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Peripheral nerve injuries (PNIs) can cause neuropathies and significantly affect the patient's quality of life. Autograft transplantation is the gold standard for conventional treatment; however, its application is limited by nerve unavailability, size mismatch, and local tissue adhesion. Tissue engineering, such as nerve guidance conduits, is an alternative and promising strategy to guide nerve regeneration for peripheral nerve repair; however, only a few conduits could reach the high repair efficiency of autografts. The healing process of PNI is frequently accompanied by not only axonal and myelination regeneration but also angiogenesis, which initializes nerve regeneration through vascular endothelial growth factor A (VEGF-A). In this study, a composite nerve conduit with a poly (lactic-co-glycolic acid) (PLGA) hollow tube as the outer layer and gelatin methacryloyl (GelMA) encapsulated with VEGF-A transfected Schwann cells (SCs) as the inner layer was established to evaluate its promising ability for peripheral nerve repair. A rat model of peripheral nerve defect was used to examine the efficiency of PLGA/GelMA-SC (VA) conduits, whereas autograft, PLGA, PLGA/GelMA, and PLGA/GelMA-SC (NC) were used as controls. VEGF-A-transfected SCs can provide a stable source for VEGF-A secretion. Furthermore, encapsulation in GelMA cannot only promote proliferation and tube formation of human umbilical vein endothelial cells but also enhance dorsal root ganglia and neuronal cell extension. Previous animal studies have demonstrated that the regenerative effects of PLGA/GelMA-SC (VA) nerve conduit were similar to those of autografts and much better than those of other conduits. These findings indicate that combination of VEGF-A-overexpressing SCs and PLGA/GelMA conduit-guided peripheral nerve repair provides a promising method that enhances angiogenesis and regeneration during nerve repair. Nerve guidance conduits shows promise for peripheral nerve repair, while achieving the repair efficiency of autografts remains a challenge. In this study, a composite nerve conduit with a PLGA hollow tube as the outer layer and gelatin methacryloyl (GelMA) encapsulated with vascular endothelial growth factor A (VEGF-A)-transfected Schwann cells (SCs) as the inner layer was established to evaluate its potential ability for peripheral nerve repair. This approach preserves growth factor bioactivity and enhances material properties. GelMA insertion promotes Schwann cell proliferation and morphology extension. Moreover, transfected SCs serve as a stable VEGF-A source and fostering angiogenesis. This study offers a method preserving growth factor efficacy and safeguarding SCs, providing a comprehensive solution for enhanced angiogenesis and nerve regeneration. [Display omitted] [ABSTRACT FROM AUTHOR]

The therapeutic role of tendon stem cells (TSCs) in tendon-related injuries has been well documented. Small extracellular vesicles (sEVs) are being increasingly used as new biotherapeutic agents for various diseases. Therefore, the potential function of TSC-sEVs in tendon injury repair warrants further investigation. In this study, we explored the effects of TSC-sEVs on TSC proliferation, migration, and differentiation in vitro in an autocrine manner. We further used a novel exosomal topical treatment with TSC-sEVs loaded with gelatin methacryloyl (GelMA) hydrogel in vivo ; we mixed sufficient amounts of TSC-sEVs with GelMA hydrogel to cover the damaged molded Achilles tendon tissue and then exposed them to UV irradiation for coagulation. GelMA loading ensured that TSC-sEVs were slowly released at the injury site over a long period, thereby achieving their full local therapeutic effects. Treatment with TSC-sEVs loaded with GelMA significantly improved the histological score of the regenerated tendon by increasing the tendon expression while inhibiting the formation of excessive ossification and improving the mechanical properties of the tissue. Moreover, miRNA sequencing in TSC-sEVs, TSCs, and TSCs receiving sEVs revealed that TSC-sEVs altered the miRNA expression profile of TSCs, with increased expression of miR-145-3p. In conclusion, our study demonstrates that TSC-sEVs can play a key role in treating tendon injuries and that loading them with GelMA can enhance their effect in vivo. Moreover, miR-145-3p has a major functional role in the effect of TSC-sEVs. This study offers new therapeutic ideas for the local treatment of Achilles tendon injuries using sEVs. In this study, we demonstrated that TSC-sEVs play a key role in treating tendon injuries and that loading them with GelMA hydrogel can act as a fixation and slow release in vivo. Moreover, it identifies the major functional role of miR-145-3p in the effect of TSCs that were identified and validated by miRNA sequencing. Our study provides a basis for further research on GelMA slow-release assays that have potential clinical applications. It offers new therapeutic ideas for the local treatment of Achilles tendon injuries using TSC-sEVs. [Display omitted] [ABSTRACT FROM AUTHOR]

The incidence of osteochondral defect is increasing year by year, but there is still no widely accepted method for repairing the defect. Hydrogels loaded with bioactive molecules have provided promising alternatives for in-situ osteochondral regeneration. Kartogenin (KGN) is an effective and steady small molecule with the function of cartilage regeneration and protection which can be further boosted by TGF-β. However, the high cost, instability, and immunogenicity of TGF-β would limit its combined effect with KGN in clinical application. In this study, a composite hydrogel CM-KGN@GelMA, which contained TGF-β1 analog short peptide cytomodulin-10 (CM-10) and KGN, was fabricated. The results indicated that CM-10 modified on GelMA hydrogels exerted an equivalent role in enhancing chondrogenesis as TGF-β1, and this effect was also boosted when combined with KGN. Moreover, it was revealed that CM-10 and KGN had a synergistic effect on promoting the chondrogenesis of BMSCs by up-regulating the expression of RUNX1 and SOX9 at both mRNA and protein levels in vitro. Finally, the composite hydrogel exhibited a satisfactory osteochondral defect repair effect in vivo , showing similar structures close to the native tissue. Taken together, this study has revealed that CM-10 may serve as an alternative for TGF-β1 and can collaborate with KGN to accelerate chondrogenesis, which suggests that the fabricated CM-KGN@GelMA composite hydrogel can be acted as a potential scaffold for osteochondral defect regeneration. Kartogenin and TGF-β have shown great value in promoting osteochondral defect regeneration, and their combined application can enhance the effect and show great potential for clinical application. Herein, a functional CM-KGN@GelMA hydrogel was fabricated, which was composed of TGF-β1 mimicking peptide CM-10 and KGN. CM-10 in hydrogel retained an activity like TGF-β1 to facilitate BMSC chondrogenesis and exhibited boosting chondrogenesis by up-regulating RUNX1 and SOX9 when being co-applied with KGN. In vivo , the hydrogel promoted cartilage regeneration and subchondral bone reconstruction, showing similar structures as the native tissue, which might be vital in recovering the bio-function of cartilage. Thus, this study developed an effective scaffold and provided a promising way for osteochondral defect repair. [Display omitted] [ABSTRACT FROM AUTHOR]

Three-dimensional (3D) printing of soft biomaterials facilitates the progress of personalized medicine. The development for different forms of 3D-printable biomaterials can promotes the potential manufacturing for artificial organs and provides biomaterials with the required properties. In this study, gelatin methacryloyl (GelMA) and dialdehyde-functionalized polyurethane (DFPU) were combined to create a double crosslinking system and develop 3D-printable GelMA-PU biodegradable hydrogel and cryogel. The GelMA-PU system demonstrates a combination of self-healing ability and 3D printability and provides two distinct forms of 3D-printable biomaterials with smart functions, high printing resolution, and biocompatibility. The hydrogel was printed into individual modules through an 80 µm or larger nozzle and further assembled into complex structures through adhesive and self-healing abilities, which could be stabilized by secondary photocrosslinking. The 3D-printed hydrogel was adhesive, light transmittable, and could embed a light emitting diode (LED). Furthermore, the hydrogel laden with human mesenchymal stem cells (hMSCs) was successfully printed and showed cell proliferation. Meanwhile, 3D-printed cryogel was achieved by printing on a subzero temperature platform through a 210 µm nozzle. After secondary photocrosslinking and drying, the cryogel was deliverable through a 16-gage (1194 µm) syringe needle and can promote the proliferation of hMSCs. The GelMA-PU system extends the ink pool for 3D printing of biomaterials and has potential applications in tissue engineering scaffolds, minimally invasive surgery devices, and electronic wound dressings. The 3D-printable biomaterials developed in this work are GelMA-based ink with smart funcitons and have potentials for various customized medical applications. The synthesized GelMA-polyurethane double network hydrogel can be 3D-printed into individual modules (e.g., 11 × 11 × 5 mm3) through an 80 μm or larger size nozzle, which are then assembled into a taller structure over five times of the initial height by self-healing and secondary photocrosslinking. The hydrogel is adhesive, light transmittable, and biocompatible that can either carry human mesenchymal stem cells (hMSCs) as bioink or embed a red light LED (620 nm) with potential applications in electronic skin dressing. Meanwhile, the 3D-printed highly compressible cryogel (e.g., 6 × 6 × 1 mm3) is deliverable by a 16-gage (1194 μm) syringe needle and supports the proliferation of hMSCs also. [Display omitted] [ABSTRACT FROM AUTHOR]

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

Polymer-based composite scaffolds are an attractive class of biomaterials due to their suitable physical and mechanical performance as well as appropriate biological properties. When such composites contain osteoinductive ceramic nanopowders, it is possible, in principle, to stimulate the seeded cells to differentiate into osteoblasts. However, reproducibly fabricating and developing an appropriate niche for cells' activities in three-dimensional (3D) scaffolds remains a challenge using conventional fabrication techniques. Additive manufacturing provides a new strategy for the fabrication of complex 3D structures. Here, an extrusion-based 3D printing method was used to fabricate the Alginate (Alg)/Tri-calcium silicate (C 3 S) bone scaffolds. To improve physical and biological attributes, scaffolds were coated with gelatin methacryloyl (GelMA), a biocompatible viscose hydrogel. Conducting a combination of experimental techniques and molecular dynamics simulations, it is found that the composition ratio of Alg/C 3 S governs intermolecular interactions among the polymer and ceramic, affecting the product performance. Investigating the effects of various C 3 S amounts in the bioinks, the 90/10 composition ratio of Alg/C 3 S is known as the optimum content in developed bioinks. Accordingly, the printability of high-viscosity inks is boosted by improved hierarchical interactions among assemblies, which in turn leads to better nanoscale alignment in extruded macroscopic filaments. Conducting multiple tests on specimens, the GelMA-coated Alg/C 3 S scaffolds (with a composition ratio of 90/10) were shown to have improved mechanical qualities and cell adhesion, spreading, proliferation, and osteogenic differentiation, compared to the bare scaffolds, making them better candidates for further future research. Overall, the in-silico and in vitro studies of GelMA-coated 3D-printed Alg/C 3 S scaffolds open new aspects for biomaterials aimed at the regeneration of large- and complicated-bone defects through modifying the extrusion-based 3D-printed constructs. [ABSTRACT FROM AUTHOR]

Skin wounds, prevalent and fraught with complications, significantly impact individuals and society. Wound healing encounters numerous obstacles, such as excessive reactive oxygen species (ROS) production and impaired angiogenesis, thus promoting the development of chronic wound. Traditional clinical interventions like hemostasis, debridement, and surgery face considerable challenges, including the risk of secondary infections. While therapies designed to scavenge excess ROS and enhance proangiogenic properties have shown effectiveness in wound healing, their clinical adoption is hindered by high costs, complex manufacturing processes, and the potential for allergic reactions. Lotus root, distinguished by its natural micro and macro porous architecture, exhibits significant promise as a tissue engineering scaffold. This study introduced a novel scaffold based on hybridization of lotus root-inspired and Gelatin Methacryloyl (GelMA), verified with satisfactory physicochemical properties, biocompatibility, antioxidative capabilities and proangiogenic abilities. In vivo tests employing a full-thickness wound model revealed that these scaffolds notably enhanced micro vessel formation and collagen remodeling within the wound bed, thus accelerating the healing process. Given the straightforward accessibility of lotus roots and the cost-effective production of the scaffolds, the novel scaffolds with ROS scavenging, pro-angiogenesis and re-epithelialization abilities are anticipated to have clinical applicability for various chronic wounds. [Display omitted] [ABSTRACT FROM AUTHOR]

Cryopreserved testicular tissue offers a promising method to restore fertility in male infertility patients. Current protocols rely on high concentrations of penetrating cryoprotectants (pCPAs), such as dimethyl sulfoxide (DMSO), which necessitating complex washing procedures and posing risks of toxicity. Hydrogel encapsulation presents a non-toxic alternative for cellular cryopreservation. This study investigates the effects of various types, concentrations, and thicknesses of hydrogel encapsulation on the cryopreservation of mouse testicular tissue. Testicular tissues loaded with varying concentrations of DMSO were encapsulated in alginate or gelatin-methacryloyl (GelMA) hydrogels. We evaluated hydrogels as potential CPAs to reduce pCPA concentrations and determine optimal combinations for cryopreservation. Post-cryopreservation, tissues were cultured using organ culture methods to assess spermatogenesis progression. Cryomicroscopy and differential scanning calorimetry (DSC) were used to examine ice crystal formation, melting enthalpy, and non-freezing water content in different hydrogels during cooling. Results indicate that 3 % alginate or 5 % GelMA hydrogel with thin encapsulation optimally preserves mouse testicular tissue. Using 20 % DMSO in 5 % GelMA thin encapsulation showed comparable apoptosis rates, improved morphology, higher mitochondrial activity, and enhanced antioxidant capacity compared to conventional 30 % DMSO without encapsulation. This suggests that hydrogel encapsulation reduces pCPA concentration by 10 %, thereby mitigating toxic damage. Hydrogel encapsulation can reduce basement membrane shrinkage of testicular tissue during cryopreservation. Moreover, frozen tissues remained viable with preserved germ cells after being cultured for one week on alginate methacryloyl (AlgMA) hydrogel using the gas-liquid interphase method. Cryomicroscopy and DSC studies confirmed the hydrogel's ability to inhibit ice crystal growth. In conclusion, this study introduces novel strategies for male fertility preservation and advances cryopreservation technology for clinical applications in assisted reproduction. [Display omitted] • GelMA and alginate hydrogels were used for testicular tissue cryopreservation. • Hydrogels can serve as non-toxic cryoprotectants for tissue cryopreservation. • Hydrogel encapsulation can protect the basement membrane of testicular tissue. • The 3D network structure of the hydrogel system can restrict the growth of ice crystals. [ABSTRACT FROM AUTHOR]

[Display omitted] • GelMA-SilMA hydrogels with good mechanical properties modified the tissue suitability of polypropylene mesh. • GelMA-SilMA hydrogel demonstrated biocompatibility, biodegradability, and bioactivity in vitro. • GelMA-SilMA hydrogel enhanced the efficiency of open abdominal wound repair in vivo. • GelMA-SilMA hydrogel accelerated wound repair by activating specific signaling pathways. Open abdomen (OA), a major advance in modern trauma surgery, enables the treatment of severe abdominal trauma, infections, and hypertension by temporarily closing the abdominal cavity without suturing. Although OA can reduce mortality rates, it also presents challenges such as disruption of the abdominal environment, intestinal exposure, and impaired wound healing. Current temporary abdominal closure (TAC) techniques using polypropylene (PP) mesh are susceptible to abrasion and rupture of the intestine, leading to adhesions and serious complications such as intestinal fistulas and chronic wounds. These complications seriously impact outcomes due to mesh rigidity and its incompatibility with surrounding tissues. In this study, we designed a multifunctional hydrogel composed of GelMA (Gelatin Methacryloyl) and SilMA (Silk Fibroin Methacryloyl) as a promising solution for open abdominal wound repair. In vitro experiments confirmed the biocompatibility, self-healing properties, pro-angiogenic effects, and promotion of macrophage polarization. In vivo studies revealed that the GelMA-SilMA hydrogel could enhance abdominal wall tissue thickness and integrity via isolating the peritoneal cavity, protecting the intestinal tract, polarizing macrophages, promoting collagen formation, inducing neovascularization, inhibiting oxidative stress, and suppressing inflammation. Furthermore, immunofluorescence, immunohistochemistry, and RNA sequencing were employed to evaluate the wound healing mechanisms of GelMA-SilMA hydrogels. The results demonstrated that the hydrogels can promote angiogenesis, inhibit inflammation and immune responses, and enhance wound healing by activating the HIF-a-VEGF signaling pathway, RAP1 signaling pathway, and PI3K-AKT signaling pathway. Hence, the multifunctional GelMA-SilMA hydrogel has tremendous potential for clinical use in open abdominal wound repair. [ABSTRACT FROM AUTHOR]

This work sought to formulate photocrosslinkable chlorhexidine (CHX)-laden methacrylated gelatin (CHX/GelMA) hydrogels with broad spectrum of action against endodontic pathogens as a clinically viable cell-friendly disinfection therapy prior to regenerative endodontics procedures. CHX/GelMA hydrogel formulations were successfully synthesized using CHX concentrations between 0.12 % and 5 % w/v. Hydrogel microstructure was evaluated by scanning electron microscopy (SEM). Swelling and enzymatic degradation were assessed to determine microenvironmental effects. Compression test was performed to investigate the influence of CHX incorporation on the hydrogels' biomechanics. The antimicrobial and anti-biofilm potential of the formulated hydrogels were assessed using agar diffusion assays and a microcosms biofilm model, respectively. The cytocompatibility was evaluated by exposing stem cells from human exfoliated deciduous teeth (SHEDs) to hydrogel extracts (i.e. , leachable byproducts obtained from overtime hydrogel incubation in phosphate buffer saline). The data were analyzed using One- and Two-way ANOVA and Tukey's test (α = 0.05). CHX/GelMA hydrogels were effectively prepared. NMR spectroscopy confirmed the incorporation of CHX into GelMA. The addition of CHX did not change the micromorphology (pore size) nor the swelling profile (p > 0.05). CHX incorporation reduced the degradation rate of the hydrogels (p < 0.001); whereas, it contributed to increased compressive modulus (p < 0.05). Regarding the antimicrobial properties, the incorporation of CHX showed a statistically significant decrease in the number of bacteria colonies at 0.12 % and 0.5 % concentration (p < 0.001) and completely inhibited the growth of biofilm at concentration levels 1 %, 2 %, and 5 %. Meanwhile, the addition of CHX, regardless of the concentration, did not lead to cell toxicity, as cell viability values were above 70 %. The addition of CHX into GelMA showed significant antimicrobial action against the pathogens tested, even at low concentrations, with the potential to be used as a cell-friendly injectable drug delivery system for root canal disinfection prior to regenerative endodontics. [Display omitted] • Chlorhexidine-laden gelatin methacrylate hydrogel (CHX/GelMA) was synthesized. • CHX/GelMA showed significant antimicrobial action against endodontic pathogens. • CHX/GelMA holds potential for infection eradication prior to regenerative procedures. [ABSTRACT FROM AUTHOR]

3D bioprinting is an emerging technique employed for engineering complex structures that can be used for regenerative medicine. Extrusion of hydrogels through a nozzle has produced layer by layer designs towards engineering patterns. Despite the significant advances of these systems in the biomedical field, there are some inherent constraints to achieve higher resolutions without impacting the viability of the cells contained in the bioinks. Recently, there has been research on polymerization using light and photosensitive materials that point toward finer details within more reproducible manufacturing conditions and more complex products. Recent advances in bioprinting include the implementation of the construction of multimaterial structures to mimic in a more precise way a complex tissue. This paper showcases the development of a novel design using a retrofitting strategy toward a Material Efficient and Low-Cost Bioprinting system based on a Liquid Crystal Display (LCD) technique that reduces the required materials with a low-volume material reservoir and optimizes the processing parameters. Towards a new generation of devices, we present a novel open-source retrofitting kit for adapting a low-cost commercially available Anycubic 3D printer to process a bioink. As a proof-of-concept, an initial study of the concentration of gelatin methacryloyl (GelMa) and Lithium Phenyl -2, 4, 6 -trimethylbenzoylphosphinate (LAP) photoinitiator and the manufacturability is hereby presented for hexagonal, circular, and square features. The design of a new setup enabled a reduction of 90% of the required bioink. While further research is required to validate this concept, this is a step towards a new generation of affordable bioprinting systems. [ABSTRACT FROM AUTHOR]

Hydrogels incorporating natural biopolymer and adhesive substances have extensively been used to develop bioactive drugs and to design cells encapsulating sturdy structure for biomedical applications. However, the conjugation of the adhesive in most hydrogels is insufficient to maintain long-lasting biocompatibility inadequate to accelerate internal organ tissue repair in the essential native cellular microenvironment. The current work elaborates the synthesis of charged choline-catechol ionic liquid (BIL) adhesive and a hydrogel with an electronegative atom rich polyphenol (PU)-laden gelatinmethacryloyl (GelMA) to improve the structural bioactivities for in vivo tracheal repair by inducing swift crosslinking along with durable mechanical and tissue adhesive properties. It was observed that bioactive BIL and PU exhibited potent antioxidant (IC 50 % of 7.91 μg/mL and 24.55 μg/mL) and antibacterial activity against E. coli , P. aeruginosa and S. aureus. The novel integration of photocurable GelMA-BIL-PU revealed outstanding mechanical strength, biodegradability and sustained drug release. The in vitro study showed exceptional cell migration and proliferation in HBECs, while in vivo investigation of the GelMA-BIL-PU hydrogel on a rat's tracheal model revealed remarkable tracheal reconstruction, concurrently reducing tissue inflammation. Furthermore, the optimized GelMA-BIL-PU injectable adhesive bioink blend demonstrated superior MSCs migration and proliferation, which could be a strong candidate for developing stem cell-rich biomaterials to address multiple organ defects. • Polyphenol and choline-catechol ionic liquid revealed robust therapeutic agents. • Bioactive adhesive hydrogels improved the biocompatibility of mesenchymal stem cells. • Bioinspired adhesive polymer hydrogels accelerated tracheal repair and regeneration. [ABSTRACT FROM AUTHOR]

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. ● 10% GelMA bioprinted scaffolds loaded with DPSCs have good osteogenic potential. ● Activation of ephrinB2/EphB4 signaling promoted osteogenic differentiation of DPSCs in 10% GelMA. ● The 10% GelMA bioprinted scaffold loaded with DPSCs has good bone regeneration effect in vivo. [ABSTRACT FROM AUTHOR]

For incompressible and irregularly shaped wounds, developing a novel dressing based on photo-crosslinked hydrogel that has both hemostasis and antibacterial functions is highly desirable. In this study, photoreactive substrate gelatin methacrylate (GelMA) and Poly (ethylene glycol) diacrylate (PEGDA) were combined with water-soluble quaternary ammonium antibacterial monomers (DMC). Interestingly, they can quickly change from liquid to hydrogel under visible light at 405 nm within 1 min, which is suitable for small incompressible wounds. Regarding the biosafety of the dressing, cell viability and blood viability test indicated that the GelMA/PEGDA/DMC 3 dressing has no cytotoxicity toward L929 cells and red blood cells. The antibacterial performance test proved that the addition of DMC significantly improved the antibacterial performance of the dressing. Moreover, the GelMA/PEGDA/DMC 3 dressing showed rapid hemostasis ability in tail clipping hemostasis test and liver hemostasis test. Taken together, this new type of convenient hydrogel dressing exhibits great potential as a quick hemostasis and antibacterial wound dressing candidate for small bleeding wounds. [Display omitted] [ABSTRACT FROM AUTHOR]

[Display omitted] • A hydrogel-based drug release system formed on framework nucleic acids for transporting miR29c has been developed and applied to promote bone healing in critical size bone defects. • stFNAs-miR29c and GelMA-stFNAs-miR29c have an efficient miRNA cell uptake rate, excellent stability, and good biocompatibility. • GelMA-stFNAs-miR29c enhances the osteogenesis ability of BMSCs by up regulating the Wnt signaling pathway and promoting the expression of osteogenic protein including ALP, RUNX2, OSX, and OPN. Bone defects affect the daily activities of patients and are prevalent complications of various skeletal disorders. The miR29 family regulates bone physiology and pathological processes. MiR29c can inhibit Dickkopf-1 (DKK1) expression, up-regulate the Wnt-signaling pathway, and modify the intracellular microenvironment. However, its application is hindered by poor stability and low bioavailability. This study sought to optimize the nano miR29c delivery system, enable enhanced drug effects, stable drug in situ retention, and sustained drug release. Tetrahedral framework nucleic acids (tFNAs), which have excellent drug-loading ability, endocytic capacity, and stability, were used with sticky ends to deliver miR29c (i.e., stFNAs-miR29c). Porous gelatin methacryloyl (GelMA) was selected as a scaffold for the in situ sustained release of stFNAs-miR29c and to provide a growth environment for bone marrow mesenchymal stem cells (BMSCs). This research developed a miR29c sustained-release system in situ : GelMA-stFNAs-miR29c and demonstrated its osteogenesis in vitro and in vivo. GelMA, stFNAs, and miR29c can function synergistically at nano-, micro-, and macro- scales that achieves high stability and efficiency on microRNA nano-delivery, regulates the local microenvironment, maintains the macro-osteogenic space, accelerates the osteogenic process, and ensures excellent osteogenesis effects, contributing to the broader application of miRNAs in biomedicine and improved bone regeneration in situ. [ABSTRACT FROM AUTHOR]

[Display omitted] Three-dimensional liver bioprinting is an emerging technology in the field of regenerative medicine that aids in the creation of functional tissue constructs that can be used as transplantable organ substitutes. During transplantation, the bioprinted donor liver must be protected from the oxidative stress environment created by various factors during the transplantation procedure, as well as from drug-induced damage from medications taken as part of the post-surgery medication regimen following the procedure. In this study, Silymarin, a flavonoid with the hepatoprotective properties were introduced into the GelMA bioink formulation to protect the bioprinted liver against hepatotoxicity. The concentration of silymarin to be added in GelMA was optimised, bioink properties were evaluated, and HepG2 cells were used to bioprint liver tissue. Carbon tetrachloride (CCl 4) was used to induce hepatotoxicity in bioprinted liver, and the effect of this chemical on the metabolic activities of HepG2 cells was studied. The results showed that Silymarin helps with albumin synthesis and shields liver tissue from the damaging effects of CCl 4. According to gene expression analysis, CCl 4 treatment increased TNF-α and the antioxidant enzyme SOD expression in HepG2 cells while the presence of silymarin protected the bioprinted construct from CCl 4 -induced damage. Thus, the outcomes demonstrate that the addition of silymarin in GelMA formulation protects liver function in toxic environments. [ABSTRACT FROM AUTHOR]

In bone tissue engineering, vascularization is one of the critical factors that limit the effect of biomaterials for bone repair. While various approaches have been tried to build vascular networks in bone grafts, lack of endothelialization still constitutes a major technical hurdle. In this study, we have developed a facile technique to fabricate endothelialized biomimetic microvessels (BMVs) from alginate-collagen composite hydrogels within a single step using microfluidic technology. BMVs with different sizes could be readily prepared by adjusting the flow rate of microfluids. All BMVs supported perfusion and outward penetration of substances in the tube. Endothelial cells could adhere and proliferate on the inner wall of tubes. It was also found that the expression of CD31 and secretion of BMP-2 and PDGF-BB were higher in the rat umbilical vein endothelial cells (RUVECs) in BMVs than those cultured on hydrogel. When co-cultured with bone marrow mesenchymal stem cells (BMSCs), endothelialized BMVs promoted the osteogenic differentiation of BMSCs compared to those in acellular BMV group. In vivo , markedly enhanced new bone formation was achieved by endothelialized BMVs in a rat critical-sized calvarial defect model compared to those with non-endothelialized BMVs or without BMVs. Together, findings from both in vitro and in vivo studies have proven that endothelialized BMVs function to facilitate osteogenesis and promote bone regeneration, and therefore might present an effective strategy in bone tissue engineering. In bone tissue engineering, limited vascularization is one of the critical factors that limit the effect of biomaterials for bone repair. In this study, we developed a facile technique to fabricate endothelialized biomimetic microvessels (BMVs) from alginate-collagen composite hydrogels within a single step using microfluidic technology. Both in vitro and in vivo studies have proven that endothelialized BMVs function to facilitate osteogenesis and promote bone regeneration, and therefore might present an effective strategy in bone tissue engineering. [Display omitted] [ABSTRACT FROM AUTHOR]

Hydrogels were prepared by mixing protein and carbohydrate-based biopolymers to increase the mechanical properties and efficient cell adhesion and proliferation for wound healing applications. Microcrystalline cellulose (MCC) and its 6-deoxy-aminocellulose derivatives (6-deoxy-6-hydrazide Cellulose (Cell-Hyd), 6-deoxy-6-diethylamide Cellulose (Cell-DEA), and 6-deoxy-6-diethyltriamide Cellulose (Cell-DETA)) were embedded in methacrylated gelatin (GelMA). GelMA and 6-deoxy-aminocellulose derivatives were synthesized and characterized by spectroscopic techniques. MCC and cellulose derivatives embedded GelMA gels were characterized by FTIR, SEM and Tensile mechanical testing. SEM images revealed that, porosity of the amine MCC incorporated GelMA was decreased compared to GelMA and MCC incorporated GelMA. Tensile strain of GelMA 61.30% at break was increased to 64.3% in case of GelMA/Cell-HYD. In vitro cytocompatibility and cell proliferation using NIH-3T3 cell lines showed cell density trend on scaffold as GelMA/Cell-DETA>GelMA/Cell-Hyd > GelMA. Scratch assay for wound healing revealed that GelMA/Cell-DETA showed complete wound closure, while GelMA/Cell-Hyd and GelMA exhibited 85.7%, and 66.1% wound healing, respectively in 8 h. In vivo tests on rats revealed that GelMA/Cell-DETA exhibited 98% wound closure on day 9, whereas GelMA/Cell-Hyd exhibited 97.7% and GelMA 66.1% wound healing on day 14. Our findings revealed that GelMA embedded amine MCC derivatives hydrogels can be applied for achieving accelerated wound healing. [ABSTRACT FROM AUTHOR]

Corneal transplantation serves as the standard clinical therapy for serious corneal disorders. However, rejection of grafts, significant expenditures, and most crucially, the global donor shortage, may affect the outcome. Recently, 3D bioprinting using biodegradable polymeric materials has become a suitable method for creating tissue replicas with identical architecture. One such most renowned material is GelMA, for its scaffold's three-dimensional structure, biocompatibility, robust mechanics, and favourable optical transmittance. However, GelMA's inadequate viscosity to print at body temperature with better form integrity remains an obstacle. The aim of this work is to create 3D printed GelMA/MC hydrogels for corneal stroma tissue engineering using MC's printability at room temperature and GelMA's irreversible photo cross-linking with UV irradiation. The print speed and pressure conditions for 3D GelMA/MC hydrogels were tuned. Thermal, morphological and physicochemical characteristics were studied for two distinct concentrations of GelMA/MC hydrogels. The hydrogels achieved a transparency of ~78 % (at 700 nm), which was on par with that of the normal cornea (80 %). The in vitro studies conducted using goat corneal stromal cells demonstrated the ability of both hydrogels to promote cell adhesion and proliferation. Expression of Vimentin and keratan sulphate validated the phenotype of keratocytes in the hydrogel. This 3D printed GelMA/MC hydrogel model mimics biophysical characteristics of the native corneal stroma, which may hold promise for clinical corneal stromal tissue engineering. [Display omitted] [ABSTRACT FROM AUTHOR]

Cardiovascular diseases, particularly myocardial infarction (MI), remain a leading cause of morbidity and mortality worldwide. Current treatments for MI, more palliative than curative, have limitations in reversing the disease completely. Tissue engineering (TE) has emerged as a promising strategy to address this challenge and may lead to improved therapeutic approaches for MI. Gelatin-based scaffolds, including gelatin and its derivative, gelatin methacrylate (GelMA), have attracted significant attention in cardiac tissue engineering (CTE) due to their optimal physical and biochemical properties and capacity to mimic the native extracellular matrix (ECM). CTE mainly recruits two classes of gelatin/GelMA-based scaffolds: hydrogels and nanofibrous. This article reviews state-of-the-art gelatin/GelMA-based hybrid scaffolds currently applied for CTE and regenerative therapy. Hybrid scaffolds, fabricated by combining gelatin/GelMA hydrogel or nanofibrous scaffolds with other materials such as natural/synthetic polymers, nanoparticles, protein-based biomaterials, etc., are explored for enhanced cardiac tissue regeneration functionality. The engraftment of stem/cardiac cells, bioactive molecules, or drugs into these hybrid systems shows great promise in cardiac tissue repair and regeneration. Finally, the role of gelatin/GelMA scaffolds combined with the 3D bioprinting strategy in CTE will also be briefly highlighted. • Myocardial Infarction (MI) is one of the most common types of cardiovascular diseases. • Gelatin and hydrogel have attracted significant attention in cardiac tissue engineering • This review covers the prominent roles of nanomaterials in the development of gelatin-based scaffolds for MI. • Future perspectives and challenges of gelatin-based scaffolds for cardiac tissue Engineering and regeneration are discussed briefly. [ABSTRACT FROM AUTHOR]

Testicular tissue culture in vitro is considered an important tool for the study of spermatogenesis and the treatment of male infertility. Although agarose hydrogel is commonly used in testicular tissue culture, the efficiency of spermatogenesis in vitro is limited. In this study, testicular tissues from adult mice were cultured using a gas-liquid interphase method based on agarose (Agarose), gelatin methacryloyl (GelMA), alginate methacryloyl (AlgMA), dextran methacryloyl (DexMA), and mixture GelMA-Agarose, AlgMA-Agarose, and DexMA-Agarose hydrogels, respectively, for 32 days in vitro. The integrity of the seminiferous tubules, the density and proportions of spermatogonia, spermatocytes, Sertoli cells, and testosterone concentrations were quantified and compared between groups. Properties of different hydrogels including compression modulus, Fourier Infrared Spectroscopy (FITR) spectra, pore size, water absorption, and water retention were tested to investigate how biochemical and physical properties of hydrogels affect the results of testicular tissue culture. The results indicate that testicular tissues cultured on AlgMA exhibited the highest seminiferous tubule integrity rate (0.835 ± 0.021), the presence of a high density of spermatocytes (2107.627 ± 232.082/mm2), and a high proportion of SOX9-positive well-preserved seminiferous tubules (0.473 ± 0.047) compared to all remaining experimental groups on day 32. This may be due to the high water content of AlgMA reducing the toxic effect of oxygen on testicular tissue. In the later period of culture, testicular tissues cultured on DexMA, not DexMA-Agarose, produced significantly more testosterone (18.093 ± 3.302 ng/mL) than the other groups, suggesting that DexMA is friendly to Leydig cells. Our study provides a new idea for the optimization of the gas-liquid interphase method for achieving in vitro spermatogenesis, facilitating the future achievement of efficient in vitro spermatogenesis in more species, including humans. [ABSTRACT FROM AUTHOR]

Cardiac failure can be a life-threatening condition that, if left untreated, can have significant consequences. Functional hydrogel has emerged as a promising platform for cardiac tissue engineering. In the proposed study, gelatin methacrylate (GelMA) and alginate, as a primary matrix to maintain cell viability and proliferation, and polypyrrole and carboxyl-graphene, to improve mechanical and electrical properties, are thoroughly evaluated. Initially, a polymer blend of GelMA/Alginate (1:1) was prepared, and then the addition of 2–5 wt% of polypyrrole was evaluated. Next, the effect of incorporating graphene-carboxyl nanosheets (1, 2, and 3 wt%) within the optimized scaffold with 2 wt% polypyrrole was thoroughly studied. The electrical conductivity of the hydrogels was significantly enhanced from 0.0615 ± 0.007 S/cm in GelMA/alginate to 0.124 ± 0.04 S/cm with the addition of 5 wt% polypyrrole. Also, 3 wt% carboxyl graphene improved the electrical conductivity to 0.27 ± 0.09 S/cm. The compressive strength of carboxyl-graphene-containing hydrogel was in the range of 175 to 520 kPa, and tensile strength was 61 and 133 kPa. The simplicity and low-cost fabrication, tunable mechanical properties, optimal electrical conductivity, blood compatibility, and non-cytotoxicity of GelMA/alginate/polypyrrole/graphene biocomposite hydrogel is a promising construct for cardiac tissue engineering. [Display omitted] [ABSTRACT FROM AUTHOR]

In this study, supra-CNDs@GelMA composite hydrogel dressings for the photothermal treatment of melanoma were successfully developed. The prepared supra-CNDs (supra-carbon nanodots) exhibited remarkable photothermal properties, with a photothermal conversion efficiency of 55.29 % (47.12 %) under 730 nm (808 nm) laser irradiation, which is a promising material for photothermal reagents. The integrated GelMA (gelatine methacryloyl hydrogel) further enhanced the photothermal effects of the supra-CNDs@GelMA composite hydrogels and also shortened the exposure time, which could rapidly reach 50 ℃ within 70 s under 808 nm laser irradiation (1 W/cm2). Additionally, the thermal conductivity of the composite hydrogels was investigated at a laser spot diameter of 2 mm. Moreover, the supra-CNDs@GelMA composite hydrogels exhibited good biocompatibility and excellent photothermal ablation of melanoma cells. These findings demonstrate the potential of the supra-CNDs@GelMA composite hydrogels as dressings for the photothermal treatment of skin cancers. [Display omitted] [ABSTRACT FROM AUTHOR]

Schematic illustration of GelMA-LDH-calcein scaffolds synthesis and its excellent osteogenic and angiogenic properties for in vivo transplantation and bone regeneration. [Display omitted] • Bioactive layered double hydroxide nanoparticles with different elemental compositions were synthesized to optimize the osteogenic differentiation process. • Layered double hydroxide loaded calcein under gelatin methacryloyl composites were screened for cell compatibility and cell attachment. • The optimized nanocomposite promoted the osteogenic and angiogenesis bioactivity in vitro and in vivo. In regenerative medicine and tissue engineering, the repair and replacement of damaged or lost bone tissue remains an enduring challenge. Traditional approaches often fail to achieve desired outcomes, but recent advancements in material science have introduced innovative solutions to this issue. Gelatin methacryloyl (GelMA), which is derived from gelatin, has a unique combination of biocompatibility and tunable physical properties for bone tissue engineering applications. In this study, a novel composite was constructed to combine the characteristics of GelMA and bioactive layered double hydroxide (LDH) loaded calcein. The GelMA-LDH-calcein (GLC) scaffold is designed to promote the osteogenic differentiation of mesenchymal stem cells (MSCs) and provide a microenvironment conducive to osteogenic differentiation, ultimately increasing the osteogenic activity to support bone regeneration. Our data demonstrated that GLC promoted the osteogenic differentiation related gene (ALP, Runx2, and OPG) expression in bone marrow-derived MSCs (BMSCs) and angiogenesis of human vascular epithelial cells (HUVECs), making it particularly valuable in the application of bone regeneration in vivo. Through the design, synthesis, and optimization of GLC composites, the optimized scaffolds can provide structure supporting and biological activity for cell proliferation, which promoted bone defect regeneration and could be used for further clinical applications. [ABSTRACT FROM AUTHOR]

The human amniotic membrane (HAM) collagen matrix derived from human placenta can be decellularized (dHAM) to form a natural biocompatible material. dHAM has different bioactive substances and has been used widely in human tissue engineering research. However, dHAM has some disadvantages, e.g., poor mechanical properties, easy degradation and inconvenient operation and use, so it is not conducive to large-area or full-thickness skin defect healing. To overcome these limitations, for the first time, dHAM was grafted with methacrylic anhydride (MA) to form photocrosslinked dHAM methacrylate (dHAMMA); dHAMMA was then blended with methacrylated gelatin (GelMA), followed by the addition of a photosensitizer for photocrosslinking to obtain the fast-forming GelMA-dHAMMA composite hydrogel. Further, GelMA-dHAMMA was found to have the porous structure of a bicomponent polymer network and good physical and chemical properties. In vitro experiments, GelMA-dHAMMA was found to promote fibroblast proliferation and α-smooth muscle actin (α-SMA) expression. In vivo investigations also demonstrated that GelMA-dHAMMA promotes wound collagen deposition and angiogenesis, and accelerates tissue healing. GelMA-dHAMMA inherits the good mechanical properties of GelMA and maintains the biological activity of the amniotic membrane, promoting the reconstruction and regeneration of skin wounds. Thus, GelMA-dHAMMA can serve as a promising biomaterial in skin tissue engineering. Since the early 20th century, the human amniotic membrane (HAM) has been successfully used for trauma treatment and reconstruction purposes. dHAM has different bioactive substances and has been used widely in human tissue-engineering research. In this work, the dHAM and gelatin were grafted and modified by using methacrylic anhydride (MA) to form photocrosslinked dHAMMA and methacrylated gelatin (GelMA). Then, the dHAMMA and GelMA were blended with a photosensitizer to form the GelMA-dHAMMA composite hydrogel derived from gelatin-dHAM. GelMA-dHAMMA exhibits a bicomponent-network (BCN) interpenetrating structure. dHAM dydrogel has advantages, e.g., good mechanical properties, slow degradation and convenient operation, so it is conducive to large-area or full-thickness skin defect healing. [Display omitted] [ABSTRACT FROM AUTHOR]

Over the past decades, a variety of biomaterials have been investigated in terms of their suitability for oral mucosa tissue engineering. The aim of this study was to compare collagen and GelMA hydrogels as connective tissue scaffolds for fibroblasts and as substrates for seeding and culture of oral epithelial keratinocyte cells. Human primary oral fibroblast and keratinocyte cells were isolated from gingival biopsies. The mixture of fibroblasts with GelMA or collagen gel were aliquoted within six-well tissue culture plate inserts and cross-linked using visible light or reconstitution buffer/heat, respectively. The viability of fibroblasts in the hydrogels was investigated after one and three days of cultivation using the PrestoBlue assay. Following the addition and culture of oral keratinocytes onto the connective tissue constructs, the tissue-engineered oral mucosa was assessed histologically. The tissue viability assay shows that collagen hydrogels encapsulating fibroblasts displayed significantly higher cell viability than cell-laden GelMA constructs after 24 and 72 h (p < 0.05). A stratified and differentiated epithelium has formed on the surface of cell-laden collagen hydrogel but not on the surface of the GelMA-based substrate. Collagen-based scaffold offers superior biological properties compared to GelMA hydrogel in terms of oral fibroblast growth, as well as epithelial cell adhesion and differentiation. Therefore, collagen-based hydrogels remain the preferred choice for oral mucosa tissue engineering. [ABSTRACT FROM AUTHOR]

Repairing large segmental bone defects above a critical size remains challenging with high risk of delayed union or even non-union. From the perspective of bone development and clinical experience, periosteum plays an indispensable role in bone repair and reconstruction. In this study, we explored the feasibility of using preosteoblast-derived matrix (pODM) as a biomimetic periosteum. By culturing MC3T3-E1 cell sheet on poly(dimethylsiloxane) and performing decellularization, an integral cell-free sheet of pODM could be readily harvested. Bone marrow mesenchymal stem cells (BMSCs) adhered and proliferated well on pODM. In addition, pODM exhibited a chemotactic effect on BMSCs in a concentration-dependent manner and also promoted osteogenic differentiation of BMSCs. Following that, pODM was wrapped around a gelatin methacryloyl (GelMA) hydrogel to construct an engineered periosteum-bone substitute. A rabbit radius segmental bone defect model was used to examine the bone repair efficacy of pODM/GelMA. Upon implantation of pODM/GelMA construct for 12 weeks, the critical-sized bone defects completely healed with remarkable full reconstruction of medullary cavity at the radial diaphysis. Together, this work proposes a high potency of using precursor cell-derived matrix as a biomimetic periosteum, which preserves the beneficial biological factors while avoids the limitations of using exogenous cells for bone regeneration. Combining precursor cell-derived matrix with hydrogel may provide a promising periosteum-bone biomimetic substitute for bone repair. Repairing large segmental bone defects above a critical size remains challenging. As the periosteum plays an essential role in bone repair, this study aimed to explore the use of preosteoblast-derived matrix (pODM), harvested from decellularized MC3T3-E1 cell sheet, as a biomimetic periosteum to facilitate bone repair. We found that in vitro , pODM exhibited considerable chemotactic effect and osteogenic induction capability to bone marrow mesenchymal stem cells (BMSCs). In vivo , implantation of pODM/gelatin methacryloyl (GelMA) constructs as engineered periosteum-bone substitutes effectively repaired the critical-sized segmental bone defects at rabbit radius. Surprisingly, remarkable full reconstruction of medullary cavity at the diaphysis was achieved. Therefore, combining pODM with hydrogel may provide a promising biomimetic substitute for bone repair. Image, graphical abstract [ABSTRACT FROM AUTHOR]

This study demonstrates the effect of substrate's geometrical cues on viability and the efficacy of an anti-cancer drug, doxorubicin (DOX), on breast cancer cells. It is hypothesized that the surface topographical properties can mediate the cellular drug intake. Pseudo-three dimensional (3D) platforms were fabricated using imprinting technique from polydimethylsiloxane (PDMS) and gelatin methacryloyl (GelMA) hydrogel to recapitulate topography of cells' membranes. The cells exhibited higher viability on the cell-imprinted platforms for both PDMS and GelMA materials compared to the plain/flat counterparts. For instance, MCF7 cells showed a higher metabolic activity (11.9%) on MCF7-imprinted PDMS substrate than plain PDMS. The increased metabolic activity for the imprinted GelMA was about 44.2% compared to plain hydrogel. The DOX response of cells was monitored for 24 h. Although imprinted substrates demonstrated enhanced biocompatibility, the cultured cells were more susceptible to the drug compared to the plain substrates. In particular, MCF7 cells on imprinted PDMS and GelMA substrates showed 37% and 50% higher in cell death compared to the corresponding plain PDMS and GelMA, respectively. Interestingly, the drug susceptibility of the cells on the imprinted hydrogel was about 70% higher than the cells cultured on imprinted PDMS substrates. Having MCF7 cell-imprinted substrates, DOX responses of two other breast cancer cell lines, SKBR3 and ZR-75-1, were also evaluated. The results support that cell membrane curvature developed by multiscale topography is able to mediate intracellular signaling and drug intake. Research in biological sciences and drug discovery mostly rely on two dimensional (2D) cell culture techniques which cannot provide a reliable physiologically relevant environment. Lack of extracellular matrix and a large shift in physicochemical properties of conventional 2D substrates can induce aberrant cellular behaviors. While chemical composition, topographical, and mechanical properties of substrates have remarkable impacts on drug susceptibility, gene expression, and protein synthesis, the most cell culture plates are from rigid and plain substrates. A number of (bio)polymeric 3D-platforms have been introduced to resemble innate cell microenvironment. However, their intricate culture protocols restrain their applications in demanding high-throughput drug screening. To address the above concerns, in the present study, a hydrogel-based pseudo-3D substrate with imprinted cell features has been introduced. Image, graphical abstract [ABSTRACT FROM AUTHOR]

• Stem cells from the apical papilla (SCAPs) show increased spreading on hydrogel substrates with increased stiffness. • SCAPs align along micropatterned substrates acquiring morphologies reminiscent of odontoblasts. • Patterned substrate supported enhanced odontogenic differentiation when compared to non-patterned controls. An understanding of the extracellular matrix characteristics which stimulate and guide stem cell differentiation in the dental pulp is fundamental for the development of enhanced dental regenerative therapies. Our objectives, in this study, were to determine whether stem cells from the apical papilla (SCAP) responded to substrate stiffness, whether hydrogels providing micropatterned topographical cues stimulate SCAP self-alignment, and whether the resulting alignment could influence their differentiation towards an odontogenic lineage in-vitro. Experiments utilized gelatin methacryloyl (GelMA) hydrogels of increasing concentrations (5, 10 and 15%). We determined their compressive modulus via unconfined compression and analyzed cell spreading via F-actin/DAPI immunostaining. GelMA hydrogels were micropatterned using photolithography, in order to generate microgrooves and ridges of 60 and 120 μm, onto which SCAP were seeded and analyzed for self-alignment via fluorescence microscopy. Lastly, we analyzed the odontogenic differentiation of SCAP using alkaline phosphatase protein expression (ANOVA/Tukey α = 0.05). SCAP appeared to proliferate better on stiffer hydrogels. Both 60 and 120 μm micropatterned hydrogels guided the self-alignment of SCAP with no significant difference between them. Similarly, both 60 and 120 μm micropattern aligned cells promoted higher odontogenic differentiation than non-patterned controls. In summary, both substrate mechanics and geometry have a statistically significant influence on SCAP response, and may assist in the odontogenic differentiation of dental stem cells. These results may point toward the fabrication of cell-guiding scaffolds for regenerative endodontics, and may provide cues regarding the development of the pulp-dentin interface during tooth formation. [ABSTRACT FROM AUTHOR]

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. [Display omitted] • 45S5 Bioglass® catalyzed using citric-acid produced a larger average BET surface area and pore size than when catalyzed with nitric acid. • GelMA/Si-BG have significantly stronger mechanical properties than GelMA/BG. • EDS mapping showed higher Ca content in GelMA/Si-BG hydrogels compared to GelMA/BG hydrogels. • 5% BG & Si-BG GelMA hydrogels was able to induce the highest MSC differentiation into bone cells, with Si-BG showing higher mineralized nodules. [ABSTRACT FROM AUTHOR]

• Preparing a GelMA fibrous membrane by electrospining. • Using photo-crosslinking to manufacture a bi-layer GelMA/PEGDA fibrous membrane. • The bi-layer fibrous membrane has better mechanical and degradation properties. • The upper side of bi-layer membrane retard the proliferation of fibroblast. • The lower side of bi-layer membrane benefit the proliferation of osteoblast. A novel bi-layer gelatin methacrylamine (GelMA)/poly (ethylene glycol) diacrylate (PEGDA) fibrous membrane was fabricated by using electronspining and photo-crosslinking techniques. Compared with the crosslinked GelMA fibrous membrane, the crosslinked GelMA/PEGDA fibrous membrane have several times stronger mechanical properties and show a controllable degradation rate of more than 8 weeks in PBS or collagenase type I solution. The upper side of crosslinked GelMA/PEGDA fibrous membrane retard the proliferation of fibroblast and lower side benefit the proliferation of osteoblast. These properties are especially beneficial to guided bone regeneration (GBR) material used in periodontal surgery. Furthermore, the physical properties, degradation ratio, cell adhesion and proliferation can be fine-tuned by control the crosslinking time and PEGDA. [ABSTRACT FROM AUTHOR]

Abstract Myocardial infarction (MI) leads to a multi-phase reparative process at the site of damaged heart that ultimately results in the formation of non-conductive fibrous scar tissue. Despite the widespread use of electroconductive biomaterials to increase the physiological relevance of bioengineered cardiac tissues in vitro , there are still several limitations associated with engineering biocompatible scaffolds with appropriate mechanical properties and electroconductivity for cardiac tissue regeneration. Here, we introduce highly adhesive fibrous scaffolds engineered by electrospinning of gelatin methacryloyl (GelMA) followed by the conjugation of a choline-based bio-ionic liquid (Bio-IL) to develop conductive and adhesive cardiopatches. These GelMA/Bio-IL adhesive patches were optimized to exhibit mechanical and conductive properties similar to the native myocardium. Furthermore, the engineered patches strongly adhered to murine myocardium due to the formation of ionic bonding between the Bio-IL and native tissue, eliminating the need for suturing. Co-cultures of primary cardiomyocytes and cardiac fibroblasts grown on GelMA/Bio-IL patches exhibited comparatively better contractile profiles compared to pristine GelMA controls, as demonstrated by over-expression of the gap junction protein connexin 43. These cardiopatches could be used to provide mechanical support and restore electromechanical coupling at the site of MI to minimize cardiac remodeling and preserve normal cardiac function. [ABSTRACT FROM AUTHOR]

[Display omitted] • Mesh size/drug size affects diffusion ratio and is the potential direction for improvement. • GelMA fits various gel manufacturing methods including spraying technique. • Therapeutic agents and GelMA can be integrated by different interaction. • Polymers crosslinking in IPN in different forms render IPN enhanced properties. • GelMA fits many fields of biomedical engineering by specific processing process. Gelatin methacryloyl (GelMA), a kind of modified biomaterials with adjustable degradability from gelatin, can composite with various composite materials and therapeutic substances including cells through various physiochemical direct/indirect interactions to achieve treatment effect. Furthermore, owing to that the GelMA possesses photocrosslinking ability and excellent rheology properties, GelMA itself and its composite materials have the potential to be manufactured to function in diversified forms with 2D or 3D structures as required, such as thin films, microswimmers, biomimetic scaffolds, etc. Combined with the excellent biocompatibility from gelatin, GelMA composite hydrogels have been widely applied in biomedical applications. Unlike published reviews concentrating on a specific application fields or construction strategies of GelMA, this review summarized the multiscale construction strategies and available forms of GelMA complex hydrogel step by step based on its excellent physical and chemical properties. These strategies could be integrated to perform more desirable effects. In the end, the relevant biomedical applications in combination with the repair requirements of different tissues are briefly discussed. This systematic review can provide assistance for the rational application of GelMA in the field of biomedical. [ABSTRACT FROM AUTHOR]

Interfacial migration is central to multiple processes including morphogenesis and wound healing. However, the sensitivity of interfacial migration to properties of the interfacial microenvironment has not been adequately explored. Here, we address this question by tracking motility of 3T3 fibroblasts at the interface of two hydrogels. By sandwiching cells between two adhesive gels (composed of methacrylated gelatin) or between an adhesive and a non-adhesive gel (composed of gellan), we show that cells are more motile in case of the latter. By tuning the bulk stiffness of the gellan gel, we then show that motility is tuned in a stiffness-dependent manner. Fastest motility observed in case of the stiffest gel was associated with increased cell height, suggestive of stiffness-mediated cytoskeletal assembly. Inhibition of cell motility by contractile agonists and actin depolymerizing drugs is indicative of a mode of migration wherein cells combine contractile tractions exerted at their base and actin-based pushing forces on the top surface to propel themselves forward. Together, our results suggest that dorso-ventral adhesion anisotropy and stiffness can be collectively tuned to engineer interfacial migration. Statement of Significance It is increasingly understood that cells migrate in vivo through confining spaces which typically occur as pores in the matrix and through naturally occurring interfaces that exist between neighbouring ECM fibers, or between the stroma and the vasculature. Such interfaces are also created when treating wounds on the skin surface by covering the wounds with adhesives. How multiple cues impact interfacial migration has not been adequately addressed. By studying cell migratory behaviour at the interface of two hydrogel substrates, we identify adhesivity and stiffness as two critical factors that can be tuned to maximize cell migration. We foresee a potential use of this knowledge in the design of tissue adhesives for wound healing applications. [ABSTRACT FROM AUTHOR]

Heart failure is a critical and ultimate phase of cardiovascular ailment that leads to a considerable incidence of disability and mortality. Among various factors contributing to heart failure, myocardial infarction is one of the most frequent and significant causes, which is still difficult to manage effectively. An innovative therapeutic strategy, namely a 3D bio-printed cardiac patch, has recently emerged as a promising approach to substitute damaged cardiomyocytes in a localized infarct region. Nevertheless, the efficacy of this treatment primarily relies on the long-term viability of the transplanted cells. In this study, we aimed to construct acoustically sensitive nano oxygen carriers to improve cell survival inside the bio-3D printed patch. In this study, we initially created nanodroplets capable of phase transition triggered by ultrasound and integrated them into GelMA (Gelatin Methacryloyl) hydrogels, which were then employed for 3D bioprinting. After adding nanodroplets and ultrasonic irradiation, numerous pores appeared inside the hydrogel with improved permeability. We further encapsulated hemoglobin into nanodroplets (ND-Hb) to construct oxygen carriers. Results of in vitro experiments showed the highest cell survival within the patch of ND-Hb irradiated by the low-intensity pulsed ultrasound (LIPUS) group. The genomic analysis discovered that the increased survival of seeded cells within the patch might be related to the protection of mitochondrial function owing to the improved hypoxic state. Eventually, in vivo studies revealed that the LIPUS+ND-Hb group had improved cardiac function and increased revascularization after myocardial infarction. To summarize, our study successfully improved the permeability of the hydrogel in a non-invasive and efficient manner, facilitating the exchange of substances in the cardiac patch. Moreover, ultrasound-controlled oxygen release augmented the viability of the transplanted cells and expedited the repair of infarcted tissues. [ABSTRACT FROM AUTHOR]

Bone tissue is a natural composite, exhibiting complicated structures and unique mechanical/biological properties. With an attempt of mimicking the bone tissue, a novel inorganic-organic composite scaffolds (ZrO 2 -GM/SA) was designed and prepared via the vacuum infiltration method and the single/double cross-linking strategy by blending GelMA/alginate (GelMA/SA) interpenetrating polymeric network (IPN) into the porous zirconia (ZrO 2) scaffold. The structure, morphology, compressive strength, surface/interface properties, and biocompatibility of the ZrO 2 -GM/SA composite scaffolds were characterized to evaluate the performance of the composite scaffolds. Results showed that compared to ZrO 2 bare scaffolds with well-defined open pores, the composite scaffolds prepared by double cross-linking of GelMA hydrogel and sodium alginate (SA) presented a continuous, tunable and honeycomb-like microstructure. Meanwhile, GelMA/SA showed favorable and controllable water-uptake capacity, swelling property and degradability. After the introduction of IPN components, the mechanical strength of composite scaffolds was further improved. The compressive modulus of composite scaffolds was significantly higher than the bare ZrO 2 scaffolds. In addition, ZrO 2 -GM/SA composite scaffolds had highly biocompatibility and displayed a potent proliferation and osteogenesis of MC3T3-E1 pre-osteoblasts compared to bare ZrO 2 scaffolds and ZrO 2 -GelMA composite scaffolds. At the same time, ZrO 2 -10GM/1SA composite scaffold regenerated significantly greater bone than other groups in vivo. This study demonstrated that the proposed ZrO 2 -GM/SA composite scaffolds had great research and application potential in bone tissue engineering. [ABSTRACT FROM AUTHOR]

• GelMA/Pluronic F127 (permanent bath/fugitive ink) is a E3DP promising combination. • GelMA retains printed structure shape. • Pluronic F127 forms open channel with dimensions comparable to human vessels. • GelMA recapitulates soft tissues (e.g., adipose tissue) mechanical characteristics. • Developed 3D scaffold sustains embedded preadipocytes and endothelial cells growth. Hydrogels are widely investigated to develop 3D in vitro models for mimicking tissue microenvironment since their properties well match soft tissues ones. One concern is the lack of an adequate channel network, mimicking the tissue vascularization. Optimizing a vascularization strategy still remains challenging. We optimized and characterized a GelMA/Pluronic combination by using embedded 3D printing for the realization of a channel network in a GelMA scaffold. [ABSTRACT FROM AUTHOR]

Hydrogel-based bioadhesives have emerged as alternatives for sutureless wound closure, since they can mimic the composition and physicochemical properties of the extracellular matrix. However, they are often associated with poor mechanical properties, low adhesion to native tissues, and lack of antimicrobial properties. Herein, a new sprayable, elastic, and biocompatible composite hydrogel, with broad-spectrum antimicrobial activity, for the treatment of chronic wounds is reported. The composite hydrogels were engineered using two ECM-derived biopolymers, gelatin methacryloyl (GelMA) and methacryloyl-substituted recombinant human tropoelastin (MeTro). MeTro/GelMA composite hydrogel adhesives were formed via visible light-induced crosslinking. Additionally, the antimicrobial peptide Tet213 was conjugated to the hydrogels, instilling antimicrobial activity against Gram (+) and (−) bacteria. The physical properties (e.g. porosity, degradability, swellability, mechanical, and adhesive properties) of the engineered hydrogel could be fine-tuned by varying the ratio of MeTro/GelMA and the final polymer concentration. The hydrogels supported in vitro mammalian cellular growth in both two-dimensional and three dimensional cultures. The subcutaneous implantation of the hydrogels in rats confirmed their biocompatibility and biodegradation in vivo . The engineered MeTro/GelMA-Tet213 hydrogels can be used for sutureless wound closure strategies to prevent infection and promote healing of chronic wounds. [ABSTRACT FROM AUTHOR]

Biochemically modified proteins have attracted significant attention due to their widespread applications as biomaterials. For instance, chemically modified gelatin derivatives have been widely explored to develop hydrogels for tissue engineering and regenerative medicine applications. Among the reported methods, modification of gelatin with methacrylic anhydride (MA) stands out as a convenient and efficient strategy to introduce functional groups and form hydrogels via photopolymerization. Combining light-activation of modified gelatin with soft lithography has enabled the materialization of microfabricated hydrogels. So far, this gelatin derivative has been referred to in the literature as gelatin methacrylate, gelatin methacrylamide, or gelatin methacryloyl, with the same abbreviation of GelMA. Considering the complex composition of gelatin and the presence of different functional groups on the amino acid residues, both hydroxyl groups and amine groups can possibly react with methacrylic anhydride during functionalization of the protein. This can also apply to the modification of other proteins, such as recombinant human tropoelastin to form MA-modified tropoelastin (MeTro). Here, we employed analytical methods to quantitatively determine the amounts of methacrylate and methacrylamide groups in MA-modified gelatin and tropoelastin to better understand the reaction mechanism. By combining two chemical assays with instrumental techniques, such as proton nuclear magnetic resonance ( 1 H NMR) and liquid chromatography tandem-mass spectrometry (LC-MS/MS), our results indicated that while amine groups had higher reactivity than hydroxyl groups and resulted in a majority of methacrylamide groups, modification of proteins by MA could lead to the formation of both methacrylamide and methacrylate groups. It is therefore suggested that the standard terms for GelMA and MeTro should be defined as gelatin methacryloyl and methacryloyl-substituted tropoelastin, respectively, to remain consistent with the widespread abbreviations used in literature. [ABSTRACT FROM AUTHOR]

A major challenge for clinical use of skin substitutes is insufficient host tissue integration leading to loosening and partial necrosis of the implant. In this present study, a three-dimensional (3D) coculture system constructed using human umbilical cord mesenchymal stem cells (uc-MSCs) and umbilical vein endothelial cells (HUVECs) encapsulated in gelatin methacryloyl (GelMA) hydrogels was evaluated to determine the outcomes of cell-cell interactions in vitro and in vivo . The results revealed that GelMA hydrogels displayed minor cytotoxicity on both cell types. An uc-MSC:HUVEC ratio of 50:50 demonstrated the highest cell proliferation and expression of angiogenic markers. The supplement of basic fibroblast growth factors (bFGF) in coculture system further induced cell proliferation and gene expression in vitro . In vivo transplantation of this cocultured constructs efficiently enhanced the implant and host tissue integration. Additionally, the proliferation of keratinocytes was well maintained on GelMA hydrogels and the gene expression related to cell proliferation and differentiation was significantly increased in coculture system comparing to monoculture. Mechanistically, AKT signaling pathways were activated in cocultures. Our findings suggest that coculturing MSC and EC in GelMA hydrogels could be a promising approach to substantially improve the integration of exogenous skin substitutes and host tissues. Statement of Significance In this study, the co-culture of uc-MSCs and HUVECs in photocrosslinkable GelMA hydrogels significantly enhanced host tissue integration. Cell proliferation, ECM deposition and angiogenic genes expression were all substantially improved in vitro and the excellent host tissue integration into the implanted tissue was observed in vivo . When served as a dermal layer, the scaffold with co-cultured cells enhanced the proliferation and differentiation of keratinocytes. AKT signaling was proved to be involved in the regulation of cell survival and fate determination. This work demonstrated the importance of 3D cell co-culture to facilitate host tissue integration that can be a promising approach for long-term survival of skin substitutes. [ABSTRACT FROM AUTHOR]

Naturally-bioactive hydrogels like gelatin provide favorable properties for tissue-engineering but lack sufficient mechanical strength for use as implantable tissue engineering substrates. Complex fabrication or multi-component additives can improve material strength, but often compromises other properties. Studies have shown gelatin methacrylate (GelMA) as a bioactive hydrogel with diverse tissue growth applications. We hypothesize that, with suitable material modifications, GelMA could be employed for growth and implantation of tissue-engineered human corneal endothelial cell (HCEC) monolayer. Tissue-engineered HCEC monolayer could potentially be used to treat corneal blindness due to corneal endothelium dysfunction. Here, we exploited a sequential hybrid (physical followed by UV) crosslinking to create an improved material, named as GelMA+, with over 8-fold increase in mechanical strength as compared to regular GelMA. The presence of physical associations increased the subsequent UV-crosslinking efficiency resulting in robust materials able to withstand standard endothelium insertion surgical device loading. Favorable biodegradation kinetics were also measured in vitro and in vivo . We achieved hydrogels patterning with nano-scale resolution by use of oxygen impermeable stamps that overcome the limitations of PDMS based molding processes. Primary HCEC monolayers grown on GelMA+ carrier patterned with pillars of optimal dimension demonstrated improved zona-occludin-1 expression, higher cell density and cell size homogeneity, which are indications of functionally-superior transplantable monolayers. The hybrid crosslinking and fabrication approach offers potential utility for development of implantable tissue-engineered cell-carrier constructs with enhanced bio-functional properties. [ABSTRACT FROM AUTHOR]

With Gelma hydrogel microspheres as the base carriers, we designed and fabricated an injectable, macrophage-targeted, engineered micro/nano microsphere reprogramming system. This system could significantly prolong the release time of active ingredients and promote polarization of macrophages to the M2 phenotype, leading to the reactivation of bone marrow-derived mesenchymal stem cell osteogenic differentiation and human umbilical vein endothelial cell angiogenesis. [Display omitted] • An injectable, macrophage-targeted, engineered micro/nano microsphere reprogramming system was designed and fabricated. • Gelma@Lip@Pla prolonged the release time of active ingredients. • Gelma@Lip@Pla promoted the polarization of macrophages to the M2 phenotype. • Gelma@Lip@Pla reactivated osteogenic differentiation and angiogenesis. • Gelma@Lip@Pla can help treat bone defects and other immune-related diseases. Imbalance in the local immune microenvironment plays a vital role in the nonunion or delayed healing of bone defects. Additionally, there exists a cross-connection between material design of microfluidics and immune regulation. Therefore, we aimed to investigate whether epigenetic reprogramming of the microfluidic microsphere systems could regulate microenvironmental homeostasis in the acute phase of fracture and facilitate bone regeneration. To this end, we used Gelma hydrogel microspheres as the base carriers to design and fabricate an injectable, macrophage-targeted, engineered micro/nano microsphere reprogramming system (Gelma@Lip@Pla). Liposome (Lip) coating and macrophage targeting were improved by adding DSPE-PEG-CHO and phosphatidylserine (Pla). the surface of Gelma was coated with a lipid membrane, Schiff base, and hydrogel matrix network; the resultant macrophage-targeted liposomes activated AKT signaling in the local microenvironment by releasing the AKT signal activator dihydrocapsaicin and amplifiers (pcDNA3.1-AKT), triggering gene reprogramming in the local microenvironment and restarting the bone healing process. Compared with pcDNA3.1-AKT and dihydrocapsaicin-loaded liposomes (Lip@Pla) and pure Gelma hydrogel microgels (Gelma), the Gelma@Lip@Pla group significantly prolonged the release time of active ingredients. They also promoted the polarization of macrophages to the M2 phenotype, leading to the reactivation of bone marrow-derived mesenchymal stem cell osteogenic differentiation and human umbilical vein endothelial cell angiogenesis. Furthermore, in vivo experiments confirmed that local injection of Gelma@Lip@Pla could significantly accelerate the regeneration of a defective rat femoral condyle. Collectively, the Gelma@Lip@Pla microgel exhibits considerable potential as an extended delivery platform for treating bone defects and other immune-related diseases involving macrophages. [ABSTRACT FROM AUTHOR]

Gelatin methacryloyl (GelMA) hydrogels have been widely used for various biomedical applications due to their suitable biological properties and tunable physical characteristics. 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. 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 tissue engineering applications including engineering of bone, cartilage, cardiac, and vascular tissues, among others. Other applications of GelMA hydrogels, besides tissue engineering, include fundamental cell research, cell signaling, drug and gene delivery, and bio-sensing. [ABSTRACT FROM AUTHOR]

[Display omitted] • A multilayer strategy was applied to produce a Janus nanofibrous barrier readily. • The obtained barrier had favorable architecture, good permeability and stability. • The barrier exhibited excellent anti-fibroblast ability and lubrication efficiency. • Janus nanofibrous barrier showed great potential in anti-adhesion applications. Postoperative adhesions are very common complications after various abdominal surgeries. Although numerous strategies have been applied to reduce or prevent adhesion formation, the clinical efficacy is still far from satisfactory. In this study, a multilayer electrospun nanomaterial (GelMA-PLA/PGA/Lec), composed of lecithin-doped polylactide/polyglycolide nanofiber membrane (PLA/PGA/Lec) and gelatin methacrylate (GelMA) nanofiber hydrogel, was developed to act as a physical barrier for the first time. The resulting barrier exhibited unique micro/nanopore architecture, excellent permeability, and proper water content. Besides structural stability, the PLA/PGA/Lec layer endowed the barrier with good mechanical properties and anti-fibroblast adhesion. Meanwhile, the GelMA layer imparted an acid-neutralizing effect for alleviating acidic environment during degradation and a lubrication capacity for reduced interfacial friction as well as inhibited excessive fibroblast proliferation. These results indicated that the GelMA-PLA/PGA/Lec barrier with efficient lubrication and anti-fibroblast capability has potential application in minimizing postoperative adhesions. [ABSTRACT FROM AUTHOR]

The natural process of endochondral bone formation in the growing skeletal system is increasingly inspiring the field of bone tissue engineering. However, in order to create relevant-size bone grafts, a cell carrier is required that ensures a high diffusion rate and facilitates matrix formation, balanced by its degradation. Therefore, we set out to engineer endochondral bone in gelatin methacrylamide (GelMA) hydrogels with embedded multipotent stromal cells (MSCs) and cartilage-derived matrix (CDM) particles. CDM particles were found to stimulate the formation of a cartilage template by MSCs in the GelMA hydrogel in vitro . In a subcutaneous rat model, this template was subsequently remodeled into mineralized bone tissue, including bone-marrow cavities. The GelMA was almost fully degraded during this process. There was no significant difference in the degree of calcification in GelMA with or without CDM particles: 42.5 ± 2.5% vs. 39.5 ± 8.3% (mean ± standard deviation), respectively. Interestingly, in an osteochondral setting, the presence of chondrocytes in one half of the constructs fully impeded bone formation in the other half by MSCs. This work offers a new avenue for the engineering of relevant-size bone grafts, by the formation of endochondral bone within a degradable hydrogel. [ABSTRACT FROM AUTHOR]

[Display omitted] • A novel bioactive injectable GelMA / Sr-substituted xonotlite nanowires (GelMA/Sr-CSH) nanocomposite hydrogel was developed. • The integration of Sr-CSH nanowires improved the mechanical property of GelMA hydrogel. • The integration of Sr-CSH nanowires facilitated osteogenic differentiation of BMSCs via ERK/p38 signaling pathway. • The GelMA/ Sr-CSH nanocomposite hydrogel has great potential for in-situ bone regeneration. Gelatin-methacryloyl (GelMA) has received extensive attention in tissue engineering because of its low antigenicity, suitable biodegradability, and similarity to ECM. However, it is still a challenge to induce in-situ bone regeneration for bone defects due to the absence of osteogenic factors or other mineral ions. In this study, a novel injectable organic–inorganic nanocomposite GelMA hydrogel system doped Sr-substituted xonotlite (Sr-CSH) nanofibers was developed. The integration of Sr-CSH nanowires improved the mechanical property of GelMA hydrogels. In addition, GelMA/Sr-CSH hydrogels facilitated cell adhesion, proliferation, ALP activity and the expression of osteogenic genes (BSP, OPN and OCN) and angiogenesis genes (VEGF, ANG-1 and CD31) by activating the ERK/p38 signaling pathway in vitro. Moreover, in vivo results of in-situ bone regeneration in rat calvarial defects model demonstrated that the incorporation of Sr-CSH nanowires could apparently accelerate new bone formation of GelMA. Overall, the prepared injectable organic–inorganic nanocomposite of GelMA/Sr-CSH hydrogel system has great potential for in-situ bone regeneration of bone defect area. [ABSTRACT FROM AUTHOR]