Hydrogel composite scaffolds achieve recruitment and chondrogenesis in cartilage tissue engineering applications

A sequential drug delivery system based on silk fibroin scaffold for effective cartilage repair

Endogenous repair of cartilage defects is a preferential strategy for cartilage repair, but always hindered by insufficient early-stage cells and incomplete cell differentiation at later stages. For in-situ cartilage regeneration, it is crucial to develop a sequential drug release system capable of recruiting endogenous bone marrow mesenchymal stem cells (BMSCs) and promoting their chondrogenic differentiation. Herein, based on our long-term and fruitful research on silk fibroin (SF) porous scaffolds, a cell-free sequential drug delivery SF scaffold was developed. BMSCs affinity peptide PFSSTKT (PFS) was coated on the surface of SF scaffold, in which chondrogenic inducer kartogenin (KGN) and anti-inflammatory factor dexamethasone (DEX) were loaded. PFS was rapidly released within the first 10 days while KGN and DEX could be released over 28 days. The scaffold promoted BMSCs migration and chondrogenic differentiation through the release of PFS and KGN in vitro. Finally, the sequential drug released by the implanted SF scaffolds in rats indeed recruited endogenous BMSCs and significantly promoted the in-situ regeneration of their knee cartilage defects. In summary, this study not only introduces a green and environmentally friendly all silk-based sequential drug delivery system, but also provides an effective tissue engineering functional scaffold for in-situ cartilage regeneration.

Precision repair of zone-specific meniscal injuries using a tunable extracellular matrix-based hydrogel system

Meniscus injuries present significant therapeutic challenges due to their limited self-healing capacity and the diverse biological and mechanical properties across the tissue. Conventional repair strategies do not replicate the complex zonal characteristics within the meniscus, resulting in suboptimal outcomes. In this study, we introduce an innovative fetal/adult and stiffness-tunable meniscus decellularized extracellular matrix (DEM)-based hydrogel system designed for precision repair of heterogeneous, zonal-dependent meniscus injuries. By synthesizing fetal and adult DEM hydrogels, we identified distinct cellular responses, including that hydrogels with adult meniscus-derived DEM promote more fibrochondrogenic phenotypes. The incorporation of methacrylated hyaluronic acid (MeHA) further refined the mechanical properties and injectability of the DEM-based hydrogels. The combination of fetal and adult DEM with MeHA allowed for precise tuning of stiffness, influencing cell differentiation and closely mimicking native tissue environments. In vivo tests confirmed the biocompatibility of hydrogels and their integration with native meniscus tissues. Furthermore, advanced 3D bioprinting techniques enabled the fabrication of hybrid hydrogels with biomaterial and mechanical gradients, effectively emulating the zonal properties of meniscus tissue and enhancing cell integration. This study represents a significant advance in meniscus tissue engineering, providing a promising platform for customized regenerative therapies across a range of heterogeneous fibrous connective tissues.

Mussel-inspired bifunctional chimeric peptides macromolecules functionalize 3D-printed porous scaffolds for enhanced antimicrobial and osseointegration properties in bone defect repair

Polyetheretherketone (PEEK) is a promising material for bone defect repair due to its superior mechanical properties and chemical stability. However, its limited bioactivity and susceptibility to infection hinder its clinical use. To address these limitations, we developed antibacterial and osteogenic bifunctional chimeric peptides (CP) and integrated them onto 3D-printed PEEK scaffolds (3DP) using the adhesive properties of 3,4-dihydroxy-L-phenylalanine (DOPA). The CP, composed of antimicrobial peptide (GL13K) and osteogenic peptide (PFS) linked by DOPA, enhances bacterial membrane disruption while promoting bone marrow mesenchymal stem cell (BMSCs) adhesion and osteogenic differentiation. Through DOPA-mediated attachment, a hydrophilic and stable layer is formed on the scaffold surface via a simple immersion process. In vitro studies showed that CP@3DP effectively destroys bacterial membranes of Staphylococcus aureus and Escherichia coli, while promoting BMSCs adhesion, proliferation, and differentiation. In a rat skull defect model infected with S. aureus, CP@3DP demonstrated synergistic antibacterial effects and enhanced bone regeneration. Micro-CT imaging and histologic analysis confirmed that CP@3DP was firmly bound to host bone. This study highlights the potential of DOPA as a versatile adhesion molecule and the CP's bifunctional design for bone defect repair in infected environments, offering a novel approach for tissue engineering applications.

Single BMSC-derived cartilage organoids for gradient heterogeneous osteochondral regeneration by leveraging native vascular microenvironment

Heterogeneous osteochondral regeneration remains a significant challenge due to the distinct microenvironments across the cartilage, calcified cartilage, and subchondral bone layers. The natural gradient of vascularization from the superficial to deep layers of osteochondral tissue plays a critical role in guiding the differentiation of bone marrow stem cells (BMSCs) into chondrocytes and osteoblasts. In this study, we propose a strategy for gradient heterogeneous osteochondral regeneration using cartilage organoids derived from single BMSCs, leveraging the natural vascularization gradient within osteochondral tissue. We successfully isolated BMSCs from rabbits and generated cartilage organoids via in vitro three-dimensional chondrogenic culture. To mimic the pro-vascular microenvironment, we introduced vascular endothelial growth factor, which promoted the hypertrophic differentiation of the cartilage organoids. We then prepared cartilage organoid/GelMA complexes, with or without the anti-vascular drug Axitinib, and implanted them subcutaneously in nude mice. The vascularized subcutaneous microenvironment induced osteogenic differentiation, while Axitinib treatment created an anti-vascular microenvironment, inhibiting osteogenesis and preserving chondrogenesis within the complexes. Both in vitro and in vivo data demonstrated the crucial role of the vascular microenvironment in regulating osteogenic differentiation of cartilage organoids. Finally, organoid/GelMA cylinders were implanted into a rabbit osteochondral defect, where the gradient vascularization at the defect site guided the organoids to differentiate into both cartilage and bone. This single BMSC-derived cartilage organoid approach enables precise gradient heterogeneous osteochondral regeneration, guided by the natural microenvironment within the osteochondral defect site, representing a significant advancement for clinical applications.

Transcriptomic analysis reveals distinct molecular signatures and regulatory networks of osteoarthritic chondrocytes versus mesenchymal stem cells during chondrogenesis

BACKGROUND

Recent regenerative studies imply conflicting results on knee osteoarthritic (OA) chondrocytes and mesenchymal stem cells (MSC)-mediated cartilage constructs in terms of compressive properties and tensile strength. This could be attributed to different gene expression patterns between MSC and OA chondrocytes during chondrogenic differentiation. Therefore, we analyzed differentially expressed genes (DEGs) between OA and MSC-derived chondrocytes using bioinformatics tools.

METHODS

We downloaded and analyzed the GSE19664 dataset from the Gene Expression Omnibus to identify DEGs. DAVID was used to perform Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analyses, while a protein-protein interaction network of DEGs was constructed through the Search Tool for the Retrieval of Interacting Genes (STRING) and identified hub genes by CytoHubba.

RESULTS

A total of 43 DEGs identified (15 downregulated and 28 upregulated) were found to be deregulated between OA and MSC-derived chondrocytes. KEGG analysis revealed the enrichment of complement and coagulation cascades and other pathways among the studied chondrocytes. The pathway enrichment identified top KEGG, gene ontology biological process, molecular function, and cellular component. The hub networks identified the top 5 hub genes involved in chondrogenesis, including CLU, PLAT, CP, TIMP3, and SERPINA1.

CONCLUSIONS

Our results identified significant genes involved in chondrogenesis. These findings provide new avenues for exploring the genetic mechanism underlying cartilage synthesis and novel targets for preclinical intervention and clinical treatment.

An "EVs-in-ECM" mimicking system orchestrates transcription and translation of RUNX1 for in-situ cartilage regeneration

The self-repair ability of articular cartilage is limited, which is one of the most difficult diseases to treat clinically. Kartogenin (KGN) induces chondrogenesis by regulating RUNX1 mRNA translation and the small molecule compound TD-198946 (TD) promotes chondrogenic differentiation of mesenchymal stem cells (MSCs) through increasing the transcription of RUNX1 mRNA. GelMA hydrogel and liposomes are respectively similar to the extracellular matrix (ECM) and extracellular vesicles (EVs). So, we developed an "EVs-in-ECM" mimicking system by incorporating GelMA and KGN/TD-loaded liposomes to investigate the repair effects of cartilage defect. First, western-blot, RNA fluorescence in situ hybridization (FISH), cellular immuno-fluorescence, co-immuno-precipitation (CO-IP), and qRT-PCR techniques showed that KGN regulated RUNX1 mRNA expression, and then promote chondrogenic differentiation of MSCs. Second, the role of RUNX1 was amplified by orchestrating RUNX1 transcription and translation through TD-198946 (TD) and KGN respectively, and the synergistic effects of TD and KGN on chondrogenesis of MSCs in vitro were discovered. Finally, an "EVs-in-ECM" mimicking system was designed for in situ cartilage repair. When GelMA loaded with KGN and TD liposomes, the hydrogel (KGN + TD@ GelMA) showed biological functions by the continuously controlled release of KGN and TD while maintaining its porous structure and mechanical strength, which enhanced the chondrogenesis of MSCs in one system. The repair performance of "EVs-in-ECM" in vivo was assessed using the articular osteochondral defect model of rat. The implantation of KGN + TD@ GelMA hydrogels effectively exerted favorable osteochondral repair effects showing structures similar to the native tissue, and prevented chondrocyte hypertrophy. The study indicate that the "EVs-in-ECM" mimicking system can act as a highly efficient and potent scaffold for osteochondral defect regeneration.

Effects of protein conformational transition accompanied with crosslinking density cues in silk fibroin hydrogels on the proliferation and chondrogenesis of encapsulated stem cells

Silk fibroin (SF) hydrogels possess excellent biocompatibility and biomimetic properties of the extracellular matrix. Among them, the mild chemical crosslinked SF hydrogels show great application potential in the fields of 3D cell culture and tissue repairing and thus have attracted widespread attention. However, the mobility of hydrophobic chain segments of SF molecules in these chemical crosslinked hydrogels can easily cause the molecules to undergo a self-assembly process from random coil to β-sheet conformation due to its lower energy state, thus inducing an inevitable conformational transition process. This process further leads to dynamic changes of important material features, such as the hydrogel pore size and mechanical properties, which can probably bring some non-negligible and unknown impacts on cell behaviors and their biomedical applications. In this study, a typical mild crosslinking system composed of horseradish peroxidase and hydrogen peroxide was chosen to prepare SF hydrogels. A feasible protein conformational transition rate controlling strategy based on hydrogel crosslinking density regulation was also proposed. Our results demonstrate that the lower the hydrogel crosslinking density, the faster the conformational transition rate. Subsequently, SF hydrogels with different conformational transition rates were successfully constructed to investigate the impact of the protein conformational transition rate accompanied with initial crosslinking density on the proliferation and chondrogenic differentiation of encapsulated stem cells. Results comprehensively illustrated that the conformational transition process could effectively regulate cell behavior. The hydrogel with an appropriate conformational transition rate obviously promoted the proliferation and chondrogenesis of encapsulated stem cells, while too fast or too slow transition processes slowed down these cell activities. These findings are hopefully to provide valuable guidance for the development and efficient usage of SF hydrogels in the fields of 3D cell culture and tissue engineering.

A shear-responsive and lubricating hyaluronic acid-chondroitin sulfate-decellularized matrix hydrogel for articular cartilage regeneration

The high-dynamic, high-loading environment in the joint cavity puts urgent demands on the cartilage regenerative materials with shear responsiveness and lubrication. Here, a new type of injectable hydrogel composed of oxidized hyaluronic acid (OHA), adipic dihydrazide-grafted hyaluronic acid (HA-ADH), oxidized chondroitin sulfate (OChs), and decellularized extracellular matrix methacrylate (dECMMA) was fabricated. The aldehyde groups in OHA and OChs reacted with the amino groups in HA-ADH to form a dynamic hydrogel, which was then covalently crosslinked with dECMMA to create a dual-crosslinked hydrogel with sufficient mechanical strength. This hydrogel possesses injectability and self-healing capabilities, making it suitable for use in the dynamic and high-frequency loading environment of joint cartilage. dECMMA fibers in this hydrogel could be oriented and aligned under certain shear forces, together with the biopolymers, giving the hydrogel lubricity and low strain-liquid transition properties that do not interfere with the daily mobility of the joint. In vitro and in vivo experiments showed that the hydrogel has sufficient tissue adhesion and excellent biocompatibility, promotes chondrocyte migration, and induces stem cell differentiation. The animal experiments demonstrated that the hydrogel promoted cartilage repair, and the lubricating effect of the newborn cartilage was close to that of normal cartilage.

Identification and function of periosteal skeletal stem cells in skeletal development, homeostasis, and disease

Background

Periosteum-resident skeletal stem cells (SSCs) are essential for the growth, maintenance, and repair of the skeletal system. These cells exhibit self-renewal ability and clonal pluripotency. Compared to the diverse bone marrow mesenchymal stem cells (BMSCs), periosteal skeletal stem cells (P-SSCs) represent a purified stem cell population and are preferable for bone tissue engineering.

Methods

This review covers the histological structure of the periosteum, process of isolating and characterising P-SSCs, and spatiotemporal distribution and characteristics of P-SSCs from different lineages. Additionally, the roles of P-SSCs in bone injury, disease, and periosteal niche regulation are discussed.

Results

Intramembrane and intraconal ossification of P-SSCs exhibits favourable therapeutic potential. Osteogenesis using P-SSCs is an ideal process for bone repair.

Conclusions

P-SSCs are vital for bone formation, maintenance, and repair. P-SSCs are essential components of the periosteal microenvironment. Therefore, it is essential to investigate their critical clinical applications and translational functions. By targeting and inducing endogenous stem cells, the in situ repair of bone defects can be facilitated, leading to the development of more effective novel therapies.

The translational potential of this article

To enhance our understanding of the function of P-SSCs in bone repair and skeleton-related diseases, it is imperative to elucidate the current research status of P-SSCs and ascertain the prospective trajectory for their advancement and refinement in bone tissue engineering. P-SSCs are expected to play an expanded role in treating bone abnormalities, leading to the optimisation of bone tissue treatment.

Effects of Silk Fibroin Hydrogel Degradation on the Proliferation and Chondrogenesis of Encapsulated Stem Cells

Silk fibroin (SF) hydrogels are widely used in three-dimensional (3D) cell culture and tissue repair. Despite their importance, few studies have focused on regulating their degradation and further revealing the effects of the degradation process on encapsulated cell behaviors. Herein, SF hydrogels with equivalent initial properties and different degradation rates were prepared by adjusting the ratios between the hydrogel-encapsulated normal SF microspheres (MSN) and enzyme-loaded SF microspheres (MSE). Further, cell experiments revealed that moderately accelerating the hydrogel degradation obviously improved the proliferation of MSCs during 7 days of culture. Slightly accelerating the hydrogel degradation promoted MSC chondrogenesis. However, too rapid of a hydrogel degradation was unfavorable for these cell behaviors. The relevant studies are expected to provide useful strategies for regulating SF hydrogel degradation and also afford new references for the development of excellent SF hydrogels and other protein-based biomaterials for cartilage regeneration.

Injectable acellular matrix microgel assembly with stem cell recruitment and chondrogenic differentiation functions promotes microfracture-based articular cartilage regeneration

Articular cartilage repair and regeneration is still a significant challenge despite years of research. Although microfracture techniques are commonly used in clinical practice, the newborn cartilage is usually fibrocartilage rather than hyaline cartilage, which is mainly attributed to the inadequate microenvironment for effectively recruiting, anchoring, and inducing bone marrow mesenchymal stem cells (BMSCs) to differentiate into hyaline cartilage. This paper introduces a novel cartilage acellular matrix (CACM) microgel assembly with excellent microporosity, injectability, tissue adhesion, BMSCs recruitment and chondrogenic differentiation capabilities to improve the microfracture-based articular cartilage regeneration. Specifically, the sustained release of simvastatin (SIM) from the SIM@CACM microgel assembly efficiently recruits BMSCs in the early stage of cartilage regeneration, while the abundant interconnected micropores and high specific area assure the quick adhesion, proliferation and infiltration of BMSCs. Additionally, the active factors within the CACM matrix, appropriate mechanical properties of the microgel assembly, and excellent tissue adhesion provide a conductive environment for the continuous chondrogenic differentiation of BMSCs into hyaline cartilage. Owing to the synergistic effect of the above-mentioned factors, good articular cartilage repair and regeneration is achieved.

Reinforced enzyme mineralized chitosan hydrogels with superior mechanical and osteogenic properties

As a natural cationic polymer material, the application of chitosan hydrogel for bone tissue engineering has been greatly limited due to its poor mechanical strength. Enzymatic mineralization has drawn increased attention to effectively improve the mechanical properties of hydrogels. In this study, carboxymethyl chitosan (CMCS) hydrogels cross-linked with different concentrations of genipin (2.5 %, 5 % and 10 %) were prepared and further mineralized through enzyme-induced biomimetic mineralization. The mechanical properties of the CMCS hydrogels were significantly increased as a result of mineralization, showing improvement of 1200-1500 % on storage moduli, and even exhibiting certain tensile behavior with the elongation rate of 30-35 %, likely due to the uniform formation and small size of mineralized products. Interestingly, the cationicity of chitosan also exerted an important modulation effect and the mineralization behavior and mechanical properties of mineralized hydrogels. In addition, the enzymatic mineralized hydrogels showed enhanced biocompatibility and osteogenic differentiation in-vitro, likely due to its superior mechanical properties and the introduction of calcium phosphate biominerals. In vivo experiments further suggest excellent bone-forming activity for the enzymatic mineralized hydrogels. Overall, tuning cationicity and enzymatic mineralization provide an effective approach for the preparation of chitosan hydrogels with superior mechanical and biological properties for bone tissue engineering application.

Differentiation of stem cells into chondrocytes and their potential clinical application in cartilage regeneration

Cartilage diseases and injuries are considered difficult to treat owing to the low regenerative capacity of this tissue. Using stem cells (SCs) is one of the potential methods of treating cartilage defects and creating functional cartilage models for transplants. Their ability to proliferate and to generate functional chondrocytes, a natural tissue environment, and extracellular cartilage matrix, makes SCs a new opportunity for patients with articular injuries or incurable diseases, such as osteoarthritis (OA). The review summarizes the most important scientific reports on biology and mechanisms of SC-derived chondrogenesis and sources of SCs for chondrogenic purposes. Additionally, it focuses on the genetic mechanisms, microRNA (miRNA) regulation, and epigenetic processes steering the chondrogenic differentiation of SCs. It also describes the attempts to create functional cartilage with tissue engineering using growth factors and scaffolds. Finally, it presents the challenges that researchers will have to face in the future to effectuate SC differentiation methods into clinical practice for treating cartilage diseases.

Self-Healing Hyaluronic Acid-based Hydrogel with miRNA140-5p Loaded MON-PEI Nanoparticles for Chondrocyte Regeneration: Schiff Base Self-Assembly Approach

Articular cartilage defects present a significant therapeutic challenge due to the inherent avascular and aneural characteristics of cartilage tissue. Gene therapy has emerged as a promising strategy for cartilage regeneration, particularly through the use of functional RNA and biomaterial-assisted frameworks. In this study, an innovative gene-activated self-healing hydrogel is developed and fabricated for the controlled release of miR140-5p, a key regulator of cartilage regeneration. The hydrogel, crosslinked via UV radiation, is composed of aminated hyaluronic acid and a modified photosensitizer (NB). To enhance the scaffold's structural integrity and gene delivery efficiency, mineralized silk fibroin and miR140-5p-loaded MON-PEI nanoparticles are incorporated. These findings demonstrate that this novel hydrogel (miR140-5p-CaP@mSF-HA-NB) effectively encapsulates and releases miR140-5p, exhibits excellent biocompatibility, and promotes enhanced cartilage regeneration in both in vitro and in vivo models. Therefore, this gene-activated hydrogel holds significant potential for clinical applications in the treatment of articular cartilage defects.

Glucosamine sulfate-loaded nanofiber reinforced carboxymethyl chitosan sponge for articular cartilage restoration

Cartilage is severely limited in self-repair after damage, and tissue engineering scaffold transplantation is considered the most promising strategy for cartilage regeneration. However, scaffolds without cells and growth factors, which can effectively avoid long cell culture times, high risk of infection, and susceptibility to contamination, remain scarce. Hence, we developed a cell- and growth factor-dual free hierarchically structured nanofibrous sponge to mimic the extracellular matrix, in which the encapsulated core-shell nanofibers served both as mechanical supports and as long-lasting carriers for bioactive biomass molecules (glucosamine sulfate). Under the protection of the nanofibers in this designed sponge, glucosamine sulfate could be released continuously for at least 30 days, which significantly accelerated the repair of cartilage tissue in a rat cartilage defect model. Moreover, the nanofibrous sponge based on carboxymethyl chitosan as the framework could effectively fill irregular cartilage defects, adapt to the dynamic changes during cartilage movement, and maintain almost 100 % elasticity even after multiple compression cycles. This strategy, which combines fiber freeze-shaping technology with a controlled-release method for encapsulating bioactivity, allows for the assembly of porous bionic scaffolds with hierarchical nanofiber structure, providing a novel and safe approach to tissue repair.

Transglutaminase-triggered dual gradients of mechanical and biochemical cues self-assembling peptide hydrogel for guiding MC3T3-E1 cell behaviors

The mechanical properties and bioactive motif densities of extracellular matrix materials play crucial roles in regulating cell behaviors, such as cell adhesion, migration, proliferation, and differentiation. However, current studies on cellular responses to ECM predominantly concentrated on polymer hydrogels featuring a single factor, such as the mechanical strength, the types of bioactive motifs, and the morphology of the polymers. This limited focus may overlook the complex interplay of multiple factors. Here, we developed dual gradient peptide Q3GT-I3K hydrogels with tunable mechanical strength (0.3-4.0 kPa) and different density of bioactive motif (0.45-3.67 mM) by enzymatic crosslinking. These hydrogels can mimic the viscoelasticity of natural soft tissues. The properties of mechanical strength and cell responsive motif density could be controlled by modulating the proportion of the substrates in the enzymatic reaction. MC3T3 cells significantly differentiated into osteoblasts after seeded on the Q3GT-I3K hydrogel (2.8 kPa, 1.83 mM Q3GT) for 21 days, identifying from the elevated expression of alkaline phosphatase and substantial calcium nodule formation. Importantly, the engineered hydrogels exert a synergistic effect on the cell behaviors such as early adhesion, late proliferation, and differentiation of MC3T3-E1 cells. This paper introduces a new strategy for designing tissue engineering scaffold materials with specific functions.

[Research progress on bone repair biomaterials with the function of recruiting endogenous mesenchymal stem cells]

Objective

To review the research progress on bone repair biomaterials with the function of recruiting endogenous mesenchymal stem cells (MSCs).

Methods

An extensive review of the relevant literature on bone repair biomaterials, particularly those designed to recruit endogenous MSCs, was conducted, encompassing both domestic and international studies from recent years. The construction methods and optimization strategies for these biomaterials were summarized. Additionally, future research directions and focal points concerning this material were proposed.

Results

With the advancement of tissue engineering technology, bone repair biomaterials have increasingly emerged as an ideal solution for addressing bone defects. MSCs serve as the most critical "seed cells" in bone tissue engineering. Historically, both MSCs and their derived exosomes have been utilized in bone repair biomaterials; however, challenges such as limited sources of MSCs and exosomes, low survival rates, and various other issues have persisted. To address these challenges, researchers are combining growth factors, bioactive peptides, specific aptamers, and other substances with biomaterials to develop constructs that facilitate stem cell recruitment. By optimizing mechanical properties, promoting vascular regeneration, and regulating the microenvironment, it is possible to create effective bone repair biomaterials that enhance stem cell recruitment.

Conclusion

In comparison to cytokines, phages, and metal ions, bioactive peptides and aptamers obtained through screening exhibit more specific and targeted recruitment functions. Future development directions for bone repair biomaterials will involve the modification of peptides and aptamers with targeted recruitment capabilities in biological materials, as well as the optimization of the mechanical properties of these materials to enhance vascular regeneration and adjust the microenvironment.

Cell-free decellularized skin matrix scaffolds: A promising approach for meniscus regeneration in a rabbit meniscectomy model

Tissue engineering presents a promising approach for the treatment of meniscal injuries, yet the development of meniscal scaffolds that exhibit both superior biomechanical properties and biocompatibility remains a considerable challenge. In this study, decellularized skin matrix (DSM) scaffolds were first prepared using porcine skin through decellularization and freeze-drying techniques. The DSM scaffold has favorable porosity, hydrophilicity, and biocompatibility. Importantly, the collagen content and tensile modulus of the scaffold are comparable to those of native meniscus (44.13 ± 2.396 mg/g vs. 42.41 ± 2.40 mg/g and 103.30 ± 2.98 MPa vs. 128.80 ± 9.115 MPa). Subsequently, the peptide PFSSTKT (PFS) with mesenchymal stem cells (MSCs) recruitment capability was used to modify DSM to construct DSM-PFS scaffolds. Compared to the DSM scaffold, the optimized DSM-PFS scaffold enhanced in vitro collagen and glycosaminoglycan (GAG) production and upregulated the expression of cartilage-specific genes. Furthermore, the DSM-PFS scaffold was more effective in recruiting MSCs in vitro. In vivo studies in rabbit models showed that the DSM-PFS scaffold successfully promoted meniscus tissue regeneration. Three months post-implantation, meniscus tissue formation can be observable, and after six months, the neo-meniscus exhibited tissue structure and tensile properties similar to the native meniscus. Notably, the DSM-PFS scaffold exhibited significant chondroprotective effects, slowing osteoarthritis (OA) progression. In conclusion, the DSM-PFS scaffold may represent a promising candidate for future applications in meniscus tissue engineering. STATEMENT OF SIGNIFICANCE: We developed a decellularized skin matrix (DSM) meniscus scaffold using whole-layer porcine skin, demonstrating superior biomechanical strength and biocompatibility. Following modification with the stem cell-recruiting peptide PFS, the optimized DSM-PFS scaffold outperformed the DSM scaffold in cell attraction, collagen and glycosaminoglycan production, and cartilage-specific gene expression. Implanted into rabbit knee joints, the cell-free DSM-PFS scaffold induced meniscal tissue formation within three months, achieving the histological structure and tensile strength of the native meniscus by six months. Moreover, it significantly protected the cartilage. Our findings provide new insights into the fabrication of scaffolds for meniscal tissue engineering, with the DSM-PFS scaffold emerging as an ideal candidate for future applications.

Precision Repair of Zone-Specific Meniscal Injuries Using a Tunable Extracellular Matrix-Based Hydrogel System

Meniscus injuries present significant therapeutic challenges due to their limited self-healing capacity and diverse biological and mechanical properties across meniscal tissue. Conventional repair strategies neglect to replicate the complex zonal characteristics within the meniscus, resulting in suboptimal outcomes. In this study, we introduce an innovative, age- and stiffness-tunable meniscus decellularized extracellular matrix (DEM)-based hydrogel system designed for precision repair of heterogeneous, zonal-dependent meniscus injuries. By synthesizing age-dependent DEM hydrogels, we identified distinct cellular responses: fetal bovine meniscus-derived DEM promoted chondrogenic differentiation, while adult meniscus-derived DEM supported fibrochondrogenic phenotypes. The incorporation of methacrylate hyaluronic acid (MeHA) further refined the mechanical properties and injectability of the DEM-based hydrogels. The combination of age-dependent DEM with MeHA allowed for precise stiffness tuning, influencing cell differentiation and closely mimicking native tissue environments. In vivo tests confirmed the biocompatibility of hydrogels and their integration with native meniscus tissues. Furthermore, advanced 3D bioprinting techniques enabled the fabrication of hybrid hydrogels with biomaterial and mechanical gradients, effectively emulating the zonal properties of meniscus tissue and enhancing cell integration. This study represents a significant advancement in meniscus tissue engineering, providing a promising platform for customized regenerative therapies across a range of heterogeneous fibrous connective tissues.

Tissue engineering strategies hold promise for the repair of articular cartilage injury

Articular cartilage damage and wear can result in cartilage degeneration, ultimately culminating in osteoarthritis. Current surgical interventions offer limited capacity for cartilage tissue regeneration and offer only temporary alleviation of symptoms. Tissue engineering strategies are increasingly recognized as promising modalities for cartilage restoration. Currently, various biological scaffolds utilizing tissue engineering materials are extensively employed in both fundamental and clinical investigations of cartilage repair. In order to optimize the cartilage repair ability of tissue engineering scaffolds, researchers not only optimize the structure and properties of scaffolds from the perspective of materials science and manufacturing technology to enhance their histocompatibility, but also adopt strategies such as loading cells, cytokines, and drugs to promote cartilage formation. This review provides an overview of contemporary tissue engineering strategies employed in cartilage repair, as well as a synthesis of existing preclinical and clinical research. Furthermore, the obstacles faced in the translation of tissue engineering strategies to clinical practice are discussed, offering valuable guidance for researchers seeking to address these challenges.

Research Progress in Hydrogels for Cartilage Organoids

The repair and regeneration of cartilage has always been a hot topic in medical research. Cartilage organoids (CORGs) are special cartilage tissue created using tissue engineering techniques outside the body. These engineered organoids tissues provide models that simulate the complex biological functions of cartilage, opening new possibilities for cartilage regenerative medicine and treatment strategies. However, it is crucial to establish suitable matrix scaffolds for the cultivation of CORGs. In recent years, utilizing hydrogel to culture stem cells and induce their differentiation into chondrocytes has emerged as a promising method for the in vitro construction of CORGs. In this review, the methods for establishing CORGs are summarized and an overview of the advantages and limitations of using matrigel in the cultivation of such organoids is provided. Furthermore, the importance of cartilage tissue ECM and alternative hydrogel substitutes for Matrigel, such as alginate, peptides, silk fibroin, and DNA derivatives is discussed, and the pros and cons of using these hydrogels for the cultivation of CORGs are outlined. Finally, the challenges and future directions in hydrogel research for CORGs are discussed. It is hoped that this article provides valuable references for the design and development of hydrogels for CORGs.

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.

Endogenous Tissue Engineering for Chondral and Osteochondral Regeneration: Strategies and Mechanisms

Increasing attention has been paid to the development of effective strategies for articular cartilage (AC) and osteochondral (OC) regeneration due to their limited self-reparative capacities and the shortage of timely and appropriate clinical treatments. Traditional cell-dependent tissue engineering faces various challenges such as restricted cell sources, phenotypic alterations, and immune rejection. In contrast, endogenous tissue engineering represents a promising alternative, leveraging acellular biomaterials to guide endogenous cells to the injury site and stimulate their intrinsic regenerative potential. This review provides a comprehensive overview of recent advancements in endogenous tissue engineering strategies for AC and OC regeneration, with a focus on the tissue engineering triad comprising endogenous stem/progenitor cells (ESPCs), scaffolds, and biomolecules. Multiple types of ESPCs present within the AC and OC microenvironment, including bone marrow-derived mesenchymal stem cells (BMSCs), adipose-derived mesenchymal stem cells (AD-MSCs), synovial membrane-derived mesenchymal stem cells (SM-MSCs), and AC-derived stem/progenitor cells (CSPCs), exhibit the ability to migrate toward injury sites and demonstrate pro-regenerative properties. The fabrication and characteristics of scaffolds in various formats including hydrogels, porous sponges, electrospun fibers, particles, films, multilayer scaffolds, bioceramics, and bioglass, highlighting their suitability for AC and OC repair, are systemically summarized. Furthermore, the review emphasizes the pivotal role of biomolecules in facilitating ESPCs migration, adhesion, chondrogenesis, osteogenesis, as well as regulating inflammation, aging, and hypertrophy-critical processes for endogenous AC and OC regeneration. Insights into the applications of endogenous tissue engineering strategies for in vivo AC and OC regeneration are provided along with a discussion on future perspectives to enhance regenerative outcomes.

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.

Nanoclay Reinforced Integrated Scaffold for Dual-Lineage Regeneration of Cartilage and Subchondral Bone

Tissue engineering is theoretically considered a promising approach for repairing osteochondral defects. Nevertheless, the insufficient osseous support and integration of the cartilage layer and the subchondral bone frequently lead to the failure of osteochondral repair. Drawing from this, it was proposed that incorporating glycine-modified attapulgite (GATP) into poly(1,8-octanediol-co-citrate) (POC) scaffolds via the one-step chemical cross-linking is proposed to enhance cartilage and subchondral bone defect repair simultaneously. The effects of the GATP incorporation ratio on the physicochemical properties, chondrocyte and MC3T3-E1 behavior, and osteochondral defect repair of the POC scaffold were also evaluated. In vitro studies indicated that the POC/10% GATP scaffold improved cell proliferation and adhesion, maintained cell phenotype, and upregulated chondrogenesis and osteogenesis gene expression. Animal studies suggested that the POC/10% GATP scaffold has significant repair effects on both cartilage and subchondral bone defects. Therefore, the GATP-incorporated scaffold system with dual-lineage bioactivity showed potential application in osteochondral regeneration.

DLM-GelMA/tumor slice sandwich structured tumor on a chip for drug efficacy testing

The in vitro recapitulation of tumor microenvironment is of great interest to preclinical screening of drugs. Compared with culture of cell lines, tumor organ slices can better preserve the complex tumor architecture and phenotypic activity of native cells, but are limited by their exposure to fluid shear and gradual degradation under perfusion culture. Here, we established a decellularized liver matrix (DLM)-GelMA "sandwich" structure and a perfusion-based microfluidic platform to support long-term culture of tumor slices with excellent structural integrity and cell viability over 7 days. The DLM-GelMA was able to secrete cytokines and growth factors while providing shear protection to the tumor slice via the sandwich structure, leading to the preservation of the tumor microenvironment where immune cells (CD3, CD8, CD68), tumor-associated fibroblasts (α-SMA), and extracellular matrix components (collagen I, fibronectin) were well maintained. Furthermore, this chip presented anti-tumor efficacy at cisplatin (20 μM) on tumor patients, demonstrating our platform's efficacy to design patient-specific treatment regimens. Taken together, the successful development of this DLM-GelMA sandwich structure on the chip could faithfully reflect the tumor microenvironment and immune response, accelerating the screening process of drug molecules and providing insights for practical medicine.

Synergistic large segmental bone repair by 3D printed bionic scaffolds and engineered ADSC nanovesicles: Towards an optimized regenerative microenvironment

Achieving sufficient bone regeneration in large segmental defects is challenging, with the structure of bone repair scaffolds and their loaded bioactive substances crucial for modulating the local osteogenic microenvironment. This study utilized digital laser processing (DLP)-based 3D printing technology to successfully fabricate high-precision methacryloylated polycaprolactone (PCLMA) bionic bone scaffold structures. Adipose-derived stem cell-engineered nanovesicles (ADSC-ENs) were uniformly and stably modified onto the bionic scaffold surface using a perfusion device, constructing a conducive microenvironment for tissue regeneration and long bone defect repair through the scaffold's structural design and the vesicles' biological functions. Scanning electron microscopy (SEM) examination of the scaffold surface confirmed the efficient loading of ADSC-ENs. The material group loaded with vesicles (PCLMA-BAS-ENs) demonstrated good cell compatibility and osteogenic potential when analyzed for the adhesion and osteogenesis of primary rabbit bone marrow mesenchymal stem cells (BMSCs) on the material surface. Tested in a 15 mm critical rabbit radial defect model, the PCLMA-BAS-ENs scaffold facilitated near-complete bone defect repair after 12 weeks. Immunofluorescence and proteomic results indicated that the PCLMA-BAS-ENs scaffold significantly improved the osteogenic microenvironment at the defect site in vivo, promoted angiogenesis, and enhanced the polarization of macrophages towards M2 phenotype, and facilitated the recruitment of BMSCs. Thus, the PCLMA-BAS-ENs scaffold was proven to significantly promote the repair of large segmental bone defects. Overall, this strategy of combining engineered vesicles with highly biomimetic scaffolds to promote large-segment bone tissue regeneration holds great potential in orthopedic and other regenerative medicine applications.

Enhanced chondrogenic potential in GelMA-based 3D cartilage model via Wnt3a surface immobilization

Cartilage tissue engineering aims to develop functional substitutes for treating cartilage defects and osteoarthritis. Traditional two-dimensional (2D) cell culture systems lack the complexity of native cartilage, leading to the development of 3D regenerative cartilage models. In this study, we developed a 3D model using Gelatin Methacryloyl (GelMA)-based hydrogels seeded with Y201 cells, a bone marrow mesenchymal stem cell line. The model investigated chondrogenic differentiation potential in response to Wnt3a stimulation within the GelMA scaffold and validated using known chondrogenic agonists. Y201 cells demonstrated suitability for the model, with increased proteoglycan content and upregulated chondrogenic marker expression under chondrogenic conditions. Wnt3a enhanced cell proliferation, indicating activation of the Wnt/β-catenin pathway, which plays a role in cartilage development. GelMA hydrogels provided an optimal scaffold, supporting cell viability and proliferation. The 3D model exhibited consistent responses to chondrogenic agonists, with TGF-β3 enhancing cartilage-specific extracellular matrix (ECM) production and chondrogenic differentiation. The combination of Wnt3a and TGF-β3 showed synergistic effects, promoting chondrogenic differentiation and ECM production. This study presents a 3D regenerative cartilage model with potential for investigating cartilage biology, disease mechanisms, and drug screening. The model provides insights into complex cartilage regeneration mechanisms and offers a platform for developing therapeutic approaches for cartilage repair and osteoarthritis treatment.

[Research progress of three-dimensional bioprinting technology in auricle repair and reconstruction]

Objective

To review the research progress on the application of three-dimensional (3D) bioprinting technology in auricle repair and reconstruction.

Methods

The recent domestic and international research literature on 3D printing and auricle repair and reconstruction was extensively reviewed, and the concept of 3D bioprinting technology and research progress in auricle repair and reconstruction were summarized.

Results

The auricle possesses intricate anatomical structure and functionality, necessitating precise tissue reconstruction and morphological replication. Hence, 3D printing technology holds immense potential in auricle reconstruction. In contrast to conventional 3D printing technology, 3D bioprinting technology not only enables the simulation of auricular outer shape but also facilitates the precise distribution of cells within the scaffold during fabrication by incorporating cells into bioink. This approach mimics the composition and structure of natural tissues, thereby favoring the construction of biologically active auricular tissues and enhancing tissue repair outcomes.

Conclusion

3D bioprinting technology enables the reconstruction of auricular tissues, avoiding potential complications associated with traditional autologous cartilage grafting. The primary challenge in current research lies in identifying bioinks that meet both the mechanical requirements of complex tissues and biological criteria.

Unveiling the versatility of gelatin methacryloyl hydrogels: a comprehensive journey into biomedical applications

Gelatin methacryloyl (GelMA) hydrogels have gained significant recognition as versatile biomaterials in the biomedical domain. GelMA hydrogels emulate vital characteristics of the innate extracellular matrix by integrating cell-adhering and matrix metalloproteinase-responsive peptide motifs. These features enable cellular proliferation and spreading within GelMA-based hydrogel scaffolds. Moreover, GelMA displays flexibility in processing, as it experiences crosslinking when exposed to light irradiation, supporting the development of hydrogels with adjustable mechanical characteristics. The drug delivery landscape has been reshaped by GelMA hydrogels, offering a favorable platform for the controlled and sustained release of therapeutic actives. The tunable physicochemical characteristics of GelMA enable precise modulation of the kinetics of drug release, ensuring optimal therapeutic effectiveness. In tissue engineering, GelMA hydrogels perform an essential role in the design of the scaffold, providing a biomimetic environment conducive to cell adhesion, proliferation, and differentiation. Incorporating GelMA in three-dimensional printing further improves its applicability in drug delivery and developing complicated tissue constructs with spatial precision. Wound healing applications showcase GelMA hydrogels as bioactive dressings, fostering a conducive microenvironment for tissue regeneration. The inherent biocompatibility and tunable mechanical characteristics of GelMA provide its efficiency in the closure of wounds and tissue repair. GelMA hydrogels stand at the forefront of biomedical innovation, offering a versatile platform for addressing diverse challenges in drug delivery, tissue engineering, and wound healing. This review provides a comprehensive overview, fostering an in-depth understanding of GelMA hydrogel's potential impact on progressing biomedical sciences.

Recent advancements in cartilage tissue engineering innovation and translation

Articular cartilage was expected to be one of the first successfully engineered tissues, but today, cartilage repair products are few and they exhibit considerable limitations. For example, of the cell-based products that are available globally, only one is marketed for non-knee indications, none are indicated for severe osteoarthritis or rheumatoid arthritis, and only one is approved for marketing in the USA. However, advances in cartilage tissue engineering might now finally lead to the development of new cartilage repair products. To understand the potential in this field, it helps to consider the current landscape of tissue-engineered products for articular cartilage repair and particularly cell-based therapies. Advances relating to cell sources, bioactive stimuli and scaffold or scaffold-free approaches should now contribute to progress in therapeutic development. Engineering for an inflammatory environment is required because of the need for implants to withstand immune challenge within joints affected by osteoarthritis or rheumatoid arthritis. Bringing additional cartilage repair products to the market will require an understanding of the translational vector for their commercialization. Advances thus far can facilitate the future translation of engineered cartilage products to benefit the millions of patients who suffer from cartilage injuries and arthritides.

Tissue regeneration properties of hydrogels derived from biological macromolecules: A review

The successful tissue engineering depends on the development of biologically active scaffolds that possess optimal characteristics to effectively support cellular functions, maintain structural integrity and aid in tissue regeneration. Hydrogels have emerged as promising candidates in tissue regeneration due to their resemblance to the natural extracellular matrix and their ability to support cell survival and proliferation. The integration of hydrogel scaffold into the polymer has a variable impact on the pseudo extracellular environment, fostering cell growth/repair. The modification in size, shape, surface morphology and porosity of hydrogel scaffolds has consequently paved the way for addressing diverse challenges in the tissue engineering process such as tissue architecture, vascularization and simultaneous seeding of multiple cells. The present review provides a comprehensive update on hydrogel production using natural and synthetic biomaterials and their underlying mechanisms. Furthermore, it delves into the application of hydrogel scaffolds in tissue engineering for cardiac tissues, cartilage tissue, adipose tissue, nerve tissue and bone tissue. Besides, the present article also highlights various clinical studies, patents, and the limitations associated with hydrogel-based scaffolds in recent times.

Enhanced ·OH-Scavenging Activity of Cu-CeOx Nanozyme via Resurrecting Macrophage Nrf2 Transcriptional Activity Facilitates Diabetic Wound Healing

Diabetic wounds are a prevalent and devastating complication of diabetes, which may impede their healing and regeneration. In diabetic wounds, excess reactive oxygen species (ROS) activate the nuclear factor kappa-B pathway, leading to transcriptional silencing of nuclear factor erythroid 2-related factor 2 (Nrf2), resulting in a vicious cycle of oxidative stress and inflammation. Conventional nanozymes have limitations in preventing the continuous production of ROS, including the most oxidizing reactive hydroxyl radical (·OH), although they can remove pre-existing ROS. Herein, a novel antioxidant nanoplatform addresses this challenge by incorporating JSH-23 into the mesoporous of cupric-doped cerium oxide nanozymes. Additionally, for rapid wound adaptability and durable tissue adhesion, a nanozyme hydrogel spray consisting of oxidized sodium alginate and methacrylate gelatin is constructed, named OG@CCJs. This platform resurrects Nrf2 transcriptional activity of macrophages in vitro, curbing the production of ROS at its source, particularly ·OH, while enabling the nanozymes to scavenge previously generated ROS. OG@CCJs significantly alleviate oxidative stress in diabetic wounds in vivo, promoting wound healing. Overall, the proposed nanozyme-hydrogel spray with enhanced ·OH-scavenging activity uses a "two-track" antioxidant strategy to rebuild the antioxidant defense barrier of macrophages. This pioneering approach highlights the tremendous potential of OG@CCJs for facilitating diabetic wound healing.

2-N, 6-O sulfated chitosan evokes periosteal stem cells for bone regeneration

Musculoskeletal injuries and bone defects represent a significant clinical challenge, necessitating innovative approaches for effective bone tissue regeneration. In this study, we investigated the potential of harnessing periosteal stem cells (PSCs) and glycosaminoglycan (GAG)-mimicking materials for in situ bone regeneration. Our findings demonstrated that the introduction of 2-N, 6-O sulfated chitosan (26SCS), a GAG-like polysaccharide, enriched PSCs and promoted robust osteogenesis at the defect area. Mechanistically, 26SCS amplifies the biological effect of endogenous platelet-derived growth factor-BB (PDGF-BB) through enhancing the interaction between PDGF-BB and its receptor PDGFRβ abundantly expressed on PSCs, resulting in strengthened PSC proliferation and osteogenic differentiation. As a result, 26SCS effectively improved bone defect repair, even in an osteoporotic mouse model with lowered PDGF-BB level and diminished regenerative potential. Our findings suggested the significant potential of GAG-like biomaterials in regulating PSC behavior, which holds great promise for addressing osteoporotic bone defect repair in future applications.

Cartilage-on-a-chip with magneto-mechanical transformation for osteoarthritis recruitment

Osteoarthritis (OA) is a prevalent joint disease primarily induced by overstrain, leading to disability and significantly impacting patients' quality of life. However, current OA studies lack an ideal in vitro model, which can recapitulate the high peripheral strain of the joint and precisely model the disease onset process. In this paper, we propose a novel cartilage-on-a-chip platform that incorporates a biohybrid hydrogel comprising Neodymium (NdFeB)/Poly-GelMA-HAMA remote magneto-control hydrogel film. This platform facilitates chondrocyte culture and stress loading, enabling the investigation of chondrocytes under various stress stimuli. The Neodymium (NdFeB)/Poly-GelMA-HAMA hydrogel film exhibits magneto-responsive shape-transition behavior, further dragging the chondrocytes cultured in hydrogels under magnetic stimulation. It was investigated that inflammation-related genes and proteins in chondrocytes are changed with mechanical stress stimulation in the cartilage-on-a-chip. Especially, MMP-13 and the proportion of collagen secretion are upregulated, showing a phenotype similar to that of real human osteoarthritis. Therefore, we believed that this cartilage-on-a-chip platform provides a desired in vitro model for osteoarthritis, which is of great significance in disease research and drug development.

Injectable hydrogels as promising in situ therapeutic platform for cartilage tissue engineering

Injectable hydrogels are gaining prominence as a biocompatible, minimally invasive, and adaptable platform for cartilage tissue engineering. Commencing with their synthesis, this review accentuates the tailored matrix formulations and cross-linking techniques essential for fostering three-dimensional cell culture and melding with complex tissue structures. Subsequently, it spotlights the hydrogels' enhanced properties, highlighting their augmented functionalities and broadened scope in cartilage tissue repair applications. Furthermore, future perspectives are advocated, urging continuous innovation and exploration to surmount existing challenges and harness the full clinical potential of hydrogels in regenerative medicine. Such advancements are crucial for validating the long-term efficacy and safety of hydrogels, positioning them as a promising direction in regenerative medicine to address cartilage-related ailments.

Advancements in tissue engineering for articular cartilage regeneration

Articular cartilage injury is a prevalent clinical condition resulting from trauma, tumors, infection, osteoarthritis, and other factors. The intrinsic lack of blood vessels, nerves, and lymphatic vessels within cartilage tissue severely limits its self-regenerative capacity after injury. Current treatment options, such as conservative drug therapy and joint replacement, have inherent limitations. Achieving perfect regeneration and repair of articular cartilage remains an ongoing challenge in the field of regenerative medicine. Tissue engineering has emerged as a key focus in articular cartilage injury research, aiming to utilize cultured and expanded tissue cells combined with suitable scaffold materials to create viable, functional tissues. This review article encompasses the latest advancements in seed cells, scaffolds, and cytokines. Additionally, the role of stimulatory factors including cytokines and growth factors, genetic engineering techniques, biophysical stimulation, and bioreactor systems, as well as the role of scaffolding materials including natural scaffolds, synthetic scaffolds, and nanostructured scaffolds in the regeneration of cartilage tissues are discussed. Finally, we also outline the signaling pathways involved in cartilage regeneration. Our review provides valuable insights for scholars to address the complex problem of cartilage regeneration and repair.

The current status and development trend of hydrogel application in spinal surgery

Spinal diseases often result in compromised mobility and diminished quality of life due to the intricate anatomy surrounding the nervous system. Medication and surgical interventions remain the primary treatment methods for spinal conditions. However, currently available medications have limited efficacy in treating spinal surgical diseases and cannot achieve a complete cure. Furthermore, surgical intervention frequently results in inevitable alterations and impairments to the initial anatomical integrity of the spinal structure, accompanied by the consequential loss of certain physiological functionalities. Changes in spine surgery treatment concepts and modalities in the last decade have led to a deepening of minimally invasive treatment, with treatment strategies focusing more on repairing and reconstructing the patient's spine and preserving physiological functions. Therefore, developing novel and more efficient treatment strategies to reduce spinal lesions and iatrogenic injuries is essential. In recent years, significant advancements in biomedical research have led to the discovery that hydrogels possess excellent biocompatibility, biodegradability, and adjustable mechanical properties. The application of hydrogel-based biotechnology in spinal surgery has demonstrated remarkable therapeutic potential. This review presents the therapeutic strategies for spinal diseases based on hydrogel tissue engineering technology.

Hydrogel Breakthroughs in Biomedicine: Recent Advances and Implications

OBJECTIVE

The objective of this review is to present a succinct summary of the latest advancements in the utilization of hydrogels for diverse biomedical applications, with a particular focus on their revolutionary impact in augmenting the delivery of drugs, tissue engineering, along with diagnostic methodologies.

METHODS

Using a meticulous examination of current literary works, this review systematically scrutinizes the nascent patterns in applying hydrogels for biomedical progress, condensing crucial discoveries to offer a comprehensive outlook on their ever-changing importance.

RESULTS

The analysis presents compelling evidence regarding the growing importance of hydrogels in biomedicine. It highlights their potential to significantly enhance drug delivery accuracy, redefine tissue engineering strategies, and advance diagnostic techniques. This substantiates their position as a fundamental element in the progress of modern medicine.

CONCLUSION

In summary, the constantly evolving advancement of hydrogel applications in biomedicine calls for ongoing investigation and resources, given their diverse contributions that can revolutionize therapeutic approaches and diagnostic methods, thereby paving the way for improved patient well-being.

Photo-cross-linked Hydrogels for Cartilage and Osteochondral Repair

Photo-cross-linked hydrogels, which respond to light and induce structural or morphological transitions, form a microenvironment that mimics the extracellular matrix of native tissue. In the last decades, photo-cross-linked hydrogels have been widely used in cartilage and osteochondral tissue engineering due to their good biocompatibility, ease of fabrication, rapid in situ gel-forming ability, and tunable mechanical and degradable properties. In this review, we systemically summarize the different types and physicochemical properties of photo-cross-linked hydrogels (including the materials and photoinitiators) and explore the biological properties modulated through the incorporation of additives, including cells, biomolecules, genes, and nanomaterials, into photo-cross-linked hydrogels. Subsequently, we compile the applications of photo-cross-linked hydrogels with a specific focus on cartilage and osteochondral repair. Finally, current limitations and future perspectives of photo-cross-linked hydrogels are also discussed.

Nanofiber Composite Microchannel-Containing Injectable Hydrogels for Cartilage Tissue Regeneration

Articular cartilage tissue is incapable of self-repair and therapies for cartilage defects are still lacking. Injectable hydrogels have drawn much attention in the field of cartilage regeneration. Herein, the novel design of nanofiber composite microchannel-containing hydrogels inspired by the tunnel-piled structure of subway tunnels is proposed. Based on the aldehydized polyethylene glycol/carboxymethyl chitosan (APA/CMCS) hydrogels, thermosensitive gelatin microrods (GMs) are used as a pore-forming agent, and coaxial electrospinning polylactic acid/gelatin fibers (PGFs) loaded with kartogenin (KGN) are used as a reinforcing agent and a drug delivery system to construct the nanofiber composite microchannel-containing injectable hydrogels (APA/CMCS/KGN@PGF/GM hydrogels). The in situ formation, micromorphology and porosity, swelling and degradation, mechanical properties, self-healing behavior, as well as drug release of the nanofiber composite microchannel-containing hydrogels are investigated. The hydrogel exhibits good self-healing ability, and the introduction of PGF nanofibers can significantly improve the mechanical properties. The drug delivery system can realize sustained release of KGN to match the process of cartilage repair. The microchannel structure effectively promotes bone marrow mesenchymal stem cell (BMSC) proliferation and ingrowth within the hydrogels. In vitro and animal experiments indicate that the APA/CMCS/KGN@PGF/GM hydrogels can enhance the chondrogenesis of BMSCs and promote neocartilage formation in the rabbit cartilage defect model.

Advancing drug delivery to articular cartilage: From single to multiple strategies

Articular cartilage (AC) injuries often lead to cartilage degeneration and may ultimately result in osteoarthritis (OA) due to the limited self-repair ability. To date, numerous intra-articular delivery systems carrying various therapeutic agents have been developed to improve therapeutic localization and retention, optimize controlled drug release profiles and target different pathological processes. Due to the complex and multifactorial characteristics of cartilage injury pathology and heterogeneity of the cartilage structure deposited within a dense matrix, delivery systems loaded with a single therapeutic agent are hindered from reaching multiple targets in a spatiotemporal matched manner and thus fail to mimic the natural processes of biosynthesis, compromising the goal of full cartilage regeneration. Emerging evidence highlights the importance of sequential delivery strategies targeting multiple pathological processes. In this review, we first summarize the current status and progress achieved in single-drug delivery strategies for the treatment of AC diseases. Subsequently, we focus mainly on advances in multiple drug delivery applications, including sequential release formulations targeting various pathological processes, synergistic targeting of the same pathological process, the spatial distribution in multiple tissues, and heterogeneous regeneration. We hope that this review will inspire the rational design of intra-articular drug delivery systems (DDSs) in the future.

Harnessing knee joint resident mesenchymal stem cells in cartilage tissue engineering

Osteoarthritis (OA) is a widespread clinical disease characterized by cartilage degeneration in middle-aged and elderly people. Currently, there is no effective treatment for OA apart from total joint replacement in advanced stages. Mesenchymal stem cells (MSCs) are a type of adult stem cell with diverse differentiation capabilities and immunomodulatory potentials. MSCs are known to effectively regulate the cartilage microenvironment, promote cartilage regeneration, and alleviate OA symptoms. As a result, they are promising sources of cells for OA therapy. Recent studies have revealed the presence of resident MSCs in synovial fluid, synovial membrane, and articular cartilage, which can be collected as knee joint-derived MSCs (KJD-MSC). Several preclinical and clinical studies have demonstrated that KJD-MSCs have great potential for OA treatment, whether applied alone, in combination with biomaterials, or as exocrine MSCs. In this article, we will review the characteristics of MSCs in the joints, including their cytological characteristics, such as proliferation, cartilage differentiation, and immunomodulatory abilities, as well as the biological function of MSC exosomes. We will also discuss the use of tissue engineering in OA treatment and introduce the concept of a new generation of stem cell-based tissue engineering therapy, including the use of engineering, gene therapy, and gene editing techniques to create KJD-MSCs or KJD-MSC derivative exosomes with improved functionality and targeted delivery. These advances aim to maximize the efficiency of cartilage tissue engineering and provide new strategies to overcome the bottleneck of OA therapy. STATEMENT OF SIGNIFICANCE: This research will provide new insights into the medicinal benefit of Joint resident Mesenchymal Stem Cells (MSCs), specifically on its cartilage tissue engineering ability. Through this review, the community will further realize promoting joint resident mesenchymal stem cells, especially cartilage progenitor/MSC-like progenitor cells (CPSC), as a preventive measure against osteoarthritis and cartilage injury. People and medical institutions may also consider cartilage derived MSC as an alternative approach against cartilage degeneration. Moreover, the discussion presented in this study will convey valuable information for future research that will explore the medicinal benefits of cartilage derived MSC.

A biphasic calcium phosphate/acylated methacrylate gelatin composite hydrogel promotes osteogenesis and bone repair

PURPOSE/AIM

Bone defects caused by trauma, tumors, congenital malformation, or inflammation are very common in orthopedics. In recent years, mimicking the composition and structure of natural bone tissue has become a hot topic in biomaterial research, with the aim of developing an ideal biomaterial for bone defect transplantation. Here, the feasibility of a biphasic calcium phosphate (BCP)/acylated methacrylate gelatin (GelMA) composite hydrogel to repair bone defects was evaluated in vitro and in rats.

MATERIALS AND METHODS

The biocompatibility of a biphasic calcium phosphate (BCP)/acylated methacrylate gelatin (GelMA) composite hydrogel was evaluated by cytoskeleton staining, live/dead cell staining and cell proliferation assays. The in vitro osteogenic activities of the composite hydrogel were evaluated by alkaline phosphatase and alizarin red staining, as well as osteogenic gene expression analysis at both transcript and protein levels. The in vivo bone repair activities were evaluated using the rat skull defect model.

RESULTS

The BCP/GelMA composite hydrogel displayed excellent biocompatibility and promoted osteogenesis of bone marrow mesenchymal stem cells in vitro. In addition, the BCP/GelMA composite hydrogel markedly promoted new bone formation in the rat skull-defect model.

CONCLUSIONS

BCP/GelMA composite hydrogel may be an effective artificial material for bone tissue engineering.

Gelatin Methacryloyl Hydrogel, from Standardization, Performance, to Biomedical Application

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

Engineered biochemical cues of regenerative biomaterials to enhance endogenous stem/progenitor cells (ESPCs)-mediated articular cartilage repair

As a highly specialized shock-absorbing connective tissue, articular cartilage (AC) has very limited self-repair capacity after traumatic injuries, posing a heavy socioeconomic burden. Common clinical therapies for small- to medium-size focal AC defects are well-developed endogenous repair and cell-based strategies, including microfracture, mosaicplasty, autologous chondrocyte implantation (ACI), and matrix-induced ACI (MACI). However, these treatments frequently result in mechanically inferior fibrocartilage, low cost-effectiveness, donor site morbidity, and short-term durability. It prompts an urgent need for innovative approaches to pattern a pro-regenerative microenvironment and yield hyaline-like cartilage with similar biomechanical and biochemical properties as healthy native AC. Acellular regenerative biomaterials can create a favorable local environment for AC repair without causing relevant regulatory and scientific concerns from cell-based treatments. A deeper understanding of the mechanism of endogenous cartilage healing is furthering the (bio)design and application of these scaffolds. Currently, the utilization of regenerative biomaterials to magnify the repairing effect of joint-resident endogenous stem/progenitor cells (ESPCs) presents an evolving improvement for cartilage repair. This review starts by briefly summarizing the current understanding of endogenous AC repair and the vital roles of ESPCs and chemoattractants for cartilage regeneration. Then several intrinsic hurdles for regenerative biomaterials-based AC repair are discussed. The recent advances in novel (bio)design and application regarding regenerative biomaterials with favorable biochemical cues to provide an instructive extracellular microenvironment and to guide the ESPCs (e.g. adhesion, migration, proliferation, differentiation, matrix production, and remodeling) for cartilage repair are summarized. Finally, this review outlines the future directions of engineering the next-generation regenerative biomaterials toward ultimate clinical translation.

The Effect of the Mechanical Properties of the 3D Printed Gelatin/Hyaluronic Acid Scaffolds on hMSCs Differentiation Towards Chondrogenesis

BACKGROUND

Tissue engineering, including 3D bioprinting, holds great promise as a therapeutic tool for repairing cartilage defects. Mesenchymal stem cells have the potential to treat various fields due to their ability to differentiate into different cell types. The biomimetic substrate, such as scaffolds and hydrogels, is a crucial factor that affects cell behavior, and the mechanical properties of the substrate have been shown to impact differentiation during incubation. In this study, we examine the effect of the mechanical properties of the 3D printed scaffolds, made using different concentrations of cross-linker, on hMSCs differentiation towards chondrogenesis.

METHODS

The 3D scaffold was fabricated using 3D bioprinting technology with gelatin/hyaluronic acid (HyA) biomaterial ink. Crosslinking was achieved by using different concentrations of 4-(4,6-dimethoxy-1,3,5-triazin-2-yl)-4-methlymorpholinium chloride n-hydrate (DMTMM), allowing for control of the scaffold's mechanical properties. The printability and stability were also evaluated based on the concentration of DMTMM used. The effects of the gelatin/HyA scaffold on chondrogenic differentiation was analyzed by utilizing various concentrations of DMTMM.

RESULTS

The addition of HyA was found to improve the printability and stability of 3D printed gelatin/HyA scaffolds. The mechanical properties of the 3D gelatin/HyA scaffold could be regulated through the use of different concentrations of DMTMM cross-linker. In particular, the use of 0.25 mM DMTMM for crosslinking the 3D gelatin/HyA scaffold resulted in enhanced chondrocyte differentiation.

CONCLUSION

The mechanical properties of 3D printed gelatin/HyA scaffolds cross-linked using various concentrations of DMTMM can influence the differentiation of hMSCs into chondrocytes.

Functional hydrogels for the repair and regeneration of tissue defects

Tissue defects can be accompanied by functional impairments that affect the health and quality of life of patients. Hydrogels are three-dimensional (3D) hydrophilic polymer networks that can be used as bionic functional tissues to fill or repair damaged tissue as a promising therapeutic strategy in the field of tissue engineering and regenerative medicine. This paper summarises and discusses four outstanding advantages of hydrogels and their applications and advances in the repair and regeneration of tissue defects. First, hydrogels have physicochemical properties similar to the extracellular matrix of natural tissues, providing a good microenvironment for cell proliferation, migration and differentiation. Second, hydrogels have excellent shape adaptation and tissue adhesion properties, allowing them to be applied to a wide range of irregularly shaped tissue defects and to adhere well to the defect for sustained and efficient repair function. Third, the hydrogel is an intelligent delivery system capable of releasing therapeutic agents on demand. Hydrogels are capable of delivering therapeutic reagents and releasing therapeutic substances with temporal and spatial precision depending on the site and state of the defect. Fourth, hydrogels are self-healing and can maintain their integrity when damaged. We then describe the application and research progress of functional hydrogels in the repair and regeneration of defects in bone, cartilage, skin, muscle and nerve tissues. Finally, we discuss the challenges faced by hydrogels in the field of tissue regeneration and provide an outlook on their future trends.

Anatomy, molecular structures, and hyaluronic acid - Gelatin injectable hydrogels as a therapeutic alternative for hyaline cartilage recovery: A review

Cartilage damage caused by trauma or osteoarthritis is a common joint disease that can increase the social and economic burden in society. Due to its avascular characteristics, the poor migration ability of chondrocytes, and a low number of progenitor cells, the self-healing ability of cartilage defects has been significantly limited. Hydrogels have been developed into one of the most suitable biomaterials for the regeneration of cartilage because of its characteristics such as high-water absorption, biodegradation, porosity, and biocompatibility similar to natural extracellular matrix. Therefore, the present review article presents a conceptual framework that summarizes the anatomical, molecular structure and biochemical properties of hyaline cartilage located in long bones: articular cartilage and growth plate. Moreover, the importance of preparation and application of hyaluronic acid - gelatin hydrogels for cartilage tissue engineering are included. Hydrogels possess benefits of stimulating the production of Agc1, Col2α1-IIa, and SOX9, molecules important for the synthesis and composition of the extracellular matrix of cartilage. Accordingly, they are believed to be promising biomaterials of therapeutic alternatives to treat cartilage damage.

3D Bioprintable Hypoxia-Mimicking PEG-Based Nano Bioink for Cartilage Tissue Engineering

As hypoxia plays a significant role in the formation and maintenance of cartilage tissue, aiming to develop native hypoxia-mimicking tissue engineering scaffolds is an efficient method to treat articular cartilage (AC) defects. Cobalt (Co) is documented for its hypoxic-inducing effects in vitro by stabilizing the hypoxia-inducible factor-1α (HIF-1α), a chief regulator of stem cell fate. Considering this, we developed a novel three-dimensional (3D) bioprintable hypoxia-mimicking nano bioink wherein cobalt nanowires (Co NWs) were incorporated into the poly(ethylene glycol) diacrylate (PEGDA) hydrogel system as a hypoxia-inducing agent and encapsulated with umbilical cord-derived mesenchymal stem cells (UMSCs). In the current study, we investigated the impact of Co NWs on the chondrogenic differentiation of UMSCs in the PEGDA hydrogel system. Herein, the hypoxia-mimicking nano bioink (PEGDA+Co NW) was rheologically optimized to bioprint geometrically stable cartilaginous constructs. The bioprinted 3D constructs were evaluated for their physicochemical characterization, swelling-degradation behavior, mechanical properties, cell proliferation, and the expression of chondrogenic markers by histological, immunofluorescence, and reverse transcription-quantitative polymerase chain reaction (RT-qPCR) methods. The results disclosed that, compared to the control (PEGDA) group, the hypoxia-mimicking nano bioink (PEGDA+Co NW) group outperformed in print fidelity and mechanical properties. Furthermore, live/dead staining, double-stranded DNA (dsDNA) content, and glycosaminoglycans (GAGs) content demonstrated that adding low amounts of Co NWs (<20 ppm) into PEGDA hydrogel system supported UMSC adhesion, proliferation, and differentiation. Histological and immunofluorescence staining of the PEGDA+Co NW bioprinted structures revealed the production of type 2 collagen (COL2) and sulfated GAGs, rendering it a feasible option for cartilage repair. It was further corroborated by a significant upregulation of the hypoxia-mediated chondrogenic and downregulation of the hypertrophic/osteogenic marker expression. In conclusion, the hypoxia-mimicking hydrogel system, including PEGDA and Co²⁺ ions, synergistically directs the UMSCs toward the chondrocyte lineage without using expensive growth factors and provides an alternative strategy for translational applications in the cartilage tissue engineering field.