Combining frontal ultrafiltration (FU) and ultrasound (US) processes, an orthotropic organization of cellulose nanocrystals (CNCs) suspensions was achieved and characterized at multiscale, from the nanometer length scale by small angle X-ray scattering (SAXS) and dichroism, to the micrometer length scale by small angle light scattering (SALS). A dedicated channel cell has been developed to simultaneously generate a vertical acoustic force via a vibrating blade at the top and a transmembrane pressure force through the membrane at the bottom. Three specific orientations in three successive layers were revealed in a one-step FU-US process. In a first layer at the bottom, the CNCs were concentrated under the action of transmembrane pressure with their director aligned parallel to the horizontal membrane surface. In a second upper layer a random orientation of the CNCs was detected. Finally, in the upper part of the channel, a third layer of CNCs with their director vertically oriented was revealed. Near the membrane surface, transmembrane pressure forces dominate, leading to highly concentrated CNCs deposition with enough consistency to avoid any change in orientation induced by the US at the top of the channel. At increasing distances from the membrane, acoustic radiation forces become predominant, reorienting the CNCs vertically.

Hemiarthroplasty consists of the replacement of local cartilage defects by a partial implant and provides a less aggressive alternative to total joint replacement. The material frequently selected nowadays for partial implants is CoCrMo alloy, which results in a sliding contact between articular cartilage and the alloy. Since the geometry of the implant needs to be tailored to the patient, partial implant technology would greatly profit from novel additive manufacturing techniques. This study examines the feasibility of using additive manufacturing techniques on partial implants made of CoCrMo alloys, with a particular focus on the impact of manufacturing technique on mechanical stimulation, cartilage analysis, and friction performance. To this end, in vitro biotribological experiments were performed between CoCrMo samples and bovine articular cartilage using PBS as simulated body fluid. Key findings reveal significant changes in microstructure between laser beam melted (LBM) and wrought CoCrMo alloys, despite having a comparable elemental composition. The coefficient of friction (CoF) measured between bovine articular cartilage and the CoCrMo specimens during biotribocorrosive testing revealed no significant differences resulting from the manufacturing techniques, even though wrought CoCrMo resulted in a higher reproducibility. Conventionally produced CoCrMo also exhibited a more anodic open circuit potential during the experiments, likely due to the significant differences in microstructure that affect corrosion resistance. The tested cartilage samples showed a slight increase in MMP13 (Matrix Metalloproteinases - degradative enzymes) in comparison to the controls, indicating potential remodeling effects, especially for the LBM CoCrMo alloy. Additionally, the metabolic activity in the cartilage specimens increased due to mechanical stimulation. No cracks or fissures were detected in histological imaging thus highlighting that the cartilage samples were not damaged during harvesting or testing. These findings indicate the possibility of an equivalent use of additive manufactured CoCrMo, enabling patient-specific surgeries and encourage further research to explore the long-term impact of corrosion stability on implant longevity and functionality.

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.

Glycosaminoglycan (GAG) represents an important extracellular matrix (ECM), particularly in GAG-rich tissues such as nucleus pulposus and cartilage. The ratio of GAGs/hydroxyproline (HYP) is an indicator of the relative abundance of the space-filling GAG matrix to the fibrous collagen matrix in a particular tissue. Here, we hypothesize that ECM niche with different GAG/HYP ratios will affect the outcomes of multiple differentiation of human mesenchymal stem cells (hMSCs). Specifically, we fabricated collagen-based biomaterials with different GAG/HYP ratios, and differentiate hMSCs in these materials towards osteogenic, chondrogenic and discogenic lineages. In osteogenic differentiation, Collagen without GAG (GAG/HYP ratio 0) showed higher calcium (Ca) and phosphorus (P) deposition and Ca/P ratio, more biomimetic ultrastructure, and better osteogenic phenotypic expression. For chondrogenic differentiation, aminated collagen (aCol-GAG) with intermediate GAG content (GAG/HYP ratio 5.0:1) showed higher GAG deposition, more biomimetic ultrastructure, and better chondrogenic phenotype. In discogenic differentiation, aminated collagen-aminated hyaluronic acid (aHA)-GAG (aCol-aHA-GAG) with the highest GAG content (GAG/HYP ratio 19.8:1), showed intensive GAG deposition, biomimetic ultrastructure, and higher phenotypic marker expression. This study contributes to developing collagen-based biomimetic materials with different GAG/HYP ratios and suggests the use of tissue-specific GAG/HYP ratio as a scaffold design parameter for hMSCs-based musculoskeletal tissue engineering. (198 words).

Recent findings suggest that cartilage mechanical function may be a biomarker for early osteoarthritis (OA) pathology. Thus, the development of methodologies for in-vivo applications has expanded. However, when creep tests are performed, inconsistency in applied stress and testing duration impede meaningful comparisons. Therefore, this study investigates the impact of creep duration on cartilage mechanics through ex-vivo confined and unconfined compression experiments on healthy bovine cartilage samples (n = 20), subjected to 1 MPa stress for 5 h. A Zener model was fitted to unconfined data and a nonlinear biphasic model was fitted to confined data using durations ranging from 15 min to 5 h. Mechanical properties were compared against the full 5-h dataset to determine relative errors (RE) associated with insufficient creep duration. Based on our findings, we aim to establish a common ground for both in vivo and ex vivo environments. Both unconfined (R2 = 0.96 ± 0.02) and confined (R2 = 0.997 ± 0.003) models fitted the data well over 5 h. For confined creep tests, the aggregate modulus (HA) was 0.34 ± 0.12 MPa after 5 h and 0.27 ± 0.12 MPa after 1 h (RE ∼ 20 %), while initial permeability (k0) increased from 0.17 × 10-15 m4N-1s-1 to 0.56 × 10-15 m4N-1s-1 (RE ∼ 49 %). The Zener model estimated the initial (E1) and steady-state (E2) modulus to be 3.6 ± 0.7 MPa and 3.2 ± 0.3 MPa after 5 h, respectively. After 1 h, these values were 4.7 ± 1.0 MPa (RE ∼ 29 %) and 3.2 ± 0.3 MPa (RE ∼ 2 %). A larger RE (∼57 %) was observed for the relaxation time constant (τ) determined after 5 h (1688 ± 556 s) and 1 h (781 ± 170 s) with the Zener model. The benefit of extended creep duration diminished after 1-1.5 h for confined compression and 2 h for unconfined compression for non-rate dependent stiffness parameters (i.e., HA, E1, E2). This aligned well with the predefined equilibrium criteria of less than 0.6 μm/min, with equilibrium reached at 71 ± 23 min for confined experiments and 94 ± 25 min for unconfined experiments. In contrast, for parameters controlling the nonlinear material response (i.e., τ, k0,M), 4 h were required for unconfined compression and 1.5 h for confined compression to achieve RE ∼ 10 %. Thus, insufficient creeping duration resulted in large RE, especially for strain-dependent parameters. Therefore, it is recommended to use a clear equilibrium definition when conducting ex vivo experiments. In the context of clinically viable testing duration (i.e., 45-60 min) RE was ∼20 % for the predicted aggregate modulus and ∼10 % for the nonlinear permeability coefficient. While these errors appear substantial, they may still estimate cartilage mechanics within reasonable limits given the associated variability in healthy and OA cartilage characteristics. Therefore, within a limited timeframe, it could be possible to estimate mechanical properties using in vivo creep experiments that may serve as biomarkers for early OA.

ObjectiveIntegrin α10β1-selected mesenchymal stem cells (integrin α10-MSCs) have previously shown potential in treating cartilage damage and osteoarthritis (OA) in vitro and in animal models in vivo. The aim of this study was to further investigate disease-modifying effects of integrin α10-MSCs.DesignOA was surgically induced in 17 horses. Eighteen days after surgery, horses received 2 × 107 integrin α10-MSCs intra-articularly or were left untreated. Lameness and response to carpal flexion was assessed weekly along with synovial fluid (SF) analysis. On day 52 after treatment, horses were euthanized, and carpi were evaluated by computed tomography (CT), MRI, histology, and for macroscopic pathology and integrin α10-MSCs were traced in the joint tissues.ResultsLameness and response to carpal flexion significantly improved over time following integrin α10-MSC treatment. Treated horses had milder macroscopic cartilage pathology and lower cartilage histology scores than the untreated group. Prostaglandin E2 and interleukin-10 increased in the SF after integrin α10-MSC injection. Integrin α10-MSCs were found in SF from treated horses up to day 17 after treatment, and in the articular cartilage and subchondral bone from 5 of 8 treated horses after euthanasia at 52 days after treatment. The integrin α10-MSC injection did not cause joint flare.ConclusionThis study demonstrates that intra-articular (IA) injection of integrin α10-MSCs appears to be safe, alleviate pathological changes in the joint, and improve joint function in an equine post-traumatic osteoarthritis (PTOA) model. The results suggest that integrin α10-MSCs hold promise as a disease-modifying osteoarthritis drug (DMOAD).

Chondrocytes, the sole cellular components in articular cartilage, are mechanosensitive and undergo significant morphological and volumetric changes in response to mechanical loading. These changes activate ion channels, initiating cellular mechanotransduction processes crucial for maintaining cartilage health. Dynamic loading has been shown to elicit anabolic responses that preserve cartilage integrity, while prolonged mechanical unloading leads to atrophy. However, the intricacies of how chondrocytes respond to dynamic loading remain poorly understood, largely due to technical limitations in capturing real-time cellular responses during loading cycles. This study aimed to advance our understanding of chondrocyte behavior during dynamic cyclic compression loading through high-speed imaging techniques. We developed a protocol to capture changes in chondrocyte volume, shape, and surface area at critical moments of maximal and minimal tissue stress during cyclic loading. Our findings revealed that chondrocyte volume fluctuated cyclically during the first 20 loading cycles, increasing by up to 4 % during load application and decreasing by as much as 8 % during unloading. These volume fluctuations stabilized over time, returning to baseline levels after approximately 100 cycles. Volume changes over time translate to shape change, causing similar oscillatory pattern in cell width and depth strains but not height strain, which remained relatively constant throughout the loading protocol. Changes in surface area mirrored the volume changes but were less pronounced (< 2 % increase), suggesting a protective mechanism against cell membrane rupture. This research offers valuable insights into the dynamic behavior of chondrocytes during cyclic loading, highlighting the importance of considering dynamic environments in cellular biomechanics studies.

Platelet-rich plasma (PRP) has emerged as a promising biological therapy in regenerative medicine due to its high concentration of growth factors and cytokines, which promote tissue healing and regeneration. In recent years, its application in cartilage tissue engineering has garnered significant attention. This study explores the synergistic interaction between PRP and cartilage organoids, a novel three-dimensional in vitro culture system that closely mimics the structural and functional properties of native cartilage. Cartilage organoids serve as a physiologically relevant model for studying cartilage development, disease progression, and regeneration. By integrating PRP with cartilage organoids, this review aims to enhance chondrogenesis, extracellular matrix synthesis, and cellular proliferation within the organoids. Emerging evidence suggests that PRP supplementation significantly improves chondrocyte viability, growth, and differentiation in cartilage organoids, thereby accelerating their maturation. This combination holds great potential for advancing cartilage repair strategies, providing a robust platform for preclinical studies, and paving the way for innovative therapeutic approaches for cartilage-related injuries and degenerative diseases. These key aspects-chondrogenesis, matrix synthesis, and cellular proliferation-were specifically selected due to their fundamental roles in cartilage tissue engineering and regeneration. Chondrogenesis is crucial for chondrocyte differentiation and maintenance, matrix synthesis ensures the structural integrity and functional properties of regenerated cartilage, and cellular proliferation supports tissue viability and repair. Addressing these factors is essential, as current cartilage regeneration strategies often suffer from limited long-term efficacy and inadequate extracellular matrix production. By elucidating the synergistic effects of PRP and cartilage organoids in these areas, this study seeks to bridge existing knowledge gaps and provide valuable insights for improving regenerative approaches in clinical applications, particularly for osteoarthritis and cartilage defects.

Articular cartilage, vital to the health and functioning of joints, remains challenging to regenerate. The pericellular matrix (PCM) is critical for transducing biophysical stimuli to the articular chondrocytes (ACs) that it envelops. Given the mechanobiological sensitivity of ACs, it is pivotal in maintaining the chondrogenic phenotype and the production of extracellular matrix (ECM) during articular cartilage tissue engineering. While the maintenance of the native PCM significantly improves the quality of neocartilage, current isolation methods are limited. A solution to this challenge is facilitating ACs to regenerate their PCM. However, the regulation of PCM synthesis remains poorly understood, hindering the development of effective tissue engineering strategies. This narrative review aims to provide a comprehensive analysis of the complex interplay between extracellular cues and intracellular pathways regulating PCM synthesis during articular cartilage tissue engineering. Our analysis reveals that mechanical cues, such as material stiffness and mechanical stimulation, are the primary regulators of PCM synthesis. Additionally, the use of scaffold-free techniques potentially affects the structuring of newly created PCM. Tuning these stimuli can significantly impact the quality of the formed PCM, ultimately influencing neocartilage quality. Furthermore, we highlight intracellular mechanisms involved in the transduction of these extracellular cues, including actin polymerization, yes-associated protein and transcriptional coactivator with PDZ-binding motif localization, and transforming growth factor beta-induced Smad signaling. Although the current literature suggests the involvement of these signaling pathways in regulating the synthesis of PCM components, we found that studies investigating these processes in ACs are lacking. Elucidating the relationships between extracellular stimuli, intracellular signaling, and the expression of PCM components could provide a framework for designing new cartilage tissue engineering approaches that facilitate proper PCM synthesis. Ultimately, this can improve ECM quality and advance articular cartilage regeneration.

Chondrocytes, the only native cell type in cartilage, use mechanosensitive ion channels such as Transient Receptor Potential Vanilloid 4 (TRPV4) and PIEZO1 to transduce mechanical forces into transcriptomic changes that regulate cell behavior under both physiologic and pathologic conditions. Recent work has identified and characterized the differentially expressed genes (DEGs) that are upregulated following TRPV4 or PIEZO1 activation, but the transcriptomic systems downregulated by these ion channels also represent an important aspect of the chondrocyte regulatory process that remains poorly studied.

Here, we utilized previously established bulk RNAsequencing libraries to analyze the transcriptomes downregulated by activation of TRPV4 and PIEZO1 through differential gene expression analysis (using DESeq2), Gene Ontology, RT-qPCR, and Weighted Gene Correlation Network Analysis (WGCNA).

TRPV4 and PIEZO1 activations downregulated largely unique sets of DEGs, though the set of DEGs downregulated by TRPV4 exhibited a notable overlap with genes downregulated by treatment with inflammatory mediator Interleukin-1 (IL-1). The DEG set downregulated by PIEZO1 activation included genes associated with the G2/M cell cycle checkpoint, a system that checks cells for DNA damage prior to entry into mitosis, and this result was confirmed with RT-qPCR. WGCNA revealed modules of gene regulation negatively correlated with TRPV4, PIEZO1, and IL-1, outlining how these downregulated DEGs may interact to form gene regulatory networks (GRNs).

This study complements previous work in describing the full mechanosensitive transcriptome (or "mechanome") of differential gene expression in response to activation of mechanosensitive ion channels TRPV4 and PIEZO1 Q2 and suggests potential avenues for future therapeutic treatment design.

Vertical ground reaction force (vGRF) is a promising target for modifying aberrant gait biomechanics in individuals post-anterior cruciate ligament reconstruction (ACLR). However, an adequate sample size and arandomized, mechanistic study is needed to determine acute effects of vGRF biofeedback on biomechanical outcomes. The purpose of the study is to determine differences in discrete gait biomechanical variables (i.e., first and second peak vGRF, midstance vGRF, peak knee flexion angle (KFA), KFA range-of-motion (ROM), peak knee extension moment (KEM), and peak knee abduction moment (KAM) following a treadmill walking protocol between limbs and across four separate conditions in individuals 6-12 months post-ACLR. We utilized a randomized, cross-over mechanistic trial where participants walked for 3000 steps for three visual feedback conditions (i.e., HIGH, LOW, and SYMMETRICAL vGRF loading) and a control condition on a dual-belt treadmill. We constructed a mixed effects linear model to determine within-subject biomechanical changes between limbs and conditions. The HIGH condition elicited greater first peak vGRF, sagittal plane motion (i.e., peak KFA, KFA ROM), and peak KEM compared to the control condition (p < 0.01). The LOW condition observed first peak vGRF and KFA ROM decreases but increased peak KFA and KEM (p < 0.01) compared to the control condition. No notable biomechanical changes were observed between the SYMMETRICAL and control conditions. The HIGH condition produced acute, sagittal plane kinematic and kinetic profile improvements in ACLR individuals. vGRF is a viable target for modifying gait biomechanics; future work should determine the long-term health effects of vGRF-driven feedback treatment to improve gait profiles post-ACLR.

Osteoarthritis, a major global cause of pain and disability, is driven by the irreversible degradation of hyaline cartilage in the joints. Cartilage tissue engineering presents a promising therapeutic avenue, but success hinges on replicating the native physiological environment to guide cellular behavior and generate tissue constructs that mimic natural cartilage. Although electrical stimulation has been shown to enhance chondrogenesis and extracellular matrix production in two-dimensional (2D) cultures, the mechanisms underlying these effects remain poorly understood, particularly in three-dimensional (3D) models. Here, we report that direct scaffold-coupled electrical stimulation applied to 3D graphene foam bioscaffolds significantly enhances the mechanical properties of the resulting graphene foam-cell constructs. Using custom 3D-printed electrical stimulus chambers, we applied biphasic square impulses (20, 40, 60 mVpp at 1 kHz) for 5 min daily over 7 days. Stimulation at 60 mVpp increased the steady-state energy dissipation and equilibrium modulus by approximately 65 and 25%, respectively, as compared with unstimulated controls. 60 mVpp stimulation also yielded the highest cell density among stimulated samples. In addition, our custom chambers facilitated full submersion of the hydrophobic graphene foam in media, leading to enhanced cell attachment and integration across the scaffold surface and within its hollow branches. To assess this cellular integration, we employed colocalized confocal fluorescence microscopy and X-ray microCT imaging enabled by colloidal gold nanoparticle and fluorophore staining, which allowed visualization of cell distribution within the opaque scaffold's internal structure. These findings highlight the potential of a direct scaffold-coupled electrical stimulus to modulate the mechanical properties of engineered tissues and offer insights into the emergent behavior of cells within conductive 3D bioscaffolds.

Articular cartilage regeneration after injury remains a difficult clinical problem. Studies have revealed that adipose-derived stem cells (ADSCs) can promote chondrocyte regeneration. This study explored the role of Periostin, a multifunctional extracellular matrix protein, in enhancing the paracrine-mediated effects of ADSCs to promote chondrocyte regeneration.

ADSCs were isolated from murine adipose tissue and characterized. Periostin was overexpressed via a lentiviral vector in ADSCs (P-ADSCs). Chondrocytes were isolated and cocultured with P-ADSCs, followed by assessing of cell viability, apoptosis, cell migration and adhesion. In addition, periostin concentrations in the co-culture medium were measured over time by ELISA and detailed densitometric analyses of signaling proteins were performed.

Compared with control ADSCs, P-ADSCs significantly enhanced chondrocyte proliferation, reduced apoptosis, and promoted migration and adhesion. ELISA quantification revealed that chondrocytes co-cultured with P-ADSCs showed a significant decrease in pro-inflammatory cytokines of IL-1β, IL-6, IL-18 with less than 0.6 fold-changes, and a significant increase in growth factors of TGF-β, b-FGF, PDGF with more than 4 fold-changes. Moreover, qPCR and immunoblotting demonstrated upregulation of key chondrocyte markers collagen II and Sox9, and activation of FAK/PI3K/Akt/ERK signals.

Periostin overexpression in ADSCs enhances their paracrine effect, promoting chondrocyte proliferation, adhesion, migration, and favorable phenotypic marker expression while modulating cytokine secretion. These findings provide a potential strategy for enhancing ADSC-mediated cartilage repair.

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.

Advancements in tissue engineering and regenerative medicine have highlighted different strategies of engineering and designing hydrogels to replicate the intricate structure of cartilage extracellular matrix (ECM) for effective cartilage regeneration. However, despite efforts to meet the elevated structural and mechanical demands of cartilage repair, researchers often overlook the challenging environmental conditions at damaged cartilage sites such as inflammation, hypoxia, and the limited availability of nutrients and energy, which are critical for supporting tissue regeneration. The insufficient oxygen, nutrient availability, and oxidative stress in avascular cartilage limit the oxidative phosphorylation-mediated bioenergetics in cells needed for energy demands required for anabolic biosynthesis, cell division, and migration during tissue repair. Thus, there is a need to develop an advanced approach to engineer a unique hydrogel system that not only provides intricate structural properties but also integrates therapeutics (like anti-inflammatory, reactive oxygen species (ROS) scavenging) and bioenergetics (like oxygen, energy demand) into the hydrogel, which may offer a holistic and effective solution for repairing cartilage defects under a harsh microenvironment. In this study, we engineered an innovative approach to develop a new class of theraoenergetic hydrogel system by reinforcing a Janus nanofiber (JNF) carrying therapeutic (MgO) and bioenergetic (polyglutamic acid), PGA) components into a dual network photo-crosslinkable hydrogel. Reinforcement of JNF microfragments and the photo-crosslinking dual network of synthesized gelatin methacryloyl (GelMA) and carboxymethyl chitosan (CMCh) not only enhances the hydrogel's mechanical properties by 800% to withstand mechanical load but also ensures a controlled release of magnesium, oxygen, and PGA over 30 days. Co-delivery of magnesium and bioenergetic PGA with oxygen helped synergistically to reduce intracellular ROS and inflammatory markers IL-6 and TNF-α, providing a supportive environment for enhancing cell mitochondrial oxidative metabolism leading to active proliferation and chondrogenic differentiation of stem cells to deposit glycosaminoglycan (GAG)-rich extracellular matrix to regenerate cartilage. The developed theraoenergetic hydrogel system represents a promising solution for regenerating cartilage under a harsh microenvironment to treat osteoarthritis, a rising global health burden.

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.

Dysregulation of extracellular matrix (ECM) homeostasis plays a pivotal role in the accelerated degradation of cartilage, presenting a notable challenge for effective osteoarthritis (OA) treatment and cartilage regeneration. In this study, we introduced an injectable hydrogel based on streamlined-zinc oxide (ZnO), which is responsive to matrix metallopeptidase (MMP), for the delivery of miR-17-5p. This approach aimed to address cartilage damage by regulating ECM homeostasis. The ZnO/miR-17-5p composite functions by releasing zinc ions to attract native bone marrow mesenchymal stem cells, thereby fostering ECM synthesis through the proliferation of new chondrocytes. Concurrently, sustained delivery of miR-17-5p targets enzymes responsible for matrix degradation, thereby mitigating the catabolic process. Notably, the unique structure of the streamlined ZnO nanoparticles is distinct from their conventional spherical counterparts, which not only optimizes the rheological and mechanical properties of the hydrogels, but also enhances the efficiency of miR-17-5p transfection. Our male rat model demonstrated that the combination of streamlined ZnO, MMP-responsive hydrogels, and miRNA-based therapy effectively managed the equilibrium between catabolism and anabolism within the ECM, presenting a fresh perspective in the realm of OA treatment.

Various findings on the correlations of the continuous wave (CW-) T1ρ relaxation with properties of articular cartilage have been reported, suggesting its potential for cartilage diagnostics. The aim of the study was to combine all the previously reported aspects and investigate the association of CW-T1ρ relaxation time in healthy bovine cartilage to different properties of cartilage with a range of spin-lock amplitudes and cartilage orientations. Bovine cartilage-bone plugs (n = 11) were imaged in four orientations at 9.4T to measure T1, T2, and CW-T1ρ with spin-lock amplitudes varying between 100 and 5000 Hz. For reference, biomechanical moduli, polarized light microcopy anisotropy and optical density were measured. Correlation between the relaxation times and the reference parameters were determined for each spin-lock amplitude and sample orientation. Significant increase in both CW-T1ρ and T2 relaxation times was observed, especially in the deep layers of cartilage, when the sample was oriented to 55° orientation. The CW-T1ρ relaxation anisotropy was reduced with increasing spin-lock amplitude and reached a stable level of about 10% at a spin-lock amplitude of 1500 Hz or higher. Young's modulus, instantaneous modulus and optical density correlated negatively with the T1ρ relaxation times measured with spin-lock amplitudes higher than 500 Hz. The results demonstrate that CW-T1ρ relaxation time is highly dependent on the orientation of cartilage with respect to the main magnetic field (B0), and the level of orientation dependence is related to the spin-lock amplitude. Correlation of CW-T1ρ with cartilage properties is dependent both on the orientation and spin-lock amplitude.

Musculoskeletal tissue injuries of the bone, cartilage, ligaments, tendons, and skeletal muscles are among the most common injuries experienced in medicine and become increasingly problematic in cases of significant tissue damage, such as nonunion bone defects and volumetric muscle loss. Current gold standard treatment options for musculoskeletal injuries, although effective, have limited capability to fully restore native tissue structure and function. To overcome this challenge, three-dimensional (3D) printing techniques have emerged as promising therapeutic options for tissue regeneration. Melt electrowriting (MEW), a recently developed advanced 3D printing technique, has gained significant traction in the field of tissue regeneration because of its ability to fabricate complex customizable scaffolds via high-precision microfiber deposition. The tailorability at microscale levels offered by MEW allows for enhanced recapitulation of the tissue microenvironment. Here, we survey the recent contributions of MEW in advancing musculoskeletal tissue engineering. More specifically, we briefly discuss the principles and technical aspects of MEW, provide an overview of current printers on the market, review in-depth the latest biomedical applications in musculoskeletal tissue regeneration, and, lastly, examine the limitations of MEW and offer future perspectives.

Articular cartilage defects, as a core pathologic feature in the progression of osteoarthritis, and their irreversible degenerative changes lead to functional impairment and socioeconomic burden for tens of millions of patients worldwide. Hydrogels have become key biomaterials in cartilage regeneration with the three-dimensional network structure, programmable mechanical properties, and cell-adaptive microenvironment of biomimetic extracellular matrix. In recent years, several hydrogel systems with in vitro/in vivo repair potential have been developed by modulating the material topology, dynamic mechanical response, and delivery of bioactive factors, and some of them have entered the clinical translation stage. This review systematically explains the biomimetic design principles of hydrogels. It analyzes the immunomodulation and chondrogenic mechanisms mediated by hydrogels, providing a theoretical framework for the development of next-generation smart cartilage repair materials.

Degeneration of articular cartilage is the key underlying cause of most joint-related diseases and yet little is known about its regeneration. Here, we report that skeletal interoception induces anabolic synthesis of superficial membrane by tuning down sympathetic norepinephrine (NE). Specifically, the superficial membrane is consumed during animal activity and anabolically renewed by the underneath chondrocytes in the superficial zone (SFZ). Notably, by stereotactic knockdown of sympathetic NE synthesis in the paraventricular nucleus, articular cartilage thickness increases. Moreover, deletion of the gene encoding the prostaglandin E2 (PGE2) receptor, EP4, in sensory nerves for ascending interoceptive pathway induces damage of superficial membrane and articular cartilage degeneration. In contrast, increase of interoceptive signaling by elevation of local PGE2 reduces sympathetic outflow to promote the anabolic renewal of superficial membrane. Importantly, inducible knockout of the β-2-adrenergic-receptor (Adrb2) in the SFZ chondrocytes damages superficial membrane and treadmill running aggravates the damage. Mechanistically, NE-mediated activation of Adrb2 induces internalization of Adrb2 and TGF-β type II receptor as a complex, thereby regulating TGF-β activity for articular cartilage homeostasis regeneration. Together, physical activity induces an anabolic renewal of the superficial membrane by downregulation hypothalamic NE for optimized thickness and integrity of articular cartilage.

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.

Osteoarthritis (OA) is a painful joint condition primarily caused by cartilage degradation, leading to pain and reduced mobility. Given the side effects of current treatments, this study investigates Osteo-F, a novel herbal-based functional ingredient formulated with Schizandra chinensis, Lycium chinense, and Eucommia ulmoides, traditionally valued for their bioactive and health-promoting properties. Network pharmacology analysis identified significant interactions involving Osteo-F within the TNF signaling pathway, highlighting its role in modulating key inflammatory processes in OA. In vivo experiments using a monosodium iodoacetate-induced OA rat model demonstrated significant improvements in arthritis scores, bone mineral content, and bone mineral density, alongside preservation of cartilage integrity, as confirmed by histological analyses. In vitro studies further revealed that this formulation reduced the activation of JNK and NF-κB pathways, decreasing inflammatory cytokines and matrix metalloproteinases critical in cartilage breakdown. These findings underscore the potential of Osteo-F as a functional food candidate to reduce inflammation and support cartilage preservation in OA. Future clinical trials are required to validate these findings and explore its dietary integration in OA management.

Osteoarthritis (OA), a degenerative disease characterized by cartilage degradation and inflammation, occurs due to trauma caused by external stimuli or cartilage aging. Pyropia yezoensis is a red alga that belongs to the Porphyra family and is consumed as food in Asia, especially Korea, Japan, and China. P. yezoensis contains various bioactive substances, including carotenoids, flavonoids, and vitamins, that exert anti-inflammatory, antioxidant, and anti-photoaging effects. In the present study, the anti-osteoarthritic effects of 30% fermented alcohol extract of P. yezoensis (30% FEPY) on interleukin-1 beta (IL-1β)-stimulated chondrocytes and a destabilization of the medial meniscus (DMM)-induced OA rat model were investigated. The results showed that pretreatment with 30% FEPY significantly reduced the IL-1β-induced expression of inflammatory factors (e.g., inducible nitric oxide synthase and cyclooxygenase-2) and cartilage-degrading enzymes [matrix metalloproteinase (MMP) 1, MMP3, MMP13, a disintegrin and metalloproteinase with thrombospondin motifs (ADAMTS) 4, and ADAMTS5], which was analyzed using Griess reaction, enzyme-linked immunosorbent assay, and Western blot analysis. The anti-osteoarthritic effects of 30% FEPY, which were mediated through mitogen-activated protein kinase and nuclear factor kappa-light-chain-enhancer of activated B cell signaling, were analyzed using Western blot analysis. In an in vivo study, Safranin O staining and immunohistochemistry analysis revealed that treatment with 30% FEPY significantly increased cartilage degradation and collagen type II protein expression in the DMM group. These findings collectively suggest that 30% FEPY is a promising candidate for alleviating OA progression and developing new therapeutic drugs.

Osteoarthritis affects the cartilage tissue lining the joint. Current management plans often require intra-articular injections to relieve symptoms. This approach is hindered by the difficulty in localising the drug released in the synovial fluid into the cartilage surrounding the affected joint. Drug delivery systems have been developed to support cartilage drug uptake, potentially reducing the number of injections required. We developed an approach to drug localisation that exploits the highly electrostatically charged nature of cartilage constituents through binding biologically active molecules to positively charged polymers, and demonstrated high efficacy and safety in ex vivo tests.

We wanted to demonstrate the potential value of cartilage drug localisation technology beyond a clinical perspective, through health economic considerations and cost-effectiveness analysis, in order for these technologies to reach patients. We also conducted threshold analyses to determine, for different effectiveness levels of reducing injections, at what price the treatment will be cost-effective.

We conducted an early health economic analysis of our technology, developing a cost-effectiveness model with a Markov structure. The analyses were conducted from an NHS perspective and the model was also used to estimate potential cost-effectiveness depending on target product profiles. The health states quality of life values were derived for a UK population through EQ-5D questionnaires collected and analysed in a Bayesian framework.

At the cost and effectiveness values set for the new treatment, it was cost-effective (increased costs of £16.28 and 0.001126 QALY per patient, resulting in an incremental cost-effectiveness ratios [ICER] of £14,459/QALY) but the results were highly uncertain (at a willingness-to-pay [WTP] of £20,000 and £30,000/QALY the probability of being cost-effective was 56.5% and 67.3%, respectively); while sensitivity analyses (one-way deterministic and probabilistic), within plausible ranges of model parameters, revealed that the efficacy of the technology in reducing intra-articular injections and its cost are the most influential parameters.

Clinical trials are needed to validate the in vivo drug delivery system efficacy, but our study suggests that the system is likely to be a cost-effective use of NHS resources, also improving healthcare providers capacity.

Macrophages are pivotal in osteoarthritis (OA) pathogenesis, as their dysregulated polarization can contribute to chronic inflammatory processes. This review explores the molecular and metabolic mechanisms that influence macrophage polarization and identifies potential strategies for OA treatment. Currently, non-surgical treatments for OA focus only on symptom management, and their efficacy is limited; thus, mesenchymal stem/stromal cells (MSCs) have gained attention for their anti-inflammatory and immunomodulatory capabilities. Emerging evidence suggests that small extracellular vesicles (sEVs) derived from MSCs can modulate macrophage function, thus offering potential therapeutic benefits in OA. Additionally, the transfer of mitochondria from MSCs to macrophages has shown promise in enhancing mitochondrial functionality and steering macrophages toward an anti-inflammatory M2-like phenotype. While further research is needed to confirm these findings, MSC-based strategies, including the use of sEVs and mitochondrial transfer, hold great promise for the treatment of OA and other chronic inflammatory diseases.

Cartilage microfracturation is a surgical technique specifically designed to address chondral defects, which are injuries to the cartilage that covers the ends of bones in joints. These defects can result from traumatic injuries, degenerative conditions such as osteoarthritis, or congenital abnormalities. The primary objective of microfracture surgery is to promote the regeneration of functional cartilage tissue, thereby restoring joint function, alleviating pain, and enhancing mobility. The procedure involves creating small, controlled perforations, or microfractures, in the subchondral bone plate beneath the damaged cartilage. This process, performed with precision to minimize damage to surrounding healthy tissue, penetrates the subchondral bone to reach the bone marrow, which is rich in mesenchymal stem cells (MSCs).

Cartilage exhibits an extremely low friction and very low wearability within the liquid environment of the joint. It is also capable of switching wettability between superhydrophilicity and hydrophobicity in both wetting and dry conditions (specific experimental operations or open wounds). Therefore, the understanding of cartilage lubrication from the perspective of wettability provides inspiration for the design of artificial cartilage and sections with motion of soft actuators with extremely low coefficients of friction (COF). In this review, the lubrication of articular cartilage is introduced and discussed from the view of wettability. First, basic principles of articular cartilage lubrication and wettability are described with a focus on compositions and wettability of articular cartilage, and in particular the relationship between the phospholipid layers and wettability on articular cartilage, and the supramolecular synergy of synovial fluid on the lubrication of articular cartilage. Subsequently, the wettability and lubrication of articular cartilage under different stimuli (such as shear, pH, temperature, and electric field) is introduced for insights into cartilage lubrication. Finally, we present a comprehensive summary and delineate the challenges within the domain of cartilage lubrication and wettability for assisting researchers in formulating viable concepts for the design of efficient cartilage substitution or smart soft lubricating devices.

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.

Traumatic or degenerative defects of articular cartilage impair joint function, and the treatment of articular cartilage damage remains a challenge. By mimicking the cartilage extracellular matrix (ECM), exosome-seeded cryogels may enhance cell proliferation and chondral repair. ECM-based cryogels were cryopolymerized with gelatin, chondroitin sulfate, and various concentrations (0%, 0.3%, 0.5%, and 1%) of hyaluronic acid (HA), and their water content, swelling ratio, porosity, mechanical properties, and effects on cell viability were evaluated. The regenerative effects of bone marrow-derived mesenchymal stem cell (BM-MSC)-derived exosome (at a concentration of 106 particles/mL)-seeded 0.3% HA cryogels were assessed in vitro and in surgically induced male New Zealand rabbit cartilage defects in vivo. The water content, swelling ratio, and porosity of the cryogels significantly (p < 0.05) increased and the Young's modulus values of the cryogels decreased with increasing HA concentrations. MTT assays revealed that the developed biomaterials had no cytotoxic effects. The optimal cryogel composition was 0.3% HA, and the resulting cryogel had favorable properties and suitable mechanical strength. Exosomes alone and exosome-seeded cryogels promoted chondrocyte proliferation (with cell optical densities that were 58% and 51% greater than that of the control). The cryogel alone and the exosome-seeded cryogel facilitated ECM deposition and sulfated glycosaminoglycan synthesis. Although we observed cartilage repair via Alcian blue staining with both the cryogel alone and the exosome-seeded cryogel, the layered arrangement of the chondrocytes was superior to that of the control chondrocytes when exosome-seeded cryogels were used. This study revealed the potential value of using BM-MSC-derived exosome-seeded ECM-based cryogels for cartilage tissue engineering to treat cartilage injury.

This study describes a novel technique to analyze the extracellular vesicle (EV)-derived microRNA (miRNA) crosstalk between equine chondrocytes and synoviocytes. Donor cells (chondrocytes, n = 8; synoviocytes, n = 9) were labelled with 5-ethynyl uridine (5-EU); EVs were isolated from culture media and incubated with recipient cells (chondrocytes [n = 5] were incubated with synoviocyte-derived EVs, and synoviocytes [n = 4] were incubated with chondrocyte-derived EVs). Total RNA was extracted from recipient cells; the 5-EU-labelled RNA was recovered and sequenced. Differential expression analysis, pathway analysis, and miRNA target prediction were performed. Overall, 198 and 213 miRNAs were identified in recipient synoviocytes and chondrocytes, respectively. The top five most abundant miRNAs were similar for synoviocytes and chondrocytes (eca-miR-21, eca-miR-221, eca-miR-222, eca-miR-100, eca-miR-26a), and appeared to be linked to joint homeostasis. There were nine differentially expressed (p < 0.05) miRNAs (eca-miR-27b, eca-miR-23b, eca-miR-31, eca-miR-191a, eca-miR-199a-5p, eca-miR-143, eca-miR-21, eca-miR-181a, and eca-miR-181b) between chondrocytes and synoviocytes, which appeared to be linked to migration of cells, apoptosis, cell viability of connective tissue cell, and inflammation. In conclusion, the reported technique was effective in recovering and characterizing the EV-derived miRNA crosstalk between equine chondrocytes and synoviocytes and allowed for the identification of EV-communicated miRNA patterns potentially related to cell viability, inflammation, and joint homeostasis.

Cartilage injury does not heal spontaneously. The current cell-based cartilage treatments have either demonstrated poor clinical outcomes, require two surgeries, or are costly and logistically challenging. To overcome these challenges, our team has developed a one-stage, two cell-type surgical cell therapy for acute chondral defects. This procedure combines allogeneic mesenchymal stromal cells (MSCs) and autologous chondrons to harness MSCs as signaling cells to stimulate chondrons to promote tissue repair. This procedure has been investigated in clinical trials conducted in both Europe and the United States which are called IMPACT and RECLAIM, respectively. This article provides a review of our preclinical and clinical research which led to the development of this cell therapy.

The combination of allogeneic MSCs and autologous chondrons in preclinical studies have demonstrated to synergistically stimulate cartilage repair, and the combination of cells outperforms either cell-type alone. In clinical trials, the combined cell therapy was safe to use, improved knee function, and demonstrated durable pain reduction. Our single-stage, combined cell therapy of allogeneic MSCs and autologous chondrons is a viable cell therapy for acute articular cartilage defects. We anticipate this combined cell therapy may be a platform cell therapy for a wide range of musculoskeletal repair applications.

Cartilage is a connective tissue composed of mainly water, collagen (COL) and proteoglycans (PGs) including chondroitin sulfate (CS). Near-infrared (NIR) spectroscopy is adequate for examination of soft and hard tissues with large amount of water non-destructively and non-invasively. We measured tablets containing CS and COL using NIR spectroscopy to develop an evaluation method for PGs in cartilage non-destructively and non-invasively. Calibration curves were constructed using the NIR spectra of the tablets that show the quantitative linear relationship between the concentration and height of the second derivative at 4260 cm-1 for COL and at 5800 cm-1 for COL and CS. An equation to calculate the CS-to-COL ratio was derived from the calibrated slopes at 5800 and 4260 cm-1, and the utility of the equation was demonstrated by the evaluation of tablets. Moreover, we conducted an evaluation of the CS-to-COL ratio in the aqueous nucleus pulposus and annulus fibrosus, and the results were consistent with the glycosaminoglycans (GAGs)-to-COL ratios obtained through Raman spectroscopy of the same specimens. Thus, this method is adequate for evaluating PGs with large amount of water non-destructively, non-invasively and with less damage.

Articular cartilage, composed of chondrocytes within a dynamic viscoelastic matrix, has limited self-repair capacity, posing a significant challenge for regeneration. Constructing high-fidelity cartilage organoids through three-dimensional (3D) bioprinting to replicate the structure and physiological functions of cartilage is crucial for regenerative medicine, drug screening, and disease modeling. However, commonly used matrix bioinks lack reversible cross-linking and precise controllability, hindering dynamic cellular regulation. Thus, encoding bioinks adaptive for cultivating cartilage organoids is an attractive idea. DNA, with its ability to be intricately encoded and reversibly cross-linked into hydrogels, offers precise manipulation at both molecular and spatial structural levels. This endows the hydrogels with viscoelasticity, printability, cell recognition, and stimuli responsiveness. This paper elaborates on strategies to encode bioink via DNA, emphasizing the regulation of predictable dynamic properties and the resulting interactions with cell behavior. The significance of these interactions for the construction of cartilage organoids is highlighted. Finally, we discuss the challenges and future prospects of using DNA-encoded hydrogels for 3D bioprinted cartilage organoids, underscoring their potential impact on advancing biomedical applications.

Osteoarthritis is a chronic degenerative disease affecting 500 million people throughout the world. Although orthobiologics have been proposed as a symptom and disease modifying treatment for osteoarthritis, there is significant heterogeneity in the results of the orthobiologic procedures in the literature. One possible explanation for the heterogeneity is the inconsistent reporting and description of the postorthobiologic protocols. The goal of this scoping review was to identify the current literature on the use of orthobiologics for osteoarthritis and critically evaluate the postorthobiologic protocol within these studies. A total of 200 identified studies met inclusion criteria. In 37.5% of studies, there was no mention of a postorthobiologic protocol. Of the 125 studies that did mention a postorthobiologic protocol, only 38.4% included a rehabilitation protocol, 21.6% included postprocedure weightbearing restrictions, and only 2 (1.6%) mentioned the use of durable medical equipment. Nonsteroidal anti-inflammatory drug restriction was described in 91.2% of study protocols, whereas corticosteroids and immunosuppressants were restricted in 84.8% and 19.2% of protocols, respectively. The results of this scoping review demonstrate the inconsistent reporting of postorthobiologic procedure protocols in the literature, with significant heterogeneity in those that are described. These findings highlight the need for future research and improved reporting of postorthobiologic protocols.

Mechanical stimulation is a widely used technique in the development of tissue engineered cartilage. While various regimes can enhance tissue growth and improve construct mechanical properties, existing outcome measures predominantly assess the anabolic effect of mechanical stimuli. Catabolic responses are generally overlooked, and a critical gap remains in how mechanical loading simultaneously affects both anabolic and catabolic processes. In this study, full-thickness articular cartilage was aseptically harvested from the metacarpal-phalangeal joints of skeletally mature bovine. Isolated chondrocytes were encapsulated in agarose gels and subjected to dynamic compressive strains from 0 % to 15 % for either 20 or 60 min using a custom-built mechanical stimulation device. Anabolism was assessed by [3H]-proline and [35S]-sulfate incorporation, while catabolism was evaluated by MMP-13 enzymatic activity. Long-term effects of dynamic loading were assessed through biochemical analyses and histological evaluation. Results showed that low-to-moderate strains (2.5 % and 5 %) induced high anabolic activity relative to control with minimal catabolic response. In contrast, high strains (15 %) resulted in elevated catabolic and reduced anabolic activity relative to control. The application of mechanical stimuli over the long-term elicited comparable responses with lower compressive stains leading to improved cartilaginous extracellular matrix accumulation. This study provides valuable insights into the complex interplay between anabolic and catabolic metabolism in chondrocyte-seeded agarose constructs subjected to dynamic compression. This research underscores the necessity of evaluating both responses to optimize the growth and properties of tissue-engineered cartilage.

The musculoskeletal system relies on critical tissue interfaces for its function; however, these interfaces are often compromised by injuries and diseases. Restoration of these interfaces is complex by nature which renders traditional treatments inadequate. An emerging solution is three-dimensional printing, which allows for precise fabrication of biomimetic scaffolds to enhance tissue regeneration. This review summarizes the use of 3D printing in creating scaffolds for musculoskeletal interfaces, mainly focusing on advanced techniques such as multi-material printing, bioprinting, and 4D printing. We emphasize the significance of mimicking natural tissue gradients and the selection of appropriate biomaterials to ensure scaffold success. The review outlines state-of-the-art 3D printing technologies, varying from extrusion, inkjet and laser-assisted bioprinting, which are crucial for producing scaffolds with tailored mechanical and biological properties. Applications in cartilage-bone, intervertebral disc, tendon/ligament-bone, and muscle-tendon junction engineering are discussed, highlighting the potential for improved integration and functionality. Furthermore, we address challenges in material development, printing resolution, and the in vivo performance of scaffolds, as well as the prospects for clinical translation. The review concludes by underscoring the transformative potential of 3D printing to advance orthopedic medicine, offering a roadmap for future research at the intersection of biomaterials, drug delivery, and tissue engineering.

Individuals with anterior cruciate ligament reconstruction (ACLR) often walk with a less dynamic vertical ground reaction force (vGRF), exemplified by a reduced first peak vGRF and elevated midstance vGRF compared with uninjured controls. However, the mechanism by which altered limb loading affects actual tibial plateau contact forces during walking remains unclear.

Our purpose was to use musculoskeletal simulation to evaluate the effects of first peak vGRF biofeedback on bilateral tibiofemoral contact forces relevant to the development of post-traumatic osteoarthritis in 20 individuals with ACLR. We hypothesized that reduced first peak vGRF would produce less dynamic tibial plateau contact forces during walking in individuals with ACLR.

As the pivotal outcome from this study, and in support of our hypothesis, we found that less dynamic vGRF profiles in individuals with ACLR-observations that have associated in prior studies with more cartilage breakdown serum biomarkers and reduced proteoglycan density-are accompanied by less dynamic tibiofemoral joint contact forces during walking.

We conclude that more sustained limb-level loading, a phenotype that associates with worse knee joint health outcomes after ACLR and was prescribed herein using biofeedback, alters the loading profile and magnitude of force applied to tibiofemoral cartilage.

Osteoarthritis (OA) is the most common degenerative disease of the joints, causing significant disability and socio-economic burden in the aging population. Simultaneously, however, it is a common occurrence in younger individuals, initiated by joint injuries or obesity alongside other factors. Intravenous and oral pharmaceutical OA management have both been associated with systemic adverse effects, thereby resulting in a growing interest in intra-articular (IA) treatment. IA-administered drugs circumvent the requirement for high dosage, offering immediate access to the site of interest while minimizing any unfavorable effects. Nonetheless, IA-injected drugs, administered in their free form, present low retention time in the knee joint raising the need for multiple injection dosage regimens, while their capability to target the cartilage or specific cell populations is limited. Liposomes, due to their unique characteristics and tunable nature, have proven to be excellent candidates for the management of knee OA. This review explores the last decade's research on the efficacy of various IA liposomal formulations, investigating their multifaceted properties as pharmaceutical carriers, lubricating agents, and a basis for combinatorial approaches paving the way to novel treatment solutions for OA.

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.

Cartilage tissue does not promptly elicit an inflammatory response upon injury, hence constraining its capacity for healing and self-regeneration. Mesenchymal Stem Cells (MSC) therapy, enhanced by nanotechnology, offers promising advancements in cartilage repair. Injuries to cartilage often cause chronic pain, where current treatments are inadequate. As MSCs can readily differentiate into chondrocytes and secrete soluble factors, they are essential components in tissue engineering of cartilage repair. Although, like other stem cell applications, clinical applications are restricted by poor post implantation survival and differentiation. Recent studies show that nanoparticles (NPs) can further improve MSC outcomes by promoting cell adhesion, and chondrogenic differentiation allowing for sustained growth factor release. In addition, nanomaterials can improve the biological activity of MSCs, by also facilitating the composition of a conducive microenvironment for cartilage repair. In this review, the application of nanofibrous scaffolds, hydrogels and nanoscale particulate matter to improve mechanical properties in cartilage tissue engineering, are discussed. Moreover, the MSCs and nanotechnology synergistic effects present hope of overcoming the limitations of conventional treatments. Nanotechnology greatly enhances the MSC based cartilage regeneration strategies and could provide better treatment for cartilage related diseases in the future. Future research should be aimed at standardizing MSC harvesting and culturing protocols and contrasting their long-term efficacy.

Developmental dysplasia of the hip (DDH) is a developmental disorder that has long-term chronic pain and limited hip joint mobility. The aim of the current study is to understand the specific chondrocyte composition involved in DDH development, identify effective biomarkers for DDH prediction, and elucidate the gene regulatory elements driving DDH progression.

In this study, we performed an integrated analysis combining single-cell RNA sequencing and single-cell assay for transposase-accessible chromatin sequencing to investigate the molecular programs and epigenetic changes governing human DDH pathogenesis. Validation of marker genes for distinct chondrocyte populations was performed via immunohistochemical assays, alongside characterization of regulatory elements specific to DDH.

Our analysis identified seven molecularly distinct chondrocyte populations in DDH cartilage, including a novel inflammatory chondrocyte population with unique molecular signatures. Furthermore, we reconstructed the differentiation trajectory of chondrocytes, shedding light on their roles in DDH pathogenesis. Integrative analyses of transcriptomic and chromatin accessibility profiles highlighted shared regulatory features and transcriptional programs among chondrocyte subtypes, with several regulatory elements linked to DDH progression. Immunohistochemical validation corroborated the presence of key marker genes in distinct chondrocyte subsets.

Our findings contribute to clarifying the cellular heterogeneity of DDH and offer insights into potential early diagnostic and therapeutic strategies for this condition.