Repair and tissue engineering techniques for articular cartilage

Performance parity in cartilage repair: SPMK-g-PEEK versus cartilage-cartilage interfaces

Effective fluid exudation and rehydration are essential for the low-friction function of healthy articular cartilage, facilitating interstitial fluid pressurisation, solute transport, and aqueous lubrication. However, current metallic biomaterials used in focal cartilage repair or hemiarthroplasty compromise this fluid-pressure dependent load support, leading to the erosion of the interfacing cartilage. This study investigates bioinspired hydrophilic 3-sulfopropyl methacrylate potassium salt (SPMK) polymer grafted onto a PEEK substrate (SPMK-g-PEEK) as a potential solution. SPMK-g-PEEK aims to mimic the natural tribology of cartilage by providing an aqueous low friction interface and polyelectrolyte-enhanced tribological rehydration (PETR), supporting fluid recovery and interstitial fluid pressurisation during cartilage sliding. We compare the tribological characteristics of physiological cartilage-cartilage interfaces, which rely on osmotic swelling and hydrodynamic tribological rehydration, with PETR enabled by SPMK-g-PEEK interfaces. This study introduces a bespoke Fuzzy-PI controlled biotribometer. Employing a dual-phase testing method, static compression followed by sliding, allows simultaneous measurement of friction and cartilage strain recovery, indicative of interstitial fluid recovery following compressive exudation. Cartilage condyle, unfunctionalised PEEK, and SPMK-g-PEEK surfaces were investigated against flat cartilage plugs, which provide no hydrodynamic entrainment zone for tribological rehydration, and convex cartilage plugs, which create a convergent hydrodynamic zone for tribological rehydration. Matched cartilage-cartilage contacts exhibited low friction coefficients of ∼ 0.04 and strain recovery of up to ∼ 14% during the sliding phase. SPMK-g-PEEK surfaces sliding against convex cartilage plugs demonstrated similar strain recovery of ∼ 13% and reduced friction coefficients of ∼ 0.01, due to the combined effects of PETR and hydrodynamic tribological rehydration. In contrast, unfunctionalised PEEK surfaces, similar to current hard biomaterials employed in cartilage resurfacing, showed significantly higher friction and inhibited rehydration. SPMK-g-PEEK effectively mimics the physiological rehydration of connatural articular cartilage surfaces, highlighting its potential as a biomimetic material for cartilage resurfacing.

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.

Semi-synthetic fibrous fibrin composites promote 3D microvascular assembly, survival, and host integration of endothelial cells without mesenchymal cell support

Vasculogenic assembly of 3D capillary networks remains a promising approach to vascularizing tissue-engineered grafts, a significant outstanding challenge in tissue engineering and regenerative medicine. Current approaches for vasculogenic assembly rely on the inclusion of supporting mesenchymal cells alongside endothelial cells, co-encapsulated within vasculo-conducive materials such as low-density fibrin hydrogels. Here, we established a material-based approach to circumvent the need for supporting mesenchymal cells and report that the inclusion of synthetic matrix fibers in dense (>3 mg mL-1) 3D fibrin hydrogels can enhance vasculogenic assembly in endothelial cell monocultures. Surprisingly, we found that the addition of non-cell-adhesive synthetic matrix fibers compared to cell-adhesive synthetic fibers best encouraged vasculogenic assembly, proliferation, lumenogenesis, a vasculogenic transcriptional program, and additionally promoted cell-matrix interactions and intercellular force transmission. Implanting fiber-reinforced prevascularized constructs to assess graft-host vascular integration, we demonstrate additive effects of enhanced vascular network assembly during in vitro pre-culture, fiber-mediated improvements in endothelial cell survival and vascular maintenance post-implantation, and enhanced host cell infiltration that collectively enabled graft vessel integration with host circulation. This work establishes synthetic matrix fibers as an inexpensive alternative to sourcing and expanding secondary supporting cell types for the prevascularization of tissue constructs.

Bi-phasic integrated silk fibroin/polycaprolactone scaffolds for osteochondral regeneration inspired by the native joint tissue and interface

Osteochondral scaffolds designed with bi-phasic and multi-phasic have typically struggled with post-implantation delamination. To address this issue, we developed a novel integrated scaffold with natural and continuous interface and heterogeneous bilayer structure. Through layer-by-layer wet electrospinning, two-dimensional (2D) bi-layer integrated membranes of silk fibroin (SF) and polycaprolactone (PCL) were fabricated. These membranes were then transformed into three-dimensional (3D) scaffolds using a CO2 gas foaming technique, followed by gelatin coating on the osteogenic layer to afford final bi-phasic porous scaffolds. In vitro studies indicated that the 3D scaffolds better-maintained cell phenotypes than conventional 2D electrospun films. Additionally, the 3D scaffolds showed superior cartilage repair and osteoinductivity potential, with increased subchondral bone volume and reduced defect area in rat osteochondral defects models at 12 weeks. Taken together, these gas-foamed scaffolds were a promising candidate for osteochondral regeneration.

Developmental dynamics mimicking inversely engineered pericellular matrix for articular cartilage regeneration

The mechanical mismatch of scaffold matrix-mesenchymal stem cells (MSCs) has been a longstanding issue in the clinical application of MSC-based therapy for articular cartilage (AC) regeneration. Existing tissue-engineered scaffolds underestimate the importance of the natural chondrocyte pericellular matrix (PCM). Here, we reveal the temporal and spatial characteristics of collagen distribution around the chondrocytes. Next, we demonstrate a rationally designed layer-by-layer single-cell encapsulation system which can mimic PCM mechanical responses and enhance MSC chondrogenesis via reestablished the mechanical coupling of PCM-like primitive matrix and chondrocytes. This successfully simulates the temporal and spatial characteristics of collagen secretion. Through investigation of the micromechanical environment of the cells and full-atom simulation analysis of TRPV4, we determine the specific mechanisms by which cellular mechanical forces near the cell are converted into biological signals. The TRPV4-YAP/TAZ-PI3K-Akt signaling pathway is involved in MSC cartilage formation through a joint analysis of the mRNA sequencing and spatial transcriptome results. In a rat model of articular cartilage defects, our inversely engineered pericellular matrix-encapsulated MSC-loaded scaffolds show regenerative performance that are superior to those of scaffolds loaded with only MSCs. These results demonstrate the feasibility of using a PCM-mimicking system to improve MSC chondrogenesis and the efficacy of AC repair.

The biomechanical and functional outcomes of fresh osteochondral allograft for the knee: A systematic review

Background

Fresh osteochondral allograft (FOCA) is a treatment option for osteochondral lesions of the knee which cause pain, locking, and joint instability. While FOCA aims to eliminate these mechanical symptoms, the biomechanical outcomes of the procedure remain poorly understood. This systematic review aimed to collate and interpret the available literature on the biomechanical outcomes of FOCA.

Methods

Systematic searches were performed in three databases using the terms '(Knee OR knee joint) AND (FOCA OR fresh osteochondral allograft OR fresh OCA)'. Eligible studies contained objective biomechanical or functional outcomes, such as knee range of motion, strength, or parameters of gait. The National Institute of Health Quality Assessment Tool assessed study quality. Extracted data were synthesised in a spreadsheet and then a linear regression analysis was performed on the available range of motion data (p = 0.05). Data from a prior systematic review on the biomechanical outcomes of autologous chondrocyte implantation (ACI) were also included in this analysis to facilitate interpretation of the results. PROSPERO ID: CRD42024531998.

Results

Eight studies with 54 participants met the inclusion criteria. On average, studies included 10 participants with a follow up range of 9-108 months.Knee range of motion was reported to improve post-operatively in each study, and the post-operative range of motion was generally reported to be > 120°. A linear regression analysis showed no correlation between final range of motion and follow-up time (p value - 0.860; R2 - 0.019). These results did not differ statistically from the range of motion data reported in a prior review on ACI outcomes (F = 0.003; p = 0.874).One study also reported an improvement in knee strength following FOCA, while two others commented on improvements to gait, although little numerical data was provided.

Conclusion

The limited reporting of improvements to knee range of motion suggest that FOCA has the potential to improve patient quality of life through improved knee function. Linear regression analyses of data presented in this study and obtained from a prior report on the biomechanical outcomes of ACI suggest that the knee ranges of motion following both procedures are comparable. However, further research with larger patient cohorts and consistent methodologies are required to corroborate existing data. This knowledge is important for optimising outcomes via evidence-based rehabilitation programmes.

A versatile platform based on matrix metalloproteinase-sensitive peptides for novel diagnostic and therapeutic strategies in arthritis

Matrix metalloproteinases (MMPs), coupled with other proteinases and glycanases, can degrade proteoglycans, collagens, and other extracellular matrix (ECM) components in inflammatory and non-inflammatory arthritis, making them important pathogenic molecules and ideal disease indicators and pharmaceutical intervention triggers. For MMP responsiveness, MMP-sensitive peptides (MSPs) are among the most easily synthesized and cost-effective substrates, with free terminal amine and/or carboxyl groups extensively employed in multiple designs. We hereby provide a comprehensive review over the mechanisms and advances in MSP applications for the management of arthritis. These applications include early and precise diagnosis of MMP activity via fluorescence probe technologies; acting as nanodrug carriers to enable on-demand drug release triggered by pathological microenvironments; and facilitating cartilage engineering through MMP-mediated degradation, which promotes cell migration, matrix synthesis, and tissue integration. Specifically, the ultra-sensitive MSP diagnostic probes could significantly advance the early diagnosis and detection of osteoarthritis (OA), while MSP-based drug carriers for rheumatoid arthritis (RA) can intelligently release anti-inflammatory drugs effectively during flare-ups, or even before symptoms manifest. The continuous progress in MSP development may acceleratedly lead to novel management regimens for arthropathy in the future.

Restoring articular cartilage: insights from structure, composition and development

Articular cartilage can withstand substantial compressive and shear forces within the joint and also reduces friction during motion. The exceptional mechanical properties of articular cartilage stem from its highly organized extracellular matrix (ECM). The ECM is composed mainly of collagen type II and is pivotal in conferring mechanical durability to the tissue within its proteoglycan-rich matrix. Articular cartilage is prone to injury and degeneration, and current treatments often fail to restore the mechanical function of this tissue. A key challenge is replicating the intricate collagen-proteoglycan network, which is essential for the long-lasting restoration and mechanical durability of the tissue. Understanding articular cartilage development, which arises between late embryonic and early juvenile development, is vital for the creation of durable therapeutic strategies. The development of the articular ECM involves the biosynthesis, fibrillogenesis and self-assembly of the collagen type II network, which, along with proteoglycans and minor ECM components, shapes the architecture of adult articular cartilage. A deeper understanding of these processes could inform biomaterial-based therapies aimed at improving therapeutic outcomes. Emerging biofabrication technologies offer new opportunities to integrate developmental principles into the creation of durable articular cartilage implants. Bridging fundamental biology with innovative engineering offers novel approaches to generating more-durable 3D implants for articular cartilage restoration.

Dysregulated circular RNAs in rheumatoid arthritis: Cellular roles and clinical prospects

Rheumatoid arthritis (RA) is still a healthcare challenge, although current therapeutic strategies have substantially improved its clinical outcomes. The development of novel biomarkers and treatments can increase the likelihood of identification and disease remission in RA patients, especially for patients with seronegative RA and difficult-to-treat RA (D2T RA). Circular RNAs (circRNAs), a novel non-coding RNA species, have been reported to play crucial roles in various biological process of RA. The mechanistic functions of the dysregulated circRNAs in RA are primarily associated with miRNA sponging and regulating transcription. CircRNAs acting as miRNA sponges are further summarized by cell types, including fibroblast-like synoviocytes (FLSs), lymphocytes, macrophages, chondrocytes, and mesenchymal stem cells (MSCs)-/plasma-secreted exosomes. Besides, a description of dysregulated circRNAs in blood, synovial tissue and cartilage tissue suggests their diagnostic potential for RA. In addition, some directions for future research are provided to open the possibility that dysregulated cell- and tissue- specific circRNAs constituting a fresh reservoir of therapeutic targets, and biomarkers for diagnosis, predicting response to therapy, drug selection or patient stratification for RA.

[Arthroscopic tissue engineering scaffold repair for cartilage injuries]

OBJECTIVE

To standardize the operative procedure for tissue-engineered cartilage repair, by demonstrating surgical technique of arthroscopic implantation of decalcified cortex-cancellous bone scaffolds, and summarizing the surgical experience of the sports medicine department team at Peking University Third Hospital.

METHODS

This article elaborates on surgical techniques and skills, focusing on the unabridged implantation technology and surgical procedure of decalcified cortex-cancellous bone scaffolds under arthroscopy: First, the patient was placed in the supine position. After anesthesia had been established, the surgeon established an arthroscope and explored the damaged area under the scope. After confirming the size and location of the injury site, the surgeon cleaned the damaged cartilage, and also trimmed the edges of the cartilage to ensure that the cut surface was smooth and stable. the surgeon performed the micro-fracture surgery in the area of cartilage injury, and then measured the size of the injured area under the scope. Next, the surgeon manually trimmed the tissue-engineered scaffold based on the measurements taken under the arthroscope, and then directly implanted the scaffold using a sleeve. A honeycomb-shaped fixator was used to implant absorbable nails to fix the scaffold. After the scaffold was installed, the knee was repeatedly flexed and extended for 10-20 times to ensure stability and range of motion. Finally, the arthroscope was withdrawn and the wound was closed.

RESULTS

Decalcified cortex-cancellous bone scaffolds possessed unparalleled advantages over synthetic materials in terms of morphology and biomechanics. The cancellous bone part of the scaffold provided a three-dimensional, porous space for cell growth, while the cortical bone part offered the necessary mechanical strength. The surgery was performed entirely under arthroscopy to minimize invasiveness to the patient. Absorbable pins were used for fixation to ensure the stability of the scaffold. This technique could effectively improve the prognosis of the patients with cartilage injuries and standardized the surgical procedures for arthroscopic tissue-engineered scaffold operations in the patients with cartilage damage.

CONCLUSION

With the standard arthroscopic tissue-engineered scaffold repair technique, it is possible to successfully repair damaged cartilage, alleviate symptoms in the short term, and provide a more ideal long-term prognosis. The author and their team explain the surgical procedures for tissue-engineered scaffolds under arthroscopy, with the aim of guiding future clinical practice.

Molecular Mechanisms and Therapeutic Role of Intra-Articular Hyaluronic Acid in Osteoarthritis: A Precision Medicine Perspective

Background: Osteoarthritis (OA) is a degenerative joint disease characterized by progressive cartilage breakdown, synovial inflammation, and pain, which leads to significant disability. IAHA is widely used because of its viscoelastic properties, which restore synovial fluid homeostasis and reduce symptoms. However, emerging evidence suggests that IAHA exerts additional biological effects including chondroprotection, inflammatory modulation, oxidative stress reduction, and pain modulation, which may influence disease progression. Objective: This narrative review examines the biological mechanisms underlying IAHA's role in OA management. The review explored IAHA's effects on synovial fluid viscoelasticity, inflammatory cytokine modulation, cartilage preservation, oxidative stress regulation, and pain pathways, emphasizing the influence of molecular weight variations on therapeutic efficacy. Additionally, this review evaluates IAHA's integration into multimodal treatment strategies, its potential disease-modifying effects, and future directions for personalized treatment approaches. Methods: A comprehensive literature review was conducted using PubMed, Cochrane Library, EMBASE, Scopus, and Web of Science for studies published between January 2000 and March 2024. The search focused on IAHA's molecular, cellular, and biochemical effects in OA and clinical findings assessing its impact on joint function, pain relief, and disease progression. Results: IAHA improves synovial fluid lubrication, reduces proinflammatory cytokines (IL-1β, TNF-α), inhibits matrix metalloproteinases (MMPs), scavenges reactive oxygen species (ROS), and modulates nociceptive pathways. High-molecular-weight IAHA demonstrates superior efficacy in advanced OA, while low-molecular-weight formulations may be better suited for early-stage disease. Although IAHA's symptom relief is comparable to corticosteroids and NSAIDs, its favorable safety profile and emerging disease-modifying potential support its long-term use in OA management. Conclusions: IAHA represents a multifaceted therapeutic approach bridging symptomatic relief and regenerative strategies. While long-term efficacy, optimal administration protocols, and patient-specific responses remain subjects of ongoing research, refining treatment selection criteria, dosing regimens, and combination strategies may enhance clinical outcomes. Future studies should explore biomarker-driven approaches, standardize treatment protocols, and assess IAHA's synergy with regenerative medicine to optimize its role in OA management.

Review on application of silk fibroin hydrogels in the management of wound healing

Wounds are regarded as disruptions in the integrity of human skin tissues, and the process of wound healing is often characterized as protracted and complex, primarily due to the potential infection or inflammation caused by microorganisms. The quest for innovative solutions that accelerate wound healing while prioritizing patient safety and comfort has emerged as a focal point. Within this pursuit, silkworm silk fibroin-a natural polymer extracted from silk cocoons-exhibits a distinctive combination of properties including biocompatibility, biodegradability, superior mechanical strength, water absorption, and low immunogenicity, which align closely with the demands of contemporary wound care. Its remarkable biocompatibility facilitates seamless integration with host tissues, thereby minimizing the risk of rejection or adverse reactions. Furthermore, its intrinsic degradability permits controlled release of therapeutic agents, promoting an optimal microenvironment conducive to healing. This review investigates the multifaceted potential of silk fibroin specifically as a wound dressing material and examines the intricate nuances associated with its application in hydrogels for wound healing, aiming to furnish a thorough overview for both researchers and clinicians. By scrutinizing underlying mechanisms, current applications, and prospective directions, we aspire to cultivate new insights and inspire innovative strategies within this rapidly evolving field.

Biphasic biomimetic scaffolds based on a regionally decalcified bone framework and pre-chondrogenic microspheres for osteochondral defect repair

Osteochondral defects are still facing a significant challenge in clinical surgery, making post-trauma repair difficult. Tissue engineering has provided a promising approach to solving these defects. However, existing scaffolds cannot replicate the complex biphasic cartilage-bone microenvironment with accuracy. We aimed to develop a biphasic biomimetic scaffold with regionally regulated vascularization that promoted chondrogenesis and osteogenesis through bidirectional regulation of endochondral ossification. This scaffold consisted of pre-chondrogenic microspheres (PCMs) and a decalcified bone frame prepared by decalcifying the cartilage layer and bone layer of the scaffold to varying degrees. Incorporation of PCMs into the cartilage layer created a microenvironment that promoted cartilage regeneration while axitinib was modified to inhibit vascularization and enhance cartilage regeneration. The bone layer provided a microenvironment that promoted endochondral ossification and facilitated bone repair. In vitro studies have shown that axitinib-modified cartilage layers significantly inhibit the VEGF expression of pre-chondrogenic cells, while decalcified bone powder from the bone layer significantly promotes the ossification of PCMs. In vivo experiments indicated that this decalcified bone frame controls the endochondral ossification of PCMs through regionalized angiogenesis, promoting the integrated regeneration and reconstruction of osteochondral defects in rabbit knee joints. These results suggest that our designed demineralized bone frame can precisely engineer the osteochondral regeneration microenvironment, providing theoretical guidance for the integrated regeneration and repair of anisotropic tissue injuries.

Management strategies and outcomes for fracture-related infection of patellar fractures

INTRODUCTION

Fracture-related infection (FRI) poses a substantial challenge in orthopaedic trauma surgery, potentially leading to permanent functional impairment or necessitating amputation in patients who are expected to recover fully. Data on the incidence, pathogen detection rates, outcomes, and optimal management strategies for patellar FRI are limited. Therefore, this study aimed to identify the most common pathogens associated with patellar fixation-related infections, evaluate the functional outcome associated with FRI of the patella, and develop a management algorithm for addressing these severe complications.

METHODS

This retrospective review analyzed a prospectively maintained database to identify all patients with FRI of the patella treated at our institution between January 2015 and August 2023. Data on demographics, fracture characteristics, surgical details, and outcomes were collected. Descriptive statistical analyses were performed using SPSS software.

RESULTS

Over the 9-year period, 32 cases of patellar fractures complicated by infection following surgical treatment were identified, with complete follow-up data available (mean age, 56.5 ± 15.8 years). Infection occurred in 13 patients within 2 weeks of fixation and in 19 patients between 2 and 10 weeks postoperatively. Following debridement, nine patients retained their original fixation, eight underwent hardware removal, and 15 underwent hardware replacement. Seven patients developed septic arthritis and were managed with arthroscopic knee lavage. Metagenomic next-generation sequencing demonstrated a sensitivity of 93.8 % (30/32), which was significantly higher than that of traditional microbiological culture (53.1 %; P < 0.01). All surgical incisions achieved primary healing within 2 weeks post-closure with no recurrence of infection, skin necrosis, osteomyelitis, or nonunion. At the final follow-up, all fractures had united, with the Böstman patellar fracture functional scores ranging from 24 to 29, resulting in a 100 % excellent/good rate.

CONCLUSIONS

Comprehensive and multidisciplinary management approaches can achieve successful bone union and favourable long-term outcomes in patients with patellar FRI. However, further validation through large-scale studies is necessary to confirm these findings.

Preparation of hydrogel microsphere and its application in articular cartilage injury

In recent years, hydrogel microspheres have garnered significant attention due to their unique structure and functionality, demonstrating substantial potential in articular cartilage injury repair. This paper provides a comprehensive overview of current strategies for cartilage injury repair and summarizes the materials and preparation methods of hydrogel microspheres. Furthermore, it highlights the multiple roles of hydrogel microspheres in cartilage repair, including inflammation control, regulation of chondrocyte metabolism, drug and cell delivery, lubrication improvement, and recruitment of endogenous stem cells. Finally, the paper discusses the application prospects of hydrogel microspheres, identifies current limitations and challenges, and offers insights to guide future research and practical applications in cartilage injury repair.

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.

Crosslinking substrate regulates frictional properties of tissue-engineered cartilage and chondrocyte response to loading

Hydrogels are frequently used in regenerative medicine due to their hydrated, tissue-compatible nature, and tuneable mechanics. While many strategies enable bulk mechanical modulation, little attention is given to tuning surface tribology, and its impact on cellular behavior under mechanical stimuli. Here, we demonstrate that photocrosslinking hydrogels on hydrophobic substrates leads to significant, long-lasting reductions in surface friction, ideal for cartilage tissue regeneration. Gelatin methacryloyl and hyaluronic acid methacrylate hydrogels photocrosslinked on polytetrafluoroethylene possess more hydrated, lubricious surfaces, with lower friction coefficients and crosslinking densities than those crosslinked on glass. This facilitated self-lubrication via water exudation, limiting shear during biaxial stimulation. When subject to intermittent biaxial loading mimicking joint movement, low-friction chondrocyte-laden neo-tissues formed superior hyaline cartilage, confirming the benefits of reduced friction on tissue development. Finally, in situ photocrosslinking enabled precise hydrogel formation in a full-thickness cartilage defect, highlighting the clinical potential and emphasizing the importance of crosslinking substrate in regenerative medicine.

Platelet-Derived Growth Factor as Biomarker of Clinical Outcome for Autologous Platelet Concentrate Therapy in Grade I Knee Osteoarthritis

Introduction

Autologous platelet concentrates (APC) are widely used in the infiltrative treatment of knee osteoarthritis (OA) to enhance tissue healing and relieve pain. Aim of this study was to identify predictive biomarkers for clinical outcomes in patients with grade I knee OA.

Methods

A panel of growth factors (GFs) and cytokines was determined in peripheral blood (PB) and APC. The Numeric Pain Rating Scale (NPRS) was used as a clinical readout before and after the APC infiltration.

Results

A lower white blood cell (WBC) count and higher Monocyte-chemoattractant Protein-1 levels in PB were associated with APC-induced pain relief. Platelet-derived Growth Factor (PDGF) levels in APC were significantly higher in OA patients displaying a larger NPRS reduction, independent of platelet count. Finally, the simultaneous determination of PDGF, Vascular Endothelial Growth Factor, and Macrophage Inflammatory Protein-1α in APC discriminated OA patients with very poor or no response.

Conclusion

Platelet-released GFs rather than platelet counts may predict clinical outcomes in grade 1 knee OA.

Recapitulation of endochondral ossification by hPSC-derived SOX9+ sclerotomal progenitors

Endochondral ossification generates most of the load-bearing bones, recapitulating it in human cells remains a challenge. Here, we report generation of SOX9+ sclerotomal progenitors (scl-progenitors), a mesenchymal precursor at the pre-condensation stage, from human pluripotent stem cells and development of osteochondral induction methods for these cells. Upon lineage-specific induction, SOX9+ scl-progenitors have not only generated articular cartilage but have also undergone spontaneous condensation, cartilaginous anlagen formation, chondrocyte hypertrophy, vascular invasion, and finally bone formation with stroma, thereby recapitulating key stages during endochondral ossification. Moreover, self-organized growth plate-like structures have also been induced using SOX9+ scl-progenitor-derived fusion constructs with chondro- and osteo-spheroids, exhibiting molecular and cellular similarities to the primary growth plates. Furthermore, we have identified ITGA9 as a specific surface marker for reporter-independent isolation of SOX9+ scl-progenitors and established a culture system to support their expansion. Our work highlights SOX9+ scl-progenitors as a promising tool for modeling human skeletal development and bone/cartilage bioengineering.

Transcriptional Analysis Reveals That the FHL1/JAK-STAT Pathway is Involved in Acute Cartilage Injury in Mice

ObjectiveThis study aimed to identify genes and signaling pathways associated with acute cartilage injury using RNA sequencing (RNA-seq).MethodsKnee joint cartilage samples were collected from normal mice and 2 models of acute cartilage injury (non-invasive and groove models) within an 8-hour time limit. RNA-seq revealed differential gene expression between the injury models and controls, with subsequent validation using real-time quantitative polymerase chain reaction (RT-qPCR) for 9 representative genes.ResultsCompared to controls, the non-invasive model showed 36 differentially expressed genes (DEGs) (13 up-regulated, 23 down-regulated), with Gm14648 and Gm35438 showing the most significant upregulation and downregulation, respectively. The groove model exhibited 255 DEGs (13 up-regulated, 23 down-regulated), with Gm14648 and Gm35438 showing the (222 up-regulated, 33 down-regulated). Six overlapping genes were identified between the non-invasive and groove models, including up-regulated genes (Igfn1, Muc6, Hmox1) and down-regulated genes (Pthlh, Cyp1a1, Gm13490), validated by RT-qPCR. Gene ontology (GO) analysis highlighted involvement in environmental information processing and cartilage organ system function, while Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis implicated the JAK-STAT signaling pathway. RT-qPCR and immunohistochemistry confirmed downregulation of Fhl1 in the non-invasive model, supported by Western blotting of p-JAK2/t-JAK2 levels.ConclusionsThis study identifies DEGs (13 up-regulated, 23 down-regulated), with Gm14648 and Gm35438 showing the in acute cartilage injury, suggesting potential therapeutic targets. The role of Fhl1 in cartilage protection via the JAK-STAT pathway warrants further investigation in acute cartilage injury research.

Viscoelasticity Can Be Tuned Through Covalent Incorporation of Chondroitin Sulphate in Allylated Gelatin Hydrogels

Cartilage is a slow-remodeling tissue with limited healing capacity. This has led to decades of tissue engineering efforts where the goal is biomaterials with regenerative capacity to restore functional integrity. Achieving full functional and mechanical integrity has proven difficult as cartilage has distinct mechanical properties. Glycosaminoglycans (GAGs) play a crucial role in cartilage mechanics due to their swelling behavior, contributing to viscoelasticity. The aims of this study are to covalently incorporate thiolated chondroitin sulphate (CSSH) in allylated gelatin (gelAGE) hydrogels at different concentrations to mimic GAG-rich regions in cartilage and create platforms to study subsequent cellular behavior. Hydrogels are evaluated for soluble fraction, swelling ratio, chondroitin sulphate (CS) retention, mechanical and viscoelastic properties, and cytocompatibility. ≈80% of CSSH is retained, and samples containing CSSH has an increased swelling ratio, indicating the incorporation of GAGs. Samples containing CSSH has an increased relaxation amplitude compared to gelAGE controls with a more elastic response. The addition of CSSH has no adverse effects on cytocompatibility. In conclusion, this study demonstrates the incorporation of thiolated CS in gelAGE hydrogels at different concentrations with no adverse effects on cytocompatibility. This allows for viscoelastic tuning which is important to consider when engineering new biomaterials.

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.

Collagen hydrogel-driven pyroptosis suppression and combined microfracture technique delay osteoarthritis progression

The pathogenesis of osteoarthritis (OA), a disease causing severe medical burden and joint deformities, remains unclear. Chondrocyte death and osteochondral injury caused are the main pathological changes in OA. Thus, inhibiting chondrocyte death and repairing defective osteochondral are two important challenges in the treatment of OA. In this study, we found morphological changes consistent with cell pyroptosis in OA cartilage tissues. To inhibit chondrocyte pyroptosis and delay the progression of OA, we proposed to use decellularized extracellular matrix (dECM) and gelatin methacrylate (GelMA) to form a composite hydrogel GelMA/dECM. Regarding osteochondral defect repair, our proposed treatment strategy was hydrogel combined with microfracture (MF) surgery. MF established a biological link between the osteochondral defect and the bone-marrow cavity, prompting the recruitment of bone-marrow mesenchymal stem cells (BMSCs) to the osteochondral defect site, and the retained biopeptides in the hydrogel regulate the polarization of the BMSCs into hyaline cartilage, accelerating the repair of the defect. In vitro/vivo experiments and RNA sequencing analyses demonstrated that GelMA/dECM inhibited the occurrence of chondrocyte pyroptosis and delayed OA disease progression. Hydrogel also recruited numerous of BMSCs and contributed to chondrogenic differentiation, accelerating the in situ repair of defective osteochondral combined with MF. Collectively, GelMA/dECM composite hydrogel inhibited cartilage pyroptosis and reduced the pathway of chondrocyte death. Moreover, the hydrogel combined with microfracture technique could accelerate the repair of osteochondral defects. This is a groundbreaking attempt by tissue engineering, cell biology, and clinical medicine.

TP8, A Novel Chondroinductive Peptide, Significantly Promoted Neo-Cartilage Repair without Activating Bone Formation

The repair of large cartilage defects remains highly challenging in the fields of orthopedics and oral and maxillofacial surgery. A chondroinductive agent is promising to activate endogenous mesenchymal stem cells (MSCs) so as to facilitate cartilage regeneration. In this study, we analyze the crystallographic data of the critical binding domain of transforming growth factor β3 (TGF-β3) with its type II receptor and successfully develop a novel chondroinductive peptide - TGF-β3-derived peptide No. 8 (TP8) that can induce an ectopic cartilage formation without obvious bone formation. TP8 shows a comparable capacity as TGF-β3 in enhancing glycosaminoglycans (GAGs) and proteoglycans (PGs) secretion in the micromass of bone marrow MSCs (BMSCs) and promoting the expression of chondrogenic markers in comparison with the Control group. TP8 induces a significantly higher expression of the SRY-box transcription factor 9 (Sox9) gene than TGF-β3. Moreover, TP8 significantly upregulates the phosphorylation of Smad1/5 but not MAPK/JNK or Smad 2/3. The knockdown of low-density lipoprotein receptor (LDLR) -related protein-1 (Lrp1), a transmembrane endocytosis receptor, nullifies the TP8-induced Sox9 expression. In the critical-size cartilage defects in rabbit medial femoral condyles, TP8 can induce neo-cartilage formation with a significantly thicker deep zone in comparison with the TGF-β3 and Control. These findings suggest a promising application potential of TP8 in cartilage tissue engineering.

Intra-Articular Hyaluronic Acid for Knee Osteoarthritis: A Systematic Umbrella Review

Objective: to evaluate the efficacy, safety, and cost-effectiveness of intra-articular hyaluronic acid (IAHA) in treating osteoarthritis (OA), considering innovations in formulations, comparative outcomes, and variability in guidelines. This review aims to synthesize evidence supporting the role of IAHA in multimodal treatment strategies. Materials and Methods: A general, narrative, umbrella review of systematic reviews and meta-analyses was conducted. Clinical practice recommendations and guidelines for IAHA use were also reviewed and evaluated. A comprehensive search was conducted across the main medical data sources. Inclusion criteria focused on studies evaluating the efficacy, safety, and impact of IAHA. Key outcomes included pain reduction (e.g., WOMAC, VAS), functional improvement, safety, and cost-effectiveness. Results: IAHA showed moderate efficacy in pain relief and functional improvement, especially in early-to-moderate OA. The results indicate that hybrid formulations and combination therapies show better clinical outcomes, with expanded efficacy and potential chondroprotection. However, heterogeneity between studies was noted, reflecting variability in patient populations and intervention protocols. International guidelines varied significantly, with some opposing routine use (e.g., AAOS, NICE) and others endorsing IAHA more or less conditionally (e.g., ESCEO, OARSI). Conclusions: IAHA remains a treatment modality in the arsenal of selected populations of people with OA, especially for early and moderate disease. High-quality, standardized studies are still needed to refine IAHA's role and establish personalized guidelines for individual patients. A concerted effort to harmonize global recommendations and economic strategies, such as tiered pricing, can increase equitable access and optimize IAHA's integration of multimodal treatment for OA.

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.

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.

Functionalized conductive polymer composites for tissue engineering and biomedical applications- a mini review

Tissue engineering (TE) has emerged as a promising therapeutic strategy, employing artificial scaffolds to regenerate functional cardiac tissue and offering new hope for innovative treatment approaches. A straightforward method for producing biodegradable, conductive polymer-based composites involves blending conductive polymers directly with biodegradable ones. This approach's flexibility enables the development of diverse biodegradable, conductive polymer scaffolds, which have been extensively explored in tissue engineering and regenerative medicine. While this technique successfully combines the advantages of both polymer types, it may face challenges such as potential compromises in conductivity and biodegradability. This review emphasizes the potential to tailor degradation rates and conductivity by selecting appropriate polymer types and ratios, ensuring adaptability for various biomedical applications.

High paracrine activity of hADSCs cartilage microtissues inhibits extracellular matrix degradation and promotes cartilage regeneration

Due to its unique structure, articular cartilage has limited self-repair capacity. Microtissues are tiny tissue clusters that can mimic the function of target organs or tissues. Using cells alone for microtissue construction often results in the formation of necrotic cores. However, the extracellular matrix (ECM) of native cartilage can provide structural support and is an ideal source of microcarriers. Autologous adipose-derived mesenchymal stem cells (ADSCs) and bone marrow mesenchymal stem cells (BMSCs) are widely used in cartilage tissue engineering. In this study, we fabricated microcarriers and compared the behavior of two homologous cell types in the microcarrier environment. The microcarrier environment highlighted the advantages of ADSCs and promoted the proliferation and migration of these cells. Then, ADSCs microtissues (ADSCs-MT) and BMSCs microtissues (BMSCs-MT) were fabricated using a three-dimensional dynamic culture system. In vitro and in vivo experiments verified that the cartilage regeneration ability of ADSCs-MT was significantly superior to that of BMSCs-MT. Transcriptomics revealed that ADSCs-MT showed significantly lower expression levels of ECM degradation, osteogenesis, and fibrocartilage markers. Finally, the protective effect of microtissues on inflammatory chondrocytes was validated. Overall, the ADSCs-MT constructed in this study achieved excellent cartilage regeneration and could be promising for the autologous application of cartilage microtissues.

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.

Unlocking the therapeutic potential of WISP-1: A comprehensive exploration of its role in age-related musculoskeletal disorders

As the global population ages, the incidence of age-related musculoskeletal diseases continues to increase, driven by numerous complex and poorly understood factors. WNT-1 inducible secreted protein 1 (WISP-1), a secreted matrix protein, plays a critical role in the growth and development of the musculoskeletal system, including chondrogenesis, osteogenesis, and myogenesis. Numerous in vivo and in vitro studies have demonstrated that WISP-1 is significantly upregulated in age-related musculoskeletal conditions, such as osteoarthritis, osteoporosis, and sarcopenia, suggesting its involvement in the pathogenesis of these diseases. Regulating WISP-1 expression holds promise as a therapeutic strategy for improving musculoskeletal function, potentially offering new avenues for treating age-related musculoskeletal diseases in clinical practice. This review highlights the signaling pathways associated with WISP-1, its physiological roles within the musculoskeletal system, and its therapeutic potential in treating age-related musculoskeletal disorders.

Positive impact of pyrocarbon and mechanical loading on cartilage-like tissue synthesis in a scaffold-free process

Aiming to build a tissue analogue engineered cartilage from differentiated chondrocytes, we investigated the potential of a pyrocarbon (PyC)-based and scaffold-free process, under mechanical stimulation. PyC biomaterial has shown promise in arthroplasty and implant strategies, and mechanical stimulation is recognized as an improvement in regeneration strategies. The objective was to maintain the cell phenotype to produce constructs with cartilage-like matrix composition and mechanical properties. Primary murine chondrocytes were deposited in drop form between two biomaterial surfaces expanded to 500 μm and a uniaxial cyclic compression was applied thanks to a handmade tribo-bioreactor (0.5 Hz, 100 μm of amplitude, 17 days). Histology and immunohistochemistry analysis showed that PyC biomaterial promoted expression of cartilage-like matrix components (glycosaminoglycans, type II collagen, aggrecan). Importantly, constructs obtained in dynamic conditions were denser and showed a cohesive and compact shape. The most promising condition was the combined use of PyC and dynamic stimulation, resulting in constructs of low elasticity and high viscosity, thus with an increased damping factor. We verified that no calcium deposits were detectable and that type X collagen was not expressed, suggesting that the cells had not undergone hypertrophic maturation. While most studies focus on the comparison of different biomaterials or on the effect of different mechanical stimuli separately, we demonstrated the value of combining the two approaches to get as close as possible to the biological and mechanical qualities of natural hyaline articular cartilage.

Recent Development of Fibrous Hydrogels: Properties, Applications and Perspectives

Fibrous hydrogels (FGs), characterized by a 3D network structure made from prefabricated fibers, fibrils and polymeric materials, have emerged as significant materials in numerous fields. However, the challenge of balancing mechanical properties and functions hinders their further development. This article reviews the main advantages of FGs, including enhanced mechanical properties, high conductivity, high antimicrobial and anti-inflammatory properties, stimulus responsiveness, and an extracellular matrix (ECM)-like structure. It also discusses the influence of assembly methods, such as fiber cross-linking, interfacial treatments of fibers with hydrogel matrices, and supramolecular assembly, on the diverse functionalities of FGs. Furthermore, the mechanisms for improving the performance of the above five aspects are discussed, such as creating ion carrier channels for conductivity, in situ gelation of drugs to enhance antibacterial and anti-inflammatory properties, and entanglement and hydrophobic interactions between fibers, resulting in ECM-like structured FGs. In addition, this review addresses the application of FGs in sensors, dressings, and tissue scaffolds based on the synergistic effects of optimizing the performance. Finally, challenges and future applications of FGs are discussed, providing a theoretical foundation and new insights for the design and application of cutting-edge FGs.

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.

Research advance of 3D printing for articular cartilage regeneration

Articular cartilage lesion frequently leads to dysfunction and the development of degenerative diseases, posing a significant public health challenge due to the limited self-healing capacity of cartilage tissue. Current surgical treatments, including marrow stimulation techniques and osteochondral autografts/allografts, have limited efficacy or have significant drawbacks, highlighting the urgent need for alternative strategies. Advances in 3D printing for cartilage regeneration have shown promising potential in creating cartilage-mimicking constructs, thereby opening new possibilities for cartilage repair. In this review, we summarize current surgical treatment methods and their limitations for addressing articular cartilage lesion, various 3D printing strategies and their features in cartilage tissue engineering, seed cells from different sources, and different types of biomaterials. We also explore the benefits, current challenges, and future research directions for 3D printing in the treatment of articular cartilage lesion within the field of cartilage tissue engineering.

Innovative Biotherapies and Nanotechnology in Osteoarthritis: Advancements in Inflammation Control and Cartilage Regeneration

Osteoarthritis (OA) is among the most prevalent degenerative joint disorders worldwide, particularly affecting the aging population and imposing significant disability and economic burdens. The disease is characterized by progressive degradation of articular cartilage and chronic inflammation, with no effective long-term treatments currently available to address the underlying causes of its progression. Conventional therapies primarily manage symptoms such as pain and inflammation but fail to repair damaged tissues. Emerging biotherapies and regenerative medicine approaches offer promising alternatives by addressing cartilage repair and inflammation control at the molecular level. This review explores the recent advancements in biotherapeutic strategies, including mesenchymal stem cell (MSC) therapy, growth factors, and tissue engineering, which hold the potential for promoting cartilage regeneration and modulating the inflammatory microenvironment. Additionally, the integration of nanotechnology has opened new avenues for targeted drug delivery systems and the development of innovative nanomaterials that can further enhance the efficacy of biotherapies by precisely targeting inflammation and cartilage damage. This article concludes by discussing the current clinical applications, the ongoing clinical trials, and the future research directions necessary to confirm the safety and efficacy of these advanced therapies for OA management. With these advancements, biotherapies combined with nanotechnology may revolutionize the future of OA treatment by offering precise and effective solutions for long-term disease management and improved patient outcomes.

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.

Repair of Osteochondral Defect with Acellular Cartilage Matrix and Thermosensitive Hydrogel Scaffold

In the present study, acellular cartilage matrix (ACM) was modified with poly-l-lysine/hyaluronic acid (PLL/HA) multilayers via detergent-enzyme chemical digestion and layer-by-layer self-assembly technology. This modified ACM was then loaded with Transforming Growth Factor Beta 3 (TGF-β3) and incorporated into a thermosensitive hydrogel (TH) to create a HA/PLL-ACM/TH composite scaffold with sustained-release function. This study aimed to evaluate the efficacy of this novel composite scaffold in promoting chondrogenic differentiation of bone marrow mesenchymal stem cells (BMSCs) and facilitating osteochondral defect repair. In vitro, isolated, and cultured rat BMSCs were inoculated in equal amounts into TH, ACM/TH, and HA/PLL-ACM/TH groups, with or without TGF-β3 supplementation, for 21 days. Western blot (WB) analysis and immunofluorescence staining were employed to assess the expression levels of collagen II, aggrecan, and SOX-9. In vivo, osteochondral defect was created in the Sprague-Dawley rat trochlea using microdrilling. TH, ACM/TH, and HA/PLL-ACM/TH scaffolds, with or without TGF-β3, were implanted into the defect. After 6 weeks, the repairs were evaluated macroscopically, using Micro computed tomography (micro-CT), histological analysis, and immunohistochemistry. The results demonstrated that the HA/PLL-ACM/TH scaffold loaded with TGF-β3 significantly upregulated the expression of collagen II, aggrecan, and SOX-9 compared with the control and other experimental groups. Furthermore, at 6 weeks postsurgery, the HA/PLL-ACM/TH group loaded with TGF-β3 exhibited superior tissue formation on the joint surface, as confirmed by micro-CT and histological evidence, indicating improved osteochondral repair. These findings suggest that the HA/PLL-ACM/TH scaffold loaded with TGF-β3 holds promise as a therapeutic strategy for osteochondral defect and offers a novel approach for utilizing acellular cartilage microfilaments.

Promotion of hMDSC differentiation by combined action of scaffold material and TGF-β superfamily growth factors

Objective

Herein we propose a combined action of collagen type I (CA) or synthetic collagen-like-peptide functionalized with the cell adhesive RGD motif (PEG-CLP-RGD) hydrogels and selected growth factors to promote chondrogenic differentiation of human muscle-derived stem cells (hMDSCs) under normal and reduced oxygen conditions.

Methods

hMDSCs were set for differentiation towards chondrogenic lineage using BMP-7 and TGF-β3. Cells were seeded onto hydrogels loaded with growth factors (75ng/scaffold) and cultured for 28 days under normal (21%) and severe hypoxic (1%) conditions. Chondrogenesis was evaluated by monitoring collagen type II and GAG deposition, and quantification of ACAN expression by RT-PCR.

Results

Sustained release of TGFβ3 from the hydrogels was observed, 8.7 ± 0.5% of the initially loaded amount diffused out after 24 h from both substrates. For the BMP-7 growth factor, 14.8 ± 0.3% and 18.2 ± 0.6% of the initially loaded amount diffused out after 24 h from CA and CLP-RGD, respectively. The key findings of this study are: i) the self-supporting hydrogels themselves can stimulate hMDSC chondrogenesis by inducing gene expression of cartilage-specific proteoglycan aggrecan and ECM production; ii) the effect of dual BMP-7 and TGF-β3 loading was more pronounced on CA hydrogel under normal oxygen conditions; iii) dual loading on PEG-CLP-RGD hydrogels did not have the synergistic effect, TGF-β3 was more effective under both oxygen conditions; iv) BMP-7 can improve chondrogenic effect of TGF-β3 on CA scaffolds, and hydrogels loaded with both growth factors can induce cartilage formation in hMDSC cultures.

Conclusion

Our results support the potential strategy of combining implantable hydrogels functionalized with differentiation factors toward improving cartilaginous repair.

Magnetic Soft Catheter Robot System for Minimally Invasive Treatments of Articular Cartilage Defects

Articular cartilage defects are among the most common orthopedic diseases, which seriously affect patients' health and daily activities, without prompt treatment. The repair biocarrier-based treatment has shown great promise. Total joint injection and open surgery are two main methods to deliver functional repair biocarriers into the knee joint. However, the exhibited drawbacks of these methods hinder their utility. The repair effect of total joint injection is unstable due to the low targeting rate of the repair biocarriers, whereas open surgery causes serious trauma to patients, thereby prolonging the postoperative healing time. In this study, we develop a magnetic soft catheter robot (MSCR) system to perform precise in situ repair of articular cartilage defects with minimal incision. The MSCR processes a size of millimeters, allowing it to enter the joint cavity through a tiny skin incision to reduce postoperative trauma. Meanwhile, a hybrid control strategy combining neural network and visual servo is applied to sequentially complete the coarse and fine positioning of the MSCR on the cartilage defect sites. After reaching the target, the photosensitive hydrogel is injected and anchored into the defect sites through the MSCR, ultimately completing the in situ cartilage repair. The in vitro and ex vivo experiments were conducted on a 3D printed human femur model and an isolated porcine femur, respectively, to demonstrate the potential of our system for the articular cartilage repair.

3D-printed constructs deliver bioactive cargos to expedite cartilage regeneration

Cartilage is solid connective tissue that recovers slowly from injury, and pain and dysfunction from cartilage damage affect many people. The treatment of cartilage injury is clinically challenging and there is no optimal solution, which is a hot research topic at present. With the rapid development of 3D printing technology in recent years, 3D bioprinting can better mimic the complex microstructure of cartilage tissue and thus enabling the anatomy and functional regeneration of damaged cartilage. This article reviews the methods of 3D printing used to mimic cartilage structures, the selection of cells and biological factors, and the development of bioinks and advances in scaffold structures, with an emphasis on how 3D printing structure provides bioactive cargos in each stage to enhance the effect. Finally, clinical applications and future development of simulated cartilage printing are introduced, which are expected to provide new insights into this field and guide other researchers who are engaged in cartilage repair.

Exosomes Reshape the Osteoarthritic Defect: Emerging Potential in Regenerative Medicine-A Review

Osteoarthritis (OA) is a joint disorder caused by wear and tear of the cartilage that cushions the joints. It is a progressive condition that can cause significant pain and disability. Currently, there is no cure for OA, though there are treatments available to manage symptoms and slow the progression of the disease. A chondral defect is a common and devastating lesion that is challenging to treat due to its avascular and aneural nature. However, there are conventional therapies available, ranging from microfracture to cell-based therapy. Anyhow, its efficiency in cartilage defects is limited due to unclear cell viability. Exosomes have emerged as a potent therapeutic tool for chondral defects because they are a complicated complex containing cargo of proteins, DNA, and RNA as well as the ability to target cells due to their phospholipidic composition and the altering exosomal contents that boost regeneration potential. Exosomes are used in a variety of applications, including tissue healing and anti-inflammatory therapy. As in recent years, biomaterials-based bio fabrication has gained popularity among the many printable polymer-based hydrogels, tissue-specific decellularized extracellular matrix might boost the effects rather than an extracellular matrix imitating environment, a short note has been discussed. Exosomes are believed to be the greatest alternative option for current cell-based therapy, and future progress in exosome-based therapy could have a greater influence in the field of orthopaedics. The review focuses extensively on the insights of exosome use and scientific breakthroughs centered OA.

Strategies to engineer articular cartilage with biomimetic zonal features: a review

Articular cartilage (AC) is a highly specialized tissue with restricted ability for self-regeneration, given its avascular and acellular nature. Although a considerable number of surgical treatments is available for the repair, reconstruction, and regeneration of AC defects, most of them do not prioritize the development of engineered cartilage with zonal stratification derived from biomimetic biochemical, biomechanical and topographic cues. In the absence of these zonal elements, engineered cartilage will exhibit increased susceptibility to failure and will neither be able to withstand the mechanical loading to which AC is subjected nor will it integrate well with the surrounding tissue. In this regard, new breakthroughs in the development of hierarchical stratified engineered cartilage are highly sought after. Initially, this review provides a comprehensive analysis of the composition and zonal organization of AC, aiming to enhance our understanding of the significance of the structure of AC for its function. Next, we direct our attention towards the existing in vitro and in vivo studies that introduce zonal elements in engineered cartilage to elicit appropriate AC regeneration by employing tissue engineering strategies. Finally, the advantages, challenges, and future perspectives of these approaches are presented.

Skeletal organoids

The skeletal system, composed of bones, muscles, joints, ligaments, and tendons, serves as the foundation for maintaining human posture, mobility, and overall biomechanical functionality. However, with ageing, chronic overuse, and acute injuries, conditions such as osteoarthritis, intervertebral disc degeneration, muscle atrophy, and ligament or tendon tears have become increasingly prevalent and pose serious clinical challenges. These disorders not only result in pain, functional loss, and a marked reduction in patients' quality of life but also impose substantial social and economic burdens. Current treatment modalities, including surgical intervention, pharmacotherapy, and physical rehabilitation, often do not effectively restore the functionality of damaged tissues and are associated with high recurrence rates and long-term complications, highlighting significant limitations in their efficacy. Thus, there is a strong demand to develop novel and more effective therapeutic and reparative strategies. Organoid technology, as a three-dimensional micro-tissue model, can replicate the structural and functional properties of native tissues in vitro, providing a novel platform for in-depth studies of disease mechanisms, optimisation of drug screening, and promotion of tissue regeneration. In recent years, substantial advancements have been made in the research of bone, muscle, and joint organoids, demonstrating their broad application potential in personalised and regenerative medicine. Nonetheless, a comprehensive review of current research on skeletal organoids is still lacking. Therefore, this article aims to present an overview of the definition and technological foundation of organoids, systematically summarise the progress in the construction and application of skeletal organoids, and explore future opportunities and challenges in this field, offering valuable insights and references for researchers.

Design and Applications of Supramolecular Peptide Hydrogel as Artificial Extracellular Matrix

Supramolecular peptide hydrogels (SPHs) consist of peptides containing hydrogelators and functional epitopes, which can first self-assemble into nanofibers and then physically entangle together to form dynamic three-dimensional networks. Their porous structures, excellent bioactivity, and high dynamicity, similar to an extracellular matrix (ECM), have great potential in artificial ECM. The properties of the hydrogel are largely dependent on peptides. The noncovalent interactions among hydrogelators drive the formation of assemblies and further transition into hydrogels, while bioactive epitopes modulate cell-cell and cell-ECM interactions. Therefore, SPHs can support cell growth, making them ideal biomaterials for ECM mimics. This Review outlines the classical molecular design of SPHs from hydrogelators to functional epitopes and summarizes the recent advancements of SPHs as artificial ECMs in nervous system repair, wound healing, bone and cartilage regeneration, and organoid culture. This emerging SPH platform could provide an alternative strategy for developing more effective biomaterials for tissue engineering.

Bioinspired injectable hydrogels for bone regeneration

The effective regeneration of bone/cartilage defects remains a significant clinical challenge, causing irreversible damage to millions annually.Conventional therapies such as autologous or artificial bone grafting often yield unsatisfactory outcomes, emphasizing the urgent need for innovative treatment methods. Biomaterial-based strategies, including hydrogels and active scaffolds, have shown potential in promoting bone/cartilage regeneration. Among them, injectable hydrogels have garnered substantial attention in recent years on account of their minimal invasiveness, shape adaptation, and controlled spatiotemporal release. This review systematically discusses the synthesis of injectable hydrogels, bioinspired approaches-covering microenvironment, structural, compositional, and bioactive component-inspired strategies-and their applications in various bone/cartilage disease models, highlighting bone/cartilage regeneration from an innovative perspective of bioinspired design. Taken together, bioinspired injectable hydrogels offer promising and feasible solutions for promoting bone/cartilage regeneration, ultimately laying the foundations for clinical applications. Furthermore, insights into further prospective directions for AI in injectable hydrogels screening and organoid construction are provided.

Synthesis and characterization of methacryl glycol chitosan as a novel functionally advanced thermogel for biomedical applications

Thermo-responsive hydrogels (thermogels), known for their sol-gel transition capabilities, have garnered significant interest for biomedical applications over recent decades. However, conventional thermogels are hindered by intrinsic physicochemical and functional limitations that impede their broader utility. This study introduces methacryl glycol chitosan (MGC) as a novel thermogel, offering enhanced functionality and addressing these limitations. MGCs, synthesized through N-methacrylation of glycol chitosan, exhibit tunable thermogelling and photo-crosslinking behaviors. The thermo-reversible sol-gel transition of MGCs occurs within a 21-54 °C range, adjustable by polymer concentration and methacryl substitution degree. Photo-crosslinking using UV light further enhances the mechanical properties of MGC thermogels, creating thermo-irreversible, chemically crosslinked hydrogels. MGCs show no cytotoxic effects and effectively support cell encapsulation. In vivo studies demonstrate stable crosslinking with minimal UV-induced skin damage. Due to their unique thermo-sensitivity, multi-functionality, and customizable properties, MGC thermogels are promising novel biomaterials for various biomedical applications, particularly injectable tissue engineering and cell encapsulation, thus overcoming the limitations of conventional thermogels.