Gelatin Methacryloyl-Riboflavin (GelMA-RF) Hydrogels for Bone Regeneration

Visible light photo-crosslinking of biomimetic gelatin-hyaluronic acid hydrogels for adipose tissue engineering

Tissue engineering (TE) of adipose tissue (AT) is a promising strategy that can provide 3D constructs to be used for in vitro modelling, overcoming the limitations of 2D cell cultures by closely replicating the complex breast tissue extracellular matrix (ECM), cell-cell, and cell-ECM interactions. However, the challenge in developing 3D constructs of AT resides in designing artificial matrices that can mimic the structural properties of native AT and support adipocytes biological functions. Herein, we developed photocrosslinkable hydrogels by employing gelatin methacrylate (GelMA) and hyaluronic acid methacrylate (HAMA) to mimic the collagenous and glycosaminoglycan components of AT microenvironment, respectively. The physico-mechanical properties of the hydrogels were tuned to target AT biomimetic properties by varying the hydrogel formulation (with or without hyaluronic acid), and the amount of photoinitiator (ruthenium/sodium persulfate) used to crosslink the hydrogels via visible light. The physical and mechanical properties of the developed hydrogels were tuned by varying the material formulation and the photoinitiator concentration. Preadipocytes were encapsulated inside the hydrogels and differentiated into mature adipocytes. Findings enlightened that HAMA addition in hybrid hydrogels boosted an increased lipid accumulation. The engineered biomimetic adipocyte-based constructs resulted promising as scaffolds or 3D in vitro models of AT.

Biodegradable Natural Hydrogels for Tissue Engineering, Controlled Release, and Soil Remediation

This article provides insights into hydrogels of the most promising biodegradable natural polymers and their mechanisms of degradation, highlighting the different possibilities of controlling hydrogel degradation rates. Since biodegradable hydrogels can be designed as scaffolding materials to mimic the physical and biochemical properties of natural tissues, these hydrogels have found widespread application in the field of tissue engineering and controlled release. In the same manner, their potential as water reservoirs, macro- and microelement carriers, or matrixes for the selective adsorption of pollutants make them excellent candidates for sustainable soil amendment solutions. Accordingly, this article summarizes the recent advances in natural biodegradable hydrogels in the fields of tissue engineering, controlled release, and soil remediation, emphasizing the new opportunities that degradability and its tunability offer for the design and applicability of hydrogels.

Development of gelatin-methacryloyl composite carriers for bone morphogenetic Protein-2 delivery: A potential strategy for spinal fusion

To reduce the risk of nonunion after spinal fusion surgery, the in situ transplantation of bone marrow mesenchymal stem cells (BMSCs) induced toward osteogenic differentiation by bone morphogenetic protein-2 (BMP2) has been proven effective. However, the current biological agents used for transplantation have limitations, such as a short half-life and low bioavailability. To address this, our study utilized a safe and effective gelatin-methacryloyl (GelMA) as a carrier for BMP2. In vitro, experiments were conducted to observe the ability of this composite vehicle to induce osteogenic differentiation of BMSCs. The results showed that the GelMA hydrogel, with its critical properties and controlled release performance of BMP2, exhibited a slow release of BMP2 over 30 days. Moreover, the GelMA hydrogel not only enhanced the proliferation activity of BMSCs but also significantly promoted their osteogenic differentiation ability, surpassing the BMP2 effects. To investigate the potential of the GelMA-BMP2 composite vehicle, a rabbit model was employed to explore its ability to induce in situ intervertebral fusion by BMSCs. Transplantation experiments in rabbits demonstrated the effective induction of intervertebral bone fusion by the GelMA-BMP2-BMSC composite vehicle. In conclusion, the GelMA-BMP2-BMSC composite vehicle shows promising prospects in preclinical translational therapy for spinal intervertebral fusion. It addresses the limitations of current biological agents and offers a controlled release of BMP2, enhancing the proliferation and osteogenic differentiation of BMSCs.

Light-based 3D bioprinting technology applied to repair and regeneration of different tissues: A rational proposal for biomedical applications

3D bioprinting technology, a subset of 3D printing technology, is currently witnessing widespread utilization in tissue repair and regeneration endeavors. In particular, light-based 3D bioprinting technology has garnered significant interest and favor. Central to its successful implementation lies the judicious selection of photosensitive polymers. Moreover, by fine-tuning parameters such as light irradiation time, choice of photoinitiators and crosslinkers, and their concentrations, the properties of the scaffolds can be tailored to suit the specific requirements of the targeted tissue repair sites. In this comprehensive review, we provide an overview of commonly utilized bio-inks suitable for light-based 3D bioprinting, delving into the distinctive characteristics of each material. Furthermore, we delineate strategies for bio-ink selection tailored to diverse repair locations, alongside methods for optimizing printing parameters. Ultimately, we present a coherent synthesis aimed at enhancing the practical application of light-based 3D bioprinting technology in tissue engineering, while also addressing current challenges and future prospects.

PSO/SDF-1 composite hydrogel promotes osteogenic differentiation of PDLSCs and bone regeneration in periodontitis rats

Periodontitis is an inflammatory disease characterized by the destruction of periodontal tissues, and the promotion of bone tissue regeneration is the key to curing periodontitis. Psoralen is the main component of Psoralea corylifolia Linn, and has multiple biological effects, including anti-osteoporosis and osteogenesis. We constructed a novel hydrogel loaded with psoralen (PSO) and stromal cell-derived factor-1 (SDF-1) for direct endogenous cell homing. This study aimed to evaluate the synergistic effects of PSO/SDF-1 on periodontal bone regeneration in patients with periodontitis. The results of CCK8, alkaline phosphatase (ALP) activity assay, and Alizarin Red staining showed that PSO/SDF-1 combination treatment promoted cell proliferation, chemotaxis ability, and ALP activity of PDLSCs. qRT-PCR and western blotting showed that the expression levels of alkaline phosphatase (ALP), dwarf-associated transcription factor 2 (RUNX2), and osteocalcin (OCN) gene were upregulated. Rat periodontal models were established to observe the effect of local application of the composite hydrogel on bone regeneration. These results proved that the PSO/SDF-1 combination treatment significantly promoted new bone formation. The immunohistochemical (IHC) results confirmed the elevated expression of ALP, RUNX2, and OCN osteogenic genes. PSO/SDF-1 composite hydrogel can synergistically regulate the biological function and promote periodontal bone formation. Thus, this study provides a novel strategy for periodontal bone regeneration.

Advanced PEG-tyramine biomaterial ink for precision engineering of perfusable and flexible small-diameter vascular constructs via coaxial printing

Vascularization is crucial for providing nutrients and oxygen to cells while removing waste. Despite advances in 3D-bioprinting, the fabrication of structures with void spaces and channels remains challenging. This study presents a novel approach to create robust yet flexible and permeable small (600-1300 μm) artificial vessels in a single processing step using 3D coaxial extrusion printing of a biomaterial ink, based on tyramine-modified polyethylene glycol (PEG-Tyr). We combined the gelatin biocompatibility/activity, robustness of PEG-Tyr and alginate with the shear-thinning properties of methylcellulose (MC) in a new biomaterial ink for the fabrication of bioinspired vessels. Chemical characterization using NMR and FTIR spectroscopy confirmed the successful modification of PEG with Tyr and rheological characterization indicated that the addition of PEG-Tyr decreased the viscosity of the ink. Enzyme-mediated crosslinking of PEG-Tyr allowed the formation of covalent crosslinks within the hydrogel chains, ensuring its stability. PEG-Tyr units improved the mechanical properties of the material, resulting in stretchable and elastic constructs without compromising cell viability and adhesion. The printed vessel structures displayed uniform wall thickness, shape retention, improved elasticity, permeability, and colonization by endothelial-derived - EA.hy926 cells. The chorioallantoic membrane (CAM) and in vivo assays demonstrated the hydrogel's ability to support neoangiogenesis. The hydrogel material with PEG-Tyr modification holds promise for vascular tissue engineering applications, providing a flexible, biocompatible, and functional platform for the fabrication of vascular structures.

Three-Dimensional-Printed Spherical Hollow Structural Scaffolds for Guiding Critical-Sized Bone Regeneration

The treatment of bone tissue defects continues to be a complex medical issue. Recently, three-dimensional (3D)-printed scaffold technology for bone tissue engineering (BTE) has emerged as an important therapeutic approach for bone defect repair. Despite the potential of BTE scaffolds to contribute to long-term bone reconstruction, there are certain challenges associated with it including the impediment of bone growth within the scaffolds and vascular infiltration. These difficulties can be resolved by using scaffold structural modification strategies that can effectively guide bone regeneration. This study involved the preparation of biphasic calcium phosphate spherical hollow structural scaffolds (SHSS) with varying pore sizes using 3D printing (photopolymerized via digital light processing). The chemical compositions, microscopic morphologies, mechanical properties, biocompatibilities, osteogenic properties, and impact on repairing critical-sized bone defects of SHSS were assessed through characterization analyses, in vitro cytological assays, and in vivo biological experiments. The results revealed the biomimetic properties of SHSS and their favorable biocompatibility. The scaffolds stimulated cell adhesion, proliferation, differentiation, and migration and facilitated the expression of osteogenic genes and proteins, including Col-1, OCN, and OPN. Furthermore, they could effectively repair a critical-sized bone defect in a rabbit femoral condyle by establishing an osteogenic platform and guiding bone regeneration in the defect region. This innovative strategy presents a novel therapeutic approach for assessing critical-sized bone defects.

Leveraging the Recent Advancements in GelMA Scaffolds for Bone Tissue Engineering: An Assessment of Challenges and Opportunities

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.

3D culture of alginate-hyaluronic acid hydrogel supports the stemness of human mesenchymal stem cells

The three-dimensional (3D) cell culture system is being employed more frequently to investigate cell engineering and tissue repair due to its close mimicry of in vivo microenvironments. In this study, we developed natural biomaterials, including hyaluronic acid, alginate, and gelatin, to mimic the creation of a 3D human mesenchymal stem cell (hMSC) extracellular environment and selected hydrogels with high proliferation capacity for 3D MSC culture. Human mesenchymal stem cells were encapsulated within hydrogels, and an investigation was conducted into the effects on cell viability and proliferation, stemness properties, and telomere activity compared to the 2D monolayer culture. Hydrogel characterization, cell proliferation, Live/Dead cell viability assay, gene expression, telomere relative length, and MSC stemness-related proteins by immunofluorescence staining were examined. The results showed that 3D alginate-hyaluronic acid (AL-HA) hydrogels increased cell proliferation, and the cells were grown as cellular spheroids within hydrogels and presented a high survival rate of 77.36% during the culture period of 14 days. Furthermore, the 3D alginate-hyaluronic acid (AL-HA) hydrogels increased the expression of stemness-related genes (OCT-4, NANOG, SOX2, and SIRT1), tissue growth and development genes (YAP and TAZ), and cell proliferation gene (Ki67) after culture for 14 days. Moreover, the telomere activity of the 3D MSCs was enhanced, as indicated by the upregulation of the human telomerase reverse transcriptase gene (hTERT) and the relative telomere length (T/S ratio) compared to the 2D monolayer culture. Altogether, these data suggest that the 3D alginate-hyaluronic acid (AL-HA) hydrogels could serve as a promising material for maintaining stem cell properties and might be a suitable carrier for tissue engineering proposals.

Riboflavin mediated UV crosslinking of chitosan-gelatin cryogels for loading of hydrophobic bioactive compounds

Chitosan-gelatin cryogels with good loading capacity of hydrophobic compounds were successfully obtained by UV-induced crosslinking. Using riboflavin as photoinitiator was a suitable alternative to classical carbodiimide crosslinking in obtaining carrier matrices for bioactive hydrophobic compounds. Chitosan had a double role, acting both as a base polymer for the hydrogel network and as co-initiator in riboflavin photo-crosslinking. This co-initiator role of chitosan is due to its electron donor capacity, being well known as a Lewis base type macromolecule. The rheological behaviour of the chitosan-gelatin hydrogel precursor solutions was greatly influenced by riboflavin addition as well as by UV irradiation. As a consequence, the temperature of the sol-gel transition during cooling decreased to 25.5 °C. Compared with classical carbodiimide crosslinking, UV irradiation lead to gels with increased network stability, enhanced elastic behaviour, higher structural strength and almost total stress recovery yield (99 %), the latter indicating self-healing capacity. The cryogels manifested pH responsive swelling, this being highest at close to neutral pH of 7.4. Although hydrophilic in nature, the chitosan-gelatin cryogels crosslinked under the combined effect of riboflavin and UV exposure possess the necessary chemical functionality and morphology that allowed successful embedding of hydrophobic clove essential oil. This was loaded by immersion or fumigation and imparted antioxidant activity to the polymeric matrix.

Injectable hydrogels doped with PDA nanoparticles for photothermal bacterial inhibition and rapid wound healing in vitro

The difficulty of wound healing due to skin defects has been a great challenge due to the complex inflammatory microenvironment. Delayed wound healing severely affects the quality of life of patients and represents a significant economic burden for public health systems worldwide. Therefore, there is an urgent need for the development of novel wound dressings that can efficiently resist drug-resistant bacteria and have superior wound repair capabilities in clinical applications. In this study, we designed an adhesive antimicrobial hydrogel dressing (GMH) based on methacrylic-anhydride-modified gelatin and oxidized hyaluronic acid formed by Schiff base and UV-induced double cross-linking for infected wound repair. By inserting PDA nanoparticles into the hydrogel (GMH/PDA), the hydrogel has the capability of photothermal conversion and exhibits good photothermal antimicrobial properties under near-infrared (NIR) light irradiation, which helps to reduce the inflammatory response and avoid bacterial infections during the wound healing process. In addition, GMH/PDA hydrogel exhibits excellent injectability, allowing the hydrogel dressings to be adapted to complex wound surfaces, making them promising candidates for wound therapy. In conclusion, the multifunctional injectable GMH/PDA hydrogel possesses high antimicrobial efficiency, antioxidant properties and good biocompatibility, making them promising candidates for the treatment of infected skin wounds.

UV-polymerizable methacrylated gelatin (GelMA)-based hydrogel containing tannic acids for wound healing

Gelatin-based photopolymerizable methacrylate hydrogel (GelMA) is a promising biomaterial for in situ drug delivery, while aqueous extract of Punica granatum (AEPG) peel fruit rich in gallic acid and ellagic acid is used to improve wound healing. The aim of this study was to develop and analyze the healing properties of GelMA containing AEPG, gallic acid, or ellagic acid in a rodent model. GelMA hydrogels containing 5% AEPG (GelMA-PG), 1.6% gallic acid (GelMA-GA), or 2.1% ellagic acid (GelMA-EA) were produced and their mechanical properties, enzymatic degradation, and thermogravimetric profile determined. Wound closure rates, healing histological grading, and immunohistochemical counts of myofibroblasts were assessed over time. The swelling of hydrogels varied between 50 and 90%, and GelMA exhibited a higher swelling than the other groups. The GPG samples showed higher compression and Young's moduli than GelMA, GGA, and GAE. All samples degraded around 95% in 48 h. GPG and GGA significantly accelerated wound closure, improved collagenization, increased histological grading, and hastened myofibroblast differentiation in comparison to the control, GelMA, and GEA. GelMA containing AEPG (GPG) improved wound healing, and although gallic acid is the major responsible for such biological activity, a potential synergic effect played by other polyphenols present in the extract is evident.

From Free Tissue Transfer to Hydrogels: A Brief Review of the Application of the Periosteum in Bone Regeneration

The periosteum is a thin layer of connective tissue covering bone. It is an essential component for bone development and fracture healing. There has been considerable research exploring the application of the periosteum in bone regeneration since the 19th century. An increasing number of studies are focusing on periosteal progenitor cells found within the periosteum and the use of hydrogels as scaffold materials for periosteum engineering and guided bone development. Here, we provide an overview of the research investigating the use of the periosteum for bone repair, with consideration given to the anatomy and function of the periosteum, the importance of the cambium layer, the culture of periosteal progenitor cells, periosteum-induced ossification, periosteal perfusion, periosteum engineering, scaffold vascularization, and hydrogel-based synthetic periostea.

A Novel Injectable Piezoelectric Hydrogel for Periodontal Disease Treatment

Periodontal disease is a multifactorial, bacterially induced inflammatory condition characterized by the progressive destruction of periodontal tissues. The successful nonsurgical treatment of periodontitis requires multifunctional technologies offering antibacterial therapies and promotion of bone regeneration simultaneously. For the first time, in this study, an injectable piezoelectric hydrogel (PiezoGEL) was developed after combining gelatin methacryloyl (GelMA) with biocompatible piezoelectric fillers of barium titanate (BTO) that produce electrical charges when stimulated by biomechanical vibrations (e.g., mastication, movements). We harnessed the benefits of hydrogels (injectable, light curable, conforms to pocket spaces, biocompatible) with the bioactive effects of piezoelectric charges. A thorough biomaterial characterization confirmed piezoelectric fillers' successful integration with the hydrogel, photopolymerizability, injectability for clinical use, and electrical charge generation to enable bioactive effects (antibacterial and bone tissue regeneration). PiezoGEL showed significant reductions in pathogenic biofilm biomass (∼41%), metabolic activity (∼75%), and the number of viable cells (∼2-3 log) compared to hydrogels without BTO fillers in vitro. Molecular analysis related the antibacterial effects to be associated with reduced cell adhesion (downregulation of porP and fimA) and increased oxidative stress (upregulation of oxyR) genes. Moreover, PiezoGEL significantly enhanced bone marrow stem cell (BMSC) viability and osteogenic differentiation by upregulating RUNX2, COL1A1, and ALP. In vivo, PiezoGEL effectively reduced periodontal inflammation and increased bone tissue regeneration compared to control groups in a mice model. Findings from this study suggest PiezoGEL to be a promising and novel therapeutic candidate for the treatment of periodontal disease nonsurgically.

GelMA-based bioactive hydrogel scaffolds with multiple bone defect repair functions: therapeutic strategies and recent advances

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. 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).

Evaluation of How Methacrylate Gelatin Hydrogel Loaded with Ximenia americana L. Extract (Steam Bark) Effects Bone Repair Activity Using Rats as Models

The use of bioactive materials, such as Ximenia americana L., to stimulate the bone repair process has already been studied; however, the synergistic effects of its association with light emitting diode (LED) have not been reported. The present work aims to evaluate the effect of its stem bark extract incorporated into methacrylate gelatin hydrogel (GelMA) on the bone repair process using pure hydrogel and hydrogel associated with LED therapy. For this purpose, the GelMA hydrogel loaded with Ximenia americana L. extract (steam bark) was produced, characterized and applied in animal experiments. The tests were performed using 50 male Wistar rats (divided into 5 groups) submitted to an induced tibia diaphyseal fracture. The therapy effects were verified for a period of 15 and 30 days of treatment using histological analysis and Raman spectroscopy. After 15 days of induced lesion/treatment, the new bone formation was significantly higher in the GXG (GelMA + X. americana L.) group compared to the control group (p < 0.0001). After 30 days, a statistically significant difference was observed when comparing the GXLEDG (GelMA + X. americana L. + LED) and the control group (p < 0.0001), the GXG and the control group (p < 0.001), and when comparing the GG, GXG (p < 0.005) and GXLEDG (p < 0.001) groups. The results shows that the Ximenia americana L. stem extract incorporated into GelMA hydrogel associated with LED therapy is a potentiator for animal bone repair.

[Latest Findings on Hydrogel Drug Delivery Systems in the Treatment of Periodontitis]

Hydrogel drug delivery systems possess unique structures and properties and hence can be injected and retained in the periodontal pocket for slow and controlled release of medications with antibacterial, anti-inflammatory, and periodontal tissue regeneration-promotional effects. Due to their safety, practicability, and effectiveness, they show great potential in the treatment of periodontitis. In this paper, we gave an overview of hydrogel drug delivery systems in the treatment of periodontitis, summing up the classification and forms of the drugs delivered and the strengths and weaknesses of common types of hydrogel matrixes. In addition, we discussed properties required for hydrogel drug delivery systems applicable in the treatment of periodontitis, including a certain level of viscosity, suitable degradation cycle, and temperature sensitivity. Finally, we summarized the stimulus responsiveness types of hydrogel drug delivery systems applicable in the treatment of periodontitis, including pH-responsiveness, enzyme-responsiveness, reactive oxygen species-responsiveness, light-responsiveness, and sugar-responsiveness. In the future, researchers should make further investigation into the clinical efficacy of hydrogel drug delivery systems and promote their translation into clinical applications. Additionally, hydrogel drug delivery systems carrying biologic drugs could be further investigated to promote advancement in the field of periodontal tissue regeneration. Furthermore, the response sources, realization strategies, and safe preparation methods of smart hydrogel drug delivery systems should also be further clarified and explored to achieve drug delivery of better efficiency and safety. In addition to drug delivery, hydrogel matrixes with medicinal values also show great promises.

Dual-Crosslinking of Gelatin-Based Hydrogels: Promising Compositions for a 3D Printed Organotypic Bone Model

Gelatin-based hydrogels have emerged as a popular scaffold material for tissue engineering applications. The introduction of variable crosslinking methods has shown promise for fabricating stable cell-laden scaffolds. In this work, we examine promising composite biopolymer-based inks for extrusion-based 3D bioprinting, using a dual crosslinking approach. A combination of carefully selected printable hydrogel ink compositions and the use of photoinduced covalent and ionic crosslinking mechanisms allows for the fabrication of scaffolds of high accuracy and low cytotoxicity, resulting in unimpeded cell proliferation, extracellular matrix deposition, and mineralization. Three selected bioink compositions were characterized and the respective cell-laden scaffolds were bioprinted. Temporal stability, morphology, swelling, and mechanical properties of the scaffolds were thoroughly studied and the biocompatibility of the constructs was assessed using rat mesenchymal stem cells while focusing on osteogenesis. Experimental results showed that the composition of 1% alginate, 4% gelatin, and 5% (w/v) gelatine methacrylate, was found to be optimal among the examined, with shape fidelity of 88%, large cell spreading area and cell viability at around 100% after 14 days. The large pore diameters that exceed 100 µm, and highly interconnected scaffold morphology, make these hydrogels extremely potent in bone tissue engineering and bone organoid fabrication.

Optimizing phenol-modified hyaluronic acid for designing shape-maintaining biofabricated hydrogel scaffolds in soft tissue engineering

In this study, we developed a well-printable biomaterial ink for 3D printing of shape-maintaining hydrogel scaffolds. The hydrogel base comprised tyramine-modified hyaluronic acid (HA-Tyr) and gelatin methacrylate (GelMA) and was dually cross-linked. Using the Box-Behnken design, we explored how varying the ink composition affected fiber formation and shape preservation. By adjusting the polymer ratios, we produced a stable hydrogel with varying responses, from a viscous liquid to a thick gel, and optimized 3D scaffolds that were structurally stable both during and after printing, offering precision and flexibility. Our ink exhibited shear-thinning behavior and high swelling capacity, as well as ECM-like characteristics and biocompatibility, making it an ideal candidate for soft tissues matrices with storage modulus of around 300 Pa. Animal trials and CAM assays confirmed its biocompatibility and integration with host tissue.

Osteogenesis promotion by injectable methacryloylated gelatin containing psoralen and its bacteriostatic properties

The treatment of periodontitis focuses on controlling the progression of inflammation, reducing plaque accumulation, and promoting bone tissue reconstruction. Among them, the reconstruction of irregular bone resorption caused by periodontitis is a long-standing challenge. At present, the local drug treatment of periodontitis is mainly anti-inflammatory and antibacterial drugs. In this study, psoralen (Pso), a Chinese herbal medicine with anti-inflammatory, antibacterial, and osteogenic effects, was selected for the local treatment of periodontitis. Meanwhile, an injectable methacrylate gelatin (GelMA) platform loading with Pso was constructed. Pso-GelMA had the properties of fluidity, light cohesion, self-healing, and slow release, which could be better used in the deep and narrow structure of the periodontal pocket, and greatly increased the effectiveness of local drug delivery. The pore size of Gelma hydrogel did not change after loading Pso by SEM. In vitro, Pso-GelMA effectively upregulated the expression of osteogenic genes and proteins, increased alkaline phosphatase activity, promoted the mineralisation of rat bone marrow mesenchymal stem cells (BMSCs) extracellular matrix, and had significant antibacterial effects on Staphylococcus aureus and Fusobacterium nucleatum. Therefore, Pso-GelMA has immense promise in the adjuvant treatment of periodontitis.

Tissue-Engineered Injectable Gelatin-Methacryloyl Hydrogel-Based Adjunctive Therapy for Intervertebral Disc Degeneration

Gelatin-methacryloyl (GelMA) hydrogels are photosensitive with good biocompatibility and adjustable mechanical properties. The GelMA hydrogel composite system is a prospective therapeutic material based on a tissue engineering platform for treating intervertebral disc (IVD) degeneration (IVDD). The potential application value of the GelMA hydrogel composite system in the treatment of IVDD mainly includes three aspects: first, optimization of the current clinical treatment methods, including conservative treatment and surgical treatment; second, regeneration of IVD cells to reverse or repair IVDD; and finally, IVDD instead of injury plays a biomechanical role. In this paper, we summarized and analyzed the preparation of GelMA hydrogels and their excellent biological characteristics as carriers and comprehensively demonstrated the research status and prospects of GelMA hydrogel composite systems in IVDD treatment. In addition, the challenges facing the application of GelMA hydrogel composite systems and the progress of research on new hydrogels modified by GelMA hydrogels are presented. Hopefully, this study will provide theoretical guidance for the future application of GelMA hydrogel composite systems in IVDD.

Printable hyaluronic acid hydrogel functionalized with yeast-derived peptide for skin wound healing

Targeted delivery of bioactive agents, growth factors, and drugs to skin wounds is a growing trend in biomaterials development for wound healing. This study presents a printable hyaluronic acid (HA) based hydrogel to deliver yeast-derived ACE-inhibitory peptide of VLSTSFPPW (VW-9) to the wound site. We first conjugated tyramine (Ty) on the carboxyl groups of the HA to form a phenol-functionalized HA (HA-Ty); then, the carboxylic acid groups of HA-Ty were aminated with ethylenediamine (HA-Ty-NH2). The primary amine groups of the HA-Ty-NH2 could then react with the carboxylic acids of the peptide. The hydrogel was then 3D printed and crosslinked with visible light. The modification of HA was confirmed by 1H NMR and FTIR. The swelling capacity of the conjugated hydrogels was 1.5-fold higher compared to the HA-Ty-NH2 hydrogel. The conjugated peptide did not affect on rheological properties and morphology of the hydrogels. The 3T3-L1 fibroblast cells seeded on the peptide-modified hydrogels exhibited higher viability than the hydrogels without the peptide, indicating that the peptide-enriched hydrogels may have the potential for wound healing applications.

Engineered cell-overexpression of circular RNA hybrid hydrogels promotes healing of calvarial defects

Craniomaxillofacial bone defects seriously affect the physical and mental health of patients. Bone marrow mesenchymal stem cells (BMSCs) are "gold standard" cells used for bone repair. However, the collection of BMSCs is invasive, and the osteogenic capacity is limited with age. Human umbilical cord mesenchymal stem cells (hUCMSCs) are promising alternative seed cells for bone tissue engineering. Our group previously used high-throughput sequencing technology and bioinformatics methods to detect circ-CTTN (hsa-circ_0003376) molecules, which may play an essential role in the osteogenic differentiation of hUCMSCs. In this study, osteogenic induction in vitro showed that the overexpressing circ-CTTN (OE group) exhibits a more pronounced osteogenic phenotype. The levels of osteogenesis-related genes in the OE group were highly expressed. The gelatin-methacrylate (GelMA) hydrogel possessed excellent biocompatibility and was used to load hUCMSCs. In the rat calvarial defect, the OE group presented a larger bone healing volume and denser bone trabecular distribution than other groups. So far, the overexpression of circ-CTTN could enhance the osteogenic differentiation of hUCMSCs and accelerate bone reconstruction. Our research could provide a new strategy and a strong theoretical basis for promoting hUCMSC clinical application in bone tissue engineering.

A "T.E.S.T." hydrogel bioadhesive assisted by corneal cross-linking for in situ sutureless corneal repair

Corneal transplantation is an effective clinical treatment for corneal diseases, which, however, is limited by donor corneas. It is of great clinical value to develop bioadhesive corneal patches with functions of "Transparency" and "Epithelium & Stroma generation", as well as "Suturelessness" and "Toughness". To simultaneously meet the "T.E.S.T." requirements, a light-curable hydrogel is designed based on methacryloylated gelatin (GelMA), Pluronic F127 diacrylate (F127DA) & Aldehyded Pluronic F127 (AF127) co-assembled bi-functional micelles and collagen type I (COL I), combined with clinically applied corneal cross-linking (CXL) technology for repairing damaged cornea. The patch formed after 5 min of ultraviolet irradiation possesses transparent, highly tough, and strongly bio-adhesive performance. Multiple cross-linking makes the patch withstand deformation near 600% and exhibit a burst pressure larger than 400 mmHg, significantly higher than normal intraocular pressure (10-21 mmHg). Besides, the slower degradation than GelMA-F127DA&AF127 hydrogel without COL I makes hydrogel patch stable on stromal beds in vivo, supporting the regrowth of corneal epithelium and stroma. The hydrogel patch can replace deep corneal stromal defects and well bio-integrate into the corneal tissue in rabbit models within 4 weeks, showing great potential in surgeries for keratoconus and other corneal diseases by combining with CXL.

Enzymatically-Crosslinked Gelatin Hydrogels with Nanostructured Architecture and Self-Healing Performance for Potential Use as Wound Dressings

Development of natural protein-based hydrogels with self-healing performance and tunable physical properties has attracted increased attention owing to their wide potential not only in the pharmaceutical field, but also in wounds management. This work reports the development of a versatile hydrogel based on enzymatically-crosslinked gelatin and nanogels loaded with amoxicillin (Amox), an antibiotic used in wound infections. The transglutaminase (TGase)-crosslinked hydrogels and encapsulating nanogels were formed rapidly through enzymatic crosslinking and self-assembly interactions in mild conditions. The nanogels formed through the self-assemble of maleoyl-chitosan (MAC5) and polyaspartic acid (PAS) may have positive influence on the self-healing capacity and drug distribution within the hydrogel network through the interactions established between gelatin and gel-like nanocarriers. The physicochemical properties of the enzymatically-crosslinked hydrogels, such as internal structure, swelling and degradation behavior, were studied. In addition, the Amox release studies indicated a rapid release when the pH of the medium decreased, which represents a favorable characteristic for use in the healing of infected wounds. It was further observed through the in vitro and in vivo biocompatibility assays that the optimized scaffolds have great potential to be used as wound dressings.

Application of gelatin methacryloyl/minocycline-chitosan-nanoparticles composite hydrogel for the treatment of periodontitis

OBJECTIVES

This study aimed to investigate the feasibility of gelatin methacryloyl (GelMA) hydrogel loa-ded with minocycline-chitosan-nanoparticles (MCN) for the treatment of periodontitis in vitro and vivo.

METHODS

MCN were synthesized by ionic gel method. GelMA/MCN composite hydrogels were prepared by compounding MCN with GelMA hydrogel. The materials were characterized by transmission electron microscope, scanning electron microscopy, and Fourier transform infrared spectroscopy. The degradation behavior and drug release rates of hydrogels were evaluated. The antibacterial activity of GelMA/MCN hydrogel against Porphyromonas gingivalis was detected, and the minimum antibacterial concentration was determined. Biocompatibility and osteogenic experiments were conducted under a simulated periodontitis environment. A rat model of periodontitis was constructed to observe the therapeutic effects of GelMA/MCN hydrogel.

RESULTS

MCN was successfully synthesized with a particle size of about 80 nm, while the structures of GelMA/MCN had no significant differences from GelMA. MCN and GelMA/MCN released minocycline slowly and steadily. Bacterial growth was completely inhibited when the MCN concentration was higher than or equal to 0.2 mg·mL-1. GelMA/MCN hydrogels exhibited good biocompatibility at effective antimicrobial concentrations under the simulated periodontitis environment with the enzyme. The in vivo results showed that GelMA/MCN prevented the progression of periodontitis and promoted the repair of bone defects.

CONCLUSIONS

GelMA/MCN composite hydrogel can release minocycline slowly and steadily and has good antibacterial activity and biocompatibility to promote the repair of periodontitis bone defects.

Green Chemistry for Crosslinking Biopolymers: Recent Advances in Riboflavin-Mediated Photochemistry

Riboflavin (RF), which is also known as vitamin B2, is a water-soluble vitamin. RF is a nontoxic and biocompatible natural substance. It absorbs light (at wavelengths of 380 and 450 nm) in the presence of oxygen to form reactive singlet oxygen (¹O₂). The generated singlet oxygen acts as a photoinitiator to induce the oxidation of biomolecules, such as amino acids, proteins, and nucleotides, or to initiate chemical reactions, such as the thiol-ene reaction and crosslinking of tyramine and furfuryl groups. In this review, we focus on the chemical mechanism and utilization of the photochemistry of RF, such as protein crosslinking and hydrogel formation. Currently, the crosslinking method using RF as a photoinitiator is actively employed in ophthalmic clinics. However, a significant broadening is expected in its range of applications, such as in tissue engineering and drug delivery.

Osteogenic and anti-inflammatory effect of the multifunctional bionic hydrogel scaffold loaded with aspirin and nano-hydroxyapatite

Although tissue engineering offered new approaches to repair bone defects, it remains a great challenge to create a bone-friendly microenvironment and rebuild bone tissue rapidly by a scaffold with a bionic structure. In this study, a multifunctional structurally optimized hydrogel scaffold was designed by integrating polyvinyl alcohol (PVA), gelatin (Gel), and sodium alginate (SA) with aspirin (ASA) and nano-hydroxyapatite (nHAP). The fabrication procedure is through a dual-crosslinking process. The chemical constitution, crystal structure, microstructure, porosity, mechanical strength, swelling and degradation property, and drug-release behavior of the hydrogel scaffold were analyzed. Multi-hydrogen bonds, electrostatic interactions, and strong "egg-shell" structure contributed to the multi-network microstructure, bone tissue-matched properties, and desirable drug-release function of the hydrogel scaffold. The excellent performance in improving cell viability, promoting cell osteogenic differentiation, and regulating the inflammatory microenvironment of the prepared hydrogel scaffold was verified using mouse pre-osteoblasts (MC3T3-E1) cells. And the synergistic osteogenic and anti-inflammatory functions of aspirin and nano-hydroxyapatite were also verified. This study provided valuable insights into the design, fabrication, and biological potential of multifunctional bone tissue engineering materials with the premise of constructing a bone-friendly microenvironment.

Properties and Printability of the Synthesized Hydrogel Based on GelMA

Gelatin methacryloyl (GelMA) has recently attracted increasing attention. Unlike other hydrogels, it allows for the adjustment of the mechanical properties using such factors as degree of functionalization, concentration, and photocrosslinking parameters. In this study, GelMA with a high degree of substitution (82.75 ± 7.09%) was synthesized, and its suitability for extrusion printing, cytocompatibility, and biocompatibility was studied. Satisfactory printing quality was demonstrated with the 15% concentration hydrogel. The high degree of functionalization led to a decrease in the ability of human adipose-derived stem cells (ADSCs) to adhere to the GelMA surface. During the first 3 days after sowing, proliferation was observed. Degradation in animals after subcutaneous implantation was slowed down.

GelMA, Click-Chemistry Gelatin and Bioprinted Polyethylene Glycol-Based Hydrogels as 3D Ex Vivo Drug Testing Platforms for Patient-Derived Breast Cancer Organoids

3D organoid model technologies have led to the development of innovative tools for cancer precision medicine. Yet, the gold standard culture system (Matrigel®) lacks the ability for extensive biophysical manipulation needed to model various cancer microenvironments and has inherent batch-to-batch variability. Tunable hydrogel matrices provide enhanced capability for drug testing in breast cancer (BCa), by better mimicking key physicochemical characteristics of this disease’s extracellular matrix. Here, we encapsulated patient-derived breast cancer cells in bioprinted polyethylene glycol-derived hydrogels (PEG), functionalized with adhesion peptides (RGD, GFOGER and DYIGSR) and gelatin-derived hydrogels (gelatin methacryloyl; GelMA and thiolated-gelatin crosslinked with PEG-4MAL; GelSH). Within ranges of BCa stiffnesses (1−6 kPa), GelMA, GelSH and PEG-based hydrogels successfully supported the growth and organoid formation of HR+,−/HER2+,− primary cancer cells for at least 2−3 weeks, with superior organoid formation within the GelSH biomaterial (up to 268% growth after 15 days). BCa organoids responded to doxorubicin, EP31670 and paclitaxel treatments with increased IC50 concentrations on organoids compared to 2D cultures, and highest IC50 for organoids in GelSH. Cell viability after doxorubicin treatment (1 µM) remained >2-fold higher in the 3D gels compared to 2D and doxorubicin/paclitaxel (both 5 µM) were ~2.75−3-fold less potent in GelSH compared to PEG hydrogels. The data demonstrate the potential of hydrogel matrices as easy-to-use and effective preclinical tools for therapy assessment in patient-derived breast cancer organoids.

Visible light-curable methacrylated glycol chitosan hydrogel patches for prenatal closure of fetal myelomeningocele

In this study, we prepared visible light-curable methacrylated glycol chitosan (MGC) hydrogel patches for the prenatal treatment of fetal myelomeningocele (MMC) and investigated their feasibility using a retinoic acid-induced fetal MMC rat model. 4, 5, and 6 w/v% of MGC were selected as candidate precursor solutions, and photo-cured for 20 s, because the resulting hydrogels were found to possess concentration dependent tunable mechanical properties and structural morphologies. Moreover, these materials exhibited no foreign body reactions with good adhesive properties in animal studies. The inflammation scoring assessment in vivo exhibited the absence of foreign body reactions in MGC hydrogel treated lesion. The complete epithelial coverage of MMC was made with using 6 w/v% MGC hydrogel followed by well-organized granulation along with noticeable decrease of abortion rate and wound size that highlight the therapeutic potential for the prenatal treatment of fetal MMC.

Seamless and early gap healing of osteochondral defects by autologous mosaicplasty combined with bioactive supramolecular nanofiber-enabled gelatin methacryloyl (BSN-GelMA) hydrogel

Autologous mosaicplasty is a common approach used to treat osteochondral defects in clinical practice. Gap integration between host and transplanted plugs requires bone tissue reservation and hyaline cartilage regeneration without uneven surface, graft necrosis and sclerosis. However, poor gap integration is a serious concern, which eventually leads to deterioration of joint function. To deal with such complications, this study has developed a strategy to effectively enhance integration of the gap region following mosaicplasty by applying injectable bioactive supramolecular nanofiber-enabled gelatin methacryloyl (GelMA) hydrogel (BSN-GelMA). A rabbit osteochondral defect model demonstrated that BSN-GelMA achieved seamless osteochondral healing in the gap region between plugs of osteochondral defects following mosaicplasty, as early as six weeks. Moreover, the International Cartilage Repair Society score, histology score, glycosaminoglycan content, subchondral bone volume, and collagen II expression were observed to be the highest in the gap region of BSN-GelMA treated group. This improved outcome was due to bio-interactive materials, which acted as tissue fillers to bridge the gap, prevent cartilage degeneration, and promote graft survival and migration of bone marrow mesenchymal stem cells by releasing bioactive supramolecular nanofibers from the GelMA hydrogel. This study provides a powerful and applicable approach to improve gap integration after autologous mosaicplasty. It is also a promising off-the-shelf bioactive material for cell-free in situ tissue regeneration.

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A novel strategy that can effectively enhance post-mosaicplasty interstitial integration was developed.

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The bioactive supramolecular nanofibers (BSN) exhibited comparable bioactivity to insulin-like growth factor-1 (IGF-1).

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The BSN-GelMA hydrogel is a promising off-the-shelf bioactive material for cell-free in situ tissue regeneration.

New strategies for the treatment of intervertebral disc degeneration: cell, exosome, gene, and tissue engineering

Low back pain (LBP) caused by intervertebral disc (IVD) generation (IVDD) has always been an important problem that cannot be ignored. Traditional therapies have many deep-rooted and intractable complications that promote their treatment mode transfer to new therapies. This article mainly summarizes the shortcomings of traditional treatment methods and analyzes the research status and future development direction of IVDD treatment. We outlined the most promising IVDD therapies, including cell, exosome, gene, and tissue engineering therapy, especially tissue engineering therapy, which runs through the whole process of other therapies. In addition, the article focuses on the cellular, animal, and preclinical challenges faced by each therapeutic approach, as well as their respective advantages and disadvantages, to provide better ideas for relieving the IVDD patients' pain through new treatment methods.

Construction of a decellularized spinal cord matrix/GelMA composite scaffold and its effects on neuronal differentiation of neural stem cells

Spinal cord injury (SCI) leads to severe loss of motor and sensory functions, and the rehabilitation of SCI is a worldwide problem. Tissue-engineered scaffolds offer new hope for SCI patients, while the newly developed materials encountered a challenge in modeling the microenvironment around the lesion site. We constructed a new composite scaffold by mixing decellularized spinal cord extracellular matrix (dECM) with gelatin methacryloyl (GelMA). The dECM, as a natural biological material, retained a large number of proteins and growth factors related to neurogenesis. GelMA was a photopolymerizable material, harbored a polymer network structure, soft texture, certain shape and plenty of water. The viability, proliferation, and differentiation of neural stem cells (NSCs) on the composite scaffold were evaluated by cell count kit-8 (CCK8), Live/Dead assay, phalloidin staining, 5-Ethynyl-2'-deoxyurdine (EdU), immunofluorescence staining and western blot. The Live/Dead assay, phalloidin staining, EdU, and CCK8 assay showed that the composite scaffold had good biocompatibility and provided better support for proliferation of NSCs. Results of immunocytochemistry and western blot showed that the composite scaffolds promoted the specific differentiation of NSCs into neuron cells. Together, this dECM/GelMA composite scaffold can be used as a cell culture coating, the isolated NSCs seeded on the surface of composite scaffold expressed neuronal markers and assumed neuronal morphology. Our work provided a new method that would be widely used in tissue engineering of SCI.

Advances of Hydrogel Therapy in Periodontal Regeneration-A Materials Perspective Review

Hydrogel, a functional polymer material, has emerged as a promising technology for therapies for periodontal diseases. It has the potential to mimic the extracellular matrix and provide suitable attachment sites and growth environments for periodontal cells, with high biocompatibility, water retention, and slow release. In this paper, we have summarized the main components of hydrogel in periodontal tissue regeneration and have discussed the primary construction strategies of hydrogels as a reference for future work. Hydrogels provide an ideal microenvironment for cells and play a significant role in periodontal tissue engineering. The development of intelligent and multifunctional hydrogels for periodontal tissue regeneration is essential for future research.

Translating Material Science into Bone Regenerative Medicine Applications: State-of-The Art Methods and Protocols

In the last 20 years, bone regenerative research has experienced exponential growth thanks to the discovery of new nanomaterials and improved manufacturing technologies that have emerged in the biomedical field. This revolution demands standardization of methods employed for biomaterials characterization in order to achieve comparable, interoperable, and reproducible results. The exploited methods for characterization span from biophysics and biochemical techniques, including microscopy and spectroscopy, functional assays for biological properties, and molecular profiling. This review aims to provide scholars with a rapid handbook collecting multidisciplinary methods for bone substitute R&D and validation, getting sources from an up-to-date and comprehensive examination of the scientific landscape.

Gelatin Methacryloyl Hydrogels for Musculoskeletal Tissue Regeneration

Musculoskeletal disorders are a significant burden on the global economy and public health. Hydrogels have significant potential for enhancing the repair of damaged and injured musculoskeletal tissues as cell or drug delivery systems. Hydrogels have unique physicochemical properties which make them promising platforms for controlling cell functions. Gelatin methacryloyl (GelMA) hydrogel in particular has been extensively investigated as a promising biomaterial due to its tuneable and beneficial properties and has been widely used in different biomedical applications. In this review, a detailed overview of GelMA synthesis, hydrogel design and applications in regenerative medicine is provided. After summarising recent progress in hydrogels more broadly, we highlight recent advances of GelMA hydrogels in the emerging fields of musculoskeletal drug delivery, involving therapeutic drugs (e.g., growth factors, antimicrobial molecules, immunomodulatory drugs and cells), delivery approaches (e.g., single-, dual-release system), and material design (e.g., addition of organic or inorganic materials, 3D printing). The review concludes with future perspectives and associated challenges for developing local drug delivery for musculoskeletal applications.

Controlled Release of Epidermal Growth Factor from Furfuryl-Gelatin Hydrogel Using in Situ Visible Light-Induced Crosslinking and Its Effects on Fibroblasts Proliferation and Migration

Hydrogels are widely used in tissue engineering as materials that regulate cell proliferation, migration, and differentiation. They also act as promising biomaterials that can provide a variety of stimuli by influencing the surrounding microenvironment, which can be achieved by modulating their mechanical properties, thereby aiding soluble factor delivery. Here, we developed a gelatin-based injectable hydrogel that has controllable mechanical properties and demonstrates sustained drug release without the need for invasive surgery. Gelatin was modified with furfuryl groups, and riboflavin phosphate was used as a photoinitiator to crosslink the hydrogel using visible light. A hydrogel–with a storage modulus in the range of 0.2–15 kPa was formed by maintaining the concentration of furfuryl-gelatin within 10–30% w/v. Consequently, their mechanical properties can be tailored for their applications. The furfuryl-gelatin hydrogel was loaded with maleimide-modified epidermal growth factor (EGF) as a model drug to achieve a controlled-release system. The sustained release of maleimide-EGF due to gelatin hydrogel matrix degradation was observed. Cell proliferation and scratch assays were performed to verify its effect on fibroblasts. When EGF was physically entrapped in the hydrogel matrix, the released EGF considerably affected cell proliferation and scratch closure of fibroblasts at the beginning of the culture. By contrast, maleimide-EGF was released sustainably and steadily and affected cell proliferation and scratch closure after the initial stage. We demonstrated that the release of soluble factors could be controlled by modulating the mechanical properties. Thus, the injectable hydrogel formed by in situ visible light-induced crosslinking could be a promising biomaterial for tissue engineering and biomedical therapeutics.

Photocurable GelMA Adhesives for Corneal Perforations

The current treatments for the management of corneal and scleral perforations include sutures and adhesives. While sutures are invasive, induce astigmatism and carry a risk of infection, cyanoacrylate glues are toxic, proinflammatory and form an opaque and rough surface that precludes vision. Consequently, the clinical need for a fast curing and strong tissue adhesive with minimised cytotoxicity and host inflammation remains unmet. In this paper, we engineer a gelatine methacryloyl (GelMA) adhesive that can be crosslinked in situ within 2 min using UV or visible light and a riboflavin (RF)/sodium persulfate (SPS) system. Optical coherence tomography (OCT) images demonstrated that the flowable GelMA adhesive could completely fill corneal wounds and restore the ocular curvature by forming a smooth contour on the ocular surface. Further, ex vivo studies in porcine eyes showed that GelMA bioadhesives exhibited burst pressures that were comparable to cyanoacrylates (49 ± 9 kPa), with the hydrogels exhibiting a transmittance (90%), water content (85%) and storage modulus (5 kPa) similar to the human cornea. Finally, using human dermal fibroblasts, we showed that our GelMA adhesive was non-toxic and could effectively support cell adhesion and proliferation. Taken together, the adhesive’s performance, injectability and ease of administration, together with gelatin’s availability and cost-effectiveness, make it a potential stromal filler or sealant for corneal and conjunctival applications.

Controlled Release of Epigenetically-Enhanced Extracellular Vesicles from a GelMA/Nanoclay Composite Hydrogel to Promote Bone Repair

Extracellular vesicles (EVs) have garnered growing attention as promising acellular tools for bone repair. Although EVs' potential for bone regeneration has been shown, issues associated with their therapeutic potency and short half-life in vivo hinders their clinical utility. Epigenetic reprogramming with the histone deacetylase inhibitor Trichostatin A (TSA) has been reported to promote the osteoinductive potency of osteoblast-derived EVs. Gelatin methacryloyl (GelMA) hydrogels functionalised with the synthetic nanoclay laponite (LAP) have been shown to effectively bind, stabilise, and improve the retention of bioactive factors. This study investigated the potential of utilising a GelMA-LAP hydrogel to improve local retention and control delivery of epigenetically enhanced osteoblast-derived EVs as a novel bone repair strategy. LAP was found to elicit a dose-dependent increase in GelMA compressive modulus and shear-thinning properties. Incorporation of the nanoclay was also found to enhance shape fidelity when 3D printed compared to LAP-free gels. Interestingly, GelMA hydrogels containing LAP displayed increased mineralisation capacity (1.41-fold) (p ≤ 0.01) over 14 days. EV release kinetics from these nanocomposite systems were also strongly influenced by LAP concentration with significantly more vesicles being released from GelMA constructs as detected by a CD63 ELISA (p ≤ 0.001). EVs derived from TSA-treated osteoblasts (TSA-EVs) enhanced proliferation (1.09-fold), migration (1.83-fold), histone acetylation (1.32-fold) and mineralisation (1.87-fold) of human bone marrow stromal cells (hBMSCs) when released from the GelMA-LAP hydrogel compared to the untreated EV gels (p ≤ 0.01). Importantly, the TSA-EV functionalised GelMA-LAP hydrogel significantly promoted encapsulated hBMSCs extracellular matrix collagen production (≥1.3-fold) and mineralisation (≥1.78-fold) in a dose-dependent manner compared to untreated EV constructs (p ≤ 0.001). Taken together, these findings demonstrate the potential of combining epigenetically enhanced osteoblast-derived EVs with a nanocomposite photocurable hydrogel to promote the therapeutic efficacy of acellular vesicle approaches for bone regeneration.

From the Matrix to the Nucleus and Back: Mechanobiology in the Light of Health, Pathologies, and Regeneration of Oral Periodontal Tissues

Among oral tissues, the periodontium is permanently subjected to mechanical forces resulting from chewing, mastication, or orthodontic appliances. Molecularly, these movements induce a series of subsequent signaling processes, which are embedded in the biological concept of cellular mechanotransduction (MT). Cell and tissue structures, ranging from the extracellular matrix (ECM) to the plasma membrane, the cytosol and the nucleus, are involved in MT. Dysregulation of the diverse, fine-tuned interaction of molecular players responsible for transmitting biophysical environmental information into the cell's inner milieu can lead to and promote serious diseases, such as periodontitis or oral squamous cell carcinoma (OSCC). Therefore, periodontal integrity and regeneration is highly dependent on the proper integration and regulation of mechanobiological signals in the context of cell behavior. Recent experimental findings have increased the understanding of classical cellular mechanosensing mechanisms by both integrating exogenic factors such as bacterial gingipain proteases and newly discovered cell-inherent functions of mechanoresponsive co-transcriptional regulators such as the Yes-associated protein 1 (YAP1) or the nuclear cytoskeleton. Regarding periodontal MT research, this review offers insights into the current trends and open aspects. Concerning oral regenerative medicine or weakening of periodontal tissue diseases, perspectives on future applications of mechanobiological principles are discussed.