The structure and function of the pericellular matrix of articular cartilage

Therapeutic Controlled Release Strategies for Human Osteoarthritis

Osteoarthritis is a progressive, irreversible debilitating whole joint disease that affects millions of people worldwide. Despite the availability of various options (non-pharmacological and pharmacological treatments and therapy, orthobiologics, and surgical interventions), none of them can definitively cure osteoarthritis in patients. Strategies based on the controlled release of therapeutic compounds via biocompatible materials may provide powerful tools to enhance the spatiotemporal delivery, expression, and activities of the candidate agents as a means to durably manage the pathological progression of osteoarthritis in the affected joints upon convenient intra-articular (injectable) delivery while reducing their clearance, dissemination, or side effects. The goal of this review is to describe the current knowledge and advancements of controlled release to treat osteoarthritis, from basic principles to applications in vivo using therapeutic recombinant molecules and drugs and more innovatively gene sequences, providing a degree of confidence to manage the disease in patients in a close future.

Cartilage lacuna-biomimetic hydrogel microspheres endowed with integrated biological signal boost endogenous articular cartilage regeneration

Despite numerous studies on chondrogenesis, the repair of cartilage-particularly the reconstruction of cartilage lacunae through an all-in-one advanced drug delivery system remains limited. In this study, we developed a cartilage lacuna-like hydrogel microsphere system endowed with integrated biological signals, enabling sequential immunomodulation and endogenous articular cartilage regeneration. We first integrated the chondrogenic growth factor transforming growth factor-β3 (TGF-β3) into mesoporous silica nanoparticles (MSNs). Then, TGF-β3@MSNs and insulin-like growth factor 1 (IGF-1) were encapsulated within microspheres made of polydopamine (pDA). In the final step, growth factor-loaded MSN@pDA and a chitosan (CS) hydrogel containing platelet-derived growth factor-BB (PDGF-BB) were blended to produce growth factors loaded composite microspheres (GFs@μS) using microfluidic technology. The presence of pDA reduced the initial acute inflammatory response, and the early, robust release of PDGF-BB aided in attracting endogenous stem cells. Over the subsequent weeks, the continuous release of IGF-1 and TGF-β3 amplified chondrogenesis and matrix formation. μS were incorporated into an acellular cartilage extracellular matrix (ACECM) and combined with a polydopamine-modified polycaprolactone (PCL) structure to produce a tissue-engineered scaffold that mimicked the structure of the cartilage lacunae evenly distributed in the cartilage matrix, resulting in enhanced cartilage repair and patellar cartilage protection. This research provides a strategic pathway for optimizing growth factor delivery and ensuring prolonged microenvironmental remodeling, leading to efficient articular cartilage regeneration.

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.

Familial osteochondrodysplastic and cardiomyopathic syndrome in Chianina cattle

BACKGROUND

Skeletal dysplasia encompasses a heterogeneous group of genetic disorders characterized by an abnormal development of bones, joints, and cartilage. Two Chianina half-sibling calves from consanguineous mating with congenital skeletal malformations and cardiac abnormalities were identified.

HYPOTHESIS/OBJECTIVES

To characterize the disease phenotype, to evaluate its genetic cause, and to determine the prevalence of the deleterious alleles in the Chianina population.

ANIMALS

Two affected calves, their parents and 332 Chianina bulls.

METHODS

The affected animals underwent clinicopathological investigation. Whole-genome sequencing trio-approach and PCR-based assessment of the frequency of TDP-glucose 4,6-dehydratase (TGDS) and laminin subunit alpha 4 (LAMA4) alleles were performed.

RESULTS

The cases presented with retarded growth, poor nutritional status associated with muscular atrophy and angular deformities of the hindlimbs. Radiologic examination identified generalized osteopenia and shortening of the limb long bones. Necropsy showed osteochondrodysplastic limbs and dilatation of the heart right ventricle. On histological examination, the physeal cartilages were characterized by multifocal mild to moderate loss of the normal columnar arrangement of chondrocytes. Osteopenia also was observed. Genetic analysis identified a missense variant in TGDS and a splice-site variant in LAMA4, both of which were homozygous in the 2 cases. Parents were heterozygous and allele frequency in the Chianina population for the TGDS variant was 5% and for the LAMA4 variant was 2%.

CONCLUSIONS AND CLINICAL IMPORTANCE

Genetic findings identified 2 potentially pathogenic alleles in TGDS and LAMA4, but no clear mode of inheritance could be determined.

Diverse and multifunctional roles for perlecan (HSPG2) in repair of the intervertebral disc

Perlecan is a widely distributed, modular, and multifunctional heparan sulfate proteoglycan, which facilitates cellular communication with the extracellular environment to promote tissue development, tissue homeostasis, and optimization of biomechanical tissue functions. Perlecan-mediated osmotic mechanotransduction serves to regulate the metabolic activity of cells in tissues subjected to tension, compression, or shear. Perlecan interacts with a vast array of extracellular matrix (ECM) proteins through which it stabilizes tissues and regulates the proliferation or differentiation of resident cell populations. Here we examine the roles of the HS-proteoglycan perlecan in the normal and destabilized intervertebral disc. The intervertebral disc cell has evolved to survive in a hostile weight bearing, acidic, low oxygen tension, and low nutrition environment, and perlecan provides cytoprotection, shields disc cells from excessive compressive forces, and sequesters a range of growth factors in the disc cell environment where they aid in cellular survival, proliferation, and differentiation. The cells in mechanically destabilized connective tissues attempt to re-establish optimal tissue composition and tissue functional properties by changing the properties of their ECM, in the process of chondroid metaplasia. We explore the possibility that perlecan assists in these cell-mediated tissue remodeling responses by regulating disc cell anabolism. Perlecan's mechano-osmotic transductive property may be of potential therapeutic application.

Femtosecond Laser Maskless Optical Projection Lithography of Cartilage PCM Inspired 3D Protein Matrix to Chondrocyte Phenotype

Hydrogels containing chondrocytes have exhibited excellent potential in regenerating hyaline cartilage. However, chondrocytes are vulnerable to dedifferentiation during in vitro culture, leading to fibrosis and mechanical degradation of newly formed cartilage. It is proposed to modulate cartilage formation via the developed chondrocyte pericellular matrix (PCM) -like scaffolds for the first time, in which the S, M, and L-sized scaffolds are fabricated by femtosecond laser maskless optical projection lithography (FL-MOPL) of bovine serum albumin-glyceryl methacrylate hydrogel. Chondrocytes on the M PCM-like scaffold can maintain round morphology and synthesize extracellular matrix (ECM) to induce regeneration of hyaline cartilage microtissues by geometrical restriction. A series of M PCM-like scaffolds is fabricated with different stiffness and those with a high Young's modulus are more effective in maintaining the chondrocyte phenotype. The proposed PCM-like scaffolds are effective in modulating cartilage formation influenced by pore size, depth, and stiffness, which will pave the way for a better understanding of the geometric cues of mechanotransduction interactions in regulating cell fate and open up new avenues for tissue engineering.

Biomimetic Hyaluronan Binding Biomaterials to Capture the Complex Regulation of Hyaluronan in Tissue Development and Function

Within native ECM, Hyaluronan (HA) undergoes remarkable structural remodeling through its binding receptors and proteins called hyaladherins. Hyaladherins contain a group of tandem repeat sequences, such as LINK domains, BxB7 homologous sequences, or 20-50 amino acid long short peptide sequences that have high affinity towards side chains of HA. The HA binding sequences are critical players in HA distribution and regulation within tissues and potentially attractive therapeutic targets to regulate HA synthesis and organization. While HA is a versatile and successful biopolymer, most HA-based therapeutics have major differences from a native HA molecule, such as molecular weight discrepancies, crosslinking state, and remodeling with other HA binding proteins. Recent studies showed the promise of HA binding domains being used as therapeutic biomaterials for osteoarthritic, ocular, or cardiovascular therapeutic products. However, we propose that there is a significant potential for HA binding materials to reveal the physiological functions of HA in a more realistic setting. This review is focused on giving a comprehensive overview of the connections between HA's role in the body and the potential of HA binding material applications in therapeutics and regenerative medicine. We begin with an introduction to HA then discuss HA binding molecules and the process of HA binding. Finally, we discuss HA binding materials anf the future prospects of potential HA binding biomaterials systems in the field of biomaterials and tissue engineering.

Cartilage-derived cells display heterogeneous pericellular matrix synthesis in agarose microgels

The pericellular matrix (PCM) surrounding chondrocytes is essential for articular cartilage tissue engineering. As the current isolation methods to obtain chondrocytes with their PCM (chondrons) result in a heterogeneous mixture of chondrocytes and chondrons, regenerating the PCM using a tissue engineering approach could prove beneficial. In this study, we aimed to discern the behavior of articular chondrocytes (ACs) in regenerating the PCM in such an approach and whether this would also be true for articular cartilage-derived progenitor cells (ACPCs), as an alternative cell source. Bovine ACs and ACPCs were encapsulated in agarose microgels using droplet-based microfluidics. ACs were stimulated with TGF-β1 and dexamethasone and ACPCs were sequentially stimulated with BMP-9 followed by TGF-β1 and dexamethasone. After 0, 3, 5, and 10 days of culture, PCM components, type-VI collagen and perlecan, and ECM component, type-II collagen, were assessed using flow cytometry and fluorescence microscopy. Both ACs and ACPCs synthesized the PCM before the ECM. It was seen for the first time that synthesis of type-VI collagen always preceded perlecan. While the PCM synthesized by ACs resembled native chondrons after only 5 days of culture, ACPCs often made less well-structured PCMs. Both cell types showed variations between individual cells and donors. On one hand, this was more prominent in ACPCs, but also a subset of ACPCs showed superior PCM and ECM regeneration, suggesting that isolating these cells may potentially improve cartilage repair strategies.

Integrin signalling in joint development, homeostasis and osteoarthritis

Integrins are key regulators of cell-matrix interactions during joint development and joint tissue homeostasis, as well as in the development of osteoarthritis (OA). The signalling cascades initiated by the interactions of integrins with a complex network of extracellular matrix (ECM) components and intracellular adaptor proteins orchestrate cellular responses necessary for maintaining joint tissue integrity. Dysregulated integrin signalling, triggered by matrix degradation products such as matrikines, disrupts this delicate balance, tipping the scales towards an environment conducive to OA pathogenesis. The interplay between integrin signalling and growth factor pathways further underscores the multifaceted nature of OA. Moreover, emerging insights into the role of endocytic trafficking in regulating integrin signalling add a new layer of complexity to the understanding of OA development. To harness the therapeutic potential of targeting integrins for mitigation of OA, comprehensive understanding of their molecular mechanisms across joint tissues is imperative. Ultimately, deciphering the complexities of integrin signalling will advance the ability to treat OA and alleviate its global burden.

Metabolic Profiles of Encapsulated Chondrocytes Exposed to Short-Term Simulated Microgravity

The mechanism by which chondrocytes respond to reduced mechanical loading environments and the subsequent risk of developing osteoarthritis remains unclear. This is of particular concern for astronauts. In space the reduced joint loading forces during prolonged microgravity (10-6 g) exposure could lead to osteoarthritis (OA), compromising quality of life post-spaceflight. In this study, we encapsulated human chondrocytes in an agarose gel of similar stiffness to the pericellular matrix to mimic the cartilage microenvironment. We then exposed agarose-chondrocyte constructs to simulated microgravity (SM) using a rotating wall vessel (RWV) bioreactor to better assess the cartilage health risks associated with spaceflight. Global metabolomic profiling detected a total of 1205 metabolite features across all samples, with 497 significant metabolite features identified by ANOVA (FDR-corrected p-value < 0.05). Specific metabolic shifts detected in response to SM exposure resulted in clusters of co-regulated metabolites, as well as key metabolites identified by variable importance in projection scores. Microgravity-induced metabolic shifts in gel constructs and media were indicative of protein synthesis, energy metabolism, nucleotide metabolism, and oxidative catabolism. The microgravity associated-metabolic shifts were consistent with early osteoarthritic metabolomic profiles in human synovial fluid, which suggests that even short-term exposure to microgravity (or other reduced mechanical loading environments) may lead to the development of OA.

Structure-Mechanics Principles and Mechanobiology of Fibrocartilage Pericellular Matrix: A Pivotal Role of Type V Collagen

The pericellular matrix (PCM) is the immediate microniche surrounding resident cells in various tissue types, regulating matrix turnover, cell-matrix cross-talk and disease initiation. This study elucidated the structure-mechanical properties and mechanobiological functions of the PCM in fibrocartilage, a family of connective tissues that sustain complex tensile and compressive loads in vivo. Studying the murine meniscus as the model tissue, we showed that fibrocartilage PCM contains thinner, random collagen fibrillar networks that entrap proteoglycans, a structure distinct from the densely packed, highly aligned collagen fibers in the bulk extracellular matrix (ECM). In comparison to the ECM, the PCM has a lower modulus and greater isotropy, but similar relative viscoelastic properties. In Col5a1 +/- menisci, the reduction of collagen V, a minor collagen localized in the PCM, resulted in aberrant fibril thickening with increased heterogeneity. Consequently, the PCM exhibited a reduced modulus, loss of isotropy and faster viscoelastic relaxation. This disrupted PCM contributes to perturbed mechanotransduction of resident meniscal cells, as illustrated by reduced intracellular calcium signaling, as well as upregulated biosynthesis of lysyl oxidase and tenascin C. When cultured in vitro, Col5a1 +/- meniscal cells synthesized a weakened nascent PCM, which had inferior properties towards protecting resident cells against applied tensile stretch. These findings underscore the PCM as a distinctive microstructure that governs fibrocartilage mechanobiology, and highlight the pivotal role of collagen V in PCM function. Targeting the PCM or its molecular constituents holds promise for enhancing not only meniscus regeneration and osteoarthritis intervention, but also addressing diseases across various fibrocartilaginous tissues.

Bioprinted biomimetic hydrogel matrices guiding stem cell aggregates for enhanced chondrogenesis and cartilage regeneration

Articular cartilage tissue has limited self-repair capabilities, with damage frequently progressing to irreversible degeneration. Engineered tissues constructed through bioprinting and embedded with stem cell aggregates offer promising therapeutic alternatives. Aggregates of bone marrow mesenchymal stromal cells (BMSCs) demonstrate enhanced and more rapid chondrogenic differentiation than isolated cells, thus facilitating cartilage repair. However, it remains a key challenge to precisely control biochemical microenvironments to regulate cellular adhesion and cohesion within bioprinted matrices simultaneously. Herein, this work reports a bioprintable hydrogel matrix with high cellular adhesion and aggregation properties for cartilage repair. The hydrogel comprises an enhanced cell-adhesive gelatin methacrylate and a cell-cohesive chitosan methacrylate (CHMA), both of which are subjected to photo-initiated crosslinking. By precisely adjusting the CHMA content, the mechanical stability and biochemical cues of the hydrogels are finely tuned to promote cellular aggregation, chondrogenic differentiation and cartilage repair implantation. Multi-layer constructs encapsulated with BMSCs, with high cell viability reaching 91.1%, are bioprinted and photo-crosslinked to support chondrogenic differentiation for 21 days. BMSCs rapidly form aggregates and display efficient chondrogenic differentiation both on the hydrogels and within bioprinted constructs, as evidenced by the upregulated expression of Sox9, Aggrecan and Collagen 2a1 genes, along with high protein levels. Transplantation of these BMSC-laden bioprinted hydrogels into cartilaginous defects demonstrates effective hyaline cartilage repair. Overall, this cell-responsive hydrogel scaffold holds immense promise for applications in cartilage tissue engineering.

Growth factors that drive aggrecan synthesis in healthy articular cartilage. Role for transforming growth factor-β?

Introduction

Articular cartilage makes smooth movement possible and destruction of this tissue leads to loss of joint function. An important biomolecule that determines this function is the large aggregating proteoglycan of cartilage, aggrecan. Aggrecan has a relatively short half-life in cartilage and therefore continuous production of this molecule is essential.

Methods

In this narrative review we discuss what is the role of growth factors in driving the synthesis of aggrecan in articular cartilage. A literature search has been done using the search items; cartilage, aggrecan, explant, Transforming Growth factor-β (TGF-β), Insulin-like Growth Factor (IGF), Bone Morphogenetic Protein (BMP) and the generic term "growth factors". Focus has been on studies using healthy cartilage and models of cartilage regeneration have been excluded.

Results

In healthy adult articular cartilage IGF is the main factor that drives aggrecan synthesis and maintains adequate levels of production. BMP's and TGF-β have a very limited role but appear to be more important during chondrogenesis and cartilage development. The major role of TGF-β is not stimulation of aggrecan synthesis but maintenance of the differentiated articular cartilage chondrocyte phenotype.

Conclusion

TGF-β is a factor that is generally considered as an important factor in stimulating aggrecan synthesis in cartilage but its role in this might be very restrained in healthy, adult articular cartilage.

Development of alginate-collagen interpenetrating network for osteoarthritic cartilage by in situ softening

This study presents an alginate-collagen interpenetrating network (IPN) matrix of incorporating collagen fibrils into an alginate hydrogel by physical mixing and controlled gelation. The resulting matrix closely mimics the physiological and pathological stiffness range of the chondrocyte pericellular matrix (PCM). Chondrocytes were cultured within three-dimensional (3D) alginate-collagen IPN matrices with varying stiffness, namely Firm, Medium, and Soft. Alginate lyase was introduced to study the effects of the changes in stiffness of the Firm on chondrocyte response by in situ softening. The developed alginate-collagen IPN matrix displayed good cell-biocompatibility. Compared with stiffer tissue culture plastic (TCP), chondrocytes grown within Firm displayed a stabilized differentiated phenotype characterized by higher expression levels of aggrecan, collagen II, and SOX-9. Moreover, the developed alginate-collagen IPN matrix exhibited a gradually increased percentage of propidium iodide (PI)-positive dead cells with decreasing stiffness. Softer matrices directed cells towards higher proliferation rates and spherical morphologies while stimulating chondrocyte cluster formation. Furthermore, reducing Firm stiffness by in situ softening decreased aggrecan expression, contributing to matrix degradation similar to that seen in osteoarthritis (OA). Hence, the 3D alginate-collagen IPN constructs hold significant potential for in vitro replicating PCM stiffness changes observed in OA cartilage.

Glycosaminoglycan-Mediated Interactions in Articular, Auricular, Meniscal, and Nasal Cartilage

Glycosaminoglycans (GAGs) are ubiquitous components in the cartilage extracellular matrix (ECM). Ultrastructural arrangement of ECM and GAG-mediated interactions with collagen are known to govern the mechanics in articular cartilage, but these interactions are less clear in other cartilage types. Therefore, this article reviews the current literature on ultrastructure of articular, auricular, meniscal, and nasal septal cartilage, seeking insight into GAG-mediated interactions influencing mechanics. Ultrastructural features of these cartilages are discussed to highlight differences between them. GAG-mediated interactions are reviewed under two categories: interactions with chondrocytes and interactions with other fibrillar macromolecules of the ECM. Moreover, efforts to replicate GAG-mediated interactions to improve mechanical integrity of tissue-engineered cartilage constructs are discussed. In conclusion, studies exploring cartilage specific GAGs are poorly represented in the literature, and the ultrastructure of nasal septal and auricular cartilage is less studied compared with articular and meniscal cartilages. Understanding the contribution of GAGs in cartilage mechanics at the ultrastructural level and translating that knowledge to engineered cartilage will facilitate improvement of cartilage tissue engineering approaches.

Management of Juvenile Osteochondral Fractures Utilising Absorbable PLGA Implants

The incidence of articular injury, particularly osteochondral fractures (OCFs), has seen a cinnotable increase in recent years. Regardless of their location, fragments can be overlooked by plain radiographs, which might lead to osteoarthritis in the long run. Diagnostic imaging has a pivotal role in the assessment and classification of the fracture severity, as well as the presence of any associated dislocations. These fractures require surgical intervention for the restoration of joint function and the reduction of long-term complications. This paper aims to present the surgical correction and post-operative treatment of osteochondral fractures with absorbable implants in four children. The following affected areas are discussed: lateral condyle of the femur, patella and radial head. Utilising absorbable implants for the management of OCFs provides numerous advantages, including the elimination of the need for re-anaesthesia and reoperation, reduction of complications and facilitation of early rehabilitation. This approach also minimises the period of hospitalisation and proves effective in pediatric OCF treatment.

Pericellular Matrix Formation and Atomic Force Microscopy of Single Primary Human Chondrocytes Cultured in Alginate Microgels

One of the main components of articular cartilage is the chondrocyte's pericellular matrix (PCM), which is critical for regulating mechanotransduction, biochemical cues, and healthy cartilage development. Here, individual primary human chondrocytes (PHC) are encapsulated and cultured in 50 µm diameter alginate microgels using drop-based microfluidics. This unique culturing method enables PCM formation and manipulation of individual cells. Over ten days, matrix formation is observed using autofluorescence imaging, and the elastic moduli of isolated cells are measured using AFM. Matrix production and elastic modulus increase are observed for the chondrons cultured in microgels. Furthermore, the elastic modulus of cells grown in microgels increases ≈ten-fold over ten days, nearly reaching the elastic modulus of in vivo PCM. The AFM data is further analyzed using a Gaussian mixture model and shows that the population of PHCs grown in microgels exhibit two distinct populations with elastic moduli averaging 9.0 and 38.0 kPa. Overall, this work shows that microgels provide an excellent culture platform for the growth and isolation of PHCs, enabling PCM formation that is mechanically similar to native PCM. The microgel culture platform presented here has the potential to revolutionize cartilage regeneration procedures through the inclusion of in vitro developed PCM.

Fabrication of Customizable and Reproducible 3D Chondrocyte-Laden Nanofibrous Architectures: Effect of Specific Fiber Alignments and Porosities on Chondrocyte Response under Cyclic Compression

Electrospinning has been widely employed to fabricate complex extracellular matrix-like microenvironments for tissue engineering due to its ability to replicate structurally biomimetic micro- and nanotopographic cues. Nevertheless, these nanofibrous structures are typically either confined to bidimensional systems or confined to three-dimensional ones that are unable to provide controlled multiscale patterns. Thus, an electrospinning modality was used in this work to fabricate chondrocyte-laden nanofibrous scaffolds with highly customizable three-dimensional (3D) architectures in an automated manner, with the ultimate goal of recreating a suitable 3D scaffold for articular cartilage tissue engineering. Three distinct architectures were designed and fabricated by combining multiple nanofibrous and chondrocyte-laden hydrogel layers and tested in vitro in a compression bioreactor system. Results demonstrated that it was possible to precisely control the placement and alignment of electrospun polycaprolactone and gelatin nanofibers, generating three unique architectures with distinctive macroscale porosity, water absorption capacity, and mechanical properties. The architecture organized in a lattice-like fashion was highly porous with substantial pore interconnectivity, resulting in a high-water absorption capacity but a poor compression modulus and relatively weaker energy dissipation capacity. The donut-like 3D geometry was the densest, with lower swelling, but the highest compression modulus and improved energy dissipation ability. The third architecture combined a lattice and donut-like fibrous arrangement, exhibiting intermediary behavior in terms of porosity, water absorption, compression modulus, and energy dissipation capacity. The properties of the donut-like 3D architecture demonstrated great potential for articular cartilage tissue engineering, as it mimicked key topographic, chemical, and mechanical characteristics of chondrocytes' surrounding environment. In fact, the combination of these architectural features with a dynamically compressive mechanical stimulus triggered the best in vitro results in terms of viability and biosynthetic production.

Insufficiency of collagenases in establishment of primary chondrocyte culture from cartilage of elderly patients receiving total joint replacement

Background Collagenases are frequently used in chondrocyte isolation from articular cartilage. However, the sufficiency of this enzyme in establishing primary human chondrocyte culture remains unknown. Methods Cartilage slices shaved from femoral head or tibial plateau of patients receiving total joint replacement surgery (16 hips, 8 knees) were subjected to 0.02% collagenase IA digestion for 16 h with (N = 19) or without (N = 5) the pre-treatment of 0.4% pronase E for 1.5 h. Chondrocyte yield and viability were compared between two groups. Chondrocyte phenotype was determined by the expression ratio of collagen type II to I. The morphology of cultured chondrocytes was monitored with a light microscope.Results Cartilage with pronase E pre-treatment yielded significantly higher chondrocytes than that without the pre-treatment (3,399 ± 1,637 cells/mg wet cartilage vs. 1,895 ± 688 cells/mg wet cartilage; P = 0.0067). Cell viability in the former group was also significantly higher than that in the latter (94% ± 2% vs. 86% ± 6%; P = 0.03). When cultured in monolayers, cells from cartilage with pronase E pre-treatment grew in a single plane showing rounded shape while cells from the other group grew in multi-planes and exhibited irregular shape. The mRNA expression ratio of collagen type II to I was 13.2 ± 7.5 in cells isolated from cartilage pre-treated with pronase E, indicating a typical chondrocyte phenotype. Conclusions Collagenase IA was not sufficient in establishing primary human chondrocyte culture. Cartilage must be treated with pronase E prior to collagenase IA application.

Bilayer osteochondral graft in rabbit xenogeneic transplantation model comprising sintered 3D-printed bioceramic and human adipose-derived stem cells laden biohydrogel

Reconstruction of severe osteochondral defects in articular cartilage and subchondral trabecular bone remains a challenging problem. The well-integrated bilayer osteochondral graft design expects to be guided the chondrogenic and osteogenic differentiation for stem cells and provides a promising solution for osteochondral tissue repair in this study. The subchondral bone scaffold approach is based on the developed finer and denser 3D β-tricalcium phosphate (β-TCP) bioceramic scaffold process, which is made using a digital light processing (DLP) technology and the novel photocurable negative thermo-responsive (NTR) bioceramic slurry. Then, the concave-top disc sintered 3D-printed bioceramic incorporates the human adipose-derived stem cells (hADSCs) laden photo-cured hybrid biohydrogel (HG + 0.5AFnSi) comprised of hyaluronic acid methacryloyl (HAMA), gelatin methacryloyl (GelMA), and 0.5% (w/v) acrylate-functionalized nano-silica (AFnSi) crosslinker. The 3D β-TCP bioceramic compartment is used to provide essential mechanical support for cartilage regeneration in the long term and slow biodegradation. However, the apparent density and compressive strength of the 3D β-TCP bioceramics can be obtained for ~ 94.8% theoretical density and 11.38 ± 1.72 MPa, respectively. In addition, the in vivo results demonstrated that the hADSC + HG + 0.5AFnSi/3D β-TCP of the bilayer osteochondral graft showed a much better osteochondral defect repair outcome in a rabbit model. The other word, the subchondral bone scaffold of 3D β-TCP bioceramic could accelerate the bone formation and integration with the adjacent host cancellous tissue at 12 weeks after surgery. And then, a thicker cartilage layer with a smooth surface and uniformly aligned chondrocytes were observed by providing enough steady mechanical support of the 3D β-TCP bioceramic scaffold.

Meniscal fibrocartilage regeneration inspired by meniscal maturational and regenerative process

Meniscus is a complex and crucial fibrocartilaginous tissue within the knee joint. Meniscal regeneration remains to be a scientific and translational challenge. We clarified that mesenchymal stem cells (MSCs) participated in meniscal maturation and regeneration using MSC-tracing transgenic mice model. Here, inspired by meniscal natural maturational and regenerative process, we developed an effective and translational strategy to facilitate meniscal regeneration by three-dimensionally printing biomimetic meniscal scaffold combining autologous synovium transplant, which contained abundant intrinsic MSCs. We verified that this facilitated anisotropic meniscus-like tissue regeneration and protected cartilage from degeneration in large animal model. Mechanistically, the biomechanics and matrix stiffness up-regulated Piezo1 expression, facilitating concerted activation of calcineurin and NFATc1, further activated YAP-pSmad2/3-SOX9 axis, and consequently facilitated fibrochondrogenesis of MSCs during meniscal regeneration. In addition, Piezo1 induced by biomechanics and matrix stiffness up-regulated collagen cross-link enzyme expression, which catalyzed collagen cross-link and thereby enhanced mechanical properties of regenerated tissue.

The fibrous character of pericellular matrix mediates cell mechanotransduction

Cells in solid tissues sense and respond to mechanical signals that are transmitted through extracellular matrix (ECM) over distances that are many times their size. This long-range force transmission is known to arise from strain-stiffening and buckling in the collagen fiber ECM network, but must also pass through the denser pericellular matrix (PCM) that cells form by secreting and compacting nearby collagen. However, the role of the PCM in the transmission of mechanical signals is still unclear. We therefore studied an idealized computational model of cells embedded within fibrous collagen ECM and PCM. Our results suggest that the smaller network pore sizes associated with PCM attenuates tension-driven collagen-fiber alignment, undermining long-range force transmission and shielding cells from mechanical stress. However, elongation of the cell body or anisotropic cell contraction can compensate for these effects to enable long distance force transmission. Results are consistent with recent experiments that highlight an effect of PCM on shielding cells from high stresses. Results have implications for the transmission of mechanical signaling in development, wound healing, and fibrosis.

Exploring the Cellular and Molecular Mechanism of Discoidin Domain Receptors (DDR1 and DDR2) in Bone Formation, Regeneration, and Its Associated Disease Conditions

The tyrosine kinase family receptor of discoidin domain receptors (DDR1 and DDR2) is known to be activated by extracellular matrix collagen catalytic binding protein receptors. They play a remarkable role in cell proliferation, differentiation, migration, and cell survival. DDR1 of the DDR family regulates matrix-metalloproteinase, which causes extracellular matrix (ECM) remodeling and reconstruction during unbalanced homeostasis. Collagenous-rich DDR1 triggers the ECM of cartilage to regenerate the cartilage tissue in osteoarthritis (OA) and temporomandibular disorder (TMD). Moreover, DDR2 is prominently present in the fibroblasts, smooth muscle cells, myofibroblasts, and chondrocytes. It is crucial in generating and breaking collagen vital cellular activities like proliferation, differentiation, and adhesion mechanisms. However, the deficiency of DDR1 rather than DDR2 was detrimental in cases of OA and TMDs. DDR1 stimulated the ECM cartilage and improved bone regeneration. Based on the above information, we made an effort to outline the advancement of the utmost promising DDR1 and DDR2 regulation in bone and cartilage, also summarizing their structural, biological activity, and selectivity.

Human nasal cartilage: Functional properties and structure-function relationships for the development of tissue engineering design criteria

Nose reconstruction often requires scarce cartilage grafts. Nasal cartilage properties must be determined to serve as design criteria for engineering grafts. Thus, mechanical and biochemical properties were obtained in multiple locations of human nasal septum, upper lateral cartilage (ULC), and lower lateral cartilage (LLC). Within each region, no statistical differences among locations were detected, but anisotropy at some septum locations was noted. In the LLC, the tensile modulus and ultimate tensile strength (UTS) in the inferior-superior direction were statistically greater than in the anterior-posterior direction. Cartilage from all regions exhibited hyperelasticity in tension, but regions varied in degree of hyalinicity (i.e., Col II:Col I ratio). The septum contained the most collagen II and least collagen I and III, making it more hyaline than the ULC and LLC. The septum had a greater aggregate modulus, UTS, and lower total collagen/wet weight (Col/WW) than the ULC and LLC. The ULC had greater tensile modulus, DNA/WW, and lower glycosaminoglycan/WW than the septum and LLC. The ULC had a greater pyridinoline/Col than the septum. Histological staining suggested the presence of chondrons in all regions. In the ULC and LLC, tensile modulus correlated with total collagen content, while aggregate modulus correlated with pyridinoline content and weakly with pentosidine content. However, future studies should be performed to validate these proposed structure-function relationships. This study of human nasal cartilage provides 1) crucial design criteria for nasal cartilage tissue engineering efforts, 2) quantification of major and minor collagen subtypes and crosslinks, and 3) structure-function relationships. Surprisingly, the large mechanical properties found, particularly in the septum, suggests that nasal cartilage may experience higher-than-expected mechanical loads. STATEMENT OF SIGNIFICANCE: While tissue engineering holds promise to generate much-needed cartilage grafts for nasal reconstruction, little is known about nasal cartilage from an engineering perspective. In this study, the mechanical and biochemical properties of the septum, upper lateral cartilage (ULC), and lower lateral cartilage (LLC) were evaluated using cartilage-specific methods. For the first time in this tissue, all major and minor collagens and collagen crosslinks were measured, demonstrating that the septum was more hyaline than the ULC and LLC. Additionally, new structure-function relationships in the ULC and LLC were identified. This study greatly expands upon the quantitative understanding of human nasal cartilage and provides crucial engineering design criteria for much-needed nasal cartilage tissue engineering efforts.

Rapid specialization and stiffening of the primitive matrix in developing articular cartilage and meniscus

Understanding early patterning events in the extracellular matrix (ECM) formation can provide a blueprint for regenerative strategies to better recapitulate the function of native tissues. Currently, there is little knowledge on the initial, incipient ECM of articular cartilage and meniscus, two load-bearing counterparts of the knee joint. This study elucidated distinctive traits of their developing ECMs by studying the composition and biomechanics of these two tissues in mice from mid-gestation (embryonic day 15.5) to neo-natal (post-natal day 7) stages. We show that articular cartilage initiates with the formation of a pericellular matrix (PCM)-like primitive matrix, followed by the separation into distinct PCM and territorial/interterritorial (T/IT)-ECM domains, and then, further expansion of the T/IT-ECM through maturity. In this process, the primitive matrix undergoes a rapid, exponential stiffening, with a daily modulus increase rate of 35.7% [31.9 39.6]% (mean [95% CI]). Meanwhile, the matrix becomes more heterogeneous in the spatial distribution of properties, with concurrent exponential increases in the standard deviation of micromodulus and the slope correlating local micromodulus with the distance from cell surface. In comparison to articular cartilage, the primitive matrix of meniscus also exhibits exponential stiffening and an increase in heterogeneity, albeit with a much slower daily stiffening rate of 19.8% [14.9 24.9]% and a delayed separation of PCM and T/IT-ECM. These contrasts underscore distinct development paths of hyaline versus fibrocartilage. Collectively, these findings provide new insights into how knee joint tissues form to better guide cell- and biomaterial-based repair of articular cartilage, meniscus and potentially other load-bearing cartilaginous tissues. STATEMENT OF SIGNIFICANCE: Successful regeneration of articular cartilage and meniscus is challenged by incomplete knowledge of early events that drive the initial formation of the tissues' extracellular matrix in vivo. This study shows that articular cartilage initiates with a pericellular matrix (PCM)-like primitive matrix during embryonic development. This primitive matrix then separates into distinct PCM and territorial/interterritorial domains, undergoes an exponential daily stiffening of ≈36% and an increase in micromechanical heterogeneity. At this early stage, the meniscus primitive matrix shows differential molecular traits and exhibits a slower daily stiffening of ≈20%, underscoring distinct matrix development between these two tissues. Our findings thus establish a new blueprint to guide the design of regenerative strategies to recapitulate the key developmental steps in vivo.

HYBID in osteoarthritis: Potential target for disease progression

HYBID is a new hyaluronan-degrading enzyme and exists in various cells of the human body. Recently, HYBID was found to over-express in the osteoarthritic chondrocytes and fibroblast-like synoviocytes. According to these researches, high level of HYBID is significantly correlated with cartilage degeneration in joints and hyaluronic acid degradation in synovial fluid. In addition, HYBID can affect inflammatory cytokine secretion, cartilage and synovium fibrosis, synovial hyperplasia via multiple signaling pathways, thereby exacerbating osteoarthritis. Based on the existing research of HYBID in osteoarthritis, HYBID can break the metabolic balance of HA in joints through the degradation ability independent of HYALs/CD44 system and furthermore affect cartilage structure and mechanotransduction of chondrocytes. In particular, in addition to HYBID itself being able to trigger some signaling pathways, we believe that low-molecular-weight hyaluronan produced by excess degradation can also stimulate some disease-promoting signaling pathways by replacing high-molecular-weight hyaluronan in joints. The specific role of HYBID in osteoarthritis is gradually revealed, and the discovery of HYBID raises the new way to treat osteoarthritis. In this review, the expression and basic functions of HYBID in joints were summarized, and reveal potential role of HYBID as a key target in treatment for osteoarthritis.

Advanced Mechanical Testing Technologies at the Cellular Level: The Mechanisms and Application in Tissue Engineering

Mechanics, as a key physical factor which affects cell function and tissue regeneration, is attracting the attention of researchers in the fields of biomaterials, biomechanics, and tissue engineering. The macroscopic mechanical properties of tissue engineering scaffolds have been studied and optimized based on different applications. However, the mechanical properties of the overall scaffold materials are not enough to reveal the mechanical mechanism of the cell-matrix interaction. Hence, the mechanical detection of cell mechanics and cellular-scale microenvironments has become crucial for unraveling the mechanisms which underly cell activities and which are affected by physical factors. This review mainly focuses on the advanced technologies and applications of cell-scale mechanical detection. It summarizes the techniques used in micromechanical performance analysis, including atomic force microscope (AFM), optical tweezer (OT), magnetic tweezer (MT), and traction force microscope (TFM), and analyzes their testing mechanisms. In addition, the application of mechanical testing techniques to cell mechanics and tissue engineering scaffolds, such as hydrogels and porous scaffolds, is summarized and discussed. Finally, it highlights the challenges and prospects of this field. This review is believed to provide valuable insights into micromechanics in tissue engineering.

Extracellular matrix composition analysis of human articular cartilage for the development of organ-on-a-chip

INTRODUCTION

Articular cartilage has a complex extracellular matrix (ECM) that provides it a defined architecture for its load-bearing properties. The complete understanding of ECM components is imperative for developing biomimetic organ-on-a-chip tissue construct.

OBJECTIVE

This study aimed to decellularize and characterize the ECM for its protein profiling to generate a niche for enhanced chondrocyte proliferation.

METHODS

Articular cartilage scrapings were subjected to mechanical and collagenase digestion, followed by sodium dodecyl sulfate (SDS) treatment for 8 h and 16 h. The de-cellularization efficiency was confirmed by hematoxylin & eosin, alcian blue, masson's trichrome staining, and scanning electron microscopy (SEM). The ECM protein profile was quantified by liquid chromatography tandem mass spectrometry (LC-MS/MS) using a bottom-up approach.

RESULTS

Histological characterization revealed void lacunae that lacked staining for cellular components. The ECM, sulfated glycosaminoglycan content, and collagen fibers were preserved after 8 h and 16 h of de-cellularization. The SEM ultrastructure images showed that few chondrocytes adhered to the ECM after 8 h and cell-free ECM after 16 h of de-cellularization. LC-MS/MS analysis identified 66 proteins with heterotypic collagen types COL1A1-COL6A1, COL14A1, COL22A1 and COL25A1 showed moderate fold change and expression levels, while COL18A1, COL26A1, chondroitin sulfate, matrix metalloproteinase-9 (MMP9), fibronectin, platelet glycoprotein 1 beta alpha (GP1BA), vimentin, bone morphogenetic protein 6 (BMP6), fibroblast growth factor 4 (FGF4) and growth hormone receptor (GHR) showed maximum fold change and expression levels.

CONCLUSIONS

The standardized de-cellularization process could preserve majority of ECM components, providing structural integrity and architecture to the ECM. The Identified proteins quantified for their expression levels provided insight into engineering the ECM composition for developing cartilage-on-a-chip.

Could hypoxia rehabilitate the osteochondral diseased interface? Lessons from the interplay of hypoxia and purinergic signals elsewhere

The osteochondral unit comprises the articular cartilage (90%), subchondral bone (5%) and calcified cartilage (5%). All cells present at the osteochondral unit that is ultimately responsible for matrix production and osteochondral homeostasis, such as chondrocytes, osteoblasts, osteoclasts and osteocytes, can release adenine and/or uracil nucleotides to the local microenvironment. Nucleotides are released by these cells either constitutively or upon plasma membrane damage, mechanical stress or hypoxia conditions. Once in the extracellular space, endogenously released nucleotides can activate membrane-bound purinoceptors. Activation of these receptors is fine-tuning regulated by nucleotides' breakdown by enzymes of the ecto-nucleotidase cascade. Depending on the pathophysiological conditions, both the avascular cartilage and the subchondral bone subsist to significant changes in oxygen tension, which has a tremendous impact on tissue homeostasis. Cell stress due to hypoxic conditions directly influences the expression and activity of several purinergic signalling players, namely nucleotide release channels (e.g. Cx43), NTPDase enzymes and purinoceptors. This review gathers experimental evidence concerning the interplay between hypoxia and the purinergic signalling cascade contributing to osteochondral unit homeostasis. Reporting deviations to this relationship resulting from pathological alterations of articular joints may ultimately unravel novel therapeutic targets for osteochondral rehabilitation. At this point, one can only hypothesize how hypoxia mimetic conditions can be beneficial to the ex vivo expansion and differentiation of osteo- and chondro-progenitors for auto-transplantation and tissue regenerative purposes.

Cartilage-Related Collagens in Osteoarthritis and Rheumatoid Arthritis: From Pathogenesis to Therapeutics

Collagens serve essential mechanical functions throughout the body, particularly in the connective tissues. In articular cartilage, collagens provide most of the biomechanical properties of the extracellular matrix essential for its function. Collagen plays a very important role in maintaining the mechanical properties of articular cartilage and the stability of the ECM. Noteworthily, many pathogenic factors in the course of osteoarthritis and rheumatoid arthritis, such as mechanical injury, inflammation, and senescence, are involved in the irreversible degradation of collagen, leading to the progressive destruction of cartilage. The degradation of collagen can generate new biochemical markers with the ability to monitor disease progression and facilitate drug development. In addition, collagen can also be used as a biomaterial with excellent properties such as low immunogenicity, biodegradability, biocompatibility, and hydrophilicity. This review not only provides a systematic description of collagen and analyzes the structural characteristics of articular cartilage and the mechanisms of cartilage damage in disease states but also provides a detailed characterization of the biomarkers of collagen production and the role of collagen in cartilage repair, providing ideas and techniques for clinical diagnosis and treatment.

Superficial zone chondrocytes can get compacted under physiological loading: A multiscale finite element analysis

Recent in vivo and in vitro studies have demonstrated that superficial zone (SZ) chondrocytes within articular layers of diarthrodial joints die under normal physiologic loading conditions. In order to further explore the implications of this observation in future investigations, we first needed to understand the mechanical environment of SZ chondrocytes that might cause them to die under physiological sliding contact conditions. In this study we performed a multiscale finite element analysis of articular contact to track the temporal evolution of a SZ chondrocyte's interstitial fluid pressure, hydraulic permeability, and volume under physiologic loading conditions. The effect of the pericellular matrix modulus and permeability was parametrically investigated. Results showed that SZ chondrocytes can lose ninety percent of their intracellular fluid after several hours of intermittent or continuous contact loading, resulting in a reduction of intracellular hydraulic permeability by more than three orders of magnitude. These findings are consistent with loss of cell viability due to the impediment of cellular metabolic pathways induced by the loss of fluid. They suggest that there is a simple mechanical explanation for the vulnerability of SZ chondrocytes to sustained physiological loading conditions. Future studies will focus on validating these specific findings experimentally. STATEMENT OF SIGNIFICANCE: As with any mechanical system, normal 'wear and tear' of cartilage tissue lining joints is expected. Yet incidences of osteoarthritis are uncommon in individuals younger than 45. This counter-intuitive observation suggests there must be an intrinsic repair mechanism compensating for this wear and tear over many decades of life. Recent experimental studies have shown superficial zone chondrocytes die under physiologic loading conditions, suggesting that this repair mechanism may involve cell replenishment. To better understand the mechanical environment of these cells, we performed a multiscale computational analysis of articular contact under loading. Results indicated that normal activities like walking or standing can induce significant loss of intracellular fluid volume, potentially hindering metabolic activity and fluid transport properties, and causing cell death.

Microenvironmental mechanoactivation through Yap/Taz suppresses chondrogenic gene expression

Chondrocyte phenotype is preserved when cells are round and the actin cytoskeleton is cortical. Conversely, these cells rapidly dedifferentiate in vitro with increased mechanoactive Rho signaling, which increases cell size and causes large actin stress fiber to form. While the effects of Rho on chondrocyte phenotype are well established, the molecular mechanism is not yet fully elucidated. Yap, a transcriptional coregulator, is regulated by Rho in a mechanotransductive manner and can suppress chondrogenesis in vivo. Here, we sought to elucidate the relationship between mechanoactive Rho and Yap on chondrogenic gene expression. We first show that decreasing mechanoactive state through Rho inhibition results in a broad increase in chondrogenic gene expression. Next, we show that Yap and its coregulator Taz are negative regulators of chondrogenic gene expression, and removal of these factors promotes chondrogenesis even in environments that promote cell spreading. Finally, we establish that Yap/Taz is essential for translating Rho-mediated signals to negatively regulate chondrogenic gene expression, and that its removal negates the effects of increased Rho signaling. Together, these data indicate that Rho is a mechanoregulator of chondrogenic differentiation, and that its impact on chondrogenic expression is exerted principally through mechanically induced translocation and activity of Yap and Taz.

A guide to preclinical evaluation of hydrogel-based devices for treatment of cartilage lesions

The drive to develop cartilage implants for the treatment of major defects in the musculoskeletal system has resulted in a major research thrust towards developing biomaterial devices for cartilage repair. Investigational devices for the restoration of articular cartilage are considered as significant risk materials by regulatory bodies and therefore proof of efficacy and safety prior to clinical testing represents a critical phase of the multidisciplinary effort to bridge the gap between bench and bedside. To date, review articles have thoroughly covered different scientific facets of cartilage engineering paradigm, but surprisingly, little attention has been given to the preclinical considerations revolving around the validation of a biomaterial implant. Considering hydrogel-based cartilage products as an example, the present review endeavors to provide a summary of the critical prerequisites that such devices should meet for cartilage repair, for successful implantation and subsequent preclinical validation prior to clinical trials. Considerations pertaining to the choice of appropriate animal model, characterization techniques for the quantitative and qualitative outcome measures, as well as concerns with respect to GLP practices are also extensively discussed. This article is not meant to provide a systematic review, but rather to introduce a device validation-based roadmap to the academic investigator, in anticipation of future healthcare commercialization. STATEMENT OF SIGNIFICANCE: There are significant challenges around translation of in vitro cartilage repair strategies to approved therapies. New biomaterial-based devices must undergo exhaustive investigations to ensure their safety and efficacy prior to clinical trials. These considerations are required to be applied from early developmental stages. Although there are numerous research works on cartilage devices and their in vivo evaluations, little attention has been given into the preclinical pathway and the corresponding approval processes. With a focus on hydrogel devices to concretely illustrate the preclinical path, this review paper intends to highlight the various considerations regarding the preclinical validation of hydrogel devices for cartilage repair, from regulatory considerations, to implantation strategies, device performance aspects and characterizations.

Experimental Study on the Biological Outcome of Auricular Cartilage and Costal Cartilage at Different Time Periods After Autologous Cartilage Rhinoplasty

Since autologous cartilage is a good transplant material, it is widely used in various fields of clinical medicine. In this study, we collected clinical specimens obtained at different numbers of years after transplantation and used histologic staining to explore the post-transplantation changes in auricular cartilage and costal cartilage. A retrospective analysis was performed on patients who underwent primary autologous cartilage rhinoplasty and secondary rhinoplasty from 2017 to 2021, and the remaining autologous cartilage tissue after surgery was used for histologic testing. As time progressed after transplantation, the density of costal chondrocytes decreased first and then increased, while the secretion of type II collagen and extracellular matrix both decreased slightly. There was a clear boundary between the cartilage tissue and the surrounding connective tissue, and there was no ingrowth of blood vessels in the cartilage. Auricular cartilage showed a decrease in the integrity of the matrix edge. Moreover, local fibrosis was visible, and vascular ingrowth was observed at the edge of the cartilage. The content of type II collagen first increased and then decreased, and the cell secretion function was lower than that of normal chondrocytes. The results of the study suggest that the histologic outcome of elastic cartilage after transplantation is significantly different from that of hyaline cartilage. Moreover, costal cartilage was more stable than auricular cartilage after transplantation.

Ultrashort echo time magnetization transfer imaging of knee cartilage and meniscus after long-distance running

OBJECTIVE

To assess the detection of changes in knee cartilage and meniscus of amateur marathon runners before and after long-distance running using a 3D ultrashort echo time MRI sequence with magnetization transfer preparation (UTE-MT).

METHODS

We recruited 23 amateur marathon runners (46 knees) in this prospective cohort study. MRI scans using UTE-MT and UTE-T2* sequences were performed pre-race, 2 days post-race, and 4 weeks post-race. UTE-MT ratio (UTE-MTR) and UTE-T2* were measured for knee cartilage (eight subregions) and meniscus (four subregions). The sequence reproducibility and inter-rater reliability were also investigated.

RESULTS

Both the UTE-MTR and UTE-T2* measurements showed good reproducibility and inter-rater reliability. For most subregions of cartilage and meniscus, the UTE-MTR values decreased 2 days post-race and increased after 4 weeks of rest. Conversely, the UTE-T2* values increased 2 days post-race and decreased after 4 weeks. The UTE-MTR values in lateral tibial plateau, central medial femoral condyle, and medial tibial plateau showed a significant decrease at 2 days post-race compared to the other two time points (p < 0.05). By comparison, no significant UTE-T2* changes were found for any cartilage subregions. For meniscus, the UTE-MTR values in medial posterior horn and lateral posterior horn regions at 2 days post-race were significantly lower than those at pre-race and 4 weeks post-race (p < 0.05). By comparison, only the UTE-T2* values in medial posterior horn showed a significant difference.

CONCLUSIONS

UTE-MTR is a promising method for the detection of dynamic changes in knee cartilage and meniscus after long-distance running.

KEY POINTS

• Long-distance running causes changes in the knee cartilage and meniscus. • UTE-MT monitors dynamic changes of knee cartilage and meniscal non-invasively. • UTE-MT is superior to UTE-T2* in monitoring dynamic changes in knee cartilage and meniscus.

Healthy and Osteoarthritis-Affected Joints Facing the Cellular Crosstalk

Osteoarthritis (OA) is a chronic, progressive, severely debilitating, and multifactorial joint disease that is recognized as the most common type of arthritis. During the last decade, it shows an incremental global rise in prevalence and incidence. The interaction between etiologic factors that mediate joint degradation has been explored in numerous studies. However, the underlying processes that induce OA remain obscure, largely due to the variety and complexity of these mechanisms. During synovial joint dysfunction, the osteochondral unit undergoes cellular phenotypic and functional alterations. At the cellular level, the synovial membrane is influenced by cartilage and subchondral bone cleavage fragments and extracellular matrix (ECM) degradation products from apoptotic and necrotic cells. These "foreign bodies" serve as danger-associated molecular patterns (DAMPs) that trigger innate immunity, eliciting and sustaining low-grade inflammation in the synovium. In this review, we explore the cellular and molecular communication networks established between the major joint compartments-the synovial membrane, cartilage, and subchondral bone of normal and OA-affected joints.

Expression of Basement Membrane Molecules by Wharton Jelly Stem Cells (WJSC) in Full-Term Human Umbilical Cords, Cell Cultures and Microtissues

Wharton's jelly stem cells (WJSC) from the human umbilical cord (UC) are one of the most promising mesenchymal stem cells (MSC) in tissue engineering (TE) and advanced therapies. The cell niche is a key element for both, MSC and fully differentiated tissues, to preserve their unique features. The basement membrane (BM) is an essential structure during embryonic development and in adult tissues. Epithelial BMs are well-known, but similar structures are present in other histological structures, such as in peripheral nerve fibers, myocytes or chondrocytes. Previous studies suggest the expression of some BM molecules within the Wharton's Jelly (WJ) of UC, but the distribution pattern and full expression profile of these molecules have not been yet elucidated. In this sense, the aim of this histological study was to evaluate the expression of main BM molecules within the WJ, cultured WJSC and during WJSC microtissue (WJSC-MT) formation process. Results confirmed the presence of a pericellular matrix composed by the main BM molecules-collagens (IV, VII), HSPG2, agrin, laminin and nidogen-around the WJSC within UC. Additionally, ex vivo studies demonstrated the synthesis of these BM molecules, except agrin, especially during WJSC-MT formation process. The WJSC capability to synthesize main BM molecules could offer new alternatives for the generation of biomimetic-engineered substitutes where these molecules are particularly needed.

Cell-Cell Interactions Enhance Cartilage Zonal Development in 3D Gradient Hydrogels

Cartilage tissue is characterized by zonal organization with gradual transitions of biochemical and mechanical cues from superficial to deep zones. We previously reported that 3D gradient hydrogels made of polyethylene glycol and chondroitin sulfate can induce zonal-specific responses of chondrocytes, resulting in zonal cartilage formation that mimics native tissues. While the role of cell-matrix interactions has been studied extensively, how cell-cell interactions across different zones influence cartilage zonal development remains unknown. The goal of this study is to harness gradient hydrogels as a tool to elucidate the role of cell-cell interactions in driving cartilage zonal development. When encapsulated in intact gradient hydrogels, chondrocytes exhibited strong zonal-specific responses that mimic native cartilage zonal organization. However, the separate culture of each zone of gradient hydrogels resulted in a significant decrease in cell proliferation and cartilage matrix deposition across all zones, while the trend of zonal dependence remains. Unexpectedly, mixing the coculture of all five zones of hydrogels in the same culture well largely abolished the zonal differences, with all zones behaving similarly to the softest zone. These results suggest that paracrine signal exchange among cells in different zones is essential in driving cartilage zonal development, and a spatial organization of zones is required for proper tissue zonal development. Intact, separate, or coculture groups resulted in distinct gene expression patterns in mechanosensing and cartilage-specific markers, suggesting that cell-cell interactions can also modulate mechanosensing. We further showed that 7 days of priming in intact gradient culture was sufficient to instruct the cells to complete the zonal development, and the separate or mixed coculture after 7 days of intact culture had minimal effects on cartilage formation. This study highlights the important role of cell-cell interactions in driving cartilage zonal development and validates gradient hydrogels as a useful tool to elucidate the role of cell-matrix and cell-cell interactions in driving zonal development during tissue morphogenesis and regeneration.

Atomic Force Microscopy Micro-Indentation Methods for Determining the Elastic Modulus of Murine Articular Cartilage

The mechanical properties of biological tissues influence their function and can predict degenerative conditions before gross histological or physiological changes are detectable. This is especially true for structural tissues such as articular cartilage, which has a primarily mechanical function that declines after injury and in the early stages of osteoarthritis. While atomic force microscopy (AFM) has been used to test the elastic modulus of articular cartilage before, there is no agreement or consistency in methodologies reported. For murine articular cartilage, methods differ in two major ways: experimental parameter selection and sample preparation. Experimental parameters that affect AFM results include indentation force and cantilever stiffness; these are dependent on the tip, sample, and instrument used. The aim of this project was to optimize these experimental parameters to measure murine articular cartilage elastic modulus by AFM micro-indentation. We first investigated the effects of experimental parameters on a control material, polydimethylsiloxane gel (PDMS), which has an elastic modulus on the same order of magnitude as articular cartilage. Experimental parameters were narrowed on this control material, and then finalized on wildtype C57BL/6J murine articular cartilage samples that were prepared with a novel technique that allows for cryosectioning of epiphyseal segments of articular cartilage and long bones without decalcification. This technique facilitates precise localization of AFM measurements on the murine articular cartilage matrix and eliminates the need to separate cartilage from underlying bone tissues, which can be challenging in murine bones because of their small size. Together, the new sample preparation method and optimized experimental parameters provide a reliable standard operating procedure to measure microscale variations in the elastic modulus of murine articular cartilage.

Nanomechanics of Aggrecan: A New Perspective on Cartilage Biomechanics, Disease and Regeneration

Articular cartilage is a hydrated macromolecular composite mainly composed of type II collagen fibrils and the large proteoglycan, aggrecan. Aggrecan is a key determinant of the load bearing and energy dissipation functions of cartilage. Previously, studies of cartilage biomechanics have been primarily focusing on the macroscopic, tissue-level properties, which failed to elucidate the molecular-level activities that govern cartilage development, function, and disease. This chapter provides a brief summary of Dr. Alan J. Grodzinsky's seminal contribution to the understanding of aggrecan molecular mechanics at the nanoscopic level. By developing and applying a series of atomic force microscopy (AFM)-based nanomechanical tools, Grodzinsky and colleagues revealed the unique structural and mechanical characteristics of aggrecan at unprecedented resolutions. In this body of work, the "bottle-brush"-like ultrastructure of aggrecan was directly visualized for the first time. Meanwhile, molecular mechanics of aggrecan was studied using a physiological-like 2D biomimetic assembly of aggrecan on multiple fronts, including compression, dynamic loading, shear, and adhesion. These studies not only generated new insights into the development, aging, and disease of cartilage, but established a foundation for designing and evaluating novel cartilage regeneration strategies. For example, building on the scientific foundation and methodology infrastructure established by Dr. Grodzinsky, recent studies have elucidated the roles of other proteoglycans in mediating cartilage integrity, such as decorin and perlecan, and evaluated the therapeutic potential of biomimetic proteoglycans in improving cartilage regeneration.

Changes of Age-related Auricular Cartilage Plasticity and Biomechanical Property in a Rabbit Model

OBJECTIVES

Ear molding is an emerging technique that can correct auricular deformities. Treatment initiation time is the most important prognostic determinant of ear molding. Here, we aimed to examine why auricular cartilage plasticity appeared to diminish with age. Thus, we characterized age-related changes in the biomechanical, biochemical, and morphological properties of auricular cartilage.

METHODS

New Zealand rabbits were used as the experimental animal. We examined immature [postnatal 0 day (P0), 5 days (P5), 15 days (P15)], young [2 months (2M)], and mature [6 months (6M)] rabbits. Rabbits' ears were splinted and folded using adhesive fixation strips. Folding duration ranged from 1 day to 5 days to 10 days. Photographs were taken to calculate the retained fold angle. Cartilage morphology and extracellular matrix (ECM) content were examined histologically (using hematoxylin-eosin, Safranin O, elastic Van Gieson, and Masson's trichrome). Water content, DNA content, and cell density were also analyzed. Biomechanical properties were measured using a Nano indenter.

RESULTS

Immature ears had smaller angles after strip removal, and the angled deformation lasted a longer time. Cartilage matrix compositions, including glycosaminoglycan (GAG), elastin fiber, and collagen, increased over development. The water content, DNA content, and cell density decreased with age. Young's modulus was significantly higher in mature cartilage.

CONCLUSIONS

Here, we successfully established an animal model of ear molding and demonstrated that immature cartilage was associated with better plasticity. We also found that the cartilage's biomechanical property increased with the accumulation of ECM. The biomechanical change could underlie age-related shape plasticity.

LEVEL OF EVIDENCE

NA Laryngoscope, 133:88-94, 2023.

Injectable Decorin/Gellan Gum Hydrogel Encapsulating Adipose-Derived Stem Cells Enhances Anti-Inflammatory Effect in Cartilage Injury via Autophagy Signaling

Adipose-derived stem cells (ADSCs) are employed as a promising alternative in treating cartilage injury. Regulating the inflammatory "fingerprint" of ADSCs to improve their anti-inflammatory properties could enhance therapy efficiency. Herein, a novel injectable decorin/gellan gum hydrogel combined with ADSCs encapsulation for arthritis cartilage treatment is proposed. Decorin/gellan gum hydrogel was prepared according to the previous manufacturing protocol. The liquid-solid form transition of gellan gum hydrogel is perfectly suitable for intra-articular injection. Decorin-enriched matrix showing an immunomodulatory ability to enhance ADSCs anti-inflammatory phenotype under inflammation microenvironment by regulating autophagy signaling. This decorin/gellan gum/ADSCs hydrogel efficiently reverses interleukin-1β-induced cellular injury in chondrocytes. Through a mono-iodoacetate-induced arthritis mice model, the synergistic therapeutic effect of this ADSCs-loaded hydrogel, including inflammation attenuation and cartilage protection, is demonstrated. These results make the decorin/gellan gum hydrogel laden with ADSCs an ideal candidate for treating inflammatory joint disorders.

Nanofiber scaffolds based on extracellular matrix for articular cartilage engineering: A perspective

Articular cartilage has a low self-repair capacity due to the lack of vessels and nerves. In recent times, nanofiber scaffolds have been widely used for this purpose. The optimum nanofiber scaffold should stimulate new tissue's growth and mimic the articular cartilage nature. Furthermore, the characteristics of the scaffold should match those of the cellular matrix components of the native tissue to best merge with the target tissue. Therefore, selective modification of prefabricated scaffolds based on the structure of the repaired tissues is commonly conducted to promote restoring the tissue. A thorough analysis is required to find out the architectural features of scaffolds that are essential to make the treatment successful. The current review aims to target this challenge. The article highlights different optimization approaches of nanofibrous scaffolds for improved cartilage tissue engineering. In this context, the influence of the architecture of nanoscaffolds on performance is discussed in detail. Finally, based on the gathered information, a future outlook is provided to catalyze development in this promising field.

Mucopolysaccharidoses: Cellular Consequences of Glycosaminoglycans Accumulation and Potential Targets

Mucopolysaccharidoses (MPSs) constitute a heterogeneous group of lysosomal storage disorders characterized by the lysosomal accumulation of glycosaminoglycans (GAGs). Although lysosomal dysfunction is mainly affected, several cellular organelles such as mitochondria, endoplasmic reticulum, Golgi apparatus, and their related process are also impaired, leading to the activation of pathophysiological cascades. While supplying missing enzymes is the mainstream for the treatment of MPS, including enzyme replacement therapy (ERT), hematopoietic stem cell transplantation (HSCT), or gene therapy (GT), the use of modulators available to restore affected organelles for recovering cell homeostasis may be a simultaneous approach. This review summarizes the current knowledge about the cellular consequences of the lysosomal GAGs accumulation and discusses the use of potential modulators that can reestablish normal cell function beyond ERT-, HSCT-, or GT-based alternatives.

Changes in stiffness of the extracellular and pericellular matrix in the anulus fibrosus of lumbar intervertebral discs over the course of degeneration

Analogous to articular cartilage, changes in spatial chondrocyte organisation have been proposed to be a strong indicator for local tissue degeneration in the intervertebral disc (IVD). While a progressive structural and functional degradation of the extracellular (ECM) and pericellular (PCM) matrix occurs in osteoarthritic cartilage, these processes have not yet been biomechanically elucidated in the IVD. We aimed to evaluate the local stiffness of the ECM and PCM in the anulus fibrosus of the IVD on the basis of local chondrocyte spatial organisation. Using atomic force microscopy, we measured the Young's modulus of the local ECM and PCM in human and bovine disc samples using the spatial chondrocyte patterns as an image-based biomarker. By measuring tissue from 31 patients and six bovine samples, we found a significant difference in the elastic moduli (E) of the PCM in clusters when compared to the healthy patterns single cells (p = 0.029), pairs (p = 0.016), and string-formations (p = 0.010). The ECM/PCM ratio ranged from 0.62-0.89. Interestingly, in the bovine IVD, the ECM/PCM ratio of the E significantly varied (p = 0.002) depending on the tissue origin. Overall the reduced E in clusters demonstrates that cluster formation is not only a morphological phenomenon describing disc degeneration, but it marks a compromised biomechanical functioning. Immunohistochemical analyses indicate that collagen type III degradation might be involved. This study is the first to describe and quantify the differences in the E of the ECM in relation to the PCM in the anulus fibrosus of the IVD by means of atomic force microscopy on the basis of spatial chondrocyte organisation.

Chondrocyte De-Differentiation: Biophysical Cues to Nuclear Alterations

Autologous chondrocyte implantation (ACI) is a cell therapy to repair cartilage defects. In ACI a biopsy is taken from a non-load bearing area of the knee and expanded in-vitro. The expansion process provides the benefit of generating a large number of cells required for implantation; however, during the expansion these cells de-differentiate and lose their chondrocyte phenotype. In this review we focus on examining the de-differentiation phenotype from a mechanobiology and biophysical perspective, highlighting some of the nuclear mechanics and chromatin changes in chondrocytes seen during the expansion process and how this relates to the gene expression profile. We propose that manipulating chondrocyte nuclear architecture and chromatin organization will highlight mechanisms that will help to preserve the chondrocyte phenotype.

Targeting cell-matrix interface mechanobiology by integrating AFM with fluorescence microscopy

Mechanosensing at the interface of a cell and its surrounding microenvironment is an essential driving force of physiological processes. Understanding molecular activities at the cell-matrix interface has the potential to provide novel targets for improving tissue regeneration and early disease intervention. In the past few decades, the advancement of atomic force microscopy (AFM) has offered a unique platform for probing mechanobiology at this crucial microdomain. In this review, we describe key advances under this topic through the use of an integrated system of AFM (as a biomechanical testing tool) with complementary immunofluorescence (IF) imaging (as an in situ navigation system). We first describe the body of work investigating the micromechanics of the pericellular matrix (PCM), the immediate cell micro-niche, in healthy, diseased, and genetically modified tissues, with a focus on articular cartilage. We then summarize the key findings in understanding cellular biomechanics and mechanotransduction, in which, molecular mechanisms governing transmembrane ion channel-mediated mechanosensing, cytoskeleton remodeling, and nucleus remodeling have been studied in various cell and tissue types. Lastly, we provide an overview of major technical advances that have enabled more in-depth studies of mechanobiology, including the integration of AFM with a side-view microscope, multiple optomicroscopy, a fluorescence recovery after photobleaching (FRAP) module, and a tensile stretching device. The innovations described here have contributed greatly to advancing the fundamental knowledge of extracellular matrix biomechanics and cell mechanobiology for improved understanding, detection, and intervention of various diseases.

Instrumented nanoindentation in musculoskeletal research

Musculoskeletal tissues, such as bone, cartilage, and muscle, are natural composite materials that are constructed with a hierarchical structure ranging from the cell to tissue level. The component differences and structural complexity, together, require comprehensive multiscale mechanical characterization. In this review, we focus on nanoindentation testing, which is used for nanometer to sub-micrometer length scale mechanical characterization. In the following context, we will summarize studies of nanoindentation in musculoskeletal research, examine the critical factors that affect nanoindentation testing results, and briefly summarize other commonly used techniques that can be conjoined with nanoindentation for synchronized imaging and colocalized characterization.

Functionalized Microscaffold-Hydrogel Composites Accelerating Osteochondral Repair through Endochondral Ossification

Osteochondral regeneration remains a key challenge because of the limited self-healing ability of the bone and its complex structure and composition. Biomaterials based on endochondral ossification (ECO) are considered an attractive candidate to promote bone repair because they can effectively address the difficulties in establishing vascularization and poor bone regeneration via intramembranous ossification (IMO). However, its clinical application is limited by the complex cellular behavior of ECO and the long time required for induction of the cell cycle. Herein, functionalized microscaffold-hydrogel composites are developed to accelerate the developmental bone growth process via recapitulating ECO. The design comprises arginine-glycine-aspartic acid (RGD)-peptide-modified microscaffolds loaded with kartogenin (KGN) and wrapped with a layer of RGD- and QK-peptide-comodified alginate hydrogel. These microscaffolds enhance the proliferation and aggregation behavior of the human bone marrow mesenchymal stem cells (hBMSCs); the controlled release of kartogenin induces the differentiation of hBMSCs into chondrocytes; and the hydrogel grafted with RGD and QK peptide facilitates chondrocyte hypertrophy, which creates a vascularized niche for osteogenesis and finally accelerates osteochondral repair in vivo. The findings provide an efficient bioengineering approach by sequentially modulating cellular ECO behavior for osteochondral defect repair.

Perlecan: Roles in osteoarthritis and potential treating target

Osteoarthritis (OA) is the most common joint disease, affecting hundreds of millions of people globally, which leads to a high cost of treatment and further medical care and an apparent decrease in patient prognosis. The recent view of OA pathogenesis is that increased vascularity, bone remodeling, and disordered turnover are influenced by multivariate risk factors, such as age, obesity, and overloading. The view also reveals the gap between the development of these processes and early stage risk factors. This review presents the latest research on OA-related signaling pathways and analyzes the potential roles of perlecan, a typical component of the well-known protective structure against osteoarthritic pericellular matrix (PCM). Based on the experimental results observed in end-stage OA models, we summarized and analyzed the role of perlecan in the development of OA. In normal cartilage, it plays a protective role by maintaining the integrin of PCM and sequesters growth factors. Second, perlecan in cartilage is required to not only activate vascular epithelium growth factor receptor (VEGFR) signaling of endothelial cells for vascular invasion and catabolic autophagy, but also for different signaling pathways for the catabolic and anabolic actions of chondrocytes. Finally, perlecan may participate in pain sensitization pathways.