Unlike bone, cartilage regeneration remains elusive

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.

Immune-modulated adhesive hydrogel for enhancing osteochondral graft adhesion and cartilage repair

Osteochondral autograft transfer system (OATS) can effectively improve cartilage injuries by obtaining bone-cartilage grafts from healthy sites and implanting them into the defective areas. However, in up to 40 % of patients, the lack of a stable adhesive interface between the osteochondral graft and the normal tissue surface reduces the repair efficiency. In this work, we report an injectable and biocompatible poly (N-hydroxyethyl acrylamide-N-hydroxy succinimide)/Gelatin (PHE-Gel) hydrogel, featuring the instant formation of a tough bio-interface, which allows for robust adhesion with osteochondral grafts. Through physicochemical characterization, we found that a system composed of 10%PHE-Gel possesses superior interfacial toughness and excellent biocompatibility. In vitro, mechanistic studies and RNA-seq analysis had shown that 10%PHE-Gel promotes the expression of cartilage anabolic metabolism genes by upregulating the hypoxia-inducible factor alpha (HIF-α) signaling pathway and downregulating the tumor necrosis factor (TNF) signaling pathway. Dimethyloxalylglycine (DMOG) loaded liposome (DMOG-Lip) promotes the transition of M1 macrophages to M2 macrophages, shifting the microenvironment towards a pro-repair direction. Studies on a rabbit OATS model indicated that DMOG-Lip loaded 10%PHE-Gel (10%PHE-Gel@DMOG-Lip) effectively modulated the immune microenvironment, facilitated the repair of the hyaline cartilage, and inhibited further degeneration of cartilage. This composite hydrogel offers a promising solution for enhancing OATS repair in tissue engineering and has the potential to improve outcomes in cartilage restoration procedures.

Heterogeneous Characteristics of the CD90+ Progenitors in the Fibrocartilage of Different Joints

ObjectiveThis study aimed to isolate and compare the mesenchymal stem cell characteristics of CD90+ cells from different fibrocartilage tissues in the temporomandibular joint (TMJ), the knee joint, and the intervertebral joint to further understand the similarities and differences of these 4 fibrocartilage tissues.MethodsCD90+ cells were isolated from TMJ disc, condylar cartilage, meniscus, and intervertebral disc by using magnetic-activated cell sorting. Cellular assays including 4.5-ethynyl-2'-deoxyuridine labeling, multilineage differentiation, colony formation, and cell migration were conducted to compare their mesenchymal stem cell characteristics. Immunofluorescent staining was performed for observing the expression of actively proliferating CD90+ cells within the tissues. H&E staining and Safranine O staining were used to compare the histological features.ResultsThe CD90+ cells derived from these 4 fibrocartilage tissues exhibited comparable cell proliferation abilities. However, the cells from the TMJ disc displayed limited multilineage differentiation potential, colony formation, and cell migration abilities in comparison with the cells from the other fibrocartilage tissues. In vivo, there was relatively more abundant expression of CD90+ cells in the TMJ disc during the early postnatal stage. The limited EDU+ cell numbers signified a low proliferation capacity of CD90+ cells in the TMJ disc. In addition, we observed a significant decrease in cell density and a restriction in the synthesis of extracellular proteoglycans in the TMJ disc.ConclusionOur study highlights the spatial heterogeneity of CD90+ cells in the fibrocartilages of different joint tissues, which may contribute to the limited cartilage repair capacity in the TMJ disc.

Architecting a partial thickness cartilage substitute with mimetic, self-assembling hydrogels

Restoration of partial thickness chondral defects (PTCDs) may be achieved with a synthetic substitute that mimics the discrete mechanical properties of the superficial and transitional chondral layers. Moreover, innate adhesivity of the two components would enable the facile construction and integrity of this bilayered system. Herein, we report a PTCD bilayered substitute formed by triple network (TN) hydrogels that leverage electrostatic charge interactions to achieve mechanical mimicry and self-assembly. TN hydrogels were formed with a polyampholyte 3rd network of five different charge composition (i.e., ratio of cationic and anionic monomers), as well as two crosslink densities. All TN hydrogels exhibited cartilage-like hydration. A single superficial-like chondral layer TN hydrogel, with a somewhat more anionic 3rd network, was identified having mimetic compressive modulus (∼1.8 MPa) and strength (∼13 MPa). Additionally, three transitional-like chondral layer candidates were identified, including two TN hydrogels with a more cationic 3rd network in addition to the TN hydrogel with a 'cationic-only' 3rd network. The adhesivity of the superficial layer and the three transitional layer candidates was found to be robust (∼>100 kPa), wherein the bilayered construct exhibited cohesive rather than adhesive failure.

Innovative injectable, self-healing, exosome cross-linked biomimetic hydrogel for cartilage regeneration

The limited self-healing capacity of cartilage hinders its repair and regeneration at the defect sites. Recent research into small-molecular compounds has shown promise in achieving a better regeneration of cartilage. In this study, we encapsulate kartogenin (KGN) and transforming growth factor β1 (TGF-β1) within mesenchymal stem cells derived exosomes (EKT), and then coated them with succinylated chitosan (sCH) to create positively charged exosomes, termed CEKT. These CEKT exhibit exceptional chondrogenic promoting capabilities shown during in vitro studies with bone marrow derived mesenchymal stem cells (BMSCs). They also can penetrate deep into cartilage tissue derived from porcine knee joints guided by their positive charge. Subsequently, a dynamic exosomes-crosslinked hydrogel (Gel-CEKT) is fabricated by crosslinking CEKT with oxidized chondroitin sulfate (oCS) and Wharton's jelly (WJ) through imine bond formation. Physicochemical studies revealed the injectability, excellent adhesive, and self-healing abilities of this hydrogel, which enables minimally invasive and precise treatment of cartilage defects, assisted by the enriched and sustained administration of CEKT. In vitro cell experiments show that Gel-CEKT can efficiently recruit BMSCs and significantly promote the gene expression of Sox9 and protein expression of collagen II and aggrecan. Furthermore, we show in a rat model of cartilage defect that the Gel-CEKT demonstrates superior performance compared to Gel@EKT, which has freely encapsulated exosomes in the hydrogel. The freely encapsulated exosomes are rapidly released, whereas the exosome-crosslinked gel structure ensures sustained retention and functionality at the site of defect. This leads to impressive outcomings, including extensive new cartilage tissue formation, a smoother cartilage surface, significant chondrocyte production, and seamless integration with orderly and continuous structure formation between cartilage and subchondral bone. This study underscores the potential of exosomes-crosslinked hydrogels as a novel and promising therapeutic approach for clinical cartilage regeneration.

Acellular, bioresorbable, ultra-purified alginate gel implantation for intervertebral disc herniation: Phase 1/2, open-label, non-randomized clinical trials

Discectomy is the current surgical procedure for lumbar intervertebral disc (IVD) herniation. Discectomy was performed to remove the IVD material and relieve the pain inflicted by nerve root compression and axonotoxic effects, such as inflammatory cytokines in the IVD material; however, defects within the IVD caused by discectomy may impair tissue healing and predispose patients to subsequent IVD degeneration. Given that viable cells with the capacity for IVD regeneration are scarce, discectomy alone is not conducive to tissue repair. Here, we report the use of an acellular, bioresorbable, ultra-purified alginate (UPAL) gel implantation system to prevent IVD degeneration after discectomy and demonstrate its feasibility and safety in phase 1/2, open-label, non-randomized clinical trials conducted at a double center. This study comprised two parts: a prospective study on UPAL gel implantation after discectomy in patients with lumbar disc herniation, and a subsequent prospective study on patients who underwent discectomy without UPAL implantation as a control group. The control group was recruited separately. The primary outcomes of this study were the feasibility and safety of UPAL implantation, and the secondary outcomes included physical function scores, self-report questionnaires (SRQs) evaluating pain and health-related quality of life and magnetic resonance imaging (MRI)-based measures of IVD tissues. The UPAL gel implantation demonstrated 100% feasibility and safety (n = 40). The physical function scores improved significantly postoperatively in both groups, with the UPAL group demonstrating greater improvements over time compared to the control group. The SRQ scores were significantly higher in the UPAL group than in the control group from the early postoperative period to 12 weeks. MRI revealed that the disc degeneration score was significantly lower in IVDs with UPAL implantation than in those that underwent discectomy alone. The findings of this study suggest that the UPAL gel is a novel therapeutic strategy after discectomy in cases of lumbar IVD herniation. Trial number: UMIN000034227, UMIN000042282.

A multi-gradient organoid of articular cartilage with bionic matrix microenvironment

Reconstructing the zonal organization of articular cartilage, including the heterogeneity in matrix distribution and chondrocyte status, remains a significant challenge. In this study, we developed a compression technique to engineer artificial cartilage architecture. By controlling the orientation of fibers within a collagen hydrogel, we obtained a gradient from parallel alignment in the surface layer to random distribution in deeper layers. Simultaneously, we established a diverse concentration gradient of chondroitin sulfate to mimic cartilage composition. Encapsulating chondrocytes within this construct yielded a "cartilage organoid." In vitro culture demonstrated that the plastic compression achieved an increased density, parallel alignment, and a flattened morphology of cells in the surface layer. Especially, type II collagen and superficial zone protein (SZP), which are crucial for the functional durability of articular cartilage, were specifically excreted by the regulated cells within the surface region. Subcutaneous implantation of the cartilage organoid confirmed the stable retention of these specific features of the organoid in vivo, accompanied by further tissue maturation. Following implantation into articular cartilage defects, successful regeneration of well-integrated cartilage tissue with region-specific characteristics was achieved. These findings suggest a biomimetic cartilage organoid fully mimicking the factors in the structure and composition of natural cartilages, which may be a promising candidate for cartilage reconstruction and functional regeneration.

A Cartilaginous Organoid System Derived From Human Expanded Pluripotent Stem Cells (hEPSCs)

The development of human organotypic models of cartilage provides essential insights into chondrogenesis and chondrocyte hypertrophy while enabling advanced applications in drug discovery, gene editing, and tissue regeneration. Here, we present a robust and efficient protocol for differentiating human expanded pluripotent stem cells (hEPSCs) into hypertrophic chondrocytes through a sclerotome intermediate. The protocol involves initial sclerotome induction, followed by 3D chondrogenic culture and subsequent hypertrophic maturation induced by bone morphogenetic protein-4 (BMP4), thyroid hormone (T3), and β-glycerophosphate. This protocol also allows for sensitive testing of the effects of various compounds on hypertrophic differentiation during the maturation process. Furthermore, we identify an α-adrenergic receptor antagonist, phentolamine, as an inhibitor of hypertrophic differentiation. This organoid system provides a practical platform for exploring cartilage hypertrophy mechanisms and testing therapeutic strategies for cartilage regeneration. Key features • This differentiation protocol generates hypertrophic chondrocytes from hEPSCs through a sclerotome intermediate. • This protocol facilitates sensitive testing of compounds during the hypertrophic maturation stage, enabling the study of molecular mechanisms and therapeutic interventions for cartilage hypertrophy. • This protocol identifies the α-adrenergic receptor antagonist phentolamine as a modulator of hypertrophic differentiation.

Self-assembled organoid-tissue modules for scalable organoid engineering: Application to chondrogenic regeneration

Tissue engineering has made significant strides in creating biomimetic grafts for the repair and regeneration of damaged tissues; however, the scalability of engineered tissue constructs remains a major technical hurdle. This study introduces a method for generating organoid-tissue modules (Organoid-TMs) through scaffold-free self-assembly of microblocks (MiBs) derived from adipose-derived mesenchymal stem cells (ADMSCs). The key parameters influencing Organoid-TM formation were identified as the density of MiBs and the controlled mixing ratio of large and small MiBs. The resulting Organoid-TM exhibited a distinctive cup-shaped morphology, a millimeter-scale structure with enhanced nutrient and oxygen diffusion compared to conventional spherical aggregates. Despite their larger size, Organoid-TMs maintained ADMSC stemness and differentiation potential, while stemness and differentiation were halted during fabrication. Organoid-TMs receiving chondrogenic cues during fabrication were transplanted into cartilage defect sites in animal models, demonstrating cartilage regeneration efficacy in a scaffold-independent and xeno-free manner. This fabrication method represents a highly reproducible and consistent process for developing spheroids or organoids, offering a robust platform for regenerative medicine applications. Specifically, Organoid-TMs provide a foundational framework for therapeutic strategies targeting cartilage defects and osteoarthritis, paving the way for advancements in tissue-engineered therapeutics. STATEMENT OF SIGNIFICANCE: This study introduces a distinct approach in tissue engineering, utilizing self-assembled Organoid-Tissue Modules (Organoid-TMs) to address persistent challenges in scalable organoid production and cartilage regeneration. By leveraging adipose-derived mesenchymal stem cells (ADMSCs) and carefully optimizing the size, ratio, and spatial organization of microblocks (MiBs), we successfully generated millimeter-scale Organoid-TMs. The distinctive cup-shaped architecture of these Organoid-TMs enhances oxygen and nutrient diffusion, effectively overcoming limitations such as core necrosis typically encountered in large-scale organoid culture. This system demonstrated substantial regenerative potential, particularly in chondrogenic differentiation and cartilage repair in both rabbit and pig models, without the use of artificial scaffolds or xenogenic materials.

Localized Hydrogel Microspheres for Osteoarthritis Treatment: Recruitment and Differentiation of Stem Cells

Osteoarthritis (OA) represents a common degenerative joint disorder marked by progressive cartilage degradation, necessitating innovative therapeutic approaches beyond symptom management. Here, this study introduces a novel strategy leveraging the regenerative capabilities of mesenchymal stem cells (MSCs) by utilizing a bioactive extracellular matrix (ECM) derived from IFN-γ-stimulated MSCs, encapsulated within aldehyde- and methacrylic anhydride-modified hyaluronic acid hydrogel microspheres (AH). This engineered scaffold effectively mimics the native cartilage microenvironment, promoting targeted adhesion and retention at damaged sites via spontaneous Schiff base reactions. Notably, the IFN-γ-ECM@AH microspheres facilitate the localized release of key chemokines, such as CXCL12, enhancing endogenous stem cell recruitment, and bioactive factors (e.g., TGF-βI and TGF-β3) to drive chondrogenic differentiation. Additionally, the scaffold possesses binding sites for cellular integrins, further augmenting the regenerative potential of stem cells. Collectively, the approach presents a dual-action mechanism that supports efficient cartilage repair and regeneration, positioning this engineered microenvironment as a promising therapeutic avenue for OA and potentially other degenerative conditions.

Stable-Dynamic Hydrogels Mimicking the Pericellular Matrix for Articular Cartilage Repair

Cartilage regeneration requires a specialized biomechanical environment. Macroscopically, cartilage repair requires a protracted, stable mechanical environment, whereas microscopically, it involves dynamic interactions between cells and the extracellular matrix. Therefore, this study aims to design a hydrogel that meets the complex biomechanical requirements for cartilage repair. Dynamic hybrid hydrogels with temporal stability at the macroscale and dynamic properties at the microscale are successfully synthesized. The dynamic hybrid hydrogel simulates the stress relaxation and viscoelasticity of the pericellular matrix, facilitating effective interactions between the extracellular matrix and cells. The in vitro and in vivo experiments demonstrated that the hybrid hydrogel significantly promoted cartilage repair. The dynamic hybrid hydrogel alleviates abnormal actin polymerization, reduces intracellular stress, and increases the volume of individual cells. By modulating the cytoskeleton, the hybrid hydrogel inhibits Notch signal transduction in both the receptor and ligand cells, resulting in an improved cartilage phenotype. This study introduces an effective hybrid hydrogel scaffold that modulates the chondrocyte cytoskeleton and Notch signaling pathways by establishing an appropriate biomechanical environment, thus offering a promising material for cartilage repair.

Dominant Role of Distinct Microenvironments on Cartilage Regeneration Fate Using PLGA-Hydrogel Composite Scaffolds

Currently, bioactive composite scaffolds provide an ideal regenerative microenvironment for cartilage tissue engineering. However, the dominant regulatory role of the microenvironment in cartilage regeneration fate remains elusive, such as in situ auricle, ex situ subcutaneous, and osteogenic regions. Therefore, investigating the influence of distinct microenvironments on cartilage regeneration and long-term outcomes is important. In this study, a universal composite scaffold is developed combining 3D-printed poly(lactic-co-glycolic acid) frameworks with cartilage-specific matrix hydrogels and then systematically explored the crucial role of the microenvironment in determining the fate of cartilage regeneration. These results indicate that the in situ auricular microenvironment effectively promotes the maturation of the regenerative cartilage and maintains its chondrogenic phenotype. In contrast, ex situ subcutaneous microenvironment leads to chondrogenic phenotype loss owing to intense immune-inflammatory responses and vascularization conditions. In the osteogenic microenvironments of cranial sites, although autologous chondrocytes show good cartilage regenerative quality within 12 weeks, they are gradually replaced by regenerative bone, ultimately achieving successful cranial defect repair. Interestingly, these findings provide critical theoretical foundations for revealing the long-term outcomes of engineered cartilage and offer practical guidance for optimizing cartilage regeneration strategies in various microenvironments.

Mesenchymal Stromal Cell Chondrogenic Differentiation Induced by Continuous Stiffness Gradient in Photocrosslinkable Hydrogels

Chondrogenic differentiation of stem and progenitor cells is dependent on the biophysical properties of the surrounding matrix. Current biomaterials-based approaches for chondrogenesis are limited to discrete platforms, slowing our ability to interrogate the role of mechanical cues such as substrate stiffness and other signals. Thus, novel platforms must incorporate a range of biophysical properties within a single construct to effectively assess changes in cell response. We encapsulated human mesenchymal stromal cells (MSCs) within biodegradable, photocurable oxidized, and methacrylated alginate (OMA). Cell-laden hydrogels were crosslinked when exposed to light through a grayscale photomask to form substrates with a continuous stiffness gradient. We also tested the influence of the adhesive ligand Arg-Gly-Asp (RGD) on chondrogenic differentiation. Compared to unmodified gels possessing uniform biophysical properties, RGD-modified OMA hydrogels with the same modulus promoted chondrogenic differentiation of MSCs as evidenced by gene expression, matrix deposition, and histological analysis. MSCs entrapped in OMA hydrogels exhibiting a biologically relevant stiffness gradient (2-13 kPa over 8 mm) demonstrated increased chondrogenic differentiation with increases in stiffness. MSC chondrogenic differentiation was dependent upon the ability to mechanosense the modulus of the surrounding matrix, confirmed by the addition of Latrunculin A (LatA), a soluble inhibitor of actin polymerization. These findings validate a methodology for customizing hydrogel platforms for chondrogenic differentiation and identifying the interplay of key variables to instruct cell function.

Intelligent Manufacturing for Osteoarthritis Organoids

Osteoarthritis (OA) is the most prevalent degenerative joint disease worldwide, imposing a substantial global disease burden. However, its pathogenesis remains incompletely understood, and effective treatment strategies are still lacking. Organoid technology, in which stem cells or progenitor cells self-organise into miniature tissue structures under three-dimensional (3D) culture conditions, provides a promising in vitro platform for simulating the pathological microenvironment of OA. This approach can be employed to investigate disease mechanisms, carry out high-throughput drug screening and facilitate personalised therapies. This review summarises joint structure, OA pathogenesis and pathological manifestations, thereby establishing the disease context for the application of organoid technology. It then examines the components of the arthrosis organoid system, specifically addressing cartilage, subchondral bone, synovium, skeletal muscle and ligament organoids. Furthermore, it details various strategies for constructing OA organoids, including considerations of cell selection, pathological classification and fabrication techniques. Notably, this review introduces the concept of intelligent manufacturing of OA organoids by incorporating emerging engineering technologies such as artificial intelligence (AI) into the organoid fabrication process, thereby forming an innovative software and hardware cluster. Lastly, this review discusses the challenges currently facing intelligent OA organoid manufacturing and highlights future directions for this rapidly evolving field. By offering a comprehensive overview of state-of-the-art methodologies and challenges, this review anticipates that intelligent, automated fabrication of OA organoids will expedite fundamental research, drug discovery and personalised translational applications in the orthopaedic field.

Substrate Stiffness Modulates TGF-β1-Induced Lineage Specification in Multipotent Vascular Stem Cells

Multipotent vascular stem cells (MVSCs) are found in the vascular wall and surrounding tissues and possess the ability to differentiate into mesenchymal lineages. Previous studies have shown that MVSCs can be activated in response to vascular injury and differentiate into vascular smooth muscle cells (SMCs), contributing to vascular remodeling and microvessel formation. However, it remains unclear as to whether and how microenvironmental changes in the extracellular matrix, such as substrate stiffness, modulates MVSC differentiation under pathological conditions. This study demonstrated that MVSCs cultured on stiff substrates exhibited increased cell spreading, stronger cell adhesion, and a higher expression of SMC markers, including myosin heavy chain (MHC), myocardin (MYCD), calponin 1 (CNN1), and smooth muscle α-actin (SMA). In contrast, MVSCs on soft substrates showed an elevated expression of the chondrogenic markers aggrecan 1 (AGC1) and collagen-II (COL2A1). The presence of TGF-β1 further increased the expression of SMC markers on stiff substrates and chondrogenic markers on the soft substrates. Collectively, these results establish substrate stiffness as a key regulator of MVSC lineage commitment through cytoskeletal reorganization, with TGF-β1 acting as a biochemical amplifier. Our findings highlight the substrate-stiffness-dependent differentiation of MVSCs and provide mechanistic insights into the role of MVSCs in vascular remodeling during atherosclerosis development and blood vessel regeneration.

Bioinspired Lipid Nanoparticles with Prolonged Cartilage Retention Boost Regeneration in Early Osteoarthritis and Large Cartilage Defects

Osteoarthritis (OA) leads to the progressive degeneration of articular cartilage, yet there is currently no effective treatment available for both the early and late stages of osteoarthritis. Cartilage regeneration requires the action and prolonged retention of multiple drugs at injured sites to recruit endogenous cells and facilitate cartilage formation. Here, we propose a cartilage-binding-peptide-modified lipid nanoparticle as a drug carrier to achieve sustained release of protein (TGF-β3) and small molecular drugs (KGN) for one month. Through systematic screening of multiple peptides targeting collagen II or chondrocytes, we identify a decorin-derived-peptide-modified lipid nanoparticle with precise targeting and prolonged retention capability in cartilage. Improved nanoparticle stability, high drug loading, and sustainable dual-drug release are achieved through interbilayer cross-linking of adjacent lipid bilayers within multilamellar vesicles. In a surgical model of rat OA, the nanoparticle loading with TGF-β3 and KGN protects injured cartilage from degeneration progression. For severe cartilage injury (full-thickness defects) in a rabbit model, the nanoparticle facilitates the regeneration of high-quality hyaline-like cartilage, which is a rare achievement in full-thickness cartilage regeneration through nanoparticle-based drug delivery. This work presents a strategy for the rational design of bioinspired cartilage-binding peptide-modified lipid-based drug carriers to promote hyaline-like cartilage regeneration.

Recent Advances in Modeling Tissues Using 3D Bioprinted Nanocellulose Bioinks

Bioprinting creates 3D tissue models by depositing cells encapsulated in biocompatible materials. These 3D printed models can better emulate physiological conditions in comparison with traditional 2D cell cultures or animal models. Such models can be produced from human cells, possessing human genetics and replicating the 3D microenvironment found in vivo. Many different types of biocompatible materials serve as bioinks, including gelatin methacryloyl (GelMA), alginate, fibrin, and gelatin. Nanocellulose has emerged as a promising addition to these materials. Nanocellulose─composed of cellulose chain bundles with lateral dimensions ranging from a few to several tens of nanometers─possesses key properties for 3D bioprinting applications. It can form biocompatible hydrogels, which have excellent physical properties, and its structure resembles collagen, making it useful for modeling tissues with high collagen content such as bone, cartilage, sink, and muscle. Here we review some of the recent advances in the use of nanocellulose in bioinks for the creation of bone, cartilage, skin, and muscle tissue specific models and identify areas for future progress.

The osteoinductive and osseointegration properties of decellularized extracellular matrix bone derived from different sites

Aims

This study aimed to examine the differences in bone induction and osseointegration performance of acellular extracellular matrix bone at different sites.

Methods

We decellularized bone from bovine epiphysis near the marrow cavity (NMC), the middle of the cancellous bone (MCB), and near the cartilage (NC). The characterization, physicochemical properties, and effectiveness of the decellularization process of decellularized extracellular matrix (dECM) were analyzed. The proliferation, adhesion, seeding efficiency, and osteogenic differentiation properties of bone marrow mesenchymal stem cells (BMSCs) on decellularized extracellular matrix were investigated. The osteogenicity and osteointegration of dECM from different sources were verified in vivo by animal experiments, and the compatibility of dECM in vivo was also verified.

Results

The NC group had the most significant compressive properties, where the compressive strength was about 1.62 times higher than that of the MCB group (p = 0.022) and 1.34 times higher than that of the NMC group (p < 0.001). dECM scaffolds had good histocompatibility and supported the adhesion and proliferation of BMSCs. In vitro, compared with the remaining two groups, the MCB group significantly upregulated the expression of osteogenic genes (alkaline phosphatase (ALP), runt-related transcription factor 2 (RUNX2), osteopontin (OPN), collagen type 1 (COL1), and bone morphogenetic protein 2 (BMP2)) and marker proteins (ALP, BMP2), whereas the NC group showed the weakest osteoinductive properties. In vivo, we confirmed that the MCB group possessed the most significant osteogenic and osseointegrative properties, followed by the NMC group, and the NC group proved to be the weakest. In particular, the MCB group possessed the ability to endogenously immunomodulate macrophage M1 phenotype to M2 phenotype polarization, creating the most favourable immune microenvironment for osteogenesis.

Conclusion

Our data indicated that the xenogenic dECM scaffolds in MCB position possess the most significant biocompatibility and in vitro and in vivo induced osteogenesis and osseointegration properties. This study provides a more complete basis for the selection of dECM scaffolds in bone defect repair. In future studies of dECM composites applied to bone tissue engineering (BTE), utilizing the middle part of cancellous bone may be the best solution.

pH-Responsive Engineered Exosomes Enhance Endogenous Hyaluronan Production by Reprogramming Chondrocytes for Cartilage Repair

Trauma or inflammation-caused cartilage injury leads to joint dysfunction and pain. Exogenous hyaluronic acid (HA) injection is a well-established treatment, but it has a short duration in vivo and requires multiple injections. Here, a new strategy for in situ reprogramming chondrocytes to continuously produce endogenous high molecular weight HA is developed. This involves a pH-responsive engineered exosome decorated with vesicular stomatitis virus glycoprotein (VSV-G) and hyaluronan synthase type 2 (HAS2). Such engineered exosomes successfully deliver HAS2 to the chondrocyte membranes via VSV-G-mediated membrane fusion triggered by low pH, rather than being degraded in lysosomes. This results in the generation of HAS2-chondrocytes, which are characterized to produce high molecular weight HA in vitro and in vivo. With increased endogenous HA, the injected engineered exosomes enhance cartilage regeneration and inhibit osteoarthritis (OA) progression. Notably, one-shot administration of engineered exosomes drastically increases the intra-articular concentration of high molecular weight HA to 145% of the exogenous HA injection group. Importantly, such endogenous HA is sustained for 4 weeks, whereas the injected exogenous HA rapidly decreases within 2 weeks. The findings demonstrate that pH-responsive engineered exosomes capable of generating endogenous HA hold great potential to replace the treatment of multiple injections of exogenous HA for cartilage repair.

Intelligent Nanomaterials Design for Osteoarthritis Managements

Osteoarthritis (OA) is the most prevalent degenerative joint disorder, characterized by progressive joint degradation, pain, and diminished mobility, all of which collectively impair patients' quality of life and escalate healthcare expenditures. Current treatment options are often inadequate due to limited efficacy, adverse side effects, and temporary symptom relief, underscoring the urgent need for more effective therapeutic strategies. Recent advancements in nanomaterials and nanomedicines offer promising solutions by improving drug bioavailability, reducing side effects and providing targeted therapeutic benefits. This review critically examines the pathogenesis of OA, highlights the limitations of existing treatments, and explores the latest innovations in intelligent nanomaterials design for OA therapy, with an emphasis on their engineered properties, therapeutic mechanisms, and translational potential in clinical application. By compiling recent findings, this work aims to inspire further exploration and innovation in nanomedicine, ultimately advancing the development of more effective and personalized OA therapies.

Chondrocalcin: Insights into its regulation and multi-function in cartilage and bone

Type Ⅱ collagen (COLⅡ) is the primary constituent of the cartilage matrix, specifically present in vitreous bodies, cartilage, bone, and other skeletal elements. Therefore, the normal expression of COLⅡ is crucial for the normal development, linear growth, mechanical properties, and self-repairing ability of cartilage. Chondrocalcin, the C-propeptide of type Ⅱ procollagen, is not only a marker of COLⅡ synthesis but also one of the most abundant polypeptides in cartilage. This work examines the pivotal role of chondrocalcin in the synthesis of COLⅡ, comprehensively examining its regulation and multi-functions in cartilage and bone related diseases. Our findings suggest that mutations in the chondrocalcin-encoding domain of COL2A1 affect cartilage and bone development in clinical conditions.

MRI monitoring of USPIO-labeled BMSCs combined with alginate scaffold for cartilage defect repair

Objective

This study aimed to evaluate the effectiveness of bone marrow mesenchymal stem cells (BMSCs) combined with sodium alginate scaffolds in repairing knee cartilage defects in New Zealand rabbits. Additionally, it assessed the potential of functional magnetic resonance imaging (fMRI) for non-invasive monitoring of the dynamic repair process.

Methods

Rabbits were randomly divided into four groups: Group A (control), Group B (sodium alginate scaffold), Group C (BMSCs-sodium alginate scaffold), and Group D (USPIO-labeled BMSCs-sodium alginate scaffold). A cartilage defect model was created, and the respective materials were implanted into the defect regions. T2 mapping MRI was performed at weeks 1, 2, and 4 post-surgery to evaluate the repair process, followed by histological analysis to confirm the outcomes.

Results

BMSCs significantly promoted cartilage defect repair and accelerated the degradation of sodium alginate scaffolds. Macroscopic and histological evaluations revealed repair tissue formation in Groups C and D by week 1, with most defect regions filled with new cartilage by week 4. T2 mapping analysis showed a gradual decline in T2 values in Group B, a more pronounced decrease in Group C, and consistently lower T2 values in Group D compared to Group C, with a slow upward trend over time.

Conclusion

This study demonstrated that BMSCs exhibit significant regenerative potential for cartilage defect repair. USPIO labeling enables non-invasive, dynamic monitoring of the repair process without adverse effects on cell viability or differentiation. These findings provide experimental evidence supporting the application of BMSCs combined with magnetic labeling technology in cartilage regeneration.

Effects of Standard Physiotherapy with the Addition of Mechanical Traction on Pain, Physical Activity and Quality of Life in Patients with Knee Osteoarthritis

Background and Objectives: There is evidence of decreasing knee pain in patients with knee osteoarthritis when knee mechanical traction is performed surgically. Our aim was to measure the effects of standard physiotherapy with the addition of knee mechanical traction on pain, physical activity and quality of life in patients with knee osteoarthritis. Materials and Methods: A clinical observational study with intervention and without a control group was conducted at three outpatient health clinics on a primary level of the health care system. Twenty-three patients with knee osteoarthritis voluntarily participated in the study. Standard physiotherapy included education, therapeutic and aerobic exercise, conventional TENS, low-intensity laser and manual soft tissue techniques. Mechanical traction of 150 N continuous force for 15 min with the knee joint at 25° flexion was added to standard physiotherapy. The following outcome measures were used: VAS, Knee Injury and Osteoarthritis Outcome Score and a 30 s sit-to-stand test. Results: The pain measured for the VAS at rest (p < 0.001) and during movement (p < 0.001) as well as for the Knee Injury and Osteoarthritis Outcome Score pain part decreased (p < 0.05). The quality of life did not improve (p > 0.05), but the physical activity of the patients did (p < 0.05). A decrease in pain correlated with body mass (p < 0.05). Conclusions: Standard physiotherapy with the addition of mechanical traction had an effect on reducing pain and improving physical activity.

Biological effects, properties and tissue engineering applications of polyhydroxyalkanoates: A review

Polyhydroxyalkanoates (PHAs) are a group of polymers with a variety of monomers, which are extracted from microorganisms and plants. Due to its good biocompatibility, biodegradability, tunable mechanical property and piezoelectricity, PHAs have been widely used in biomedical fields, such as bone, cartilage, nerve, vascular and skin tissue engineering. This review focuses on the in vivo synthesis, metabolism and biological functions of PHA, and the applications of PHAs in the field of tissue engineering and commercial were also summarized and discussed. Moreover, this review hints the future perspective and research direction of PHA-based materials in the challenging field of tissue engineering. We hope that this review will catalyze the continued advancement and broadening of PHAs' applications in biomedicine.

Material-Mediated Immunotherapy to Regulate Bone Aging and Promote Bone Repair

As the global population ages, an increasing number of elderly people are experiencing weakened bone regenerative capabilities, resulting in slower bone repair processes and associated risks of various complications. This review outlines the research progress on biomaterials that promote bone repair through immunotherapy. This review examines how manufacturing technologies such as 3D printing, electrospinning, and microfluidic technology contribute to enhancing the therapeutic effects of these biomaterials. Following this, it provides detailed introductions to various anti-osteoporosis drug delivery systems, such as injectable hydrogels, nanoparticles, and engineered exosomes, as well as bone tissue engineering materials and coatings used in immunomodulation. Moreover, it critically analyzes the current limitations of biomaterial-mediated bone immunotherapy and explores future research directions for material-mediated bone immunotherapy. This review aims to inspire new approaches and broaden perspectives in addressing the challenges of bone repair and aging by exploring innovative biomaterial-mediated immunotherapy strategies.

Small extracellular vesicles derived from auricular chondrocytes promote secretion of interleukin 10 in bone marrow M1-like macrophages

Introduction

Elucidation of the paracrine interaction between chondrocytes and macrophages is useful for understanding the mechanisms of cartilage regeneration. Extracellular vesicles are granular substances with a diameter of approximately 150 nm, surrounded by a phospholipid bilayer membrane. In recent years, research has been conducted on clinical applications of extracellular vesicles. It has been shown that macrophages promote cartilage maturation, and macrophages acquire anti-inflammatory properties through cartilage, but the detailed mechanism of paracrine action involving extracellular vesicles remains unclear. Therefore, we focused on the effect of chondrocyte-derived extracellular vesicles on changes in macrophage characteristics.

Methods

Macrophages induced with granulocyte-macrophage colony stimulating factor (M1-like macrophages) and auricular chondrocytes were co-cultured using cell culture inserts and exosome inhibitors, and the expression of macrophage markers were analyzed. Next, extracellular vesicles separated from auricular chondrocytes were added to in vitro macrophage culture medium, and time-lapse observations of macrophage uptake of auricular chondrocyte-derived extracellular vesicles were performed. In addition, the effects of extracellular vesicles on the expression of macrophage markers were also analyzed.

Results

The expression of CD206, an M2 macrophage marker, was increased in macrophages due to the paracrine effect of chondrocytes, and CD206 expression was further increased by pharmacological inhibition of chondrocyte-derived exosomes. It was shown that chondrocyte-derived extracellular vesicles were taken up by macrophages and promoted the production of interleukin-10, an anti-inflammatory cytokine while reducing CD206 expression.

Conclusions

Auricular chondrocyte-derived extracellular vesicles promoted the production of interleukin-10 in bone marrow M1-like macrophages but reduced CD206 expression.

High-speed centrifugation reduces immune rejection by removing bone marrow elements from fresh osteochondral allografts

Background

Fresh osteochondral allografts (OCAs) contain numerous immunogenic components in the subchondral bone (SB). Whether high-speed centrifugation (HSC) reduces immune rejection by removing bone marrow elements (BMEs), compared to methods without HSC, remains unknown. This study aimed to validate the efficacy and safety of HSC in reducing immune rejection by removing allogeneic BMEs.

Methods

OCAs were obtained from the femoral condyles of the stifle joint in 18 pigs. Gross observations, histological staining, weight measurements, and DNA extraction were performed to assess the effects of centrifugation speed and duration on BMEs removal in OCAs. The effect of HSC on OCAs preservation was determined in vitro using microbiological testing, live/dead cell staining, and histological staining. Moreover, the co-culture effect of RAW264.7 cells and OCAs with or without HSC in vitro was evaluated using enzyme-linked immunosorbent assay (ELISA), histological staining, and immunohistochemical staining. The transplantation effect of OCAs with or without HSC was examined in vivo using a subcutaneous mouse model. Finally, the residues in the centrifuge tubes were analysed using ELISA, haematoxylin and eosin (HE) staining, and metabolomic analysis.

Results

Centrifugal speeds of 12000 rpm for 1 min were sufficient to reduce BMEs by over 90 %. HSC had a protective effect on chondrocytes and the extracellular matrix during the in vitro preservation of OCAs. In addition, OCAs using the HSC method exhibited reduced recognition by the host immune system compared with OCAs without HSC, thereby reducing immune rejection. Lipids were the most abundant and difficult-to-remove antigenic components and are the most likely to affect host macrophage polarisation, playing an important role in immune rejection.

Conclusion

Our study demonstrated that HSC method significantly reduces immune rejection by removing BMEs from OCAs.

The translational potential of this article

Our study demonstrated that HSC is a simple, efficient, and safe physical method for removing antigenic components from OCAs, effectively reducing immune rejection and highlighting its clinical potential.

ABCA6 Regulates Chondrogenesis and Inhibits Joint Degeneration via Orchestrated Cholesterol Efflux and Cellular Senescence

Patellar dysplasia (PD) can cause patellar dislocation and subsequent osteoarthritis (OA) development. Herein, a novel ABCA6 mutation contributing to a four-generation family with familiar patellar dysplasia (FPD) is identified. In this study, whole exome sequencing (WES) and genetic linkage analysis across a four-generation lineage presenting with six cases of FPD are conducted. A disease-causing mutation in ABCA6 is identified for FPD. Further analyses reveal a consistent correlation between ABCA6 expression downregulation and PD occurrence, chondrocyte degeneration, and OA onset. Moreover, ABCA6-KO mice demonstrate severe knee joint degeneration and accelerated OA progression. Besides, synovial mesenchymal stem cells (SMSCs) are extracted from WT, ABCA6-/+, and ABCA6-/- mice to create chondrogenic organoids in vitro, confirming ABCA6 deficiency can lead to chondrocyte degeneration via modulating cell cycle and activating cellular senescence. Moreover, transcriptome and metabolomic sequencing analysis on ABCA6-KO chondrocytes unveils that the ABCA6 deficiency inhibits cholesterol efflux, leading to intracellular cholesterol accumulation and subsequent cellular senescence and impaired chondrogenesis.A disease-causing mutation of ABCA6 is identified for FPD. ABCA6 is correlated with PD occurrence and subsequent OA progression. ABCA6 can serve as a potential target in chondrogenesis and OA treatment by orchestrated intracellular cholesterol efflux and delayed cellular senescence.

Cir-DNA Sequencing Revealed the Landscape of Extrachromosomal Circular DNA in Articular Cartilage and the Potential Roles in Osteoarthritis

OBJECTIVE

Extrachromosomal circular DNA (eccDNA) has been shown to be involved in several physiological and pathological processes including immunity, inflammation, aging, and tumor. However, the expression of eccDNA in cartilage has not been reported until now. In this study, we aimed to investigate the landscape of eccDNA in articular cartilage and analyze the potential roles in osteoarthritis (OA).

METHODS

The samples of articular cartilage were obtained from total knee arthroplasty (TKA) donors with OA. The mitochondrial DNA (mtDNAs) and the linear DNAs from chondrocytes of articular cartilage were removed. Then the eccDNAs were enriched for cir-DNA sequencing. After quality control evaluation, we systematically revealed the identified eccDNA data including size distribution, the size range, and sequence pattern. Moreover, we explored and discussed the potential roles of eccDNA in OA via motif analysis and Gene Ontology (GO)/Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis.

RESULTS

The chondrocytes from OA cartilage contained an abundance of eccDNAs, which was termed as OC-eccDNAs (OA cartilage-derived eccDNA). The characteristics of OC-eccDNAs were tissue-specific, including the distribution, the size range, and sequence pattern. Moreover, the functional analysis indicated that eccDNA may be involved in the homeostasis maintenance of chondrocytes and participated in the process of OA.

CONCLUSIONS

Our data first showed the landscape of eccDNA in articular cartilage and preliminarily indicated the potential roles of eccDNA in OA.

Critical roles of miR-21 in promotions angiogenesis: friend or foe?

MiRNAs are small RNA strands that are managed following transcription and are of substantial importance in blood vessel formation. It is essential to oversee the growth, differentiation, death, movement and construction of tubes by angiogenesis-affiliated cells. If miRNAs are not correctly regulated in regard to angiogenesis, it can deteriorate the health and lead to various illnesses, which include cancer, cardiovascular disorder, critical limb ischemia, Crohn's disease, ocular diseases, diabetic microvascular complications, and more. Consequently, it is vital to understand the crucial part that miRNAs play in the development of blood vessels, so we can develop reliable treatment plans for vascular diseases. This write-up will assess the critical role of miR-21/exosomal miR-21 in managing angiogenesis associated with bone growth, wound recovery, and other pathological conditions like tumor growth, ocular illnesses, diabetes, and other diseases connected to formation of blood vessels. Previous investigations have demonstrated that miR-21 is present at higher amounts in certain cancerous cells, and it influences a multitude of genes that moderate the increased creation of blood vessels. Furthermore, studies demonstrated that exosomal miR-21 has the capacity to interact with endothelial cells to foster tumor angiogenesis. For that reason, this review explains the critical importance of miR-21/exosomal miR-21 in managing both healthy and diseased states of angiogenesis.

Bio-3D printing of scaffold-free ADSC-derived cartilage constructs comparable to natural cartilage in vitro

BACKGROUND

In end-stage osteoarthritis (OA), osteochondral defects reach the subchondral bone and cartilage tissue of sufficient thickness is required to compensate for the defects. Adipose-derived mesenchymal stem/stromal cells (ADSCs), which are abundant in the body, have the potential to differentiate into cartilage and may be a useful cell source for cartilage regeneration. If it is possible to fabricate ADSC-derived cartilage constructs that can cover the damaged area, this could lead to the development of a new regenerative therapy for OA that could replace the currently available treatments. We therefore sought to produce cartilage constructs with suitable thickness and biological properties, similar to native cartilage, using the bio-three-dimensional (3D) printer. We also investigated the culture protocol to ensure that the constructs were fully mature even at the internal site.

METHODS

ADSCs were isolated from three rats and expanded to create cartilage spheroids. The spheroids were arranged into patches using a Kenzan bio-3D printer to create scaffold-free, cell-only cartilage constructs. Basic fibroblast growth factor (bFGF) was added during expansion culture and varying concentrations of bone morphogenetic protein2 (BMP2) were supplemented during chondrogenic differentiation. The levels of glycosaminoglycans (GAG) in the spheroids and constructs were measured. The histology of the spheroids and constructs and the compressive strength of the constructs were evaluated.

RESULTS

The amount of GAG in the cartilage spheroids was higher in the bFGF and high-BMP2 concentration groups than in the non-supplemented and low-BMP2 concentration groups. Chondrocytes were abundant in the spheroids and constructs, and the extracellular matrix was homogeneously positive for safranin O staining and type II collagen immunostaining. The strength of cartilage constructs was consistent with that of the native cartilage (compressive strength 4.2 ± 1.5 MPa, n = 12).

CONCLUSION

By optimizing the cell culture conditions, inducing chondrogenic differentiation, and bio-3D printing, we successfully fabricated fully mature cartilage constructs with mechanical and histological properties similar to those of articular cartilage.

A Bio-inspired Latent TGF-β Conjugated Scaffold Improves Neocartilage Development

In cartilage tissue engineering, active TGF-β is conventionally supplemented in culture medium at highly supraphysiologic doses to accelerate neocartilage development. While this approach enhances cartilage extracellular matrix (ECM) biosynthesis, it further promotes tissue features detrimental to hyaline cartilage function, including the induction of tissue swelling, hyperplasia, hypertrophy, and ECM heterogeneities. In contrast, during native cartilage development, chondrocytes are surrounded by TGF-β configured in a latent complex (LTGF-β), which undergoes cell-mediated activation, giving rise to moderated, physiologic dosing regimens that enhance ECM biosynthesis while avoiding detrimental features associated with TGF-β excesses. Here, we explore a bio-inspired strategy, consisting of LTGF-β-conjugated scaffolds, providing TGF-β exposure regimens that are moderated and uniformly administered throughout the construct. Specifically, we evaluate the performance of LTGF-β scaffolds to improve neocartilage development with bovine chondrocyte-seeded agarose constructs compared to outcomes from active TGF-β media supplementation (MS) at a physiologic 0.3 ng/mL dose (MS-0.3), supraphysiologic 10 ng/mL dose (MS-10), or TGF-β free. For small-size constructs (∅3×2 mm), LTGF-β scaffolds yield neocartilage that achieves native-matched mechanical properties (800-925 kPa) and sGAG content (6.6%-7.1%), while providing a cell morphology and collagen distribution more reminiscent of hyaline cartilage. LTGF-β scaffolds further afford an optimal chondrogenic phenotype, marked by a 12-to 28-fold reduction of COL-I expression relative to TGF-β-free and a 7-to 17-fold reduction of COL-X expression relative to MS-10. Further, for large-size constructs, which approach the dimensions needed for clinical cartilage repair, LTGF-β scaffolds significantly reduce mechanical and biochemical heterogeneities relative to MS-0.3 and MS-10. Overall, the use of LTGF-β scaffolds improves the composition, structure, material properties, and cell phenotype of neocartilage.

Collagen as a bio-ink for 3D printing: a critical review

The significance of three-dimensional (3D) bioprinting in the domain of regenerative medicine and tissue engineering is readily apparent. To create a multi-functional bioinspired structure, 3D bioprinting requires high-performance bioinks. Bio-inks refer to substances that encapsulate viable cells and are employed in the printing procedure to construct 3D objects progressive through successive layers. For a bio-ink to be considered high-performance, it must meet several critical criteria: printability, gelation kinetics, structural integrity, elasticity and strength, cell adhesion and differentiation, mimicking the native ECM, cell viability and proliferation. As an exemplar application, tissue grafting is used to repair and replace severely injured tissues. The primary considerations in this case include compatibility, availability, advanced surgical techniques, and potential complications after the operation. 3D printing has emerged as an advancement in 3D culture for its use as a regenerative medicine approach. Thus, additive technologies such as 3D bioprinting may offer safe, compatible, and fast-healing tissue engineering options. Multiple methods have been developed for hard and soft tissue engineering during the past few decades, however there are many limitations. Despite significant advances in 3D cell culture, 3D printing, and material creation, a gold standard strategy for designing and rebuilding bone, cartilage, skin, and other tissues has not yet been achieved. Owing to its abundance in the human body and its critical role in protecting and supporting human tissues, soft and hard collagen-based bioinks is an attractive proposition for 3D bioprinting. Collagen, offers a good combination of biocompatibility, controllability, and cell loading. Collagen made of triple helical collagen subunit is a protein-based organic polymer present in almost every extracellular matrix of tissues. Collagen-based bioinks, which create bioinspired scaffolds with multiple functionalities and uses them in various applications, is a represent a breakthrough in the regenerative medicine and biomedical engineering fields. This protein can be blended with a variety of polymers and inorganic fillers to improve the physical and biological performance of the scaffolds. To date, there has not been a comprehensive review appraising the existing literature surround the use of collagen-based bioink applications in 'soft' or 'hard' tissue applications. The uses of the target region in soft tissues include the skin, nerve, and cartilage, whereas in the hard tissues, it specifically refers to bone. For soft tissue healing, collagen-based bioinks must meet greater functional criteria, whereas hard tissue restoration requires superior mechanical qualities. Herein, we summarise collagen-based bioink's features and highlight the most essential ones for diverse healing situations. We conclude with the primary challenges and difficulties of using collagen-based bioinks and suggest future research objectives.

Injectable tissue-engineered human cartilage matrix composite fibrin glue for regeneration of articular cartilage defects

Due to the lack of blood vessels and nerves, the ability of cartilage to repair itself is limited, and the injury of articular cartilage urgently needs effective treatment. Currently, the limitation of clinical repair for cartilage defects is that it is difficult to form pure hyaline cartilage repair, and the source of cartilage tissue and cells is limited. To obtain high-purity regenerated hyaline cartilage, we proposed to construct an injectable hydrogel precursor by using human living hyaline cartilage graft (hLhCG) secreted by human chondrocytes as the dispersed phase and fibrinogen solution as the continuous phase, by double injection with thrombin, three-dimensional network hydrogel structure was formed under the action of thrombin to repair joint defects. The component phenotypes of hLhCG and biomechanical properties of composite gel scaffolds were verified. After 12 weeks of injection of the mixed phase at the defect site, the regenerated tissues are similar in composition to adjacent natural tissues and exhibit similar biomechanical properties. The phenotype of regenerated cartilage was verified, confirming the successful regeneration of hyaline cartilage.

Decellularized Extracellular Matrix Improves Mesenchymal Stromal Cell Spheroid Response to Chondrogenic Stimuli

Cartilage regeneration is hindered due to the low proliferative capacity of chondrocytes and the avascular nature of cartilaginous tissue. Mesenchymal stromal cells (MSCs) are widely studied for cartilage tissue engineering, and the aggregation of MSCs into high-density cell spheroids facilitates chondrogenic differentiation due to increased cell-cell contact. Despite the promise of MSCs, the field would benefit from improved strategies to regulate the chondrogenic potential of MSCs differentiated from induced pluripotent stem cells (iPSCs), which are advantageous for their capacity to yield large numbers of required cells. We previously demonstrated the ability of MSC-secreted extracellular matrix (ECM) to promote MSC chondrogenic differentiation, but the combinatorial effect of iPSC-derived MSC (iMSC) spheroids, iMSC-derived decellularized ECM (idECM), and other stimuli (e.g., oxygen tension and transforming growth factor [TGF]-β) on chondrogenic potential has not been described. Similar to MSCs, iMSCs secreted a collagen-rich ECM. When incorporated into spheroids, idECM increased spheroid diameter and promoted chondrogenic differentiation. The combination of idECM loading, chondrogenic media, and hypoxia enhanced glycosaminoglycan (GAG) content 1.6-fold (40.9 ± 4.6 ng vs. 25.6 ± 3.3 ng, p < 0.05) in iMSC spheroids. Compared with active TGF-β1, the presentation of latent TGF-β1 resulted in greater GAG content (26.6 ± 1.8 ng vs. 41.9 ± 4.3 ng, p < 0.01). Finally, we demonstrated the capacity of individual spheroids to self-assemble into larger constructs and undergo both chondrogenic and hypertrophic differentiation when maintained in lineage-inducing media. These results highlight the potential of idECM to enhance the efficacy of chondrogenic stimuli for improved cartilage regeneration using human MSCs and iMSCs.

Current Concepts and Clinical Applications in Cartilage Tissue Engineering

Cartilage injuries are extremely common in the general population, and conventional interventions have failed to produce optimal results. Tissue engineering (TE) technology has been developed to produce neocartilage for use in a variety of cartilage-related conditions. However, progress in the field of cartilage TE has historically been difficult due to the high functional demand and avascular nature of the tissue. Recent advancements in cell sourcing, biostimulation, and scaffold technology have revolutionized the field and made the clinical application of this technology a reality. Cartilage engineering technology will continue to expand its horizons to fully integrate three-dimensional printing, gene editing, and optimal cell sourcing in the future. This review focuses on the recent advancements in the field of cartilage TE and the landscape of clinical treatments for a variety of cartilage-related conditions.

Extracellular Vesicles-in-Hydrogel (EViH) targeting pathophysiology for tissue repair

Regenerative medicine endeavors to restore damaged tissues and organs utilizing biological approaches. Utilizing biomaterials to target and regulate the pathophysiological processes of injured tissues stands as a crucial method in propelling this field forward. The Extracellular Vesicles-in-Hydrogel (EViH) system amalgamates the advantages of extracellular vesicles (EVs) and hydrogels, rendering it a prominent biomaterial in regenerative medicine with substantial potential for clinical translation. This review elucidates the development and benefits of the EViH system in tissue regeneration, emphasizing the interaction and impact of EVs and hydrogels. Furthermore, it succinctly outlines the pathophysiological characteristics of various types of tissue injuries such as wounds, bone and cartilage injuries, cardiovascular diseases, nerve injuries, as well as liver and kidney injuries, underscoring how EViH systems target these processes to address related tissue damage. Lastly, it explores the challenges and prospects in further advancing EViH-based tissue regeneration, aiming to impart a comprehensive understanding of EViH. The objective is to furnish a thorough overview of EViH in enhancing regenerative medicine applications and to inspire researchers to devise innovative tissue engineering materials for regenerative medicine.

Polydeoxynucleotide-Loaded Visible Light Photo-Crosslinked Gelatin Methacrylate Hydrogel: Approach to Accelerating Cartilage Regeneration

Articular cartilage faces challenges in self-repair due to the lack of blood vessels and limited chondrocyte concentration. Polydeoxyribonucleotide (PDRN) shows promise for promoting chondrocyte growth and cartilage regeneration, but its delivery has been limited to injections. Continuous PDRN delivery is crucial for effective cartilage regeneration. This study explores using gelatin methacrylate (gelMA) hydrogel, crosslinked with visible light and riboflavin 5'-phosphate sodium (RF) as a photoinitiator, for sustained PDRN release. GelMA hydrogel's synthesis was confirmed through spectrophotometric techniques, demonstrating successful methacrylate group incorporation. PDRN-loaded gelMA hydrogels displayed varying pore sizes, swelling ratios, degradation rates, and mechanical properties based on gelMA concentration. They showed sustained PDRN release and biocompatibility, with the 14% gelMA-PDRN composition performing best. Glycosaminoglycan (GAG) activity was higher in PDRN-loaded hydrogels, indicating a positive effect on cartilage formation. RT-PCR analysis revealed increased expression of cartilage-specific genes (COL2, SOX9, AGG) in gelMA-PDRN. Histological assessments in a rabbit cartilage defect model demonstrated superior regenerative effects of gelMA-PDRN hydrogels. This study highlights the potential of gelMA-PDRN hydrogels in cartilage tissue engineering, providing a promising approach for effective cartilage regeneration.

Physiologic Doses of Transforming Growth Factor-β Improve the Composition of Engineered Articular Cartilage

Conventionally, for cartilage tissue engineering applications, transforming growth factor beta (TGF-β) is administered at doses that are several orders of magnitude higher than those present during native cartilage development. While these doses accelerate extracellular matrix (ECM) biosynthesis, they may also contribute to features detrimental to hyaline cartilage function, including tissue swelling, type I collagen (COL-I) deposition, cellular hypertrophy, and cellular hyperplasia. In contrast, during native cartilage development, chondrocytes are exposed to moderate TGF-β levels, which serve to promote strong biosynthetic enhancements while mitigating risks of pathology associated with TGF-β excesses. Here, we examine the hypothesis that physiologic doses of TGF-β can yield neocartilage with a more hyaline cartilage-like composition and structure relative to conventionally administered supraphysiologic doses. This hypothesis was examined on a model system of reduced-size constructs (∅2 × 2 mm or ∅3 × 2 mm) comprised of bovine chondrocytes encapsulated in agarose, which exhibit mitigated TGF-β spatial gradients allowing for an evaluation of the intrinsic effect of TGF-β doses on tissue development. Reduced-size (∅2 × 2 mm or ∅3 × 2 mm) and conventional-size constructs (∅4-∅6 mm × 2 mm) were subjected to a range of physiologic (0.1, 0.3, 1 ng/mL) and supraphysiologic (3, 10 ng/mL) TGF-β doses. At day 56, the physiologic 0.3 ng/mL dose yielded reduced-size constructs with native cartilage-matched Young's modulus (EY) (630 ± 58 kPa) and sulfated glycosaminoglycan (sGAG) content (5.9 ± 0.6%) while significantly increasing the sGAG-to-collagen ratio, leading to significantly reduced tissue swelling relative to constructs exposed to the supraphysiologic 10 ng/mL TGF-β dose. Furthermore, reduced-size constructs exposed to the 0.3 ng/mL dose exhibited a significant reduction in fibrocartilage-associated COL-I and a 77% reduction in the fraction of chondrocytes present in a clustered morphology, relative to the supraphysiologic 10 ng/mL dose (p < 0.001). EY was significantly lower for conventional-size constructs exposed to physiologic doses due to TGF-β transport limitations in these larger tissues (p < 0.001). Overall, physiologic TGF-β appears to achieve an important balance of promoting requisite ECM biosynthesis, while mitigating features detrimental to hyaline cartilage function. While reduced-size constructs are not suitable for the repair of clinical-size cartilage lesions, insights from this work can inform TGF-β dosing requirements for emerging scaffold release or nutrient channel delivery platforms capable of achieving uniform delivery of physiologic TGF-β doses to larger constructs required for clinical cartilage repair.

Advancements in hydrogel design for articular cartilage regeneration: A comprehensive review

This review paper explores the cutting-edge advancements in hydrogel design for articular cartilage regeneration (CR). Articular cartilage (AC) defects are a common occurrence worldwide that can lead to joint breakdown at a later stage of the disease, necessitating immediate intervention to prevent progressive degeneration of cartilage. Decades of research into the biomedical applications of hydrogels have revealed their tremendous potential, particularly in soft tissue engineering, including CR. Hydrogels are highly tunable and can be designed to meet the key criteria needed for a template in CR. This paper aims to identify those criteria, including the hydrogel components, mechanical properties, biodegradability, structural design, and integration capability with the adjacent native tissue and delves into the benefits that CR can obtain through appropriate design. Stratified-structural hydrogels that emulate the native cartilage structure, as well as the impact of environmental stimuli on the regeneration outcome, have also been discussed. By examining recent advances and emerging techniques, this paper offers valuable insights into developing effective hydrogel-based therapies for AC repair.

Osteochondral Tissue Engineering: Scaffold Materials, Fabrication Techniques and Applications

Osteochondral damage, caused by trauma, tumors, or degenerative diseases, presents a major challenge due to the limited self-repair capacity of the tissue. Traditional treatments often result in significant trauma and unpredictable outcomes. Recent advances in bone/cartilage tissue engineering, particularly in scaffold materials and fabrication technologies, offer promising solutions for osteochondral regeneration. This review highlights the selection and design of scaffolds using natural and synthetic materials such as collagen, chitosan (Cs), and polylactic acid (PLA), alongside inorganic components like bioactive glass and nano-hydroxyapatite (nHAp). Key fabrication techniques-freeze-drying, electrospinning, and 3D printing-have improved scaffold porosity and mechanical properties. Special focus is placed on the design of multiphasic scaffolds that mimic natural tissue structures, promoting cell adhesion and differentiation and supporting the regeneration of cartilage and subchondral bone. In addition, the current obstacles and future directions for regenerating damaged osteochondral tissues will be discussed.

Charting a quarter-century of commercial cartilage regeneration products

Functional cartilage regeneration remains difficult to achieve despite decades of research. Dozens of commercial products have been proposed, with each targeting different facets of successful cartilage engineering, including mechanical properties, integration, lubrication and inflammation; however, there remains a lack of breakthroughs in meaningful clinical outcomes. Prior research categorized commercial products based on their components and elucidated challenges faced during the market approval process. This paper, for the first time, comprehensively reviews the properties of commercial products covering the last 25 years, including design trends in components, compatibility with minimally invasive surgery, indications for cartilage defects, long-term follow-up, as well as active sponsorship support of the International Cartilage Regeneration and Joint Preservation Society (ICRS). We aim to summarize the key factors for potentially successful commercial products and elucidate overarching trends in technology development in this field. Given that no revolutionary products have yielded significantly improved clinical results, emerging products compete with one another on user-friendliness and cost-efficiency. Other relevant characteristics include compatibility with minimally invasive surgery, extensiveness of required surgery (one-stage vs. two-stage), use of versatile artificial polymers and application of cells and biomaterials. Specific products continue to lead the market due to their cost-efficiency or indications for larger cartilage defects. However, they have been shown to result in no significant improvement upon clinical follow-up. Thus, there is a need for products that surpass current commercial products and show clinical effectiveness. Translation potential of this article: This review analyzes product components, compatibility with minimally invasive surgery, indication for cartilage defect areas, clinical performance as well as sponsorship for the World Conference of International Cartilage Regeneration & Joint Preservation Society, based on information about cartilage regeneration products from 1997 to 2023. It shines a light on future development of design and commercialization of cartilage products.

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.

Forty Years of the Use of Cells for Cartilage Regeneration: The Research Side

Background: The treatment of articular cartilage damage has always represented a problem of considerable practical interest for orthopedics. Over the years, many surgical techniques have been proposed to induce the growth of repairing tissue and limit degeneration. In 1994, the turning point occurred: implanted autologous cells paved the way for a new treatment option based more on regeneration than repair. Objectives: This review aims to outline biological and clinical advances, from the use of mature adult chondrocytes to cell-derived products, going through progenitor cells derived from bone marrow or adipose tissue and their concentrates for articular cartilage repair. Moreover, it highlights the relevance of gene therapy as a valuable tool for successfully implementing current regenerative treatments, and overcoming the limitations of the local delivery of growth factors. Conclusions: Finally, this review concludes with an outlook on the importance of understanding the role and mechanisms of action of the different cell compounds with a view to implementing personalized treatments.

Soyasaponin Bb/Gelatin-Methacryloyl Hydrogel for Cartilage Inflammation Inhibition

The main causes of failure for cartilage tissue engineering implants are tissue integration, inflammation, and infection. The development of biomaterials with antiforeign body response (FBR) is of particular importance. Herein, we developed a hydrogel loaded with anti-inflammatory drugs to reduce the inflammatory response that follows implantation. The human chondrocytes were used for in vitro study, and cell-laden hydrogel samples were implanted with the backs of rabbits for in vivo study. Soyasaponin Bb (SsBb) as a traditional Chinese medicine could significantly (P < 0.05) downregulate the expression levels of inflammation-related markers including iNOS, COX-2, and IL-6 in chondrocytes induced by IL-1β through the NF-κB signaling pathway. The in vitro experiments demonstrated that a gelatin-methacryloyl (GelMA) hydrogel loaded with SsBb (SsBb/GelMA) could similarly reduce the gene and protein expression levels of inflammation-related markers (iNOS, COX-2, and IL-6). The in vivo anti-inflammatory effects of the SsBb/GelMA hydrogels were assessed by immunohistochemical staining. The results demonstrated that SsBb/GelMA hydrogels inhibited the inflammatory response and downregulated the expression of the inflammatory cytokine IL-6. Therefore, SsBb/GelMA hydrogels are promising candidates for promoting anti-inflammation and cartilage tissue regeneration of implant surfaces.

Morphology of the Calcaneofibular Ligament Reflects Degeneration of the Talonavicular Articular Surface: A Cadaver Study

Background: Osteoarthritis is caused by damage to the articular cartilage due to bone-on-bone collisions and friction. The length, width, and thickness of the ligaments are expected to change in order to regulate excessive bone-to-bone movement. We aimed to clarify the relationship between ligament morphology and joint surface degeneration in the ankle joints using macroscopic observations and measurements. Methods: The participants were 50 feet of 45 Japanese cadavers. The lengths, widths, and thicknesses of the tibionavicular, tibiospring, tibiocalcaneal, posterior tibiotalar, anterior tibiotalar, and calcaneofibular ligaments (CFLs) were measured. The degeneration of the talonavicular joint surface was investigated macroscopically and classified into two groups: the Degeneration (+) group and Degeneration (-) group. Unpaired t-tests were performed for each measurement. Logistic regression analysis was performed on the significantly different items to obtain cutoff values, sensitivity, and specificity. Results: Only the width of the CFL differed significantly between the Degeneration (+) (20 feet) and Degeneration (-) groups (p < 0.001). In the logistic regression analysis, the width of the CFL had an R2 of 0.262, sensitivity of 75.0%, and specificity of 83.3%, with a cutoff value of 8.7 mm. Conclusions: A wide CFL indicates a high likelihood of talonavicular articular surface degeneration.

Mechanical and Physical Characterization of a Biphasic 3D Printed Silk-Infilled Scaffold for Osteochondral Tissue Engineering

Osteochondral tissue damage is a serious concern, with even minor cartilage damage dramatically increasing an individual's risk of osteoarthritis. Therefore, there is a need for an early intervention for osteochondral tissue regeneration. 3D printing is an exciting method for developing novel scaffolds, especially for creating biological scaffolds for osteochondral tissue engineering. However, many 3D printing techniques rely on creating a lattice structure, which often demonstrates poor cell bridging between filaments due to its large pore size, reducing regenerative speed and capacity. To tackle this issue, a novel biphasic scaffold was developed by a combination of 3D printed poly(ethylene glycol)-terephthalate-poly(butylene-terephthalate) (PEGT/PBT) lattice infilled with a porous silk scaffold (derived from Bombyx mori silk fibroin) to make up a bone phase, which continued to a seamless silk top layer, representing a cartilage phase. Compression testing showed scaffolds had Young's modulus, ultimate compressive strength, and fatigue resistance that would allow for their theoretical survival during implantation and joint articulation without stress-shielding mechanosensitive cells. Fluorescent microscopy showed biphasic scaffolds could support the attachment and spreading of human mesenchymal stem cells from bone marrow (hMSC-BM). These promising results highlight the potential utilization of this novel scaffold for osteochondral tissue regeneration as well as highlighting the potential of infilling silk materials within 3D printed scaffolds to further increase their versatility.

A human organoid drug screen identifies α2-adrenergic receptor signaling as a therapeutic target for cartilage regeneration

Directed differentiation of stem cells toward chondrogenesis in vitro and in situ to regenerate cartilage suffers from off-target differentiation and hypertrophic tendency. Here, we generated a cartilaginous organoid system from human expanded pluripotent stem cells (hEPSCs) carrying a COL2A1mCherry and COL10A1eGFP double reporter, enabling real-time monitoring of chondrogenesis and hypertrophy. After screening 2,040 FDA-approved drugs, we found that α-adrenergic receptor (α-AR) antagonists, especially phentolamine, stimulated chondrogenesis but repressed hypertrophy, while α2-AR agonists reduced chondrogenesis and induced hypertrophy. Phentolamine prevented cartilage degeneration in hEPSC cartilaginous organoid and human cartilage explant models and stimulated microfracture-activated endogenous skeletal stem cells toward hyaline-like cartilage regeneration without fibrotic degeneration in situ. Mechanistically, α2-AR signaling induced hypertrophic degeneration via cyclic guanosine monophosphate (cGMP)-dependent secretory leukocyte protease inhibitor (SLPI) production. SLPI-deleted cartilaginous organoid was degeneration resistant, facilitating large cartilage defect healing. Ultimately, targeting α2-AR/SLPI was a promising and clinically feasible strategy to regenerate cartilage via promoting chondrogenesis and repressing hypertrophy.

The clinical potential of meniscal progenitor cells

Introduction

The meniscus is an important cushioning structure of the knee joint, with the maintenance of its normal structure and function playing a crucial role in protecting the joint from early degeneration. Stem/progenitor cells could be the key to help researchers to have a deeper understanding of the biological process of meniscal injury repair and may be important in the meniscus tissue regeneration processes. To the best of our knowledge, there is currently a lack of comprehensive reviews on existing research about the meniscus progenitor cells (MPCs).

Objectives

By reviewing the existing MPC literature, we aim to provide insights for future research on meniscus regeneration.

Methods

The isolation methods, biological characteristics and the translational application of MPCs were summarized.

Results

MPCs could be isolated according to their colony-forming ability, marker expression, migration ability, and differential adhesion to fibronectin. Most existing studies on surface markers of MPCs have largely followed the paradigm of mesenchymal stromal/stem cell research. Based on the information provided by their surface markers and expression profile, researchers located MPCs in the peripheral surface area of the meniscus. Few researches have investigated the translation and application of MPCs, with most studies being limited to MPCs extraction and subsequent reimplantation in vivo.

Conclusions

MPCs are a group of meniscus-resident cells, which exhibit certain stem/progenitor cell characteristics, such as the ability to undergo multilineage differentiation in in vitro culture.