GelMA hydrogels with desirable properties for specific biomedical applications limits their clinical use. Visible-light-induced cross-linking is a well-known method for the preparation of GelMA hydrogels; however, a comprehensive investigation on the influence of critical parameters such as Eosin Y (EY), triethanolamine (TEA), and N-vinyl-2-pyrrolidone (NVP) concentrations on the stiffness and gelation time has yet to be performed. In this study, we systematically investigated the effect of these critical parameters on the stiffness and gelation time of GelMA hydrogels. We developed an artificial neural network (ANN) model with three input variables, EY, TEA, and NVP concentrations, and two output variables, Young's modulus and gelation time, derived from our experimental design. Through the alteration of individual chemical concentrations, [EY] between 0.005 and 0.5 mM and [TEA] and [NVP] between 10 and 1000 mM, we studied the impact of these alterations on the real-time values of stiffness and gelation time. Furthermore, we demonstrated the validity of the ANN model in predicting the properties of GelMA hydrogels. We also studied cell survival to establish nontoxic concentration ranges for each component, enabling safer use of GelMA hydrogels in relevant biomedical applications. Our results showed that the ANN model can accurately predict the properties of GelMA hydrogels, allowing for the synthesis of hydrogels with desirable stiffness for various biomedical applications. In conclusion, our study provides a comprehensive library that characterizes the stiffness and gelation time and demonstrates the potential of the ANN model to predict these properties of GelMA hydrogels depending on the critical parameters. The ANN models developed here can facilitate the optimization of GelMA hydrogels with the most efficient mechanical properties that resemble a native extracellular matrix and better address the need in the in vivo microenvironment. The approach of this study is to bring research about the synthesis of GelMA hydrogels to a new level where the synthesis of these hydrogels can be standardized with minimum cost and effort.

Gelatin methacryloyl (GelMA) hydrogels are widely used for a variety of tissue engineering applications. The properties of gelatin can affect the mechanical properties of gelatin gels; however, the role of gelatin properties such as bloom strength on GelMA hydrogels has not yet been explored. Bloom strength is a food industry standard for describing the quality of gelatin, where higher bloom strength is associated with higher gelatin molecular weight. Here, we evaluate the role of bloom strength on GelMA hydrogel mechanical properties. We determined that both bloom strength of gelatin and weight percent of GelMA influenced both stiffness and viscoelastic ratio; however, only bloom strength affected diffusivity, permeability, and pore size. With this library of GelMA hydrogels of varying properties, we then encapsulated Swan71 trophoblast spheroids in these hydrogel variants to assess how bloom strength affects trophoblast spheroid morphology. Overall, we observed a decreasing trend of spheroid area and Feret diameter as bloom strength increased. In identifying clear relationships between bloom strength, hydrogel mechanical properties, and trophoblast spheroid morphology, we demonstrate that bloom strength should considered when designing tissue engineered constructs.

We report the development of an efficient, customized spherical indentation-based testing method to systematically estimate the hydraulic permeability of gelatin methacryloyl (GelMA) hydrogels fabricated in a wide range of mass concentrations and photocrosslinking conditions. Numerical simulations and Biot’s theory of poroelasticity were implemented to calibrate our experimental data. We correlated elastic moduli and permeability coefficients with different GelMA concentrations and crosslinking densities. It was revealed that the permeability values of GelMA followed a negative power-law function of the crosslinking time. Our model could also predict drug release rates from the GelMA hydrogels and diffusion efficiency of nutrients into the three-dimensional GelMA hydrogels. The results potentially provide a design map for choosing desired GelMA-based hydrogels for use in drug delivery, tissue engineering, and regenerative medicine, which may be further expanded to predict the permeability behaviors of various other hydrogel types.

… Gelatin methacryloyl (GelMA) hydrogels have gained significant recognition as versatile biomaterials in the biomedical domain. GelMA hydrogels … GelMA-based hydrogel scaffolds. …

… -crosslinkable hydrogels, in particular gelatin methacryloyl (… rate of reaction of GelMa hydrogels with respect to light … mechanical properties of GelMa hydrogels produced across a …

Gelatin methacryloyl (GM) hydrogels have been investigated for almost 20 years, especially for biomedical applications. Recently, strengthening effects of a sequential cross-linking procedure, whereby GM hydrogel precursor solutions are cooled before chemical cross-linking, were reported. It was hypothesized that physical and enhanced chemical cross-linking of the GM hydrogels contribute to the observed strengthening effects. However, a detailed investigation is missing so far. In this contribution, we aimed to reveal the impact of physical and chemical cross-linking on strengthening of sequentially cross-linked GM and gelatin methacryloyl acetyl (GMA) hydrogels. We investigated physical and chemical cross-linking of three different GM(A) derivatives (GM10, GM2A8 and GM2), which provided systematically varied ratios of side-group modifications. GM10 contained the highest methacryloylation degree (DM), reducing its ability to cross-link physically. GM2 had the lowest DM and showed physical cross-linking. The total modification degree, determining the physical cross-linking ability, of GM2A8 was comparable to that of GM10, but the chemical cross-linking ability was comparable to GM2. At first, we measured the double bond conversion (DBC) kinetics during chemical GM(A) cross-linking quantitatively in real-time via near infrared spectroscopy-photorheology and showed that the DBC decreased due to sequential cross-linking. Furthermore, results of circular dichroism spectroscopy and differential scanning calorimetry indicated gelation and conformation changes, which increased storage moduli of all GM(A) hydrogels due to sequential cross-linking. The data suggested that the total cross-link density determines hydrogel stiffness, regardless of the physical or chemical nature of the cross-links.

Gelatin methacryloyl (GelMA), a photocrosslinkable gelatin-based hydrogel, has been immensely used for diverse applications in tissue engineering and drug delivery. Apart from its excellent functionality and versatile mechanical properties, it is also suitable for a wide range of fabrication methodologies to generate tissue constructs of desired shapes and sizes. Despite its exceptional characteristics, it is predominantly limited by its weak mechanical strength, as some tissue types naturally possess high mechanical stiffness. The use of high GelMA concentrations yields high mechanical strength, but not without the compromise in its porosity, degradability, and three-dimensional (3D) cell attachment. Recently, GelMA has been blended with various natural and synthetic biomaterials to reinforce its physical properties to match with the tissue to be engineered. Among these, nanomaterials have been extensively used to form a composite with GelMA, as they increase its biological and physicochemical properties without affecting the unique characteristics of GelMA and also introduce electrical and magnetic properties. This review article presents the recent advances in the formation of hybrid GelMA nanocomposites using a variety of nanomaterials (carbon, metal, polymer, and mineral-based). We give an overview of each nanomaterial's characteristics followed by a discussion of the enhancement in GelMA's physical properties after its incorporation. Finally, we also highlight the use of each GelMA nanocomposite for different applications, such as cardiac, bone, and neural regeneration.

In this work, the influence of mechanical stiffness and geometrical confinement on the 3D culture of myoblast-laden gelatin methacryloyl (GelMA) photo-crosslinkable hydrogels was evaluated in terms of in vitro myogenesis. We formulated a set of cell-laden GelMA hydrogels with a compressive modulus in the range 1 ÷ 17 kPa, obtained by varying GelMA concentration and degree of cross-linking. C2C12 myoblasts were chosen as the cell model to investigate the supportiveness of different GelMA hydrogels toward myotube formation up to 2 weeks. Results showed that the hydrogels with a stiffness in the range 1 ÷ 3 kPa provided enhanced support to C2C12 differentiation in terms of myotube number, rate of formation, and space distribution. Finally, we studied the influence of geometrical confinement on myotube orientation by confining cells within thin hydrogel slabs having different cross sections: (i) 2,000 μm × 2,000 μm, (ii) 1,000 μm × 1,000 μm, and (iii) 500 μm × 500 μm. The obtained results showed that by reducing the cross section, i.e., by increasing the level of confinement—myotubes were more closely packed and formed aligned myostructures that better mimicked the native morphology of skeletal muscle.

Gelatin methacryloyl (GelMA) is a versatile material for a wide range of bioapplications. There is an intense interest in developing effective chemical strategies to prepare GelMA with a high degree of batch-to-batch consistency and controllability in terms of methacryloyl functionalization and physiochemical properties. Herein, we systematically investigated the batch-to-batch reproducibility and controllability of producing GelMA (target highly and lowly substituted versions) via a one-pot strategy. To assess the GelMA product, several parameters were evaluated, including the degree of methacryloylation, secondary structure, and enzymatic degradation, along with the mechanical properties and cell viability of GelMA hydrogels. The results showed that two types of target GelMA with five batches exhibited a high degree of controllability and reproducibility in compositional, structural, and functional properties owing to the highly controllable one-pot strategy.

Gelatin methacryloyl (GelMA) has been increasingly considered as an important bioink material due to its tailorable mechanical properties, good biocompatibility, and ability to be photopolymerized in situ as well as printability. GelMA can be classified into two types: type A GelMA (a product from acid treatment) and type B GelMA (a product from alkali treatment). In current literature, there is little research on the comparison of type A GelMA and type B GelMA in terms of synthesis, rheological properties, and printability for bioink applications. Here, we report the synthesis, rheological properties, and printability of types A and B GelMA. Types A and B GelMA samples with different degrees of substitution (DS) were prepared in a controllable manner by a time-lapse loading method of methacrylic anhydride (MAA) and different feed ratios of MAA to gelatin. Type B GelMA tended to have a slightly higher DS compared to type A GelMA, especially in a lower feed ratio of MAA to gelatin. All the type A and type B GelMA solutions with different DS exhibited shear thinning behaviours at 37 °C. However, only GelMA with a high DS had an easy-to-extrude feature at room temperature. The cell-laden printed constructs of types A and B GelMA at 20% w/v showed around 75% cell viability.

Gelatin methacryloyl (GelMA) hydrogel has adjustable physicochemical properties and a three-dimensional network structure for cell growth and hence a hot issue in the field of tissue engineering. However, its poor mechanical properties limit the application in the scaffold, especially as a bone scaffold. To date, many research studies have been carried out by adding some additives into GelMA to construct GelMA-based composites to improve the mechanical properties. However, there is a controversy as to whether the additives can improve the mechanical properties of GelMA. Herein, meta-analysis was used to evaluate the influence of the additives on the mechanical properties of GelMA-based composites, which can provide reference for the further enhancement of mechanical properties of GelMA. In this study, meta-analysis was adopted to investigate the influence of additives on the mechanical properties of GelMA composites; composites with different concentrations of GelMA, that is, ≥10% (w/v), 5–10% (w/v), and ≤5% (w/v) were found in 23 literatures and heterogeneity could be found among these references. Accordingly, it is found that additives can improve the mechanical properties in each concentration.

J. Zheng, M. Zhu, Dr. B. H. Lee School of Ophthalmology and Optometry Eye Hospital School of Biomedical Engineering Wenzhou Medical University Wenzhou, Zhejiang 325027, China E-mail: bhlee@wibe.ac.cn J. Zheng, M. Zhu, Dr. B. H. Lee Wenzhou Institute of Biomaterials and Engineering CAS, Wenzhou, Zhejiang 325011, China Dr. B. H. Lee Engineering Research Center of Clinical Functional Materials and Diagnosis and Treatment Devices of Zhejiang Province Wenzhou Institute of Biomaterials and Engineering CAS, Wenzhou, Zhejiang 325011, China G. Ferracci, Prof. N.-J. Cho School of Materials Science and Engineering Nanyang Technological University, 639798 Singapore E-mail: njcho@ntu.edu.sg The ORCID identification number(s) for the author(s) of this article can be found under https://doi.org/10.1002/macp.201800266.

… stiffness gradient hydrogels by controlling the polymerization of gelatin methacryloyl (GelMA… Based on previous observations, a stiffness gradient GelMA hydrogel was created ranging …

Gelatin methacryloyl (GelMA) hydrogels have been extensively used for drug delivery and tissue engineering applications due to their good biocompatibility, biodegradability, and controllable photocurable efficiency. Phosphate buffer solution (PBS) is the most widely used reaction system for GelMA synthesis. However, carbonate-bicarbonate buffer solution (CBS) has been tried recently for synthesizing GelMA due to its high reaction efficiency. However, there is a lack of systematic investigation into possible differences in the structure and properties of GelMA synthesized in PBS and CBS, respectively. Therefore, in the current study, GelMA molecules with two degrees of methacryloylation (∼20 and ∼80%) were synthesized under PBS and CBS reaction systems, respectively, in comparable conditions. The results showed that because of the functionalization of methacrylate groups in gelatin chains, which could interfere with the intrachain and interchain interactions, such as hydrogen bonding, the GelMA molecules synthesized in PBS had distinct physical structures and exhibited different properties in comparison with those produced in CBS. GelMA hydrogels synthesized in PBS exhibited higher gel-sol transition temperatures and better photocurable efficiencies, mechanical strength, and biological properties. In contrast, GelMA hydrogels produced in CBS showed advantages in swelling performance and microstructures, such as pore sizes and porosities. In addition, GelMA synthesized in PBS and possessing a high degree of methacryloylation (the "GelMA-PH" polymer) showed great potential for three-dimensional (3D) bioprinting. This focused study has gained helpful new insights into GelMA and can provide guidance on the application of GelMA in 3D printing and tissue engineering.

The human tissues most sensitive to electrical activity such as neural and muscle tissues are relatively soft, and yet traditional conductive materials used to interface with them are typically stiffer by many orders of magnitude. Overcoming this mismatch, by creating both very soft and electroactive materials, is a major challenge in bioelectronics and biomaterials science. One strategy is to imbue soft materials, such as hydrogels, with electroactive properties by adding small amounts of highly conductive nanomaterials. However, electroactive hydrogels reported to date have required relatively large volume fractions (>1%) of added nanomaterial, have shown only modest electroactivity, and have not been processable via additive manufacturing to create 3D architectures. Here, we describe the development and characterization of improved biocompatible photo-cross-linkable soft hybrid electroactive hydrogels based on gelatin methacryloyol (GelMA) and large area graphene oxide (GO) flakes, which resolve each of these three limitations. The addition of very small amounts (less than a 0.07% volume fraction) of GO to a 5% w/v GelMA hydrogel resulted in a dramatic (∼35-fold) decrease in the impedance at 1 Hz compared with GelMA alone. The GelMA/GO coated indium tin oxide (ITO) electrode also showed a considerable reduction in the impedance at 1 kHz (down to 170 Ω compared with 340 Ω for the GelMA-coated ITO), while charge injection capacity increased more than 6-fold. We attribute this enhanced electroactivity to the increased electroactive surface area contributed by the GO. Despite this dramatic change in electroactivity, the GelMA/GO composite hydrogels' mechanical properties were only moderately affected. Mechanical properties increased by ∼2-fold, and therefore, the hydrogels' desired softness of <4 kPa was retained. Also, we demonstrate how light attenuation through the gel can be used to create a stiffness gradient with the exposed surface of the gel having an elastic modulus of <1.5 kPa. GO addition also enhanced the rheological properties of the GelMA composites, thus facilitating 3D extrusion printing. GelMA/GO enhanced filament formation as well as improved printability and the shape fidelity/integrity of 3D printed structures compared with GelMA alone. Additionally, the GelMA/GO 3D printed structures presented a higher electroactive behavior than nonprinted samples containing the same GelMA/GO amount, which can be attributed to the higher electroactive surface area of 3D printed structures. These findings provide new rational choices of electroactive hydrogel (EAH) compositions with broad potential applications in bioelectronics, tissue engineering, and drug delivery.

We present the first cell-attachable and visible-light-crosslinkable bioinks based on gelatin methacryloyl (GelMA) with eosin Y (EY) photoinitiation for stereolithography three-dimensional (3D) bioprinting. To develop a visible-light-crosslinkable hydrogel, we systematically studied five combinations of GelMA and EY photoinitiator with various concentrations. Their mechanical properties, microstructures, and cell viability and confluency after encapsulation were investigated rigorously to elucidate the effects of the EY and GelMA macromer concentrations on the characteristics of the hydrogel. Experimental results show that the compressive Young's modulus and pore size are positively affected by the concentration of EY, whereas the mass swelling ratio and cell viability are negatively affected. Increasing the concentration of GelMA helps in improving the compressive Young's modulus and cell attachment. We further employed the developed visible-light-based stereolithography bioprinting system to print the patterned cell-laden hydrogels to demonstrate the bioprinting applications of the developed hydrogel. We observed good cell proliferation and the formation of a 3D cellular network inside the printed pattern at day 5, which proves the great feasibility of using EY-GelMA as the bioinks for biofabrication and tissue engineering.

Gelatin methacryloyl (GelMA) hydrogels have aroused considerable interests in the field of tissue engineering due to tunable physical properties and cell response parameters. A number of works have studied the impact of GelMA concentration, photo-initiator concentration, methacrylic anhydride (MA) concentration, cooling rate and temperature gradient on GelMA hydrogel generation, but little attention has been paid to the effect of the freezing temperatures and freezing time of GelMA prepolymer solution during preparation. In this study, GelMA hydrogels were synthesized with different freezing temperatures and time. It was found that the lower freezing temperatures and longer freezing time caused smaller pore sizes that realized higher cell viability and proliferation of MC3T3-E1 cells. The results showed that tunable microstructure of GelMA could be achieved by regulating the freezing conditions of GelMA, which provided a broad prospect for the applications of GelMA hydrogels in tissue engineering.

To recreate or substitute tissue in vivo is a complicated endeavor that requires biomaterials that can mimic the natural tissue environment. Gelatin methacrylate (GelMA) is created through covalent bonding of naturally derived polymer gelatin and methacrylic groups. Due to its biocompatibility, GelMA receives a lot of attention in the tissue engineering research field. Additionally, GelMA has versatile physical properties that allow a broad range of modifications to enhance the interaction between the material and the cells. In this review, we look at recent modifications of GelMA with naturally derived polymers, nanomaterials, and growth factors, focusing on recent developments for vascular tissue engineering and wound healing applications. Compared to polymers and nanoparticles, the modifications that embed growth factors show better mechanical properties and better cell migration, stimulating vascular development and a structure comparable to the natural-extracellular matrix.

Bioprinting of body tissues has gained great attention in recent years due to its unique advantages, including the creation of complex geometries and printing the patient-specific tissues with various drug and cell types. The most momentous part of the bioprinting process is bioink, defined as a mixture of living cells and biomaterials (especially hydrogels). Among different biomaterials, natural polymers are the best choices for hydrogel-based bioinks due to their intrinsic biocompatibility and minimal inflammatory response in body condition. Gelatin methacryloyl (GelMA) hydrogel is one of the high-potential hydrogel-based bioinks due to its easy synthesis with low cost, great biocompatibility, transparent structure that is useful for cell monitoring, photocrosslinkability, and cell viability. Furthermore, the potential of adjusting properties of GelMA due to the synthesis protocol makes it a suitable choice for soft or hard tissues. In this review, different methods for the bioprinting of GelMA-based bioinks, as well as various effective process parameters, are reviewed. Also, several solutions for challenges in the printing of GelMA-based bioinks are discussed, and applications of GelMA-based bioprinted tissues argued as well. Impact statement Bioprinting has been demonstrated as a promising and alternative approach for organ transplantation to develop various types of living tissue. Bioinks, with great biological characteristics similar to the host tissues and rheological/flow features, are the first requirements for the successful bioprinting approach. Gelatin methacryloyl (GelMA) hydrogel is one of the high-potential hydrogel-based bioinks. This review provides a comprehensive look at different methods for the bioprinting of GelMA-based bioinks and applications of GelMA-based bioprinted tissues for tissue repair.

… However, despite high pattern fidelity of photopolymerizable hydrogels, many such … Here, we demonstrate gelatin methacrylate (GelMA) as an inexpensive, cell-responsive hydrogel …

The generation of functional, 3D vascular networks is a fundamental prerequisite for the development of many future tissue engineering‐based therapies. Current approaches in vascular network bioengineering are largely carried out using natural hydrogels as embedding scaffolds. However, most natural hydrogels present a poor mechanical stability and a suboptimal durability, which are critical limitations that hamper their widespread applicability. The search for improved hydrogels has become a priority in tissue engineering research. Here, the suitability of a photopolymerizable gelatin methacrylate (GelMA) hydrogel to support human progenitor cell‐based formation of vascular networks is demonstrated. Using GelMA as the embedding scaffold, it is shown that 3D constructs containing human blood‐derived endothelial colony‐forming cells (ECFCs) and bone marrow‐derived mesenchymal stem cells (MSCs) generate extensive capillary‐like networks in vitro. These vascular structures contain distinct lumens that are formed by the fusion of ECFC intracellular vacuoles in a process of vascular morphogenesis. The process of vascular network formation is dependent on the presence of MSCs, which differentiate into perivascular cells occupying abluminal positions within the network. Importantly, it is shown that implantation of cell‐laden GelMA hydrogels into immunodeficient mice results in a rapid formation of functional anastomoses between the bioengineered human vascular network and the mouse vasculature. Furthermore, it is shown that the degree of methacrylation of the GelMA can be used to modulate the cellular behavior and the extent of vascular network formation both in vitro and in vivo. These data suggest that GelMA hydrogels can be used for biomedical applications that require the formation of microvascular networks, including the development of complex engineered tissues.

Given the importance of the extracellular medium during tissue formation, it was wise to develop an artificial structure that mimics the extracellular matrix while having improved physico-chemical properties. That is why the choice was focused on gelatin methacryloyl (GelMA), an inexpensive biocompatible hydrogel. Physicochemical and mechanical properties were improved by the incorporation of nanoparticles developed from two innovative fabrication processes: High shear fluid and low frequencies/high frequencies ultrasounds. Both rapeseed nanoliposomes and nanodroplets were successfully incorporated in the GelMA networks during the photo polymerization process. The impact on polymer microstructure was investigated by Fourier-transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and enzymatic degradation investigations. Mechanical stability and viscoelastic tests were conducted to demonstrate the beneficial effect of the functionalization on GelMA hydrogels. Adding nanoparticles to GelMA improved the surface properties (porosity), tuned swelling, and degradability properties. In addition, we observed that nanoemulsion didn’t change significantly the mechanical properties to shear and compression solicitations, whereas nanoliposome addition decreased Young’s modulus under compression solicitations. Thus, these ways of functionalization allow controlling the design of the material by choosing the type of nanoparticle (nanoliposome or nanoemulsion) in function of the application.

… of PEG hydrogels with GelMA will create a composite photocrosslinkable hydrogel with tunable cell responsive properties, degradation, and mechanical properties, yielding a hydrogel …

… GelMA synthesized from a widely used porcine skin gelatin has a thermal gelation problem at room temperature. Here, we present thermally stable GelMA hydrogels … GelMA. The novel …

… The introduction of small molecules is one of the approaches to improve the mechanical properties and the degradation rate of gelatin hydrogels. Carboxybetaine methacrylate (CBMA) …

… gelatin methacrylate (GelMA) as a promising hydrogel for … Compared to PEG hydrogels, GelMA hydrogels showed … Combined application of the GelMA hydrogels and the DEP technique …

Gelatin methacrylate (GelMA) has been gaining popularity in recent years as a photo-crosslinkable biomaterial widely used in a variety of bioprinting and tissue engineering applications. Several studies have established the effects of process-based and material-based parameters on the physical–mechanical properties and microstructure of GelMA hydrogels. However, the effect of encapsulated cells on the physical–mechanical properties and microstructure of GelMA hydrogels has not been fully understood. In this study, 3T3 fibroblasts were encapsulated at different cell densities within the GelMA hydrogels and incubated over 96 h. The effects of encapsulated cells were investigated in terms of mechanical properties (tensile modulus and strength), physical properties (swelling and degradation), and microstructure (pore size). Cell viability was also evaluated to confirm that most cells were alive during the incubation. It was found that with an increase in cell density, the mechanical properties decreased, while the degradation and the pore size increased.

… gelatin methacrylate (GelMA) to develop a conductive hybrid composite. We demonstrate that as compared to pure GelMA, GelMA–polyaniline (GelMA… we demonstrate that GelMA–Pani …

… micropatterned gelatin methacrylate (GelMA) hydrogels with … that the micropatterned hydrogel constructs guided the … Notably, the endothelial cords were retained within the hydrogel …

… ), methacrylate modification of gelatin offers an alternative method to better control the extent of hydrogel … and growth factor delivery of gelatin methacrylate (GMA) microparticles (MPs) …

For stem cell differentiation, the microenvironment can play an important role, and hydrogels can provide a three‐dimensional microenvironment to allow native cell growth in vitro. A challenge is that the stem cell's differentiation can be influenced by the matrix stiffness. We demonstrate a low‐toxicity method to create different stiffness matrices, by using a photopolymerizable gelatin methacrylate (GelMA) hydrogel cross‐linked by blue light (440 nm). The stiffness and porosity of GelMA hydrogel is easily modified by altering its concentration. We used human bone marrow mesenchymal stem cells (MSCs) as a cell source and cultured the GelMA‐encapsulated cells with EGM‐2 medium to induce endothelial differentiation. In our GelMA blue light hydrogel system, we found that MSCs can be differentiated into both endothelial‐like and osteogenic‐like cells. The mRNA expressions of endothelial cell markers CD31, von Willebrand factor, vascular endothelial growth factor receptor‐2, and CD34 were significantly increased in softer GelMA hydrogels (7.5% and 10%) compared with stiffer matrices (15% GelMA). On the other hand, the enhancements of osteogenic markers mRNA expressions (Alkaline phosphatase (ALP), Runx2, osteocalcin, and osteopontin) were highest in 10% GelMA. We also found that 10% GelMA hydrogel offered optimal conditions for MSCs to form capillary‐like structures. These results suggest that the mechanical properties of the GelMA hydrogel can influence both endothelial and osteogenic differentiation of MSCs and sequent capillary‐like formation.

… Gelatin methacrylate (GelMA) hydrogels have been the focus … we examined the efficacy of GelMA hydrogels as a suitable … cells cultured on GelMA hydrogels. Further, cells cultured on …

Bone tissue engineering (BTE) has made significant progress in developing and assessing different types of bio-substitutes. However, scaffolds production through standardized methods, as required for good manufacturing process (GMP), and post-transplant in vivo monitoring still limit their translation into the clinic. 3D printed 5% GelMA scaffolds have been prepared through an optimized and reproducible process in this work. Mesenchymal stem cells (MSC) were encapsulated in the 3D printable GelMA ink, and their biological properties were assessed in vitro to evaluate their potential for cell delivery application. Moreover, in vivo implantation of the pristine 3D printed GelMA has been performed in a rat condyle defect model. Whereas optimal tissue integration was observed via histology, no signs of fibrotic encapsulation or inhibited bone formation were attained. A multimodal imaging workflow based on computed tomography (CT) and magnetic resonance imaging (MRI) allowed the simultaneous monitoring of both new bone formation and scaffold degradation. These outcomes point out the direction to undertake in developing 3D printed-based hydrogels for BTE that can allow a faster transition into clinical use.

Abstract Interests in in vitro skin models have been growing. Collagen, which is a main scaffold material for in vitro 3D skin models, has weak mechanical properties, often resulting in undesirable contraction. The physiological characteristics of the skin models often depend on the matrix in which cells are cultured. In this study, we developed a 3D skin model using gelatin methacrylate. The mechanical and transport properties were studied, and attachment and growth of fibroblasts and keratinocytes were examined. Fibroblasts preferred softer matrix, whereas HaCaT cells preferred harder matrix of gelatin methacrylate. This study provides information for developing in vitro skin models.

Hydrogels with high water content and porous structures are excellent 3D scaffolds for various applications in tissue engineering. Gelatin methacryloyl (GelMA) hydrogels with cell responsive RGD and MMP peptide sequences have been widely used in tissue engineering because of its adjustable mechanical properties, good processing performance and excellent biocompatibility. Advanced manufacturing technologies such as 3D printing and electrospinning can achieve precise control of GelMA-based hydrogel microstructures. Different microstructures of GelMA hydrogel, such as microspheres, microfibers, microchannels, microgrooves/microridges and microwells/micropillars have been fabricated and studied to simulate natural extracellular matrix and regulate the proliferation, migration and differentiation of different cells. In this review, recent efforts in GelMA-based hydrogel microstructures are discussed, including their preparation methods, unique characteristics, and specific applications in cell culture and tissue engineering. Finally, the remaining challenges and future direction of microstructured GelMA hydrogels are also suggested. We believe that with these recent advances and numerous ongoing efforts, GelMA-based hydrogels could be precisely fabricated with controlled microstructures, possessing great potentials as universal scaffolds for tissue engineering.

Natural hydrogels are promising scaffolds to engineer epidermis. Currently, natural hydrogels used to support epidermal regeneration are mainly collagen‐ or gelatin‐based, which mimic the natural dermal extracellular matrix but often suffer from insufficient and uncontrollable mechanical and degradation properties. In this study, a photocrosslinkable gelatin (i.e., gelatin methacrylamide (GelMA)) with tunable mechanical, degradation, and biological properties is used to engineer the epidermis for skin tissue engineering applications. The results reveal that the mechanical and degradation properties of the developed hydrogels can be readily modified by varying the hydrogel concentration, with elastic and compressive moduli tuned from a few kPa to a few hundred kPa, and the degradation times varied from a few days to several months. Additionally, hydrogels of all concentrations displayed excellent cell viability (>90%) with increasing cell adhesion and proliferation corresponding to increases in hydrogel concentrations. Furthermore, the hydrogels are found to support keratinocyte growth, differentiation, and stratification into a reconstructed multilayered epidermis with adequate barrier functions. The robust and tunable properties of GelMA hydrogels suggest that the keratinocyte laden hydrogels can be used as epidermal substitutes, wound dressings, or substrates to construct various in vitro skin models.

Hydrogels are often used as biomimetic matrices for tissue regeneration. The source of the hydrogel is of utmost importance as it affects the physicochemical characteristics and must be carefully selected to stimulate specific cell behaviors. Naturally derived polymeric biomaterials have inherent biological moieties such as cell binding and protease cleavage sites and thus can provide a suitable microenvironment for cells. Human-derived matrices can mitigate potential risks associated with immune response and disease transmission from animal-derived biomaterials. In this paper, we developed glycidyl methacrylate-modified human-derived gelatin (hGelGMA) hydrogels for use in tissue engineering applications. By adjusting the glycidyl methacrylate concentration in the reaction mixture, we synthesized hGelGMA with low, medium, and high degrees of modification referred to hGelGMA-L, hGelGMA-M, and hGelGMA-H, respectively. The amount of polymeric networks in the hydrogels was increased proportionally with the modification degree. This change has resulted in a decreasing trend in pore size, porosity, and consequently swelling ratio. Similarly, increasing the polymer concentration also exhibited slower enzymatic degradation. On the other hand, increasing polymer concentration led to an improvement in mechanical properties, where the compressive moduli of hGelGMA-L, hGelGMA-M, and hGelGMA-H hydrogels has changed at 2.9±1.0, 13.7±0.9 and 26.4±2.5 kPa, respectively. Cytocompatibility of the hGelGMA was assessed by 3D encapsulating human derived cells, including dermal fibroblast (HDF) and mesenchymal stem cells (hMSCs), in vitro. Regardless of the degree of glycidyl methacrylate modification, the hGelGMA hydrogels preserved the viability of encapsulated cells and supported their growth and proliferation. HDF cells showed higher metabolic activity in hGelGMA-H while MSCs exhibited increased metabolic activity when they were encapsulated in hGelGMA-M or hGelGMA-H. These results showed that photocrosslinkable human-derived gelatin-based hydrogels can be synthesized and their physical properties can be distinctly fine-tuned to different extents as a function of their degree of modification depending on the needs of the target tissue. Due to its promising physical and biological properties, it is anticipated that hGelGMA can be utilized in a wide spectrum of tissue engineering applications.

Wound healing is a complex and coordinated biological process easily influenced by various internal and external factors. Hydrogels have immense practical importance in wound nursing because of their environmental moisturising, pain-relieving, and cooling effects. As photo-crosslinkable biomaterials, gelatine methacryloyl (GelMA) hydrogels exhibit substantial potential for tissue repair and reconstruction because of their tunable and beneficial properties. GelMA hydrogels have been extensively investigated as scaffolds for cell growth and drug release in various biomedical applications. They also hold great significance in wound healing because of their similarity to the components of the extracellular matrix of the skin and their favourable physicochemical properties. These hydrogels can promote wound healing and tissue remodelling by reducing inflammation, facilitating vascularisation, and supporting cell growth. In this study, we reviewed the applications of GelMA hydrogels in wound healing, including skin tissue engineering, wound dressing, and transdermal drug delivery. We aim to inspire further exploration of their potential for wound healing.

Gelatin methacrylate (GelMA) hydrogels have been widely used in various biomedical applications, especially in tissue engineering and regenerative medicine, for their excellent biocompatibility and biodegradability. GelMA crosslinks to form a hydrogel when exposed to light irradiation in the presence of photoinitiators. The mechanical characteristics of GelMA hydrogels are highly tunable by changing the crosslinking conditions, including the GelMA polymer concentration, degree of methacrylation, light wavelength and intensity, and light exposure time et al. In this regard, GelMA hydrogels can be adjusted to closely resemble the native extracellular matrix (ECM) properties for the specific functions of target tissues. Therefore, this review focuses on the applications of GelMA hydrogels for bioengineering human vascular networks in vitro and in vivo. Since most tissues require vasculature to provide nutrients and oxygen to individual cells, timely vascularization is critical to the success of tissue- and cell-based therapies. Recent research has demonstrated the robust formation of human vascular networks by embedding human vascular endothelial cells and perivascular mesenchymal cells in GelMA hydrogels. Vascular cell-laden GelMA hydrogels can be microfabricated using different methodologies and integrated with microfluidic devices to generate a vasculature-on-a-chip system for disease modeling or drug screening. Bioengineered vascular networks can also serve as build-in vasculature to ensure the adequate oxygenation of thick tissue-engineered constructs. Meanwhile, several reports used GelMA hydrogels as implantable materials to deliver therapeutic cells aiming to rebuild the vasculature in ischemic wounds for repairing tissue injuries. Here, we intend to reveal present work trends and provide new insights into the development of clinically relevant applications based on vascularized GelMA hydrogels.

A key early sign of degenerative disc disease (DDD) is the loss of nucleus pulposus (NP) cells (NPCs). Accordingly, NPC transplantation is a treatment strategy for intervertebral disc (IVD) degeneration. However, in advanced DDD, due to structural damage of the IVD and scaffold mechanical properties, the transplanted cells are less viable and secrete less extracellular matrix, and thus, are unable to efficiently promote NP regeneration. In this study, we evaluated the encapsulation of NPCs in a photosensitive hydrogel made of collagen hydrolysate gelatin and methacrylate (GelMA) to improve NP regeneration. By adjusting the concentration of GelMA, we prepared hydrogels with different mechanical properties. After examining the mechanical properties, cell compatibility and tissue engineering indices of the GelMA‐based hydrogels, we determined the optimal hydrogel concentration of the NPC‐encapsulating GelMA hydrogel for NP regeneration as 5%. NPCs effectively combined with GelMA and proliferated. As the concentration of the GelMA hydrogel increased, the survival, proliferation and matrix deposition of the encapsulated NPCs gradually decreased, which is the opposite of NPCs grown on the surface of the hydrogel. The controllability of the GelMA hydrogels suggests that these NPC‐encapsulating hydrogels are promising candidates to aid in NP tissue engineering and repairing endogenous NPCs.

To effectively repair or replace damaged tissues, it is necessary to design scaffolds with tunable structural and biomechanical properties that closely mimic the host tissue. In this paper, we describe a newly synthesized photocrosslinkable interpenetrating polymer network (IPN) hydrogel based on gelatin methacrylate (GelMA) and silk fibroin (SF) formed by sequential polymerization, which possesses tunable structural and biological properties. Experimental results revealed that IPNs, where both the GelMA and SF were independently crosslinked in interpenetrating networks, demonstrated a lower swelling ratio, higher compressive modulus and lower degradation rate as compared to the GelMA and semi-IPN hydrogels, where only GelMA was crosslinked. These differences were likely caused by a higher degree of overall crosslinking due to the presence of crystallized SF in the IPN hydrogels. NIH-3T3 fibroblasts readily attached to, spread, and proliferated on the surface of IPN hydrogels as demonstrated by F-actin staining and analysis of mitochondrial activity (MTT). In addition, photolithography combined with lyophilization techniques was used to fabricate 3D micropatterned and porous micro-scaffolds from GelMA-SF IPN hydrogels, furthering their versatility for use in various microscale tissue engineering applications. Overall, this study introduces a class of photocrosslinkable, mechanically robust and tunable IPN hydrogels that could be useful for various tissue engineering and regenerative medicine applications.

Abstract During the past decades, photo-crosslinked gelatin hydrogel (methacrylated gelatin, GelMA) has gained a lot of attention due to its remarkable application in the biomedical field. It has been widely used in cell transplantation, cell culture and drug delivery, based on its crosslinking to form hydrogels with tunable mechanical properties and excellent bio-compatibility when exposed to light irradiation to mimic the micro-environment of native extracellular matrix (ECM). Because of its unique biofunctionality and mechanical tenability, it has also been widely applied in the repair and regeneration of bone, heart, cornea, epidermal tissue, cartilage, vascular, peripheral nerve, oral mucosa, and skeletal muscle et al. The purpose of this review is to summarize the recent application of GelMA in drug delivery and tissue engineering field. Moreover, this review article will briefly introduce both the development of GelMA and the characterization of GelMA. Finally, we discuss the challenges and future development prospects of GelMA as a tissue engineering material and drug or gene delivery carrier, hoping to contribute to accelerating the development of GelMA in the biomedical field. Graphical abstract

Suturing peripheral nerve transections is the predominant therapeutic strategy for nerve repair. However, the use of sutures leads to scar tissue formation, hinders nerve regeneration, and prevents functional recovery. Fibrin-based adhesives have been widely used for nerve reconstruction, but their limited adhesive and mechanical strength and inability to promote nerve regeneration hamper their utility as a stand-alone intervention. To overcome these challenges, we engineered composite hydrogels that are neurosupportive and possess strong tissue adhesion. These composites were synthesized by photocrosslinking two naturally derived polymers, gelatin-methacryloyl (GelMA) and methacryloyl-substituted tropoelastin (MeTro). The engineered materials exhibited tunable mechanical properties by varying the GelMA/MeTro ratio. In addition, GelMA/MeTro hydrogels exhibited 15-fold higher adhesive strength to nerve tissue ex vivo compared to fibrin control. Furthermore, the composites were shown to support Schwann cell (SC) viability and proliferation, as well as neurite extension and glial cell participation in vitro, which are essential cellular components for nerve regeneration. Finally, subcutaneously implanted GelMA/MeTro hydrogels exhibited slower degradation in vivo compared with pure GelMA, indicating its potential to support the growth of slowly regenerating nerves. Thus, GelMA/MeTro composites may be used as clinically relevant biomaterials to regenerate nerves and reduce the need for microsurgical suturing during nerve reconstruction.

A major goal in the application of hydrogels for tissue engineering scaffolds, especially for load-bearing tissues such as cartilage, is to develop hydrogels with high mechanical strength. In this study, a double-network (DN) strategy was used to engineer strong hydrogels that can encapsulate cells. We improved upon previously studied double-network (DN) hydrogels by using a processing condition compatible with cell survival. The DN hydrogels were created by a two-step photocrosslinking using gellan gum methacrylate (GGMA) for the rigid and brittle first network, and gelatin methacrylamide (GelMA) for the soft and ductile second network. We controlled the degree of methacrylation of each polymer so that they obtain relevant mechanical properties as each network. The DN was formed by photocrosslinking the GGMA, diffusing GelMA into the first network, and photocrosslinking the GelMA to form the second network. The formation of the DN was examined by diffusion tests of the large GelMA molecules into the GGMA network, the resulting enhancement in the mechanical properties, and the difference in mechanical properties between GGMA/GelMA single networks (SN) and DNs. The resulting DN hydrogels exhibited the compressive failure stress of up to 6.9 MPa, which approaches the strength of cartilage. It was found that there is an optimal range of the crosslink density of the second network for high strength of DN hydrogels. DN hydrogels with a higher mass ratio of GelMA to GGMA exhibited higher strength, which shows promise in developing even stronger DN hydrogels in the future. Three dimensional (3D) encapsulation of NIH-3T3 fibroblasts and the following viability test showed the cell-compatibility of the DN formation process. Given the high strength and the ability to encapsulate cells, the DN hydrogels made from photocrosslinkable macromolecules could be useful for the regeneration of load-bearing tissues.

Nowadays, breast implants, lipofilling, and microsurgical free tissue transfer are the most often applied procedures to repair soft tissue defects resulting from mastectomies/lumpectomies following breast cancer. Due to the drawbacks and limitations associated with these conventional clinical practices, there is a need for alternative reconstructive strategies. The development of biomimetic materials able to promote cell proliferation and adipogenic differentiation has gained increasing attention in the context of adipose reconstructive purposes. Herein, thiol-norbornene crosslinkable gelatin-based materials were developed and benchmarked to the current commonly applied methacryloyl-modified gelatin (GelMA) with different degrees of substitutions focussing on bottom-up tissue engineering. The developed hydrogels resulted in similar gel fractions, swelling, and in vitro biodegradation properties compared to the benchmark materials. Furthermore, the thiol-ene hydrogels exhibited mechanical properties closer to those of native fatty tissue compared to GelMA. The mechanical cues of the equimolar GelNB DS55% + GelSH DS75% composition resulted not only in similar biocompatibility but also, more importantly, in superior differentiation of the encapsulated cells into the adipogenic lineage, as compared to GelMA. It can be concluded that the photo-crosslinkable thiol-ene systems offer a promising strategy toward adipose tissue engineering through cell encapsulation compared to the benchmark GelMA.

Hydrogels are an attractive class of biomaterials in tissue engineering due to their inherently compatible properties for cell culture. Gelatin methacryloyl (GelMA) has shown significant promise in the fields of tissue engineering and drug delivery, as its physical properties can be precisely tuned depending on the specific application. There is a growing appreciation for the interaction between biomaterials and cells of the immune system with the increasing usage of biomaterials for in vivo applications. Here, we addressed the current lack of information regarding the immune-modulatory properties of photocrosslinked GelMA. We investigated the ability of human mononuclear cells to mount inflammatory responses in the context of a GelMA hydrogel platform. Using lipopolysaccharide to stimulate a pro-inflammatory immune response, we found tumor necrosis factor-α (TNF-α) expression was suppressed in GelMA culture conditions. Our findings have important implications on the future use of GelMA, and potentially similar hydrogels, and highlight the significance of investigating the potential immune-modulatory properties of biomaterials.

Current soft tissue repair techniques for women with breast cancer remain associated with several drawbacks including surgical complications and a high resorption rate for lipofilling techniques. Hence, the need to develop improved adipose tissue reconstruction strategies. Additive manufacturing can be a promising tool towards the development of patient-specific scaffolds which are able to support adipose tissue engineering. In the present work, scaffolds composed of both methacrylamide-modified gelatin (Gel-MA) and methacrylated κ-carrageenan (Car-MA), i.e. hydrogel blends, were developed using extrusion-based 3D printing in order to establish a close resemblance to the native extracellular matrix. The hydrogel blends were benchmarked to scaffolds constituting of only Gel-MA. Our results indicate that both types of scaffolds remain stable over time (21 days), are able to absorb large amounts of water and exhibit mechanical properties comparable to those of native breast tissue (2 kPa). Furthermore, a similar cell viability (> 90%) and proliferation rate after 14 days was obtained for adipose tissue-derived stem cells (ASCs) upon seeding onto both types of scaffolds. Additionally, the ASCs were able to differentiate into the adipogenic lineage on the hydrogel blend scaffolds, although their differentiation potential was lower compared to that of ASCs seeded onto the Gel-MA scaffolds.

Gelatin and chitosan (CS) are widely used natural biomaterials for tissue engineering scaffolds, but the poor mechanical properties of pure gelatin or CS hydrogels become a big obstacle that limits their use as scaffolds, especially in load-bearing tissues. This study provided a novel mechanism of forming interpenetrating network (IPN) of gelatin methacryloyl (GelMA) and CS hydrogels by covalent bonds and hydrophobic interactions through photocrosslinking and basification, respectively. By characterization of the compressive and tensile moduli, ultimate tensile stress and strain, it was found that semi-IPN and IPN structure can greatly enhance the mechanical properties of GelMA-CS hydrogels compared to the single network CS or GelMA. Moreover, the increase of either GelMA or CS concentration can strengthen the hydrogel network. Then, the swelling, enzymatic degradation, and morphology of GelMA-CS hydrogels were also systematically investigated. The excellent biocompatibility of GelMA-CS hydrogels was demonstrated by large spreading area of bone mesenchymal stem cells on hydrogel surfaces when CS concentration was <2% (w/v). According to this study, the multiple requirements of properties can be fulfilled by carefully selecting the GelMA and CS compositions for IPN hydrogels.

… 3D bioprinted multilayered GelMA hydrogel patterns with a, b pure GelMA bioink and c, d pore-forming GelMA … /3T3 fibroblasts in GelMA hydrogel patterns bioprinted with pore-forming …

… In this paper, the m/n% GelMA/gelatin bioink indicates that GelMA and gelatin … for 3D bioprinting of low-concentration cell-laden GelMA bioinks by adding gelatin, and the 5% GelMA …

The advent of three-dimensional (3D) bioprinting offers a feasible approach to construct complex structures suitable for tissue regeneration, during which cell-laden materials are dispensed on a substrate according to a predesigned structure. However, the lack of ideal printable bioinks with high shape fidelity and improved biological stability remains a major challenge. In this study, methylcellulose/gelatin-methacryloyl (MC/GelMA) bioink with high shape integrity is presented, which takes advantage of the printability of MC and the permanent photo-cross-linking of GelMA under UV irradiation. Although MC demonstrates good printability at room temperature, the lack of cross-linking ability causes distortion and finally dissociation of printed MC in biological media within a few days. However, UV-cross-linked MC/GelMA bioink remains stable in biological media over a period of several months. The shape integrity of MC/GelMA was systematically characterized in terms of yield stress and complex modulus. Unlike pure MC ink, the MC/GelMA ink demonstrated self-supporting behavior once printed due to the higher complex modulus and yield stress induced by GelMA in the system. Shape integrity of MC/GelMA ink resulted in higher resolution and printability which are evaluated by the successful printing of various 1D, 2D, and 3D constructs. Moreover, human primary osteoblasts encapsulated within the MC/GelMA hydrogel show cell viability of >95%. Overall, this work introduces MC/GelMA bioink with high shape integrity and improved biological stability and highlights the importance of rheological properties and post-cross-linking for fabrication of physiologically scaled tissue implants.

… Of note, when using pure GelMA bioinks at lower concentrations, cellular … GelMA hydrogels at higher GelMA concentrations, which, however, may not be suited for extrusion bioprinting …

Abstract 3D bioprinting is gaining attention as a biofabrication technique due to its potential to recreate the complex structure of native human tissue, combining high precision additive manufacturing, biocompatible inks, cells and biochemical factors. In this work, we evaluated the combination of covalent and ionic crosslinking networks as a strategy to modulate the properties of hydrogel inks and stripe-pattern printed structures to induce anisotropic mechanical properties. We found that for optimum printing, gelMA-alginate concentrations should be between 11 and 15% w/v and the polymer ratio and concentration modulate the rheological and compressive moduli of hydrogels. Furthermore, degradation and swelling rates are also adjustable, with some blends showing less than 20% degradation and negligible swelling over a 14 days period. Sheep adipose derived stem cells were included in three formulations and cell viability was >75% after bioprinting in all hydrogels. Stripe-patterned hydrogels were successfully printed using a dual printhead allowing us to modify the mechanical properties of 3D printed hydrogel scaffolds in each axis. The printed structure with gelatin (10% w/v) and gelMA-alginate (8% w/v - 7%w/v) hydrogel stripes showed a noticeable anisotropic mechanical behaviour. Thus, we demonstrated that chemical and structural factors could modulate the properties of printed biocompatible hydrogels, including anisotropic mechanical behaviour, with potential application in tissue engineering.

Gelatin methacryloyl (GelMA), typically derived from mammalian sources, has recently emerged as an ideal bio-ink for three-dimensional (3D) bioprinting. Herein, we developed a fish skin-based GelMA bio-ink for the fabrication of a 3D GelMA skin substitute with a 3D bioprinter. Several concentrations of methacrylic acid anhydride were used to fabricate GelMA, in which their physical-mechanical properties were assessed. This fish skin-based GelMA bio-ink was loaded with human adipose tissue-derived mesenchymal stromal cells (ASCs) and human platelet lysate (HPL) and then printed to obtain 3D ASCs + HPL-loaded GelMA scaffolds. Cell viability test and a preliminary investigation of its effectiveness in promoting wound closure were evaluated in a critical-sized full thickness skin defect in a rat model. The cell viability results showed that the number of ASCs increased significantly within the 3D GelMA hydrogel scaffold, indicating its biocompatibility property. In vivo results demonstrated that ASCs + HPL-loaded GelMA scaffolds could delay wound contraction, markedly enhanced collagen deposition, and promoted the formation of new blood vessels, especially at the wound edge, compared to the untreated group. Therefore, this newly fish skin-based GelMA bio-ink developed in this study has the potential to be utilized for the printing of 3D GelMA skin substitutes.

The convergence of nanotechnology and bioprinting is redefining the landscape of tissue engineering, with nanocomposite gelatin methacryloyl (GelMA) bioinks emerging as a transformative platform for the biofabrication of multifunctional tissue-specific constructs. GelMA, a photocrosslinkable hydrogel, has rapidly gained attention due to its intrinsic bioactivity, tunable mechanical properties, and compatibility with living cells. However, despite its wide applicability regenerating muscle, cartilage, bone, vascular, cardiac, and neural tissues, native GelMA suffers from limited mechanical strength and insufficient biofunctionality to recapitulate the complexity of specialized tissues. To overcome these shortcomings, recent strategies have focused on the incorporation of nanomaterials into GelMA matrices, ranging from inorganic and carbon-based to metallic, polymeric, and lipidic nanomaterials. These nanocomposite bioprinted scaffolds impart critical enhancements, including improved mechanical robustness, electrical conductivity, stimuli-responsiveness, and bioactivity, while also enabling advanced functionalities such as controlled drug release and real-time responsiveness to the cellular microenvironment. This review examines the bioprinting parameters, material synergies, and design strategies governing the performance of nanocomposite GelMA bioinks. By integrating the tunability of photocrosslinkable bioinks with the multifunctionality of nanomaterials, nanocomposite GelMA bioinks represent a next-generation platform capable of addressing the complex demands of tissue repair and regeneration.

… bioink formulation and 3D printing application. In this study, we prepared GelMA hydrogels using … synthesized GelMA hydrogels and their biological responses. We also formulated a …

Regulatory T‐cells (Tregs) are important modulators of the immune system through their intrinsic suppressive functions. Systemic adoptive transfer of ex vivo expanded Tregs has been extensively investigated for allogeneic transplantation. Due to the time‐consuming and costly expansion protocols of Tregs, more targeted approaches could be beneficial. The encapsulation of human natural and induced Tregs for localized immunosuppression is described for the first time. Tregs encapsulated in alginate‐gelatin methacryloyl hydrogel remain viable, phenotypically stable, functional, and confined in the structure. Supplementation of the hydrogel with the Treg‐specific bioactive factors interleukin‐2 and chemokine ligand 1 improves Treg viability, suppressive phenotype, and function, and attracts to the structure CCR8+ T‐cells enriched with anti‐inflammatory subpopulations, including Tregs, from human peripheral blood. Furthermore, these findings are applicable to 3D bioprinting. Co‐axial printing of murine pancreatic islets with human natural and induced Tregs protects the islets from xenoresponse upon co‐culture with human peripheral blood mononuclear cells. This establishes the co‐encapsulation of Tregs by co‐axial 3D bioprinting as a valid option for providing local immune protection to allogeneic cellular transplants such as pancreatic islets.

Peripheral nerve injuries often result in substantial impairment of the neurostimulatory organs. While the autograft is still largely used as the "gold standard" clinical treatment option, nerve guidance conduits (NGCs) are currently considered a promising approach for promoting peripheral nerve regeneration. While several attempts have been made to construct NGCs using various biomaterial combinations, a comprehensive exploration of the process science associated with three-dimensional (3D) extrusion printing of NGCs with clinically relevant sizes (length: 20 mm; diameter: 2-8 mm), while focusing on tunable buildability using electroactive biomaterial inks, remains unexplored. In addressing this gap, we present here the results of the viscoelastic properties of a range of a multifunctional gelatin methacrylate (GelMA)/poly(ethylene glycol) diacrylate (PEGDA)/carbon nanofiber (CNF)/gellan gum (GG) hydrogel bioink formulations and printability assessment using experiments and quantitative models. Our results clearly established the positive impact of the gellan gum on the enhancement of the rheological properties. Interestingly, the strategic incorporation of PEGDA as a secondary cross-linker led to a remarkable enhancement in the strength and modulus by 3 and 8-fold, respectively. Moreover, conductive CNF addition resulted in a 4-fold improvement in measured electrical conductivity. The use of four-component electroactive biomaterial ink allowed us to obtain high neural cell viability in 3D bioprinted constructs. While the conventionally cast scaffolds can support the differentiation of neuro-2a cells, the most important result has been the excellent cell viability of neural cells in 3D encapsulated structures. Taken together, our findings demonstrate the potential of 3D bioprinting and multimodal biophysical cues in developing functional yet critical-sized nerve conduits for peripheral nerve tissue regeneration.

… cells cultured in 12.5% GelMA scaffolds as compared to those … the SLA 3D bioprinting method with GelMA hydrogel bioinks is … 3D bioprinting system59,61 with a GelMA-based bioink to …

Bioprinting is an emerging and promising technique for fabricating 3D cell-laden constructs for various biomedical applications. In this paper, we employed 3D bioprinted GelMA-based models to investigate the trophoblast cell invasion phenomenon, enabling studies of key placental functions. Initially, a set of optimized material and process parameters including GelMA concentration, UV crosslinking time and printing configuration were identified by systematic, parametric study. Following this, a multiple-ring model (2D multi-ring model) was tested with the HTR-8/SVneo trophoblast cell line to measure cell movement under the influence of EGF (chemoattractant) gradients. In the multi-ring model, the cell front used as a cell invasion indicator moves at a rate of 85 ± 33 µm/day with an EGF gradient of 16 µM. However, the rate was dramatically reduced to 13 ± 5 µm/day, when the multi-ring model was covered with a GelMA layer to constrain cells within the 3D environment (3D multi-ring model). Due to the geometric and the functional limitations of multi-ring model, a multi-strip model (2D multi-strip model) was developed to investigate cell movement in the presence and absence of the EGF chemoattractant. The results show that in the absence of an overlying cell-free layer of GelMA, movement of the cell front shows no significant differences between control and EGF-stimulated rates, due to the combination of migration and proliferation at high cell density (6 × 106 cells/ml) near the GelMA surface. When the model was covered by a layer of GelMA (3D multi-strip model) and migration was excluded, EGF-stimulated cells showed an invasion rate of 21 ± 3 µm/day compared to the rate for unstimulated cells, of 5 ± 4 µm/day. The novel features described in this report advance the use of the 3D bioprinted placental model as a practical tool for not only measurement of trophoblast invasion but also the interaction of invading cells with other tissue elements.

Gelatin Methacryloyl (GelMA) is one of the most used biomaterials for a wide range of applications, such as drug delivery, disease modeling and tissue regeneration. GelMA is obtained from gelatin, which can be derived from different sources (e.g., bovine skin, and porcine skin), through substitution of reactive amine and hydroxyl groups with methacrylic anhydride (MAA). The degree of functionalization (DoF) can be tuned by varying the MAA amount used; thus, different protocols, with different reaction efficiency, have been developed, using various alkaline buffers (e.g., phosphate-buffered saline, DPBS, or carbonate-bicarbonate solution). Obviously, DoF modulation has an impact on the final GelMA properties, so a deep investigation on the features of the obtained hydrogel must be carried on. The purpose of this study is to investigate how different gelatin sources and synthesis methods affect GelMA properties, as literature lacks direct and systematic comparisons between these parameters, especially between synthesis methods. The final aim is to facilitate the choice of the source or synthesis method according to the needs of the desired application. Hence, chemical and physical properties of GelMA formulations were assessed, determining the DoFs, mechanical and viscoelastic properties by rheological analysis, water absorption by swelling capacity and enzymatic degradation rates. Biological tests with lung adenocarcinoma cells (A549) were performed. Moreover, since 3D bioprinting is a rapidly evolving technology thanks to the possibility of precise deposition of cell-laden biomaterials (bioinks) to mimic the 3D structures of several tissues, the potential of different GelMA formulations as bioinks have been tested with a multi-material approach, revealing its printability and versatility in various applications.

Light-based bioprinter manufacturing technology is still prohibitively expensive for organizations that rely on accessing three-dimensional biological constructs for research and tissue engineering endeavors. Currently, most of the bioprinting systems are based on commercial-grade-based systems or modified DIY (do it yourself) extrusion apparatuses. However, to date, few examples of the adoption of low-cost equipment have been found for light-based bioprinters. The requirement of large volumes of bioinks, their associated cost, and the lack of information regarding the parameter selection have undermined the adoption of this technology. This paper showcases the retrofitting and assessing of a low-cost Light-Based 3D printing system for tissue engineering. To evaluate the potential of a proposed design, a manufacturability test for different features, machine parameters, and Gelatin Methacryloyl (GelMA) concentrations for 7.5% and 10% was performed. Furthermore, a case study of a previously seeded hydrogel with C2C12 cells was successfully implemented as a proof of concept. On the manufacturability test, deviational errors were found between 0.7% to 13.3% for layer exposure times of 15 and 20 s. Live/Dead and Actin-Dapi fluorescence assays after 5 days of culture showed promising results in the cell viability, elongation, and alignment of 3D bioprinted structures. The retrofitting of low-cost equipment has the potential to enable researchers to create high-resolution structures and three-dimensional in vitro models.

The integration of multiscale micro- and macroenvironment has been demonstrated as a critical role in designing biomimetic scaffolds for peripheral nerve tissue regeneration. While it remains a remarkable challenge for developing a biomimetic multiscale scaffold for enhancing 3D neuronal maturation and outgrowth. Herein, we present a 3D bioprinted multiscale scaffold based on a modular bioink for integrating the 3D micro- and macroenvironment of native nerve tissue. Gelatin methacryloyl (GelMA)/Chitosan Microspheres (GC-MSs) were prepared by a microfluidic approach, and the effect of these microspheres on enhancing neurite outgrowth and elongation of PC12 cells was demonstrated. The 3D multiscale composite scaffolds were bioprinted based on microspheres and hydrogel as the modular bioink. The co-culture of PC12 cells and RSC96 Schwann cells within these 3D biomimetic scaffolds were investigated to evaluate such a 3D multiscale environment for neurite outgrowth and Schwann cell proliferation. These results indicate that such multiscale composite scaffold with hydrogel microspheres provided a suitable 3D microenvironment for enhancing neurite growth, and the 3D printed hydrogel network provided a 3D macroenvironment mimicking the epineurium layer for Schwann cells proliferation and nerve cell organization, which is promising for the great potential applications in nerve tissue engineering.

The field of bone tissue engineering has seen significant advancements in recent years. Each year, over two million bone transplants are performed globally, and conventional treatments, such as bone grafts and metallic implants, have their limitations. Tissue engineering offers a new level of treatment, allowing for the creation of living tissue within a biomaterial framework. Recent advances in biomaterials have provided innovative approaches to rebuilding bone tissue function after damage. Among them, gelatin methacryloyl (GelMA) hydrogel is emerging as a promising biomaterial for supporting cell proliferation and tissue regeneration, and GelMA has exhibited exceptional physicochemical and biological properties, making it a viable option for clinical translation. Various methods and classes of additives have been used in the application of GelMA for bone regeneration, with the incorporation of nanofillers or other polymers enhancing its resilience and functional performance. Despite promising results, the fabrication of complex structures that mimic the bone architecture and the provision of balanced physical properties for both cell and vasculature growth and proper stiffness for load bearing remain as challenges. In terms of utilizing osteogenic additives, the priority should be on versatile components that promote angiogenesis and osteogenesis while reinforcing the structure for bone tissue engineering applications. This review focuses on recent efforts and advantages of GelMA-based composite biomaterials for bone tissue engineering, covering the literature from the last five years.

Biomaterials currently used in cardiac tissue engineering have certain limitations, such as lack of electrical conductivity and appropriate mechanical properties, which are two parameters playing a key role in regulating cardiac cellular behavior. In this work, we engineered myocardial tissue constructs based on reduced graphene oxide (rGO)-incorporated gelatin methacrylyol (GelMA) hybrid hydrogels. The incorporation of rGO into the GelMA matrix significantly enhanced the electrical conductivity and mechanical properties of the material. Moreover, cells cultured on composite rGO-GelMA scaffolds exhibited better biological activities such as cell viability, proliferation, and maturation compared to ones cultured on GelMA hydrogels. Cardiomyocytes showed stronger contractility and faster spontaneous beating rate on rGO-GelMA hydrogel sheets compared to those on pristine GelMA hydrogels, as well as GO-GelMA hydrogel sheets with similar mechanical property and particle concentration. Our strategy of integrating rGO within a biocompatible hydrogel is expected to be broadly applicable for future biomaterial design to improve tissue engineering outcomes. The engineered cardiac tissue constructs using rGO incorporated hybrid hydrogels can potentially provide high-fidelity tissue models for drug studies and the investigations of cardiac tissue development and/or disease processes in vitro.

… , the influence of polymer concentration for bone tissue engineering (BTE) scaffolds was not … in GelMA scaffolds on osteogenic differentiation. We prepared GelMA scaffolds with 5 and 10…

We present an integrated design and fabrication strategy for the development of hierarchically structured biomechanically and biologically functional tissue scaffold. An integration of β-TCP incorporated fluffy type nanofibers and biodegradable interpenetrating gelatin-hydrogel networks (IGN) result in biomimetic tissue engineered constructs with fully tunable properties that can match specific tissue requirements. FESEM images showed that nanofibers were efficiently assembled into an orientation of IGN without disturbing its pore architecture. The pore architecture, compressive stiffness and modulus, swelling, and the biological properties of the composite constructs can be tailored by adjusting the composition of nanofiber content with respect to IGN. Experimental results of cell proliferation assay and confocal microscopy imaging showed that the as-fabricated composite constructs exhibit excellent ability for MC3T3-E1 cell proliferation, infiltration and growth. Furthermore, β-TCP incorporated functionalized nanofiber enhanced the biomimetic mineralization, cell infiltration and cell proliferation. Within two weeks of cell-seeding, the composite construct exhibited enhanced osteogenic performance (Runx2, osterix and ALP gene expression) compared to pristine IGN hydrogel scaffold. Our integrated design and fabrication approach enables the assembly of nanofiber within IGN architecture, laying the foundation for biomimetic scaffold.

Cartilage injuries, due to their limited regenerative capacity, often result in chronic pain and functional impairment. These injuries are difficult to manage with conventional surgical repair techniques; therefore, alternative treatments are necessary. Gelatin methacrylate (GelMA) has emerged as a promising biomaterial for cartilage tissue engineering due to its biocompatibility, tunable mechanical properties, and ability to be used in advanced applications like 3D bioprinting. This review examines the synthesis, properties, and limitations of GelMA in cartilage repair, focusing on its applications in 3D bioprinting for the creation of patient-specific cartilage constructs. It also highlights preclinical studies exploring the potential of GelMA-based scaffolds in various animal models. Despite its advantages, challenges remain, such as the mechanical limitations of GelMA and its degradation rate in dynamic environments. Hybrid scaffolds, in situ bioprinting, and personalized bioinks offer solutions to these issues. Ultimately, long-term clinical trials are needed to assess the durability and efficacy of GelMA-based scaffolds in human applications. Future research is aimed at overcoming these challenges, improving the mechanical strength of GelMA scaffolds, and enhancing their clinical translation for cartilage repair.

The development of materials for 3D printing adapted for tissue engineering represents one of the main concerns nowadays. Our aim was to obtain suitable 3D-printed scaffolds based on methacrylated gelatin (GelMA). In this respect, three degrees of GelMA methacrylation, three different concentrations of GelMA (10%, 20%, and 30%), and also two concentrations of photoinitiator (I-2959) (0.5% and 1%) were explored to develop proper GelMA hydrogel ink formulations to be used in the 3D printing process. Afterward, all these GelMA hydrogel-based inks/3D-printed scaffolds were characterized structurally, mechanically, and morphologically. The presence of methacryloyl groups bounded to the surface of GelMA was confirmed by FTIR and 1H-NMR analyses. The methacrylation degree influenced the value of the isoelectric point that decreased with the GelMA methacrylation degree. A greater concentration of photoinitiator influenced the hydrophilicity of the polymer as proved using contact angle and swelling studies because of the new bonds resulting after the photocrosslinking stage. According to the mechanical tests, better mechanical properties were obtained in the presence of the 1% initiator. Circular dichroism analyses demonstrated that the secondary structure of gelatin remained unaffected during the methacrylation process, thus being suitable for biological applications.

… In order to achieve our bone formation goal, to mimic the physical architecture of the natural bone ECM, we had developed a method to fabricate biomimetic GelMA hydrogel scaffolds in …

Simple Summary Incorporating natural polymers along with semi-synthetic gelatin methacrylate (GelMA) is known to improve the mechanical properties of developed hybrid hydrogels. Here, we provide a novel comparison of bioprinted GelMA hybrid hydrogel meshes with different concentrations of collagen extracted from bovine hide and ovine skin by assessing their physicochemical characterizations. No previous work has reported the incorporation of ovine collagen with GelMA to develop hybrid hydrogels. Furthermore, different parameters of extrusion-based bioprinting of the inks, and their printing fidelity were investigated. The maximum percentage of collagen that could be incorporated into the meshes was identified as 1%, as these meshes showed good shape fidelity with stable degradation rates. The results indicate these hydrogel meshes may be suitable for specific tissue engineering applications depending on the source of collagen used. Hybrid meshes with ovine (water-soluble) were found to possess properties that could make them suitable for bone tissue engineering applications. Similarly, results indicated that hybrid meshes with bovine collagen could be used for corneal, cartilage, and various soft tissue engineering applications. Abstract Bioprinting is an emerging technology involved in the fabrication of three-dimensional tissue constructs for the repair and regeneration of various tissues and organs. Collagen, a natural protein found abundantly in the extracellular matrix of several tissues, can be extracted from collagen-rich tissues of animals such as sheep, cows, rats, pigs, horses, birds, and marine animals. However, due to the poor printability of collagen bioinks, biocompatible collagen scaffolds that mimic the extracellular matrix (ECM) are difficult to fabricate using bioprinting techniques. Gelatin methacrylate (GelMA), a semi-synthetic polymer with tunable physical and chemical properties, has been found to be a promising biomaterial in various bioprinting applications. The printability of collagen can be improved by combining it with semi-synthetic polymers such as GelMA to develop hybrid hydrogels. Such hybrid hydrogels printed have also been identified to have enhanced mechanical properties. Hybrid GelMA meshes have not previously been prepared with collagen from ovine sources. This study provides a novel comparison between the properties of hybrid meshes with ovine skin and bovine hide collagen. GelMA (8% w/v) was integrated with three different concentrations (0.5%, 1%, and 2%) of bovine and ovine collagen forming hybrid hydrogels inks that were printed into meshes with enhanced properties. The maximum percentage of collagen suitable for integration with GelMA, forming hybrid hydrogels with a stable degradation rate was 1%. The water-soluble nature of ovine collagen promoted faster degradation of the hybrid meshes, although the structural crosslinking was identified to be higher than bovine hybrid meshes. The 1% bovine collagen hybrid meshes stood out in terms of their stable degradation rates.

The design of biomimetic biomaterials for cell culture has become a great tool to study and understand cell behavior, tissue degradation, and lesion. Topographical and morphological features play an important role in modulating cell behavior. In this study, a dual methodology was evaluated to generate novel gelatin methacrylate (GelMA)-based scaffolds with nano and micro topographical and morphological features. First, electrospinning parameters and crosslinking processes were optimized to obtain electrospun nanofibrous scaffolds. GelMA mats were characterized by SEM, FTIR, DSC, TGA, contact angle, and water uptake. Various nanofibrous GelMA mats with defect-free fibers and stability in aqueous media were obtained. Then, micropatterned molds produced by photolithography were used as collectors in the electrospinning process. Thus, biocompatible GelMA nanofibrous scaffolds with micro-patterns that mimic extracellular matrix were obtained successfully by combining two micro/nanofabrication techniques, electrospinning, and micromolding. Taking into account the cell viability results, the methodology used in this study could be considered a valuable tool to develop patterned GelMA based nanofibrous scaffolds for cell culture and tissue engineering.

The purpose of tissue engineering is to reconstruct parts of injured tissues and to resolve the shortage of organ donations. However, the main concern is the limited size of engineered tissue due to insufficient oxygen and nutrition distribution in large three-dimensional (3D) tissue constructs. To provide better support for cells inside the scaffolds, the vascularization of blood vessels within the scaffold could be a solution. This study compared the effects of different culturing systems using human adipose tissue-derived stem/stromal cells (ASCs), human umbilical vein endothelial cells (HUVECs), and coculture of ASCs and HUVECs in 3D-bioprinted gelatin methacrylate (GelMA) hydrogel constructs. The in vitro results showed that the number of live cells was highest in the coculture of ASCs and HUVECs in the GelMA hydrogel after culturing for 21 days. Additionally, the tubular structure was the most abundant in the GelMA hydrogel, containing both ASCs and HUVECs. In the in vivo test, blood vessels were present in both the HUVECs and the coculture of ASCs and HUVECs hydrogels implanted in mice. However, the blood vessel density was the highest in the HUVEC and ASC coculture groups. These findings indicate that the 3D-bioprinted GelMA hydrogel coculture system could be a promising biomaterial for large tissue engineering applications.

Hyaluronic acid (HA) and gelatin (Gel) are major components of the extracellular matrix of different tissues, and thus are largely appealing for the construction of hybrid hydrogels to combine the favorable characteristics of each biopolymer, such as the gel adhesiveness of Gel and the better mechanical strength of HA, respectively. However, despite previous studies conducted so far, the relationship between composition and scaffold structure and physico-chemical properties has not been completely and systematically established. In this work, pure and hybrid hydrogels of methacroyl-modified HA (HAMA) and Gel (GelMA) were prepared by UV photopolymerization and an extensive characterization was done to elucidate such correlations. Methacrylation degrees of ca. 40% and 11% for GelMA and HAMA, respectively, were obtained, which allows to improve the hydrogels’ mechanical properties. Hybrid GelMA/HAMA hydrogels were stiffer, with elastic modulus up to ca. 30 kPa, and porous (up to 91%) compared with pure GelMA ones at similar GelMA concentrations thanks to the interaction between HAMA and GelMA chains in the polymeric matrix. The progressive presence of HAMA gave rise to scaffolds with more disorganized, stiffer, and less porous structures owing to the net increase of mass in the hydrogel compositions. HAMA also made hybrid hydrogels more swellable and resistant to collagenase biodegradation. Hence, the suitable choice of polymeric composition allows to regulate the hydrogels´ physical properties to look for the most optimal characteristics required for the intended tissue engineering application.

… with GelMA hydrogel to create a biomimetic scaffold that … -treated PCL fibers and GelMA hydrogel that enhances both cell–… the field of muscle tissue engineering, particularly for treating …

… GelMA-SFMA-AL hydrogel scaffold, while bioactive glass (BG) was integrated into the bottom subchondral bone layer to facilitate new bone regeneration (Figure 1). The bioactivity and …

Myocardial microenvironment plays a decisive role in guiding the function and fate of cardiomyocytes, and engineering this extracellular niche holds great promise for cardiac tissue regeneration. Platforms utilizing hybrid hydrogels containing various types of conductive nanoparticles have been a critical tool for constructing engineered cardiac tissues with outstanding mechanical integrity and improved electrophysiological properties. However, there has been no attempt to directly compare the efficacy of these hybrid hydrogels and decipher the mechanisms behind how these platforms differentially regulate cardiomyocyte behavior. Here, we employed gelatin methacryloyl (GelMA) hydrogels containing three different types of carbon-based nanoparticles: carbon nanotubes (CNTs), graphene oxide (GO), and reduced GO (rGO), to investigate the influence of these hybrid scaffolds on the structural organization and functionality of cardiomyocytes. Using immunofluorescent staining for assessing cellular organization and proliferation, we showed that electrically conductive scaffolds (CNT- and rGO-GelMA compared to relatively nonconductive GO-GelMA) played a significant role in promoting desirable morphology of cardiomyocytes and elevated the expression of functional cardiac markers, while maintaining their viability. Electrophysiological analysis revealed that these engineered cardiac tissues showed distinct cardiomyocyte phenotypes and different levels of maturity based on the substrate (CNT-GelMA: ventricular-like, GO-GelMA: atrial-like, and rGO-GelMA: ventricular/atrial mixed phenotypes). Through analysis of gene-expression patterns, we uncovered that the engineered cardiac tissues matured on CNT-GelMA and native cardiac tissues showed comparable expression levels of maturation markers. Furthermore, we demonstrated that engineered cardiac tissues matured on CNT-GelMA have increased functionality through integrin-mediated mechanotransduction (via YAP/TAZ) in contrast to cardiomyocytes cultured on rGO-GelMA.

… in tissue engineered vascular grafts has been registered. … based in photocrosslinkable gelatin (GelMA) and the macromers poly(… The suitability of the coated scaffolds for the intended …

Background: Fracture or bone defect caused by accidental trauma or disease is a growing medical problem that threats to human health.Currently, most orthopedic implant materials must be removed via follow-up surgery, which requires a lengthy recovery period and may result in bacterial infection. Building bone tissue engineering scaffolds with hydrogel as a an efficient therapeutic strategy has outstanding bionic efficiency.By combining some bionic inorganic particles and hydrogels to imitate the organic-inorganic characteristics of natural bone extracellular matrix, developing injectable multifunctional hydrogels with bone tissue repair effects and also displaying excellent antibacterial activity possesses attractive advantages in the field of minimally invasive therapy in clinical. Methods: In the present work, a multifunctional injectable hydrogel formed by photocrosslinking was developed by introducing hydroxyapatite (HA) microspheres to Gelatin Methacryloyl (GelMA) hydrogel. Results: The composite hydrogels exhibited good adhesion and bending resistance properties due to the existence of HA. In addition, when the concentration of GelMA is 10% and the concentration of HA microspheres is 3%, HA/GelMA hydrogel system displayed increased microstructure stability, lower swelling rate, increased viscosity, and improved mechanical properties. Furthermore, the Ag-HA/GelMA demonstrated good antibacterial activity against Staphylococcus aureus and Escherichia coli, which could signifificantly lower the risk of bacterial infection following implantation. According to cell experiment, the Ag-HA/GelMA hydrogel is capable of cytocompatibility and has low toxicity to MC3T3 cell. Conclusion: Therefore, the new photothermal injectable antibacterial hydrogel materials proposed in this study will provide a promising clinical bone repair strategy and is expected to as a minimally invasive treatment biomaterial in bone repair fields. Graphical Abstract Schematic illustration of the Ag-HA/GelMA hydrogel and the application in bone tissue engineering.

The success of tissue engineering will rely on the ability to generate complex, cell seeded three-dimensional (3D) structures. Therefore, methods that can be used to precisely engineer the architecture and topography of scaffolding materials will represent a critical aspect of functional tissue engineering. Previous approaches for 3D scaffold fabrication based on top-down and process driven methods are often not adequate to produce complex structures due to the lack of control on scaffold architecture, porosity, and cellular interactions. The proposed projection stereolithography (PSL) platform can be used to design intricate 3D tissue scaffolds that can be engineered to mimic the microarchitecture of tissues, based on computer aided design (CAD). The PSL system was developed, programmed and optimized to fabricate 3D scaffolds using gelatin methacrylate (GelMA). Variation of the structure and prepolymer concentration enabled tailoring the mechanical properties of the scaffolds. A dynamic cell seeding method was utilized to improve the coverage of the scaffold throughout its thickness. The results demonstrated that the interconnectivity of pores allowed for uniform human umbilical vein endothelial cells (HUVECs) distribution and proliferation in the scaffolds, leading to high cell density and confluency at the end of the culture period. Moreover, immunohistochemistry results showed that cells seeded on the scaffold maintained their endothelial phenotype, demonstrating the biological functionality of the microfabricated GelMA scaffolds.

… synthesis, and preventing the biomolecule from degradation. In this study, GelMA/chitosan nanoparticles composite hydrogel … The hydrogel was prepared by photopolymerization and its …

… @SiO 2 /GelMA dressings consisting of composite hydrogels. The results showed … GelMA composite hydrogel was obtained. The entire preparation flow chart of the composite hydrogel …

Gelatin methacrylate-based hydrogels (GelMA) were widely used in tissue engineering and regenerative medicine. However, to manipulate their various chemical and physical properties and create high-efficiency hydrogels, different materials have been used in their structure. Eggshell membrane (ESM) and propolis are two nature-derived materials that could be used to improve the various characteristics of hydrogels, especially structural and biological properties. Hence, the main purpose of this study is the development of a new type of GelMA hydrogel containing ESM and propolis, for use in regenerative medicine. In this regard, in this study, after synthesizing GelMA, the fragmented ESM fibers were added to it and the GM/EMF hydrogel was made using a photoinitiator and visible light irradiation. Finally, GM/EMF/P hydrogels were prepared by incubating GM/EMF hydrogels in the propolis solution for 24 h. After various structural, chemical, and biological characterizations, it was found that the hydrogels obtained in this study offer improved morphological, hydrophilic, thermal, mechanical, and biological properties. The developed GM/EMF/P hydrogel presented more porosity with smaller and interconnected pores compared to the other hydrogels. GM/EMF hydrogels due to possessing EMF showed compressive strength up to 25.95 ± 1.69 KPa, which is more than the compressive strength provided by GM hydrogels (24.550 ± 4.3 KPa). Also, GM/EMF/P hydrogel offered the best compressive strength (44.65 ± 3.48) due to the presence of both EMF and propolis. GM scaffold with a contact angle of about 65.41 ± 2.199 θ showed more hydrophobicity compared to GM/EMF (28.67 ± 1.58 θ ), and GM/EMF/P (26.24 ± 0.73 θ ) hydrogels. Also, the higher swelling percentage of GM/EMF/P hydrogels (343.197 ± 42.79) indicated the high capacity of this hydrogel to retain more water than other scaffolds. Regarding the biocompatibility of the fabricated structures, MTT assay results showed that GM/EMF/P hydrogel significantly (p-value < 0.05) supported cell viability. Based on the results, it seems that GM/EMF/P hydrogel could be a promising biomaterial candidate for use in various fields of regenerative medicine.

To date, severe bone defects remain a significant challenge to the quality of life. All clinically used bone grafts have their limitations. Bone tissue engineering offers the promise of novel bone graft substitutes. Various biomaterial scaffolds are fabricated by mimicking the natural bone structure, mechanical properties, and biological properties. Among them, gelatin methacryloyl (GelMA), as a modified natural biomaterial, possesses a controllable chemical network, high cellular stability and viability, good biocompatibility and degradability, and holds the prospect of a wide range of applications. However, because they are hindered by their mechanical properties, degradation rate, and lack of osteogenic activity, GelMA hydrogels need to be combined with other materials to improve the properties of the composites and endow them with the ability for osteogenesis, vascularization, and neurogenesis. In this paper, we systematically review and summarize the research progress of GelMA composite hydrogel scaffolds in the field of bone defect repair, and discuss ways to improve the properties, which will provide ideas for the design and application of bionic bone substitutes.

A new gelatin methacrylamine (GelMA)-poly (ethylene glycol) diacrylate (PEGDA)-nano hydroxyapatite (nHA) composite hydrogel scaffold was developed using UV photo-crosslinking technology. The Ca2+ from nHA can form a [HO]Ca2+ [OH] bridging structure with the hydroxyl group in GelMA, thereby enhancing the stability. Compared with GelMA-PEGDA hydrogel, the addition of nHA can control the mechanical properties of the composite hydrogel and reduce the degradation rate. In vitro cell culture showed that osteoblast can adhere and proliferate on the surface of the hydrogel, indicating that the GelMA-PEGDA-nHA hydrogel had good cell viability and biocompatibility. Furthermore, GelMA-PEGDA-nHA has excellent injectability and rapid prototyping properties and is a promising 3D printed bone repair scaffold material.

Abstract Methacrylated gelatin (GelMA)/bacterial cellulose (BC) composite hydrogels have been successfully prepared by immersing BC particles in GelMA solution followed by photo-crosslinking. The morphology of GelMA/BC hydrogel was examined by scanning electron microscopy and compared with pure GelMA. The hydrogels had very well interconnected porous network structure, and the pore size decreased from 200 to 10 µm with the increase of BC content. The composite hydrogels were also characterized by swelling experiment, X-ray diffraction, thermogravimetric analysis, rheology experiment and compressive test. The composite hydrogels showed significantly improved mechanical properties compared with pure GelMA. In addition, the biocompatility of composite hydrogels were preliminarily evaluated using human articular chondrocytes. The cells encapsulated within the composite hydrogels for 7 days proliferated and maintained the chondrocytic phenotype. Thus, the GelMA/BC composite hydrogels might be useful for cartilage tissue engineering.

Bioactive glass (BG) has been widely employed in the field of bone tissue engineering owing to its osteoconductive properties. These properties increase the stiffness and bioactivity of polymeric hydrogels, making them ideal for the repair, replacement, and regeneration of damaged bones. In this study, we investigated the effects of incorporating silanized 45S5 bioactive glass (Si-BG) into gelatin methacrylate (GelMA) hydrogel (GelMA/Si-BG) for potential bone tissue engineering. Our findings revealed that crosslinking GelMA with Si-BG had a striking increase in bioactivity with and without osteogenic induction of human mesenchymal stem cells (hMSCs) when compared to GelMA/BG hydrogels. Meanwhile, both GelMA/Si-BG and GelMA/BG hydrogels were able to maintain the cell viability of hMSC for up to 14 days. Additionally, GelMA/Si-BG hydrogels were shown to have a significantly higher compressive modulus than GelMA/BG hydrogels. This study has demonstrated the introduction of silanized 45S5 BG into GelMA hydrogel bioactivity and mechanical properties of GelMA hydrogels, exemplifying the potential application of silanization of BG in bone tissue engineering.

Electroconductive hydrogels are used in a wide range of biomedical applications, including electrodes for patient monitoring and electrotherapy, or as biosensors and electrochemical actuators. Approaches to design electroconductive hydrogels are often met with low biocompatibility and biodegradability, limiting their potential applications as biomaterials. In this study, composite hydrogels were prepared from a conducting polymer complex, poly(3,4-ethylenedioxythiophene):polystyrenesulfonate (PEDOT:PSS) dispersed within a photo-crosslinkable naturally derived hydrogel, gelatin methacryloyl (GelMA). To determine the impact of PEDOT:PSS loading on physical and microstructural properties and cellular responses, the electrical and mechanical properties, electrical properties, and biocompatibility of hydrogels loaded with 0–0.3% (w/v) PEDOT:PSS were evaluated and compared to GelMA control. Our results indicated that the properties of the hydrogels, such as mechanics, degradation, and swelling, could be tuned by changing the concentration of PEDOT:PSS. In particular, the impedance of hydrogels decreased from 449.0 kOhm for control GelMA to 281.2 and 261.0 kOhm for hydrogels containing 0.1% (w/v) and 0.3% (w/v) PEDOT:PSS at 1 Hz frequency, respectively. In addition, an ex vivo experiment demonstrated that the threshold voltage to stimulate contraction in explanted abdominal tissue connected by the composite hydrogels decreased from 9.3 ± 1.2 V for GelMA to 6.7 ± 1.5 V and 4.0 ± 1.0 V for hydrogels containing 0.1% (w/v) and 0.3% (w/v) PEDOT:PSS, respectively. In vitro studies showed that composite hydrogels containing 0.1% (w/v) PEDOT:PSS supported the viability and spreading of C2C12 myoblasts, comparable to GelMA controls. These results indicate the potential of our composite hydrogel as an electroconductive biomaterial.

Abstract Herein, gold/silica (Au/SiO2) hybrid nanoparticles (NPs) were incorporated into the gelatin methacrylate (GelMA) matrix to construct mechanically strong and electrically conductive GelMA hydrogel for biomedical applications. As-prepared GelMA-Au/SiO2 hydrogels were characterized by field emission scanning microscopy (FESEM), compressive strength test, and conductivity/resistivity measurement. Accordingly, to evaluate the cell compatibility of as-prepared conductive hydrogel, the in-vitro biocompatibility assay was performed in rat cardiomyoblast H9C2 cells. The results showed composite hydrogel possessed enhanced compressive strength and conductive property without compromising the beneficial properties such as porous morphology and biocompatible nature of GelMA hydrogel. After incorporation of hybrid NPs, the compressive strength and Young's modulus of composite hydrogels were increased by two-folds. Similarly, the cyclic compression test showed that the pure GelMA hydrogel loses its mechanical stability from the initial cycles, while GelMA-Au/SiO2 hydrogels were sustained up to 50 cycles. In case of cell viability study, the CCK-8 assay result showed enhanced cardiomyoblast cell adhesion and proliferation on the conductive hydrogels. Moreover, the GelMA-Au/SiO2 conductive hydrogels exhibited an increased cell viability by 15% of pure GelMA hydrogels. Similarly, the confocal laser scanning microscopy (CLSM) results showed uniformly aligned cell growth throughout the conductive hydrogels. Overall, this study presents a novel strategy for inducing electrical conductivity and improving mechanical integrity to the gelatin-based GelMA hydrogel by incorporating bifunctional hybrid NPs for regenerative medicine and tissue engineering applications.

… methacrylamide (GelMA)/hydroxyapatite (HAp) composite inks … , GelMA hydrogels with adjustable mechanical, rheological and printing properties were synthesized to screen hydrogel …

… 3D-printed GelMA/CS composite hydrogel scaffolds might be … 3D-printed GelMA/CS composite scaffolds with different … scaffolds, the good cytocompatibility of the synthetic GelMA …

Bone is a crucial organ in the human body; however, conventional bone repair materials, such as autologous and allogeneic bone, are associated with challenges like limited availability and infection risks. Therefore, the development of novel biomaterials for bone repair is essential. This study employed a hydrothermal method to synthesize hydroxyapatite (HAp) doped with various elements and characterized its physicochemical properties. These findings show that the doped HAp particles have a uniform spherical shape and an even distribution of elements. Subsequently, HAp‐GelMA composite hydrogels are synthesized, and their mechanical properties and injectability are assessed. The addition of HAp significantly enhanced the stability of the composite hydrogel, making it suitable for the rapid filling of bone defects. In vitro experiments demonstrated that the Zn/Mg dual‐doped composite hydrogel effectively promoted cell proliferation and angiogenesis. Furthermore, In vivo studies using a cranial defect model in rats show that the Zn/Mg dual‐doped group exhibited significantly better bone regeneration compared to the control group, indicating the material's potential application value in bone tissue engineering and regenerative medicine. In summary, the composite hydrogel scaffold developed in this study shows promising prospects for enhancing angiogenesis and osteogenesis.

Gelatin methacrylate (GelMA) hydrogels have been widely studied for biomedical applications, such as tissue engineering and drug delivery, because of their good biocompatibility and injectability. However, the quick degradation and low mechanical property of GelMA hydrogels need to be improved for further applications, especially for long-term implantation. In this study, a sequential double modification of gelatin was used to achieve high density of photocrosslinkable double bonds in gelatin derivatives. The amino groups in gelatin were first reacted with methacrylic anhydride. After this, the hydroxyl and carboxyl groups in gelatin were reacted with glycidyl methacrylate to obtain the double modified gelatin macromer. The double modified gelatin macromer was used to prepare gelatin hydrogels with high crosslinking density. The hydrogels exhibited high storage modulus and low degradation. Culture of bovine articular chondrocytes in the gelatin hydrogels showed that chondrocytes had round morphology and maintained a cartilaginous phenotype while cell proliferation was hampered. This method for increasing crosslinking density should be useful for preparation of stable hydrogels for cartilage tissue engineering.

… Furthermore, this study demonstrated that the swelling behavior of crosslinked gelatin gels could be adjusted over a broad range and could be reduced down to 194 ± 14 % by …

Hydrogels with or without chemical cross-linking have been studied and used for biomedical applications, such as tissue repair, surgical sealants, and three dimensional biofabrication. These materials often undergo a physical sol–gel or gel–sol transition between room and body temperatures and can also be chemically cross-linked at these temperatures to give dimensional stability. However, few studies have clearly shown the effect of heating/cooling rates on such transitions. Moreover, only a little is known about the effect of cross-linking temperature or the state on the modulus after cross-linking. We have established rheological methods to study these effects, an approach to determine transition temperatures, and a method to prevent sample drying during measurements. All the rheological measurements were performed minimizing the normal stress build-up to compensate for the shrinking and expansion due to temperature and phase changes. We chemically modified gelatin to give gelatin methacryloyl and determined the degree of methacryloylation by proton nuclear magnetic resonance. Using the gelatin methacryloyl as an example, we have found that the gel state or lower temperature can give more rigid gelatin-based polymers by cross-linking under visible light than the sol state or higher temperature. These methods and results can guide researchers to perform appropriate studies on material design and map applications, such as the optimal operating temperature of hydrogels for biomedical applications. We have also found that gelation temperatures strongly depend on the cooling rate, while solation temperatures are independent of the heating rate.

… Methacrylated gelatin (MA-gelatin) is a gelatin derivative … amines by methacrylamide groups in the gelatin is closely related to the … Our aim is to prepare a novel MA-gelatin crosslinked …

Abstract 3D printing of cell laden bioinks has the potential to recapitulate the hierarchical and spatial complexity of native tissues. However, the addition of cells can alter physical properties of printable resins, which in turn may impede or induce cellular sedimentation or affect the printability and shape fidelity of the final construct. In this study we investigated these considerations by bioprinting gelatin methacrylate (GelMA) bioinks, loaded with various concentrations of mouse fibroblast cells (L929), using extrusion-based direct-write 3D printing (EDP). The impact of various cellular concentrations on viscosity, and temperature-driven gelation of GelMA was examined with a rheometer. The effect of cell concentration on quality of 3D printed GelMA hydrogels was investigated by analyzing the geometric compliance of the 3D printed scaffolds to the theoretical model, and by studying compressive properties of the 3D printed scaffolds. The addition of cells did not significantly affect GelMA zero-shear viscosity or viscosity at shear rates associated with EDP (>102 s−1). While quality and resolution of cell-laden 3D scaffolds of GelMA hydrogel were slightly better than that of GelMA hydrogels without cells, there were no significant differences due to various cell concentrations. The cellular sedimentation in GelMA bio-inks within the printer cartridge was evaluated using DNA quantification. Sedimentation was not statistically significant at the studied cell concentrations of up to 10 × 106 cells/ml. Immunofluorescent imaging indicated improved cell spreading and more uniform scaffold coverage over time for higher cell densities. This study provides insights into the effect of cell density on the rheology, and 3D printability of GelMA bioinks which will assist in the designing and standardizing bioprinting of high-quality 3D bioengineered structures.

The extracellular microenvironment provides critical cues that guide tissue development, homeostasis, and pathology. Deciphering the individual roles of these cues in tissue function necessitates the development of physically tunable culture platforms, but current approaches to create such materials have produced scaffolds that either exhibit a limited mechanical range or are unable to recapitulate the fibrous nature of in vivo tissues. Here we report a novel interpenetrating network (IPN) of gelatin-methacrylate (gelMA) and collagen I that enables independent tuning of fiber density and scaffold stiffness across a physiologically-relevant range of shear moduli (2–12 kPa), while maintaining constant extracellular matrix content. This biomaterial system was applied to examine how changes in the physical microenvironment affect cell types associated with the tumor microenvironment. By increasing fiber density while maintaining constant stiffness, we found that MDA-MB-231 breast tumor cells required the presence of fibers to invade the surrounding matrix, while endothelial cells (ECs) did not. Meanwhile, increasing IPN stiffness independently of fiber content yielded decreased invasion and sprouting for both MDA-MB-231 cells and ECs. These results highlight the importance of decoupling features of the microenvironment to uncover their individual effects on cell behavior, in addition to demonstrating that individual cell types within a tissue may be differentially affected by the same changes in physical features. The mechanical range and fibrous nature of this tunable biomaterial platform enable mimicry of a wide variety of tissues, and may yield more precise identification of targets which may be exploited to develop interventions to control tissue function.

Methacrylated gelatin (Gel-MA) is a commonly used biomaterial in bioprinting applications. The Gel-MA synthesis procedure is inadequate and needs to be improved, particularly from the point of optimization and efficacy. We report a significantly faster (by 5 min) and effective method to controllably synthesize Gel-MA using microwave energy (Mw at 1000 W power) with ≥90% degree of methacrylation (DM) even with the use of a very low concentration of methacrylic anhydride (MA). Rheological and mechanical analyses indicated that Gel-MA synthesized by Mw-assisted methacrylation enabled the formation of hydrogels that are more elastic and stronger and have a lower degradation rate (∼27% at 35 days) than Gel-MA synthesized by the conventional method. The viscosity values of the Gel-MA bioink were in the range applicable for use in 3D bioprinters. Additionally, Mw-assisted methacrylated Gel-MA hydrogels that have mechanically superior properties significantly enhanced the viability, attachment, proliferation, alkaline phosphatase (ALP) activity, mineral deposition, and mRNA expression levels of osteogenic genes of MC3T3-E1 preosteoblastic cells.

This study deals with the development of an LED-curable methacrylated gelatin (GelMA) synthesis via microwave (MW) irradiation with a reaction and purification time-, energy-, and methacrylation reagent-saving approach. To investigate the efficiency of MW irradiation in GelMA synthesis, characteristics of the GelMAs prepared by using glycidyl methacrylate (GMA) or methacrylic anhydride (MA) via the MW-assisted (MWA) method were compared comprehensively with those synthesized via the conventional heating method. Moreover, MWA reaction conditions were optimized in terms of methacrylation reagent concentrations (C), reaction time (t), and MW power (P). Characterization and assessment of the GelMAs were conducted with 1H NMR, FT-IR, and Raman spectroscopy along with physical-mechanical, thermal, and hydrophilicity analysis. The results demonstrated that the MWA synthesized GMA–GelMA hydrogels were possessed of increased methacrylation degree (MD), gel fraction (GF), tensile strength (TS), elongation at break (EB), glass transition temperature (Tg), and water contact angle (WCA) as well as decreased swelling degree (SD) values in comparison to those of MA–GelMA and GMA–GelMA hydrogels prepared via the MWA and conventional method, respectively. Enhanced properties of the MWA synthesized GMA-hydrogels suggested an effective methacryloyl conjugation leading to a greater amount of covalent crosslinking density justified by the dipolar moment calculations. Optimal GMA C, t, P, and purification time for a highly crosslinked GelMA hydrogel (MD: 96.1%, GF: 98.3%, SD: 10.11%, TS: 6.7 MPa, EB: 175.2%, Tg: 75.34 °C, and WCA: 72.22°) were found to be a 5 times molar excess over the primary amine groups of gelatin, 5 min, 500 W, and 24 h, respectively. Thus, the optimized MW conditions offer a promising green method to prepare GelMAs for bio applications.

Synthetically-modified proteins, such as gelatin methacryloyl (GelMA), a.k.a. gelatin methacrylate or gelatin methacrylamide, are growing in popularity for bioprinting and biofabrication. GelMA is a photocurable macromer that can rapidly form hydrogels, while also presenting bioactive peptide sequences for cellular adhesion and proliferation. The mechanical properties of GelMA are highly tunable by modifying the degree of substitution via synthesis conditions, though the effects of source material and thermal gelation effects have not been comprehensively characterized at lower concentration gels. Herein, we investigate the effects of animal source and processing sequence on scaffold mechanical properties. Hydrogels of 4-6 wt% were characterized. Depending on the temperature at crosslinking, the storage moduli for GelMA derived from pigs, cows, and cold-water fish range from 723-7340 Pa, 516-3484 Pa, and 294-464 Pa, respectively. The maximum storage moduli are achieved only by coordinated physical gelation and chemical crosslinking. In this method, the classic physical, thermo-reversible gelation of gelatin occurs when GelMA is cooled below a thermal transition temperature, which is subsequently ‘locked in’ by chemical crosslinking via photocuring. The effects of coordinated physical gelation and chemical crosslinking are demonstrated by precise photopatterning of cell-laden microstructures, inducing different cellular behavior depending on the selected mechanical properties of GelMA.