Synthesis and Properties of Gelatin Methacryloyl (GelMA) Hydrogels and Their Recent Applications in Load-Bearing Tissue

Strategies of functionalized GelMA-based bioinks for bone regeneration: Recent advances and future perspectives

Gelatin methacryloyl (GelMA) hydrogels is a widely used bioink because of its good biological properties and tunable physicochemical properties, which has been widely used in a variety of tissue engineering and tissue regeneration. However, pure GelMA is limited by the weak mechanical strength and the lack of continuous osteogenic induction environment, which is difficult to meet the needs of bone repair. Moreover, GelMA hydrogels are unable to respond to complex stimuli and therefore are unable to adapt to physiological and pathological microenvironments. This review focused on the functionalization strategies of GelMA hydrogel based bioinks for bone regeneration. The synthesis process of GelMA hydrogel was described in details, and various functional methods to meet the requirements of bone regeneration, including mechanical strength, porosity, vascularization, osteogenic differentiation, and immunoregulation for patient specific repair, etc. In addition, the response strategies of smart GelMA-based bioinks to external physical stimulation and internal pathological microenvironment stimulation, as well as the functionalization strategies of GelMA hydrogel to achieve both disease treatment and bone regeneration in the presence of various common diseases (such as inflammation, infection, tumor) are also briefly reviewed. Finally, we emphasized the current challenges and possible exploration directions of GelMA-based bioinks for bone regeneration.

Harnessing the dental cells derived from human induced pluripotent stem cells for hard tissue engineering

INTRODUCTION

Most mineralized tissues in our body are present in bones and teeth. Human induced pluripotent stem cells (hiPSCs) are promising candidates for cell therapy to help regenerate bone defects and teeth loss. The extracellular matrix (ECM) is a non-cellular structure secreted by cells. Studies on the dynamic microenvironment of ECM are necessary for stem cell-based therapies.

OBJECTIVES

We aim to optimize an effective protocol for hiPSC differentiation into dental cells without utilizing animal-derived factors or cell feeders that can be applied to humans and to mineralize differentiated dental cells into hard tissues.

METHODS

For the differentiation of both dental epithelial cells (DECs) and dental mesenchymal cells (DMCs) from hiPSCs, an embryoid body (EB) was formed from hiPSCs. hiPSC were differentiated into neural crest cells with an induction medium utilized in our previous study, and hiPSC-derived DECs were differentiated with a BMP-modulated customized medium. hiPSC-dental cells were then characterized, analyzed, and validated with transcriptomic analysis, western blotting, and RT-qPCR. To form mineralized tissues, hiPSC-derived DECs were recombined with hiPSC-derived DMCs encapsulated in various biomaterials, including gelatin methacryloyl (GelMA), collagen, and agar matrix.

RESULTS

These hiPSC-derived dental cells are highly osteogenic and chondro-osteogenic in photocrosslinkable GelMA hydrogel and collagen type I microenvironments. Furthermore, hiPSC-derived dental cells in agar gel matrix induced the formation of a bioengineered tooth.

CONCLUSION

Our study provides an approach for applying hiPSCs for hard tissue regeneration, including tooth and bone. This study has immense potential to provide a novel technology for bioengineering organs for various regenerative therapies.

A multicrosslinked network composite hydrogel scaffold based on DLP photocuring printing for nasal cartilage repair

Natural hydrogels are widely employed in tissue engineering and have excellent biodegradability and biocompatibility. Unfortunately, the utilization of such hydrogels in the field of three-dimensional (3D) printing nasal cartilage is constrained by their subpar mechanical characteristics. In this study, we provide a multicrosslinked network hybrid ink made of photocurable gelatin, hyaluronic acid, and acrylamide (AM). The ink may be processed into intricate 3D hydrogel structures with good biocompatibility and high stiffness properties using 3D printing technology based on digital light processing (DLP), including intricate shapes resembling noses. By varying the AM content, the mechanical behavior and biocompatibility of the hydrogels can be adjusted. In comparison to the gelatin methacryloyl (GelMA)/hyaluronic acid methacryloyl (HAMA) hydrogel, adding AM considerably enhances the hydrogel's mechanical properties while also enhancing printing quality. Meanwhile, the biocompatibility of the multicrosslinked network hydrogels and the development of cartilage were assessed using neonatal Sprague-Dawley (SD) rat chondrocytes (CChons). Cells sown on the hydrogels considerably multiplied after 7 days of culture and kept up the expression of particular proteins. Together, our findings point to GelMA/HAMA/polyacrylamide (PAM) hydrogel as a potential material for nasal cartilage restoration. The photocuring multicrosslinked network ink composed of appropriate proportions of GelMA/HAMA/PAM is very suitable for DLP 3D printing and will play an important role in the construction of nasal cartilage, ear cartilage, articular cartilage, and other tissues and organs in the future. Notably, previous studies have not explored the application of 3D-printed GelMA/HAMA/PAM hydrogels for nasal cartilage regeneration.

Nanoliposomes Permeability in a Microfluidic Drug Delivery Platform across a 3D Hydrogel

Nanoliposomes are nano-sized vesicles that can be used as drug delivery carriers with the ability to encapsulate both hydrophobic and hydrophilic compounds. Moreover, their lipid compositions facilitate their internalization by cells. However, the interaction between nanoliposomes and the membrane barrier of the human body is not well-known. If cellular tests and animal testing offer a solution, their lack of physiological relevance and ethical concerns make them unsuitable to properly mimic human body complexity. Microfluidics, which allows the environment of the human body to be imitated in a controlled way, can fulfil this role. However, existing models are missing the presence of something that would mimic a basal membrane, often consisting of a simple cell layer on a polymer membrane. In this study, we investigated the diffusion of nanoliposomes in a microfluidic system and found the optimal parameters to maximize their diffusion. Then, we incorporated a custom made GelMA with a controlled degree of substitution and studied the passage of fluorescently labeled nanoliposomes through this barrier. Our results show that highly substituted GelMA was more porous than lower substitution GelMA. Overall, our work lays the foundation for the incorporation of a hydrogel mimicking a basal membrane on a drug delivery microfluidic platform.

GelMA micropattern enhances cardiomyocyte organization, maturation, and contraction via contact guidance

Cardiac tissue engineering has emerged as a promising approach for restoring the functionality of damaged cardiac tissues following myocardial infarction. To effectively replicate the native anisotropic structure of cardiac tissues in vitro, this study focused on the fabrication of micropatterned gelatin methacryloyl hydrogels with varying geometric parameters. These substrates were evaluated for their ability to guide induced pluripotent stem cell-derived cardiomyocytes (CMs). The findings demonstrate that the mechanical properties of this hydrogel closely resemble those of native cardiac tissues, and it exhibits high fidelity in micropattern fabrication. Micropatterned hydrogel substrates lead to enhanced organization, maturation, and contraction of CMs. A microgroove with 20-μm-width and 20-μm-spacing was identified as the optimal configuration for maximizing the contact guidance effect, supported by analyses of nuclear orientation and F-actin organization. Furthermore, this specific micropattern design was found to promote CMs' maturation, as evidenced by increased expression of connexin 43 and vinculin, along with extended sarcomere length. It also enhanced CMs' contraction, resulting in larger contractile amplitudes and greater contractile motion anisotropy. In conclusion, these results underscore the significant benefits of optimizing micropatterned gelatin methacryloyl for improving CMs' organization, maturation, and contraction. This valuable insight paves the way for the development of highly organized and functionally mature cardiac tissues in vitro.

Screening of MMP-13 Inhibitors Using a GelMA-Alginate Interpenetrating Network Hydrogel-Based Model Mimicking Cytokine-Induced Key Features of Osteoarthritis In Vitro

Osteoarthritis (OA) is a chronic joint disease characterized by irreversible cartilage degradation. Current clinical treatment options lack effective pharmaceutical interventions targeting the disease's root causes. MMP (matrix metalloproteinase) inhibitors represent a new approach to slowing OA progression by addressing cartilage degradation mechanisms. However, very few drugs within this class are in preclinical or clinical trial phases. Hydrogel-based 3D in vitro models have shown promise as preclinical testing platforms due to their resemblance to native extracellular matrix (ECM), abundant availability, and ease of use. Metalloproteinase-13 (MMP-13) is thought to be a major contributor to the degradation of articular cartilage in OA by aggressively breaking down type II collagen. This study focused on testing MMP-13 inhibitors using a GelMA-alginate hydrogel-based OA model induced by cytokines interleukin-1 beta (IL-1β) and tumor necrosis factor alpha (TNF-α). The results demonstrate a significant inhibition of type II collagen breakdown by measuring C2C concentration using ELISA after treatment with MMP-13 inhibitors. However, inconsistencies in human cartilage explant samples led to inconclusive results. Nonetheless, the study highlights the GelMA-alginate hydrogel-based OA model as an alternative to human-sourced cartilage explants for in vitro drug screening.

Live cell pool and rare cell isolation using Enrich TROVO system

Although several technologies have been developed to isolate cells of interest from a heterogenous sample, clogging and impaired cell viability limit such isolation. We have developed the Enrich TROVO system as a novel, nonfluidic technology to sort live cells. The TROVO system combines imaging-based cell selection and photo-crosslinking of (gelatin methacrylate) gelMA-hydrogel to capture cells. After capture, cells are released by enzymatic digestion of the hydrogel and then retrieved for downstream analysis or further cell culturing. The system can capture cells with a recovery rate of 48% while maintaining 90% viability. Moreover, TROVO can enrich rare cells 506-fold with 93% efficiency using single step isolation from a 1:104 cell mixture, and can also capture one target cell from 1 million cells, reaching an enrichment ratio of 9128. In addition, 100% purity and 49% recovery rate can be achieved by a following negative isolation process. Compared to existing technologies, the TROVO system is clog-resistant, highly biocompatible, and can process a wide range of sample sizes.

Incorporation of Finasteride-Loaded Microspheres into Personalized Microneedle for Sustained Transdermal Delivery

Although finasteride (FNS) tablets are considered the most effective drug for the treatment of androgenetic alopecia (AGA), their clinical applications are limited due to the associated side effects including decreased libido, breast enlargement, and liver dysfunction. In this study, we have developed a personalized microneedle (PMN) with a double-layer structure that incorporates FNS-loaded microspheres (MPs) to accommodate irregular skin surfaces. This design enables the sustained release of FNS, thereby reducing potential side effects. The needle body was synthesized with high-strength hyaluronic acid (HA) as the base material substrate. The backing layer utilized methacrylate gelatin (GelMA) with specific toughness, enabling PMN to penetrate the skin while adapting to various skin environments. The length of PMN needles (10 × 10) was approximately 600 μm, with the bottom of the needles measuring about 330 μm × 330 μm. The distance between adjacent tips was around 600 μm, allowing the drug to penetrate the stratum corneum of the skin. The results of the drug release investigation indicated the sustained and regulated release of FNS from PMN, as compared to that of pure FNS and FNS-MPs. Further, the cytotoxicity assay demonstrates that PMS displays good cytocompatibility. Altogether, this mode of administration has immense potential for the development of delivery of other drugs, as well as in the medical field.

The MnO2/GelMA Composite Hydrogels Improve the ROS Microenvironment of Annulus Fibrosus Cells by Promoting the Antioxidant and Autophagy through the SIRT1/NRF2 Pathway

Intervertebral disc degeneration (IVDD) is a worldwide disease that causes low back pain and reduces quality of life. Biotherapeutic strategies based on tissue engineering alternatives, such as intervertebral disc scaffolds, supplemented by drug-targeted therapy have brought new hope for IVDD. In this study, to explore the role and mechanism of MnO2/GelMA composite hydrogels in alleviating IVDD, we prepared composite hydrogels with MnO2 and methacrylate gelatin (GelMA) and characterized them using compression testing and transmission electron microscopy (TEM). Annulus fibrosus cells (AFCs) were cultured in the composite hydrogels to verify biocompatibility by live/dead and cytoskeleton staining. Cell viability assays and a reactive oxygen species (ROS) probe were used to analyze the protective effect of the composite hydrogels under oxidative damage. To explore the mechanism of improving the microenvironment, we detected the expression levels of antioxidant and autophagy-related genes and proteins by qPCR and Western blotting. We found that the MnO2/GelMA composite hydrogels exhibited excellent biocompatibility and a porous structure, which promoted cell proliferation. The addition of MnO2 nanoparticles to GelMA cleared ROS in AFCs and induced the expression of antioxidant and cellular autophagy through the common SIRT1/NRF2 pathway. Therefore, the MnO2/GelMA composite hydrogels, which can improve the disc microenvironment through scavenging intracellular ROS and resisting oxidative damage, have great application prospects in the treatment of IVDD.

Enhanced Vascular-like Network Formation of Encapsulated HUVECs and ADSCs Coculture in Growth Factors Conjugated GelMA Hydrogels

Tissue engineering primarily aimed to alleviate the insufficiency of organ donations worldwide. Nonetheless, the survival of the engineered tissue is often compromised due to the complexity of the natural organ architectures, especially the vascular system inside the organ, which allows food-waste transfer. Thus, vascularization within the engineered tissue is of paramount importance. A critical aspect of this endeavor is the ability to replicate the intricacies of the extracellular matrix and promote the formation of functional vascular networks within engineered constructs. In this study, human adipose-derived stem cells (hADSCs) and human umbilical vein endothelial cells (HUVECs) were cocultured in different types of gelatin methacrylate (GelMA). In brief, pro-angiogenic signaling growth factors (GFs), vascular endothelial growth factor (VEGF165) and basic fibroblast growth factor (bFGF), were conjugated onto GelMA via an EDC/NHS coupling reaction. The GelMA hydrogels conjugated with VEGF165 (GelMA@VEGF165) and bFGF (GelMA@bFGF) showed marginal changes in the chemical and physical characteristics of the GelMA hydrogels. Moreover, the conjugation of these growth factors demonstrated improved cell viability and cell proliferation within the hydrogel construct. Additionally, vascular-like network formation was observed predominantly on GelMA@GrowthFactor (GelMA@GF) hydrogels, particularly on GelMA@bFGF. This study suggests that growth factor-conjugated GelMA hydrogels would be a promising biomaterial for 3D vascular tissue engineering.

A Composite Hydrogel Functionalized by Borosilicate Bioactive Glasses and VEGF for Critical-Size Bone Regeneration

Critical-size bone defects pose a formidable challenge in clinical treatment, prompting extensive research efforts to address this problem. In this study, an inorganic-organic multifunctional composite hydrogel denoted as PLG-g-TA/VEGF/Sr-BGNPs is developed, engineered for the synergistic management of bone defects. The composite hydrogel demonstrated the capacity for mineralization, hydroxyapatite formation, and gradual release of essential functional ions and vascular endothelial growth factor (VEGF) and also maintained an alkaline microenvironment. The composite hydrogel promoted the proliferation and osteogenic differentiation of rat bone marrow mesenchymal stem cells (rBMSCs), as indicated by increased expression of osteogenesis-related genes and proteins in vitro. Moreover, the composite hydrogel significantly enhanced the tube-forming capability of human umbilical vein endothelial cells (HUVECs) and effectively inhibited the process of osteoblastic differentiation of nuclear factor kappa-B ligand (RANKL)-induced Raw264.7 cells and osteoclast bone resorption. After the implantation of the composite hydrogel into rat cranial bone defects, the expression of osteogenic and angiogenic biomarkers increased, substantiating its efficacy in promoting bone defect repair in vivo. The commendable attributes of the multifunctional composite hydrogel underscore its pivotal role in expediting hydrogel-associated bone growth and repairing critical bone defects, positioning it as a promising adjuvant therapy candidate for large-segment bone defects.

Establishment of human hematopoietic organoids for evaluation of hematopoietic injury and regeneration effect

BACKGROUND

Human hematopoietic organoids have a wide application value for modeling human bone marrow diseases, such as acute hematopoietic radiation injury. However, the manufacturing of human hematopoietic organoids is an unaddressed challenge because of the complexity of hematopoietic tissues.

METHODS

To manufacture hematopoietic organoids, we obtained CD34+ hematopoietic stem and progenitor cells (HSPCs) from human embryonic stem cells (hESCs) using stepwise induction and immunomagnetic bead-sorting. We then mixed these CD34+ HSPCs with niche-related cells in Gelatin-methacryloyl (GelMA) to form a three-dimensional (3D) hematopoietic organoid. Additionally, we investigated the effects of radiation damage and response to granulocyte colony-stimulating factor (G-CSF) in hematopoietic organoids.

RESULTS

The GelMA hydrogel maintained the undifferentiated state of hESCs-derived HSPCs by reducing intracellular reactive oxygen species (ROS) levels. The established hematopoietic organoids in GelMA with niche-related cells were composed of HSPCs and multilineage blood cells and demonstrated the adherence of hematopoietic cells to niche cells. Notably, these hematopoietic organoids exhibited radiation-induced hematopoietic cell injury effect, including increased intracellular ROS levels, γ-H2AX positive cell percentages, and hematopoietic cell apoptosis percentages. Moreover, G-CSF supplementation in the culture medium significantly improved the survival of HSPCs and enhanced myeloid cell regeneration in these hematopoietic organoids after radiation.

CONCLUSIONS

These findings substantiate the successful manufacture of a preliminary 3D hematopoietic organoid from hESCs-derived HSPCs, which was utilized for modeling hematopoietic radiation injury and assessing the radiation-mitigating effects of G-CSF in vitro. Our study provides opportunities to further aid in the standard and scalable production of hematopoietic organoids for disease modeling and drug testing.

Oral Delivery of Photopolymerizable Nanogels Loaded with Gemcitabine for Pancreatic Cancer Therapy: Formulation Design, and in vitro and in vivo Evaluations

Background

Gemcitabine (GEM) faces challenges of poor oral bioavailability and extensive first-pass metabolism. Currently, only injectable formulations are available for clinical use. Hence, there is an urgent demand for the development of advanced, efficacious, and user-friendly dosage forms to maintain its status as the primary treatment for pancreatic ductal adenocarcinoma (PDAC). Nanogels (NGs) offer a novel oral drug delivery system, ideal for hydrophilic compounds like GEM. This study aims to develop NGs tailored for GEM delivery, with the goal of enhancing cellular uptake and gastrointestinal permeability for improved administration in PDAC patients.

Methods

We developed cross-linked NGs via photopolymerization of methacryloyl for drug delivery of GEM. We reveal characterization, cytotoxicity, and cellular uptake studies in Caco-2 and MIA PaCa-2 cells. In addition, studies of in vitro permeability and pharmacokinetics were carried out to evaluate the bioavailability of the drug.

Results

Our results show NGs, formed via photopolymerization of methacryloyl, had a spherical shape with a size of 233.91±7.75 nm. Gemcitabine-loaded NGs (NGs-GEM) with 5% GelMA exhibited efficient drug loading (particle size: 244.07±19.52 nm). In vitro drug release from NGs-GEM was slower at pH 1.2 than pH 6.8. Cellular uptake studies indicated significantly enhanced uptake in both MIA PaCa-2 and Caco-2 cells. While there was no significant difference in GEM's AUC and Cmax between NGs-GEM and free-GEM groups, NGs-GEM showed markedly lower dFdU content (10.07 hr∙μg/mL) compared to oral free-GEM (19.04 hr∙μg/mL) after oral administration (p<0.01), highlighting NGs' efficacy in impeding rapid drug metabolism and enhancing retention.

Conclusion

In summary, NGs enhance cellular uptake, inhibit rapid metabolic degradation of GEM, and prolong retention after oral administration. These findings suggest NGs-GEM as a promising candidate for clinical use in oral pancreatic cancer therapy.

Dandelion-derived vesicles-laden hydrogel dressings capable of neutralizing Staphylococcus aureus exotoxins for the care of invasive wounds

Delayed wound healing caused by bacterial infection remains a major challenge in clinical treatment. Exotoxins incorporated in bacterial extracellular vesicles play a key role as the disease-causing virulence factors. Safe and specific antivirulence agents are expected to be developed as an effective anti-bacterial infection strategy, instead of single antibiotic therapy. Plant-derived extracellular vesicle-like nanoparticles have emerged as promising therapeutic agents for skin diseases, but the elucidations of specific mechanisms of action and clinical transformation still need to be advanced. Here, dandelion-derived extracellular vesicle-like nanoparticles (TH-EVNs) are isolated and exert antivirulence activity through specifically binding to Staphylococcus aureus (S. aureus) exotoxins, thereby protecting the host cell from attack. The neutralization of TH-EVNs against exotoxins has considerable binding force and stability, showing complete detoxification effect in vivo. Then gelatin methacryloyl hydrogel is developed as TH-EVNs-loaded dressing for S. aureus exotoxin-invasive wounds. Hydrogel dressings demonstrate good physical and mechanical properties, thus achieving wound retention and controlled release of TH-EVNs, in addition to promoting cell proliferation and migration. In vivo results show accelerated re-epithelialization, promotion of collagen maturity and reduction of inflammation after treatment. Collectively, the developed TH-EVNs-laden hydrogel dressings provide a potential therapeutic approach for S. aureus exotoxin- associated trauma.

3D Bioprinting-Based Dopamine-Coupled Flexible Material for Nasal Cartilage Repair

INTRODUCTION

Since 3D printing can be used to design implants according to the specific conditions of patients, it has become an emerging technology in tissue engineering and regenerative medicine. How to improve the mechanical, elastic and adhesion properties of 3D-printed photocrosslinked hydrogels is the focus of cartilage tissue repair and reconstruction research.

MATERIALS AND METHODS

We established a strategy for toughening hydrogels by mixing GelMA-DOPA (GD), which is prepared by coupling dopamine (DA) with GelMA, with HAMA, bacterial cellulose (BC) to produce composite hydrogels (HB-GD). HB-GD hydrogel scaffolds were characterized in vitro by scanning electron microscopy (SEM), Young's modulus, swelling property and rheological property tests. And biocompatibility and chondrogenic ability were tested by live/dead staining, DNA quantitative analysis and immunofluorescence staining. Combined with 3D bioprinting technology, mouse chondrocytes (ADTC5) were added to form a biological chain to construct an in vitro model, and the feasibility of the model for nasal cartilage regeneration was verified by cytology evaluation.

RESULTS

With the increase of GD concentration, the toughness of the composite hydrogel increased (47.0 ± 2.7 kPa (HB-5GD)-158 ± 3.2 kPa (HB-20GD)), and it had excellent swelling properties, rheological properties and printing properties. The HB-GD composite hydrogel promoted the proliferation and differentiation of ATDC5. Cells in 3D printed scaffolds had higher survival rates (> 95%) and better protein expression than the encapsulated cultures.

CONCLUSION

The HB-10GD hydrogel can be made into a porous scaffold with precise shape, good internal pore structure, high mechanical strength and good swelling rate through extrusion 3D printing.

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Progress in cardiac tissue engineering and regeneration: Implications of gelatin-based hybrid scaffolds

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.

Construction of Integral Decellularized Cartilage Using a Novel Hydrostatic Pressure Bioreactor

The decellularized extracellular matrix (ECM) of cartilage is a widely used natural bioscaffold for constructing tissue-engineered cartilage due to its good biocompatibility and regeneration properties. However, current decellularization methods for accessing decellularized cartilaginous tissues require multiple steps and a relatively long duration to produce decellularized cartilage. In addition, most decellularization strategies lead to damage of the microstructure and loss of functional components of the cartilaginous matrix. In this study, a novel decellularization strategy based on a hydrostatic pressure (HP) bioreactor was introduced, which aimed to improve the efficiency of producing integral decellularized cartilage pieces by combining physical and chemical decellularization methods in a perfusing manner. Two types of cartilaginous tissues, auricular cartilage (AC) and nucleus pulposus (NP) fibrocartilage, were selected for comparison of the effects of ordinary, positive, and negative HP-based decellularization according to the cell clearance ratio, microstructural changes, ECM components, and mechanical properties. The results indicated that applying positive HP improved the efficiency of producing decellularized AC, but no significant differences in decellularization efficiency were found between the ordinary and negative HP-treated groups. However, compared with the ordinary HP treatment, the application of the positive or negative HP did not affect the efficiency of decellularized NP productions. Moreover, neither positive nor negative HP influenced the preservation of the microstructure and components of the AC matrix. However, applying negative HP disarranged the fibril distribution of the NP matrix and reduced glycosaminoglycans and collagen type II contents, two essential ECM components. In addition, the positive HP was beneficial for maintaining the mechanical properties of decellularized cartilage. The recellularization experiments also verified the good biocompatibility of the decellularized cartilage produced by the present bioreactor-based decellularization method under positive HP. Overall, applying positive HP-based decellularization resulted in a superior effect on the production of close-to-natural scaffolds for cartilage tissue engineering. Impact statement In this study, we successfully constructed a novel hydrostatic pressure (HP) bioreactor and used this equipment to produce decellularized cartilage by combining physical and chemical decellularization methods in a perfusing manner. We found that positive HP-based decellularization could improve the production efficiency of integral decellularized cartilage pieces and promote the maintenance of matrix components and mechanical properties. This new decellularization strategy exhibited a superior effect in the production of close-to-natural scaffolds and positively impacts cartilage tissue engineering.

Microfabrication of Gelatin Methacrylate/Hydroxyapatite Composites by Utilizing Alternate Soaking Process

To construct a complex three-dimensional (3D) structure mimicking bone microstructure, hydrogel models of polymerized gelatin methacrylate (pGelMA) were fabricated by using stereolithography and modified with hydroxyapatite (HAp) via an alternate soaking process (ASP) using a solution of calcium and phosphate ions. Fabricated pGelMA line models whose widths were designed as 100, 300, and 600 μm were modified with HAp by ASP by changing the immersion time and number of cycles. After ASP, all of the line models with widths of 100, 300, and 600 μm were successfully modified with HAp, and large amounts of HAp were covered with the fabricated models by increasing both the immersion time and the number of cycles in ASP. HAp was observed near the surface of the line model with a width of 600 μm after ASP at an immersion time of 10 s, while the entire model was modified with HAp using ASPs for longer immersion times. The adhesion and spread of mesenchymal stem cells (MSCs) on the pGelMA-HAp discs depended on the ASP conditions. Moreover, the HAp modification of 3D pyramid models without alteration of the microstructure was also conducted. This two-step fabrication method of first fabricating frameworks of hydrogel models by stereolithography and subsequently modifying the fabricated models with HAp will lead to the development of 3D cell culture systems to support bone grafts or to create biological niches, such as artificial bone marrow.

The Long Road to Develop Custom-built Livers: Current Status of 3D Liver Bioprinting

Although liver transplantation is the gold-standard therapy for end-stage liver disease, the shortage of suitable organs results in only 25% of waitlisted patients undergoing transplants. Three-dimensional (3D) bioprinting is an emerging technology and a potential solution for personalized medicine applications. This review highlights existing 3D bioprinting technologies of liver tissues, current anatomical and physiological limitations to 3D bioprinting of a whole liver, and recent progress bringing this innovation closer to clinical use. We reviewed updated literature across multiple facets in 3D bioprinting, comparing laser, inkjet, and extrusion-based printing modalities, scaffolded versus scaffold-free systems, development of an oxygenated bioreactor, and challenges in establishing long-term viability of hepatic parenchyma and incorporating structurally and functionally robust vasculature and biliary systems. Advancements in liver organoid models have also increased their complexity and utility for liver disease modeling, pharmacologic testing, and regenerative medicine. Recent developments in 3D bioprinting techniques have improved the speed, anatomical, and physiological accuracy, and viability of 3D-bioprinted liver tissues. Optimization focusing on 3D bioprinting of the vascular system and bile duct has improved both the structural and functional accuracy of these models, which will be critical in the successful expansion of 3D-bioprinted liver tissues toward transplantable organs. With further dedicated research, patients with end-stage liver disease may soon be recipients of customized 3D-bioprinted livers, reducing or eliminating the need for immunosuppressive regimens.

Fabrication of Fish Scale-Based Gelatin Methacryloyl for 3D Bioprinting Application

Gelatin methacryloyl (GelMA) is an ideal bioink that is commonly used in bioprinting. GelMA is primarily acquired from mammalian sources; however, the required amount makes the market price extremely high. Since garbage overflow is currently a global issue, we hypothesized that fish scales left over from the seafood industry could be used to synthesize GelMA. Clinically, the utilization of fish products is more advantageous than those derived from mammals as they lower the possibility of disease transmission from mammals to humans and are permissible for practitioners of all major religions. In this study, we used gelatin extracted from fish scales and conventional GelMA synthesis methods to synthesize GelMA, then tested it at different concentrations in order to evaluated and compared the mechanical properties and cell responses. The fish scale GelMA had a printing accuracy of 97%, a swelling ratio of 482%, and a compressive strength of about 85 kPa at a 10% w/v GelMA concentration. Keratinocyte cells (HaCaT cells) were bioprinted with the GelMA bioink to assess cell viability and proliferation. After 72 h of culture, the number of cells increased by almost three-fold compared to 24 h, as indicated by many fluorescent cell nuclei. Based on this finding, it is possible to use fish scale GelMA bioink as a scaffold to support and enhance cell viability and proliferation. Therefore, we conclude that fish scale-based GelMA has the potential to be used as an alternative biomaterial for a wide range of biomedical applications.

A personalized biomimetic dual-drug delivery system via controlled release of PTH1-34 and simvastatin for in situ osteoporotic bone regeneration

Patients with osteoporosis often encounter clinical challenges of poor healing after bone transplantation due to their diminished bone formation capacity. The use of bone substitutes containing bioactive factors that increase the number and differentiation of osteoblasts is a strategy to improve poor bone healing. In this study, we developed an in situ dual-drug delivery system containing the bone growth factors PTH1-34 and simvastatin to increase the number and differentiation of osteoblasts for osteoporotic bone regeneration. Our system exhibited ideal physical properties similar to those of natural bone and allowed for customizations in shape through a 3D-printed scaffold and GelMA. The composite system regulated the sustained release of PTH1-34 and simvastatin, and exhibited good biocompatibility. Cell studies revealed that the composite system reduced osteoblast death, and promoted expression of osteoblast differentiation markers. Additionally, by radiographic analysis and histological observation, the dual-drug composite system demonstrated promising bone regeneration outcomes in an osteoporotic skull defect model. In summary, this composite delivery system, comprising dual-drug administration, holds considerable potential for bone repair and may serve as a safe and efficacious therapeutic approach for addressing bone defects in patients with osteoporosis.

Histological evaluation of the regenerative potential of a novel photocrosslinkable gelatin-treated dentin matrix hydrogel in direct pulp capping: an animal study

BACKGROUND

To assess histologically the success of the pulp capping approach performed in traumatically exposed dogs' teeth using a novel injectable gelatin-treated dentin matrix light cured hydrogel (LCG-TDM) compared with LCG, MTA and TheraCal LC.

METHODS

Sixty-four dogs' teeth were divided into two groups (each including 32 teeth) based on the post-treatment evaluation period: group I: 2 weeks and group II: 8 weeks. Each group was further subdivided according to the pulp capping material into four subgroups (n = 8), with subgroup A (light-cured gelatin hydrogel) as the control subgroup, subgroup B (LCG-TDM), subgroup C (TheraCal LC), and subgroup D (MTA). Pulps were mechanically exposed in the middle of the cavity floor and capped with different materials. An assessment of periapical response was performed preoperatively and at 8 weeks. After 2 and 8-week intervals, the dogs were sacrificed, and the teeth were stained with hematoxylin-eosin and graded by using a histologic scoring system. Statistical analysis was performed using the chi-square and Kruskal-Wallis tests (p = 0.05).

RESULTS

All subgroups showed mild inflammation with normal pulp tissue at 2 weeks with no significant differences between subgroups (p ≤ 0.05), except for the TheraCal LC subgroup, which exhibited moderate inflammation (62.5%). Absence of a complete calcified bridge was reported in all subgroups at 2 weeks, while at 8 weeks, the majority of samples in the LCG-TDM and MTA-Angelus subgroups showed complete dentin bridge formation and absence of inflammatory pulp response with no significant differences between them (p ≤ 0.05). However, the formed dentin in the LCG-TDM group was significantly thicker, with layers of ordered odontoblasts identified to create a homogeneous tubular structure and numerous dentinal tubule lines suggesting a favourable trend towards dentin regeneration. TheraCal LC samples revealed a reasonably thick dentin bridge with moderate inflammation (50%) and LCG showed heavily fibrous tissue infiltrates with areas of degenerated pulp with no signs of hard tissue formation.

CONCLUSIONS

LCG-TDM, as an extracellular matrix-based material, has the potential to regenerate dentin and preserve pulp vitality, making it a viable natural alternative to silicate-based cements for healing in vivo dentin defects in direct pulp-capping procedures.

Development of Human-Derived Photocrosslinkable Gelatin Hydrogels for Tissue Engineering

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

GelMA/TCP nanocomposite scaffold for vital pulp therapy

Pulp capping is a necessary procedure for preserving the vitality and health of the dental pulp, playing a crucial role in preventing the need for root canal treatment or tooth extraction. Here, we developed an electrospun gelatin methacryloyl (GelMA) fibrous scaffold incorporating beta-tricalcium phosphate (TCP) particles for pulp capping. A comprehensive morphological, physical-chemical, and mechanical characterization of the engineered fibrous scaffolds was performed. In vitro bioactivity, cell compatibility, and odontogenic differentiation potential of the scaffolds in dental pulp stem cells (DPSCs) were also evaluated. A pre-clinical in vivo model was used to determine the therapeutic role of the GelMA/TCP scaffolds in promoting hard tissue formation. Morphological, chemical, and thermal analyses confirmed effective TCP incorporation in the GelMA nanofibers. The GelMA+20%TCP nanofibrous scaffold exhibited bead-free morphology and suitable mechanical and degradation properties. In vitro, GelMA+20%TCP scaffolds supported apatite-like formation, improved cell spreading, and increased deposition of mineralization nodules. Gene expression analysis revealed upregulation of ALPL, RUNX2, COL1A1, and DMP1 in the presence of TCP-laden scaffolds. In vivo, analyses showed mild inflammatory reaction upon scaffolds' contact while supporting mineralized tissue formation. Although the levels of Nestin and DMP1 proteins did not exceed those associated with the clinical reference treatment (i.e., mineral trioxide aggregate), the GelMA+20%TCP scaffold exhibited comparable levels, thus suggesting the emergence of differentiated odontoblast-like cells capable of dentin matrix secretion. Our innovative GelMA/TCP scaffold represents a simplified and efficient alternative to conventional pulp-capping biomaterials. STATEMENT OF SIGNIFICANCE: Vital pulp therapy (VPT) aims to preserve dental pulp vitality and avoid root canal treatment. Biomaterials that bolster mineralized tissue regeneration with ease of use are still lacking. We successfully engineered gelatin methacryloyl (GelMA) electrospun scaffolds incorporated with beta-tricalcium phosphate (TCP) for VPT. Notably, electrospun GelMA-based scaffolds containing 20% (w/v) of TCP exhibited favorable mechanical properties and degradation, cytocompatibility, and mineralization potential indicated by apatite-like structures in vitro and mineralized tissue deposition in vivo, although not surpassing those associated with the standard of care. Collectively, our innovative GelMA/TCP scaffold represents a simplified alternative to conventional pulp capping materials such as MTA and Biodentine™ since it is a ready-to-use biomaterial, requires no setting time, and is therapeutically effective.

Antisense yycF and BMP-2 co-delivery gelatin methacryloyl and carboxymethyl chitosan hydrogel composite for infective bone defects regeneration

Repairing infected bone defects remains a challenge in clinical work. Intractable bacterial infections and insufficient osseointegration are major concerns for infected bone defects. To address these issues, we developed a gelatin methacryloyl (GelMA) and carboxymethyl chitosan (CMCS) composite hydrogel with BMP-2 growth factor and GO based antisense technology supported by a PLGA spring. In vitro, photo-crosslinked GelMA composite hydrogels shown excellent biocompatibility and degradability. Relying on the release of BMP-2 from the composite hydrogel provides osteogenic effects. The antisense yycF and BMP-2 were released with the degradation of GelMA and CMCS composite hydrogel. In terms of antimicrobial properties, CMCS, GO and post-transcriptional regulatory antisense yycF from the composite hydrogel synergistically kill S. aureus. In vivo, we implanted the composite hydrogel in a rat model of S. aureus infected femur defect, effectively accelerating bone healing in an infectious microenvironment. This research provides a novel biomaterial that is both antimicrobial and promotes bone regeneration, with the potential to treat infected bone defects.

Photo-Cross-Linkable, Injectable, and Highly Adhesive GelMA-Glycol Chitosan Hydrogels for Cartilage Repair

Hydrogels provide a promising platform for cartilage repair and regeneration. Although hydrogels have shown some efficacy, they still have shortcomings including poor mechanical properties and suboptimal integration with surrounding cartilage. Herein, hydrogels that are injectable, cytocompatible, mechanically robust, and highly adhesive to cartilage are developed. This approach uses GelMA-glycol chitosan (GelMA-GC) that is crosslinkable with visible light and photoinitiators (lithium acylphosphinate and tris (2,2'-bipyridyl) dichlororuthenium (II) hexahydrate ([RuII(bpy)3 ]2+ and sodium persulfate (Ru/SPS)). Ru/SPS-cross-linked hydrogels have higher compressive and tensile modulus, and most prominently higher adhesive strength with cartilage, which also depends on inclusion of GC. Tensile and push-out tests of the Ru/SPS-cross-linked GelMA-GC hydrogels demonstrate adhesive strength of ≈100 and 46 kPa, respectively. Hydrogel precursor solutions behave in a Newtonian manner and are injectable. After injection in focal bovine cartilage defects and in situ cross-linking, this hydrogel system remains intact and integrated with cartilage following joint manipulation ex vivo. Cells remain viable (>85%) in the hydrogel system and further show tissue regeneration potential after three weeks of in vitro culture. These preliminary results provide further motivation for future research on bioadhesive hydrogels for cartilage repair and regeneration.

The Mechanical and Biological Performance of Photopolymerized Gelatin-Based Hydrogels as a Function of the Reaction Media

From the first experiments with biomaterials to mimic tissue properties, the mechanical and biochemical characterization has evolved extensively. Several properties can be described, however, what should be essential is to conduct a proper and physiologically relevant characterization. Herein, the influence of the reaction media (RM) and swelling media (SM)-phosphate buffered saline (PBS) and Dulbecco's modified Eagle's medium (DMEM) with two different glucose concentrations-is described in gelatin methacrylamide (GelMA) hydrogel mechanics and in the biological behavior of two tumoral cell lines (Caco-2 and HCT-116). All scaffolds are UV-photocrosslinked under identical conditions and evaluated for mass swelling ratio and stiffness. The results indicate that stiffness is highly susceptible to the RM, but not to the SM. Additionally, PBS-prepared hydrogels exhibited a higher photopolymerization degree according to high resolution magic-angle spinning (HR-MAS) NMR. These findings correlate with the biological response of Caco-2 and HCT-116 cells seeded on the substrates, which demonstrated flatter morphologies on stiffer hydrogels. Overall, cell viability and proliferation are excellent for both cell lines, and Caco-2 cells displayed a characteristic apical-basal polarization based on F-actin/Nuclei fluorescence images. These characterization experiments highlight the importance of conducting mechanical testing of biomaterials in the same medium as cell culture.

Biohybrid Hydrogels for Tumoroid Culture

Tumoroids are 3D in vitro models that recapitulate key features of in vivo tumors, such as their architecture - hypoxic center and oxygenated outer layer - in contrast with traditional 2D cell cultures. Moreover, they may be able to preserve the patient-specific signature in terms of cell heterogeneity and mutations. Tumoroids are, therefore, interesting tools for improving the understanding of cancer biology, developing new drugs, and potentially designing personalized therapeutic plans. Currently, tumoroids are most often established using basement membrane extracts (BME), which provide a multitude of biological cues. However, BME are characterized by a lack of well-defined composition, limited reproducibility, and potential immunogenicity as a consequence of their natural origin. Synthetic polymers can overcome these problems but lack structural and biochemical complexity, which can limit the functional capabilities of organoids. Biohybrid hydrogels consisting of both natural and synthetic components can combine their advantages and offer superior 3D culture systems. In this review, it is summarized efforts devoted to producing tumoroids using different types of biohybrid hydrogels, which are classified according to their crosslinking mechanism.

Small extracellular vesicles derived from tendon stem cells promote the healing of injured Achilles tendons by regulating miR-145-3p

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. STATEMENT OF SIGNIFICANCE: 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.

Construction of a novel cell-free tracheal scaffold promoting vascularization for repairing tracheal defects

Functional vascularization is crucial for maintaining the long-term patency of tissue-engineered trachea and repairing defective trachea. Herein, we report the construction and evaluation of a novel cell-free tissue-engineered tracheal scaffold that effectively promotes vascularization of the graft. Our findings demonstrated that exosomes derived from endothelial progenitor cells (EPC-Exos) enhance the proliferation, migration, and tube formation of endothelial cells. Taking advantage of the angiogenic properties of EPC-Exos, we utilized methacrylate gelatin (GelMA) as a carrier for endothelial progenitor cell exosomes and encapsulated them within a 3D-printed polycaprolactone (PCL) scaffold to fabricate a composite tracheal scaffold. The results demonstrated the excellent angiogenic potential of the methacrylate gelatin/vascular endothelial progenitor cell exosome/polycaprolactone tracheal scaffold. Furthermore, in vivo reconstruction of tracheal defects revealed the capacity of this composite tracheal stent to remodel vasculature. In conclusion, we have successfully developed a novel tracheal stent composed of methacrylate gelatin/vascular endothelial progenitor exosome/polycaprolactone, which effectively promotes angiogenesis for tracheal repair, thereby offering significant prospects for clinical and translational medicine.

Metal Organic Framework-Incorporated Three-Dimensional (3D) Bio-Printable Hydrogels to Facilitate Bone Repair: Preparation and In Vitro Bioactivity Analysis

Hydrogels are three-dimensional (3D) water-swellable polymeric matrices that are used extensively in tissue engineering and drug delivery. Hydrogels can be conformed into any desirable shape using 3D bio-printing, making them suitable for personalized treatment. Among the different 3D bio-printing techniques, digital light processing (DLP)-based printing offers the advantage of quickly fabricating high resolution structures, reducing the chances of cell damage during the printing process. Here, we have used DLP to 3D bio-print biocompatible gelatin methacrylate (GelMA) scaffolds intended for bone repair. GelMA is biocompatible, biodegradable, has integrin binding motifs that promote cell adhesion, and can be crosslinked easily to form hydrogels. However, GelMA on its own is incapable of promoting bone repair and must be supplemented with pharmaceutical molecules or growth factors, which can be toxic or expensive. To overcome this limitation, we introduced zinc-based metal-organic framework (MOF) nanoparticles into GelMA that can promote osteogenic differentiation, providing safer and more affordable alternatives to traditional methods. Incorporation of this nanoparticle into GelMA hydrogel has demonstrated significant improvement across multiple aspects, including bio-printability, and favorable mechanical properties (showing a significant increase in the compressive modulus from 52.14 ± 19.42 kPa to 128.13 ± 19.46 kPa with the addition of ZIF-8 nanoparticles). The designed nanocomposite hydrogels can also sustain drug (vancomycin) release (maximum 87.52 ± 1.6% cumulative amount) and exhibit a remarkable ability to differentiate human adipose-derived mesenchymal stem cells toward the osteogenic lineage. Furthermore, the formulated MOF-integrated nanocomposite hydrogel offers the unique capability to coat metallic implants intended for bone healing. Overall, the remarkable printability and coating ability displayed by the nanocomposite hydrogel presents itself as a promising candidate for drug delivery, cell delivery and bone tissue engineering applications.

Graphene Oxide Functionalized Gelatin Methacryloyl Microgel for Enhanced Biomimetic Mineralization and in situ Bone Repair

Introduction

The formation of bone-like apatite (Ap) on natural polymers through biomimetic mineralization using simulated body fluid (SBF) can improve osteoconductivity and biocompatibility, while lowering immunological rejection. Nonetheless, the coating efficiency of the bone-like Ap layer on natural polymers requires improvement. Carbonyls (-COOH) and hydroxyls (-OH) are abundant in graphene oxide (GO), which may offer more active sites for biomimetic mineralization and promote the proliferation of rat bone marrow stromal cells (BMSCs).

Methods

In this study, gelatin methacryloyl (GelMA) microgels were infused with GO (0, 0.5, 1, and 2 mg/mL) and embedded into microgels in SBF for 1, 7, and 14 days. Systematic in vitro and in vivo experiments were performed to evaluate the structure of the microgel and its effect on cell proliferation and ability to repair bone defects in rats.

Results

The resulting GO-GelMA-Ap microgels displayed a porous, interconnected structure with uniformly coated surfaces in bone-like Ap, and the Ca/P ratio of the 1 mg/mL GO-GelMA-Ap group was comparable to that of natural bone tissue. Moreover, the 1 mg/mL GO-GelMA-Ap group exhibited a greater Ap abundance, enhanced proliferation of BMSCs in vitro and increased bone formation in vivo compared to the GelMA-Ap group.

Discussion

Overall, this study offers a novel method for incorporating GO into microgels for bone tissue engineering to promote biomimetic mineralization.

Synthesis of Silanized Bioactive Glass/Gelatin Methacrylate (GelMA/Si-BG) composite hydrogel for Bone Tissue Engineering Application

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.

A Multidrug Delivery Microrobot for the Synergistic Treatment of Cancer

Multidrug combination therapy provides an effective strategy for malignant tumor treatment. This paper presents the development of a biodegradable microrobot for on-demand multidrug delivery. By combining magnetic targeting transportation with tumor therapy, it is hypothesized that loading multiple drugs on different regions of a single magnetic microrobot can enhance a synergistic effect for cancer treatment. The synergistic effect of using two drugs together is greater than that of using each drug separately. Here, a 3D-printed microrobot inspired by the fish structure with three hydrogel components: skeleton, head, and body structures is demonstrated. Made of iron oxide (Fe3 O4 ) nanoparticles embedded in poly(ethylene glycol) diacrylate (PEGDA), the skeleton can respond to magnetic fields for microrobot actuation and drug-targeted delivery. The drug storage structures, head, and body, made by biodegradable gelatin methacryloyl (GelMA) exhibit enzyme-responsive cargo release. The multidrug delivery microrobots carrying acetylsalicylic acid (ASA) and doxorubicin (DOX) in drug storage structures, respectively, exhibit the excellent synergistic effects of ASA and DOX by accelerating HeLa cell apoptosis and inhibiting HeLa cell metastasis. In vivo studies indicate that the microrobots improve the efficiency of tumor inhibition and induce a response to anti-angiogenesis. The versatile multidrug delivery microrobot conceptualized here provides a way for developing effective combination therapy for cancer.

Toroidal-spiral particles as a CAR-T cell delivery device for solid tumor immunotherapy

Chimeric antigen receptor (CAR) T cell therapy has resulted in positive effects on patients with hematologic malignancy but shows limited efficacy in solid tumor treatments due to insufficient trafficking and tumor infiltration, intensive CAR-T-related toxicities, and antigen escape. In this work, we developed and investigated a biodegradable and biocompatible polymeric toroidal-spiral particle (TSP) as a in vivo cell incubator and delivery device that can be implanted near tumor through a minimally invasive procedure or injected near or into solid tumors by using a biopsy needle. The main matrix structure of the millimeter-sized TSP is made from crosslinking of gelatin methacrylamine (GelMA) and poly (ethylene glycol) diacrylate (PEGDA) with a tunable degradation rate from a few days to months, providing appropriate mechanical properties and sustained release of co-encapsulated drugs and/or stimulation compounds. The toroidal-spiral layer of the particles, presenting an internal void volume for high-capacity cell loading and flexibility of co-encapsulating small and large molecular compounds with individually manipulated release schedules, is filled with collagen and suspended T cells. The TSPs promote cell proliferation, activation, and migration in the tumor micro-environment in a prolonged and sustained manner. In this study, the efficacy of mesothelin (MSLN) CAR-T cells released from the TSPs was tested in preclinical mouse tumor models. Compared to systemic and intratumoral injection, peritumoral delivery of MSLN CAR-T cells using the TSPs resulted in a superior antitumor effect. The TSPs made of FDA approved materials as an in vivo reactor may provide an option for efficiently local delivery of CAR-T cells to solid tumors for higher efficacy and lower toxicity, with a minimally invasive administration procedure.

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).

Preclinical Testing Techniques: Paving the Way for New Oncology Screening Approaches

Prior to clinical trials, preclinical testing of oncology drug candidates is performed by evaluating drug candidates with in vitro and in vivo platforms. For in vivo testing, animal models are used to evaluate the toxicity and efficacy of drug candidates. However, animal models often display poor translational results as many drugs that pass preclinical testing fail when tested with humans, with oncology drugs exhibiting especially poor acceptance rates. The FDA Modernization Act 2.0 promotes alternative preclinical testing techniques, presenting the opportunity to use higher complexity in vitro models as an alternative to in vivo testing, including three-dimensional (3D) cell culture models. Three-dimensional tissue cultures address many of the shortcomings of 2D cultures by more closely replicating the tumour microenvironment through a combination of physiologically relevant drug diffusion, paracrine signalling, cellular phenotype, and vascularization that can better mimic native human tissue. This review will discuss the common forms of 3D cell culture, including cell spheroids, organoids, organs-on-a-chip, and 3D bioprinted tissues. Their advantages and limitations will be presented, aiming to discuss the use of these 3D models to accurately represent human tissue and as an alternative to animal testing. The use of 3D culture platforms for preclinical drug development is expected to accelerate as these platforms continue to improve in complexity, reliability, and translational predictivity.

GelMA-glycol chitosan hydrogels for cartilage regeneration: The role of uniaxial mechanical stimulation in enhancing mechanical, adhesive, and biochemical properties

Untreated osteochondral defects are a leading cause of osteoarthritis, a condition that places a heavy burden on both patients and orthopedic surgeons. Although tissue engineering has shown promise for creating mechanically similar cartilage-like constructs, their integration with cartilage remains elusive. Therefore, a formulation of biodegradable, biocompatible biomaterial with sufficient mechanical and adhesive properties for cartilage repair is required. To accomplish this, we prepared biocompatible, photo-curable, mechanically robust, and highly adhesive GelMA-glycol chitosan (GelMA-GC) hydrogels. GelMA-GC hydrogels had a modulus of 283 kPa and provided a biocompatible environment (>70% viability of embedded chondrocytes) in long-term culture within a bovine cartilage ring. The adhesive strength of bovine chondrocyte-laden GelMA-GC hydrogel to bovine cartilage increased from 38 to 52 kPa over four weeks of culture. Moreover, intermittent uniaxial mechanical stimulation enhanced the adhesive strength to ∼60 kPa, indicating that the cartilage-hydrogel integration could remain secure and functional under dynamic loading conditions. Furthermore, gene expression data and immunofluorescence staining revealed the capacity of chondrocytes in GelMA-GC hydrogel to synthesize chondrogenic markers (COL2A1 and ACAN), suggesting the potential for tissue regeneration. The promising in vitro results of this work motivate further exploration of the potential of photo-curable GelMA-GC bioadhesive hydrogels for cartilage repair and regeneration.

Triaxial bioprinting large-size vascularized constructs with nutrient channels

Bioprinting has demonstrated great advantages in tissue and organ regeneration. However, constructing large-scale tissue and organsin vitrois still a huge challenge due to the lack of some strategies for loading multiple types of cells precisely while maintaining nutrient channels. Here, a new 3D bioprinting strategy was proposed to construct large-scale vascularized tissue. A mixture of gelatin methacrylate (GelMA) and sodium alginate (Alg) was used as a bioink, serving as the outer and middle layers of a single filament in the triaxial printing process, and loaded with human bone marrow mesenchymal stem cells and human umbilical vein endothelial cells, respectively, while a calcium chloride (CaCl2) solution was used as the inner layer. The CaCl2solution crosslinked with the middle layer bioink during the printing process to form and maintain hollow nutrient channels, then a stable large-scale construct was obtained through photopolymerization and ion crosslinking after printing. The feasibility of this strategy was verified by investigating the properties of the bioink and construct, and the biological performance of the vascularized construct. The results showed that a mixture of 5% (w/v) GelMA and 1% (w/v) Alg bioink could be printed at room temperature with good printability and perfusion capacity. Then, the construct with and without channels was fabricated and characterized, and the results revealed that the construct with channels had a similar degradation profile to that without channels, but lower compressive modulus and higher swelling rate. Biological investigation showed that the construct with channels was more favorable for cell survival, proliferation, diffusion, migration, and vascular network formation. In summary, it was demonstrated that constructing large-scale vascularized tissue by triaxial printing that can precisely encapsulate multiple types of cells and form nutrient channels simultaneously was feasible, and this technology could be used to prepare large-scale vascularized constructs.

Gelatin Methacryloyl (GelMA) Hydrogel Scaffolds: Predicting Physical Properties Using an Experimental Design Approach

There is a growing interest for complex in vitro environments that closely mimic the extracellular matrix and allow cells to grow in microenvironments that are closer to the one in vivo. Protein-based matrices and especially hydrogels can answer this need, thanks to their similarity with the cell microenvironment and their ease of customization. In this study, an experimental design was conducted to study the influence of synthesis parameters on the physical properties of gelatin methacryloyl (GelMA). Temperature, ratio of methacrylic anhydride over gelatin, rate of addition, and stirring speed of the reaction were studied using a Doehlert matrix. Their impact on the following parameters was analyzed: degree of substitution, mass swelling ratio, storage modulus (log(G')), and compression modulus. This study highlights that the most impactful parameter was the ratio of methacrylic anhydride over gelatin. Although, temperature affected the degree of substitution, and methacrylic anhydride addition flow rate impacted the gel's physical properties, namely, its storage modulus and compression modulus. Moreover, this experimental design proposed a theoretical model that described the variation of GelMA's physical characteristics as a function of synthesis conditions.

Polymeric and biological membranes for organ-on-a-chip devices

Membranes are fundamental elements within organ-on-a-chip (OOC) platforms, as they provide adherent cells with support, allow nutrients (and other relevant molecules) to permeate/exchange through membrane pores, and enable the delivery of mechanical or chemical stimuli. Through OOC platforms, physiological processes can be studied in vitro, whereas OOC membranes broaden knowledge of how mechanical and chemical cues affect cells and organs. OOCs with membranes are in vitro microfluidic models that are used to replace animal testing for various applications, such as drug discovery and disease modeling. In this review, the relevance of OOCs with membranes is discussed as well as their scaffold and actuation roles, properties (physical and material), and fabrication methods in different organ models. The purpose was to aid readers with membrane selection for the development of OOCs with specific applications in the fields of mechanistic, pathological, and drug testing studies. Mechanical stimulation from liquid flow and cyclic strain, as well as their effects on the cell's increased physiological relevance (IPR), are described in the first section. The review also contains methods to fabricate synthetic and ECM (extracellular matrix) protein membranes, their characteristics (e.g., thickness and porosity, which can be adjusted depending on the application, as shown in the graphical abstract), and the biological materials used for their coatings. The discussion section joins and describes the roles of membranes for different research purposes and their advantages and challenges.

A novel poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV)-PEG-melatonin composite scaffold enhances for inhibiting bone tumor recurrence and enhancing bone regeneration

Introduction: Postoperative comprehensive treatment has become increasingly important in recent years. This study was to repair tissue defects resulting from the removal of diseased tissue and to eliminate or inhibit the recurrence and metastasis of residual tumors under the condition of reducing the systemic side effects of chemotherapeutic drugs. To address these challenges, multifunctional scaffolds based local drug delivery systems will be a promising solution. Methods: An optimal drug-loaded scaffold material PHBV-mPEG5k (PP5) was prepared, which is biocompatible, hydrophilic and biodegradable. Furthermore, this material showed to promote bone healing, and could be conveniently prepared into porous scaffold by freeze-drying the solution. By means of introducing melatonin (MT) into the porous surfaces, the MT loaded PP5 scaffold with desirable sustained release ability was successfully prepared. The effectiveness of the MT loaded PP5 scaffold in promoting bone repair and anti-tumor properties was evaluated through both in vivo and in vitro experiments. Results and Discussion: The MT loaded PP5 scaffold is able to achieve the desired outcome of bone tissue repair and anti-bone tumor properties. Furthermore, our study demonstrates that the PP5 scaffold was able to enhance the anti-tumor effect of melatonin by improving cellular autophagy, which provided a therapeutic strategy for the comprehensive postoperative treatment of osteosarcoma.

Mimicking Molecular Pathways in the Design of Smart Hydrogels for the Design of Vascularized Engineered Tissues

Biomaterials are pivotal in supporting and guiding vascularization for therapeutic applications. To design effective, bioactive biomaterials, understanding the cellular and molecular processes involved in angiogenesis and vasculogenesis is crucial. Biomaterial platforms can replicate the interactions between cells, the ECM, and the signaling molecules that trigger blood vessel formation. Hydrogels, with their soft and hydrated properties resembling natural tissues, are widely utilized; particularly synthetic hydrogels, known for their bio-inertness and precise control over cell-material interactions, are utilized. Naturally derived and synthetic hydrogel bases are tailored with specific mechanical properties, controlled for biodegradation, and enhanced for cell adhesion, appropriate biochemical signaling, and architectural features that facilitate the assembly and tubulogenesis of vascular cells. This comprehensive review showcases the latest advancements in hydrogel materials and innovative design modifications aimed at effectively guiding and supporting vascularization processes. Furthermore, by leveraging this knowledge, researchers can advance biomaterial design, which will enable precise support and guidance of vascularization processes and ultimately enhance tissue functionality and therapeutic outcomes.

The third dimension of tumor microenvironment-The importance of tumor stroma in 3D cancer models

Recent advances in the three-dimensional (3D) cancer models give rise to a plethora of new possibilities in the development of anti-cancer drug therapies and bring us closer to personalized medicine. Three-dimensional models are undoubtedly more authentic than traditional two-dimensional (2D) cell cultures. Nowadays, they are becoming preferentially used in most cancer research fields due to their more accurate biomimetic characteristics. On the contrary, they still lack the cellular and matrix complexity of the native tumor microenvironment (TME). This review focuses on the description of existing 3D models, the incorporation of TME and fluidics into these models, and their perspective in the future research. It is clear that such an improvement would need not only biological but also technical progress. Therefore, the modern approach to anti-cancer drug discovery should involve various fields.

Hydrogel-Forming Microneedles with Applications in Oral Diseases Management

Controlled drug delivery in the oral cavity poses challenges such as bacterial contamination, saliva dilution, and inactivation by salivary enzymes upon ingestion. Microneedles offer a location-specific, minimally invasive, and retentive approach. Hydrogel-forming microneedles (HFMs) have emerged for dental diagnostics and therapeutics. HFMs penetrate the stratum corneum, undergo swelling upon contact, secure attachment, and enable sustained transdermal or transmucosal drug delivery. Commonly employed polymers such as polyvinyl alcohol (PVA) and polyvinyl pyrrolidone are crosslinked with tartaric acid or its derivatives while incorporating therapeutic agents. Microneedle patches provide suture-free and painless drug delivery to keratinized or non-keratinized mucosa, facilitating site-specific treatment and patient compliance. This review comprehensively discusses HFMs' applications in dentistry such as local anesthesia, oral ulcer management, periodontal treatment, etc., encompassing animal experiments, clinical trials, and their fundamental impact and limitations, for example, restricted drug carrying capacity and, until now, a low number of dental clinical trial reports. The review explores the advantages and future perspectives of HFMs for oral drug delivery.

Multifunctional and biodegradable methacrylated gelatin/Aloe vera nanofibers for endodontic disinfection and immunomodulation

Currently employed approaches and materials used for vital pulp therapies (VPTs) and regenerative endodontic procedures (REPs) lack the efficacy to predictably achieve successful outcomes due to their inability to achieve adequate disinfection and/or lack of desired immune modulatory effects. Natural polymers and medicinal herbs are biocompatible, biodegradable, and present several therapeutic benefits and immune-modulatory properties; thus, standing out as a clinically viable approach capable of establishing a conducive environment devoid of bacteria and inflammation to support continued root development, dentinal bridge formation, and dental pulp tissue regeneration. However, the low stability and poor mechanical properties of the natural compounds have limited their application as potential biomaterials for endodontic procedures. In this study, Aloe vera (AV), as a natural antimicrobial and anti-inflammatory agent, was incorporated into photocrosslinkable Gelatin methacrylate (GelMA) nanofibers with the purpose of developing a highly biocompatible biomaterial capable of eradicating endodontic infection and modulating inflammation. Stable GelMA/AV nanofibers with optimal properties were obtained at the ratio of (70:30) by electrospinning. In addition to the pronounced antibacterial effect against Enterococcus faecalis, the GelMA/AV (70:30) nanofibers also exhibited a sustained antibacterial activity over 14 days and significant biofilm reduction with minimal cytotoxicity, as well as anti-inflammatory properties and immunomodulatory effects favoring healing. Our results indicate that the novel GelMA/AV (70:30) nanofibers hold great potential as a biomaterial strategy for endodontic infection eradication and enhanced healing.

The effect of GelMA/alginate interpenetrating polymeric network hydrogel on the performance of porous zirconia matrix for bone regeneration applications

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 (ZrO2-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 (ZrO2) scaffold. The structure, morphology, compressive strength, surface/interface properties, and biocompatibility of the ZrO2-GM/SA composite scaffolds were characterized to evaluate the performance of the composite scaffolds. Results showed that compared to ZrO2 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 ZrO2 scaffolds. In addition, ZrO2-GM/SA composite scaffolds had highly biocompatibility and displayed a potent proliferation and osteogenesis of MC3T3-E1 pre-osteoblasts compared to bare ZrO2 scaffolds and ZrO2-GelMA composite scaffolds. At the same time, ZrO2-10GM/1SA composite scaffold regenerated significantly greater bone than other groups in vivo. This study demonstrated that the proposed ZrO2-GM/SA composite scaffolds had great research and application potential in bone tissue engineering.

Modulating design parameters to drive cell invasion into hydrogels for osteochondral tissue formation

Background

The use of acellular hydrogels to repair osteochondral defects requires cells to first invade the biomaterial and then to deposit extracellular matrix for tissue regeneration. Due to the diverse physicochemical properties of engineered hydrogels, the specific properties that allow or even improve the behaviour of cells are not yet clear. The aim of this study was to investigate the influence of various physicochemical properties of hydrogels on cell migration and related tissue formation using in vitro, ex vivo and in vivo models.

Methods

Three hydrogel platforms were used in the study: Gelatine methacryloyl (GelMA) (5% wt), norbornene hyaluronic acid (norHA) (2% wt) and tyramine functionalised hyaluronic acid (THA) (2.5% wt). GelMA was modified to vary the degree of functionalisation (DoF 50% and 80%), norHA was used with varied degradability via a matrix metalloproteinase (MMP) degradable crosslinker and THA was used with the addition of collagen fibrils. The migration of human mesenchymal stromal cells (hMSC) in hydrogels was studied in vitro using a 3D spheroid migration assay over 48h. In addition, chondrocyte migration within and around hydrogels was investigated in an ex vivo bovine cartilage ring model (three weeks). Finally, tissue repair within osteochondral defects was studied in a semi-orthotopic in vivo mouse model (six weeks).

Results

A lower DoF of GelMA did not affect cell migration in vitro (p ​= ​0.390) and led to a higher migration score ex vivo (p ​< ​0.001). The introduction of a MMP degradable crosslinker in norHA hydrogels did not improve cell infiltration in vitro or in vivo. The addition of collagen to THA resulted in greater hMSC migration in vitro (p ​= ​0.031) and ex vivo (p ​< ​0.001). Hydrogels that exhibited more cell migration in vitro or ex vivo also showed more tissue formation in the osteochondral defects in vivo, except for the norHA group. Whereas norHA with a degradable crosslinker did not improve cell migration in vitro or ex vivo, it did significantly increase tissue formation in vivo compared to the non-degradable crosslinker (p ​< ​0.001).

Conclusion

The modification of hydrogels by adapting DoF, use of a degradable crosslinker or including fibrillar collagen can control and improve cell migration and tissue formation for osteochondral defect repair. This study also emphasizes the importance of performing both in vitro and in vivo testing of biomaterials, as, depending on the material, the results might be affected by the model used.The translational potential of this article: This article highlights the potential of using acellular hydrogels to repair osteochondral defects, which are common injuries in orthopaedics. The study provides a deeper understanding of how to modify the properties of hydrogels to control cell migration and tissue formation for osteochondral defect repair. The results of this article also highlight that the choice of the used laboratory model can affect the outcome. Testing hydrogels in different models is thus advised for successful translation of laboratory results to the clinical application.

Injectable antibacterial Ag-HA/ GelMA hydrogel for bone tissue engineering

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

3D-printed hydrogel particles containing PRP laden with TDSCs promote tendon repair in a rat model of tendinopathy

Long-term chronic inflammation after Achilles tendon injury is critical for tendinopathy. Platelet-rich plasma (PRP) injection, which is a common method for treating tendinopathy, has positive effects on tendon repair. In addition, tendon-derived stem cells (TDSCs), which are stem cells located in tendons, play a major role in maintaining tissue homeostasis and postinjury repair. In this study, injectable gelatine methacryloyl (GelMA) microparticles containing PRP laden with TDSCs (PRP-TDSC-GM) were prepared by a projection-based 3D bioprinting technique. Our results showed that PRP-TDSC-GM could promote tendon differentiation in TDSCs and reduce the inflammatory response by downregulating the PI3K-AKT pathway, thus promoting the structural and functional repair of tendons in vivo.