Summary Statement. This work raises the potential of utilizing stem cells to catalyze cartilage regeneration by a minimal number of neonatal chondrocytes via controlling cell distribution in 3D matrices, and may solve the challenge of scarce donor availability associated with cell-based therapy. Introduction. Cartilage loss is a leading cause of disability among adults and represents a huge socio-economical burden. Allogeneic neonatal articular chondrocytes (NChons) is a promising cell source for cartilage regeneration because these cells are highly proliferative, immune-privileged, and readily produce abundant cartilage matrix. However, scarce donor availability for NChons greatly hinders their broad clinical application. Besides their ability to differentiate into different tissue types, stem cells may contribute to tissue regeneration through the secretion of paracrine factors. Here we examined the potential for using a minimal number of NChons to catalyze cartilage tissue formation by co-culturing them with adipose-derived stem cells (ADSCs) in 3D biomimetic hydrogels. Materials & Methods. NChons were isolated from articular cartilage of a three-day old calf. Human adult ADSCs were expanded to passage 5. Cells were photo-encapsulated in a hydrogel consisting of 7% w/v poly(ethylene glycol diacrylate) and 3% w/v chondroitin sulfate-methacrylate. To examine the effects of different paracrine concentrations, NChons and ADSCs were co-cultured in three different co-culture models: 1) cells cultured with conditioned medium supplementation from the other cell type (CM), 2) bi-layered co-culture confining each cell type to its own layer (BI), and 3) mixed cell co-culture at different ratios (75C:25A, 50C:50A, 25C:75A, 10C:90A). Cell-hydrogel constructs were cultured for 3 weeks in chondrogenic medium with 10ng/ml TGF-β3 and analyzed for biochemical content (DNA, sulfated glycosaminoglycan (sGAG), and collagen) and immunostaining. Fluorescent cell membrane labeling was used to identify ADSCs in mixed co-culture. To quantify interaction synergy, the interaction index, defined as the measured biochemical content in the mixed co-culture normalised by the expected value based on cell ratio and the measured content in the controls, was calculated (2). Statistical significance (∗) was set to p<0.05. Results. At day 21, mixed co-culture with as low as 25% NChons led to higher cell number and cartilage matrix content than NChon control. ADSC control had significantly lower matrix content. In mixed co-culture, the interaction index for DNA, sGAG, and collagen increased with an increase in ADSC ratio, reaching up to 5–6 at 90% ADSCs. Immunostaining of collagen II revealed that mixed co-culture resulted in the formation of large cartilage nodules, and that nodule size increased with an increase ADSC ratio. Cell tracking showed that the labeled ADSCs always resided outside the cartilage noduless, indicating the cartilage nodules are composed entirely of NChons. Discussion & Conclusion. In this study, we demonstrated the efficacy of harnessing the paracrine effects ADSCs to catalyze cartilage tissue formation by a small number of NChons in biomimetic hydrogels. The mild effects of CM and BI co-culture on cartilage tissue formation along with the increase in interaction synergy with ADSC ratio in mixed co-culture highlighted the importance of using 3D scaffolds to probe cell-cell interactions in a spatially controlled manner. Such strategy significantly reduces the number of NChons needed, which may accelerate the translation of NChon for cartilage repair by alleviating donor scarcity limitation, and may be broadly applicable to regenerating other tissue types

In the native articular cartilage microenvironment, chondrocytes are constantly subjected to dynamic physical stimuli that maintains tissue homeostasis. They produce extra cellular matrix (ECM) components such as collagens (type II mainly, 50-75%), proteoglycans (10-30%) and other type of proteins. 1. . While collagen offers a large resistance in tension, proteoglycans are the responsible of the viscoelastic response under compression due to the negative charge they confer to the ECM allowing it to entrap a large amount of interstitial fluid. In pathologic states (e.g. osteoarthritis), this ECM is degenerated and the negative charge becomes unbalanced, losing the chondroprotective properties and resulting on an overloaded chondrocytes that further degenerate the matrix. Low-Intensity Pulsed Ultrasound Stimulation (LIPUS) has been used to generate acoustic (pressure) waves that create bubbles that collapse with cells, inducing a stimulus that can modulate cell response. 2. This mechanical stimulation promotes the expression of type II collagen, type X collagen, aggrecan and TGF-β, appearing as a great strategy to regenerate cartilage. However, current strategies make use of extrinsic forces to stimulate cartilage formation overlooking the physico-chemical properties of the degenerated cartilage, resulting in an excessive load-transfer to chondrocytes and the consequent hypertrophy and degeneration. Here, interpenetrated networks (IPNs) with different compositions were created using methacrylated gelatin (GelMA), to mimic the collagen, and alginate functionalized with tyramine (Alg-tyr) to mimic glycosaminoglycans and to introduce a negative charge in the model. Within the matrix chondrocytes where encapsulated and stimulated under different conditions to identify the ultrasound parameters that enhance tissue formation. Samples with and without stimulation were compared analysing the expression and deposition of collagen II, aggrecan, collagen X and TGF-β. The results suggested that the chondrogenic marker expression of the samples stimulated for 10 minutes per day for 28 days, was two times higher overall in all of the cases, which was correlated to the tissue formation detected. Acknowledgments: The authors would like to thank the Basque Government for the “Predoctoral Training Program for Non-Doctoral Research Staff 2021-2022” (Grant ref.: PRE_2021_1_0403). This work was supported by the RETOS grant PID2020-114901RA-I00 of the Ministry of Science and Innovation (MICINN)

Osteoarthritis is a degenerative disease that results in changes in cartilage extracellular matrix. In vitro studies have shown that IL-1β inhibits cartilage formation in chondrocytes or MSCs undergoing chondrogenesis. In vivo, articular chondrocytes and bone marrow reside under hypoxic or physioxic environment (1–5% oxygen) and previous investigations have shown an increase in cartilage matrix proteins and reduced hypertrophy for MSC chondrogenesis, especially for MSCs expanded and differentiated under physioxia. Our hypothesis was that physioxic preconditioning reduces the effects of IL-1β inhibited MSC chondrogenesis. Methods. Human MSCs (Male donors; aged 18–60 years, n = 6) were isolated from bone marrow and expanded for one passage and split into hyperoxic and physioxic MSC cultures, the latter conditions were isolated and expanded using a hypoxia controlled incubator. MSCs with or without physioxic preconditioning were aliquoted into wells of a 96-well cell culture plate in the presence of 10ng/ml TGF-β. 1. or in combination with either 0.1 or 0.5ng/ml IL-1ß and centrifuged to form pellets. Pellets were then differentiated under their isolation conditions. Pellets removed from culture on days 7, 14 and 21, were evaluated for wet weight, histological (DMMB staining, collagen type I, II, MMP-13 and TGF-β receptor II) and collagen type II ELISA analysis. Results. Preconditioned MSCs demonstrated an enhanced collagen type II and GAG production undergoing chondrogenesis compared to hyperoxic pellets. In the presence of IL-1β, preconditioned MSCs reduced the inhibitory effect of IL-1ß compared to the equivalent conditions under hyperoxic, whereby there was a significant increase in wet weight, GAG and collagen type II production (p < 0.05). Furthermore, preconditioning MSCs had reduced collagen type X expression compared to hyperoxic cultures. Discussion. Preconditioned MSCs had enhanced matrix formation compared to hyperoxic cultures. In the presence of IL-1ß, preconditioned MSCs and physioxic differentiation reduced the inhibitory effects of IL-1ß. This may be related to restoration of TGF-ß receptor II expression (anabolic effect) and reduced expression of catabolic enzyme, MMP-13. The latter enzyme is also involved in hypertrophy and so physioxia helps to partially restore articular cartilage phenotype

Herein we address, hyaline cartilage regeneration issue by engineering a synthetic biocompatible hydrogel scaffold capable to promote chondrogenic differentiation. In this study, the chemically crosslinked hydrogels consisting of synthetic peptides that have the collagen-like sequence Cys-Gly-(Pro-Lys-Gly)4 (Pro-Hyp-Gly)4 (Asp-Hyp-Gly)4- conjugated with RGD sequence (CLP-RGD) and crosslinked hydrogels of type I collagen (CA) were used. For cartilage formation, we used human skeletal muscle-derived stem/progenitor cells (hMDSPCs) set for differentiation towards a chondrogenic lineage by BMP-7 and TGF-ß3 growth factors. Initially 150, 100 and 75 ng of BMP-7and TGF-ß3 growth factors were inserted in each scaffold and amount of growth factors diffusing out of the scaffolds was observed by ELISA assays. In vitro experiments were performed by seeding hMDSPCs onto hydrogels loaded with growth factors (75ng/scaffold) and cultured for 28 days. Cartilage formation was monitored by ELISA and RT-PCR assays. All experiments were performed in triplicates or quadruplicates. Growth factors incorporation strategy allowed a sustained release of TGF-ß3 growth factor, 6.00.3% of the initially loaded amount diffused out after 4 h and 2.70.5% already at the second time point (24h) from CA and CLP-RGD substrates. For the BMP-7 growth factor, 13.12.3% and 15.751.6% of the initially loaded amount diffused out after 4 h, 1.70.2% and 2.450.3% at the second time point (24 h) from CA and CLP-RGD respectively. In vitro experiments shown that scaffolds with immobilized growth factors resulted in higher collagen type II accumulation when compared to the scaffolds alone. The gene expression on CLP-RGD hydrogels with growth factors has shown lower collagen type I expression and higher aggrecan expression compared to day 0. However, we also report increased collagen X gene expression on CA hydrogels (with growth factors). Our results support the potential of the strategy of combining hydrogels functionalized with differentiation factors toward improving cartilage repair

Patients with bone and muscle weakness from disuse have higher risk of fracture and worse post-injury mortality rates. The goal of this current study was to better inform post-fracture rehabilitation strategies by investigating if physical remobilization following disuse by hindlimb unloading improves osteochondral callus formation compared to continued disuse by hindlimb suspension (HLS). We hypothesized that continued HLS would impair callus bone and cartilage formation and that physical rehabilitation after HLS would increase callus properties. All animal procedures were approved by the VCU IACUC. Skeletally mature, male and female C57BL/6J mice (18 weeks) underwent HLS for 3 weeks. Mice then had their right femur fractured by open surgical dissection (stabilized with 24-gauge pin). Mice were then either randomly assigned to continued HLS or allow normal physical weight-bearing remobilization (HLS + R). Mice allowed normal cage activity throughout the experiment served as controls (GC). All mice were sacrificed 14-days following fracture with 4-8 mice (male and female) per treatment. Data analyzed by respective ANOVA with Tukey post-hoc (*p< 0.05; # p < 0.10). Male and female mice showed conserved and significant decreases in hindlimb callus bone formation from continued HLS versus HLS + R. Combining treatment groups regardless of mouse sex, histological analyses using staining on these same calluses demonstrated that HLS resulted in trends toward decreased cartilage cross-sectional area and increased osteoclast density in woven bone versus physically rehabilitated mice. In support of our hypothesis, physical remobilization increases callus bone formation following fracture compared to continued disuse potentially due to increased endochondral ossification and decreased bone resorption. In all, partial weight-bearing exercise immediately following fracture may improve callus healing compared to delayed rehabilitation regimens that are frequently used

Osteoarthritis is the most common chronic condition of the joints. It is characterized by the degeneration of articular cartilage, formation of osteophytes and alterations in the synovium. This process has a severe impact on the quality of life of the patients and the currently available treatments are unsatisfactory and often merely focused on pain relief. In our group we are working on the development of in situ cross-linkable hydrogel platforms that could be used for resurfacing the damaged articular cartilage using a minimally invasive arthroscopic procedure. Stable fixation of the gel at the joint surface, facilitating the ingrowth of local stem and progenitor cell populations and supporting intrinsic repair mechanisms are considered minimal design parameters. To achieve this, we are exploring the use of enzymatically cross-linkable natural polymer-tyramine conjugates. Dextran-tyramine conjugates were prepared by activation of dextran-OH and subsequent reaction with tyramine. Hyaluronic acid-tyramine and protein-tyramine conjugates were prepared using DMTMM coupling. In situ crosslinking is achieved by mixing the polymer conjugates with the enzyme HRP and minute, non-toxic amounts of H2O2 as oxidizing agent. Support of cartilage formation was studied after mixing of the polymer conjugates with mesenchymal stem cells, chondrocytes or combinations of both prior to crosslinking. Cell ingrowth was studied by implanting the hydrogels in an ex-vivo cartilage defect while mechanically loading the explant in a bioreactor and cell migration in the hydrogels was evaluated by tracking the sprouting of fluorescently labelled cell-spheroids. We prepared dextran-tyramine conjugates with a degree of substitution of 10 tyramine residues per 100 monosaccharide units. The conjugated hyaluronic acid-tyramine had a degree of substitution of 10% of the carboxylic acid groups, while for the proteins the substitution was dependent on the protein type. Enzymatically crosslinked hydrogels, based on dextran and hyaluronic acid, with the addition of co-cross linkable proteins show excellent properties for application in the regeneration of damaged cartilage

Osteoarthritis (OA) is the most common joint disease, which is characterized by a progressive loss of proteoglycans and the destruction of extracellular matrix (ECM), leading to a loss of cartilage integrity and joint function. During OA development, chondrocytes alter ECM synthesis and change their gene expression profile including upregulation of hypertrophic markers known from the growth plate. Although physiological mechanical loading can support cartilage formation and maintenance, mechanical overload represents one major risk factor for OA development. To date, little is known on how an OA-like hypertrophic chondrocyte phenotype alters the response of cartilage tissue to mechanical loading. The aim of this study was to investigate whether a hypertrophic phenotype change of chondrocytes affects the response to physiological mechanical loading and to reveal differences compared to normal control cartilage. Cartilage replacement tissue was generated using human articular chondrocytes (normal control cartilage, n=3–5) or human mesenchymal stromal cells which develop a hypertrophic phenotype similar to the one observed in OA (OA cartilage model, n=3–6). Cells were seeded in a collagen type I/III carrier and attached to a beta-TCP bone replacement phase, building an osteochondral unit for simulation of natural conditions. After 21 and 35 days of chondrogenic (re)differentiation, a single physiological mechanical compression episode (1 Hz, 25 %, 3 h) was applied, imitating three hours of normal walking in ten-minute intervals. Proteoglycan and collagen synthesis, gene expression and activation of signaling pathways were assessed. Cartilage replacement tissue of both groups had similar proteoglycan and collagen type II content as well as hardness properties. During (re)differentiation, both cell types showed a comparable upregulation of the chondrogenic marker genes COL2A1 and ACAN. As expected, hypertrophic marker genes (COL10A1, ALPL, MEF2C, IBSP) were only upregulated in the OA cartilage model. Mechanotransduction in both tissues was confirmed by load-induced activation of pERK1/2 signaling. While the 3 h loading episode significantly increased proteoglycan synthesis in normal control cartilage at day 35, the same protocol resulted in a suppression of proteoglycan and collagen synthesis in the OA cartilage model, which was accompanied by a downregulation of COL2A1 gene expression. In addition, hypertrophic marker genes COL10A1, ALPL and IBSP were significantly reduced after loading. Along lower load-induced SOX9 mRNA and protein stimulation in the OA cartilage tissue, a weaker induction of mechanosensitive BMP2, BMP6, FOS and FOSB gene expression was observed. While stable cartilage showed anabolic effects after physiological loading, the hypertrophic chondrocytes reacted with a reduced extracellular matrix synthesis. This could be explained by a lower mechanoinduction of the BMP signaling cascade and insufficient SOX9 stimulation. Progressive OA development could thus be influenced by a reduced mechanocompetence of osteoarthritic chondrocytes

Cartilage injuries often represent irreversible tissue damage because cartilage has only a low ability to regenerate. Thus, cartilage loss results in permanent damage, which can become the starting point for osteoarthritis. In the past, bioactive glass scaffolds have been developed for bone replacement and some of these variants have also been colonized with chondrocytes. However, the hydroxylapaptite phase that is usually formed in bioglass scaffolds is not very suitable for cartilage formation (chondrogenesis). This interdisciplinary project was undertaken to develop a novel slowly degrading bioactive glass scaffold tailored for cartilage repair by resembling the native extracellular cartilage matrix (ECM) in structure and surface properties. When colonized with articular chondrocytes, the composition and topology of the scaffolds should support cell adherence, proliferation and ECM synthesis as a prerequisite for chondrogenesis in the scaffold. To study cell growth in the scaffold, the scaffolds were colonized with human mesenchymal stromal cells (hMSCs) and primary porcine articular chondrocytes (pACs) (27,777.8 cells per mm. 3. ) for 7 – 35 d in a rotatory device. Cell survival in the scaffold was determined by vitality assay. Scanning electron microscopy (SEM) visualized cell ultramorphology and direct interaction of hMSCs and pACs with the bioglass surface. Cell proliferation was detected by CyQuant assay. Subsequently, the production of sulphated glycosaminoglycans (sGAGs) typical for chondrogenic differentiation was depicted by Alcian blue staining and quantified by dimethylmethylene blue assay assay. Quantitative real-time polymerase chain reaction (QPCR) revealed gene expression of cartilage-specific aggrecan, Sox9, collagen type II and dedifferentiation-associated collagen type I. To demonstrate the ECM-protein synthesis of the cells, the production of collagen type II and type I was determined by immunolabelling. The bioactive glass scaffold remained stable over the whole observation time and allowed the survival of hMSCs and pACs for 35 days in culture. The SEM analyses revealed an intimate cell-biomaterial interaction for both cell types showing cell spreading, formation of numerous filopodia and ECM deposition. Both cell types revealed initial proliferation, decreasing after 14 days and becoming elevated again after 21 days. hMSCs formed cell clusters, whereas pACs showed an even distribution. Both cell types filled more and more the pores of the scaffold. The relative gene expression of cartilage-specific markers could be proven for hMSCs and pACs. Cell associated sGAGs deposition could be demonstrated by Alcian blue staining and sGAGs were elevated in the beginning and end of the culturing period. While the production of collagen type II could be observed with both cell types, the synthesis of aggrecan could not be detected in scaffolds seeded with hMSCs. hMSCs and pACs adhered, spread and survived on the novel bioactive glass scaffolds and exhibited a chondrocytic phenotype

Recent advances in tissue engineering have made progress towards the development of biomaterials with the capability for delivery of growth factors to promote enhanced tissue repair. However, controlling the release of these growth factors is a major challenge and the associated high costs and side effects of uncontrolled delivery of has proved increasingly problematic in clinical orthopaedics. Gene therapy might be a valuable tool to avoid these limitations. While non-viral vectors are typically inefficient at transfecting cells, our group have had significant success in this area using a scaffold-mediated gene therapy approach for regenerative applications. These gene activated scaffold platforms not only act as a template for cell infiltration and tissue formation, but also as a ‘factory’ to provoke autologous host cells to take up specific genes and then engineer therapeutic proteins in a sustained but eventually transient fashion. Alternatively, scaffold-mediated delivery of siRNAs and miRNAs can be used to silence specific genes associated with pathological states in orthopaedics. This presentation will provide an overview of some of this research with a particular focus on gene-activated biomaterials for promoting stable cartilage formation in joint repair and on scaffold-based delivery of therapeutics for enhancing vascularization & bone repair

Use of scaffolds for articular cartilage repair (ACR) has increased over the last years with many biomaterials options suggested for this purpose. It is known that scaffolds for ACR have to be optimally biodegradable with simultaneous promotion of chondrogenesis, favouring hyaline cartilage formation under rather complex biomechanical and physiological conditions. Whereas improvement of the scaffolds by their conditioning with stem cells or adult chondrocytes can be employed in bioreactors, “ideal” scaffolds should be capable of performing such functions directly after implantation. It was previously considered that scaffold structure and composition would be the best if it mimics the structure of native cartilage. However, in this case no clear reparative stimuli are being imposed on the scaffold area, which would drive chondrocytes activity in a desired way. In this work, we studied new xeno-free, recombinant human type III collagen-laden polylactide (PLA) mesh scaffolds, which have been designed, produced, and biomechanically optimized in vitro and in vivo validated in a porcine and equine model. The scaffolds were additionally assessed for relative performance simulated synovial fluids for both human conditions and veterinary cases. It was experimentally shown that success of the scaffolds in ACR eventually require lower stiffness than surrounding cartilage yet matching the strain compliance, different in static and dynamic conditions. This ensures an optimal combination of load transfer and oscillatory nutrients supply to the cells, which otherwise is difficult to rely on just with a passive diffusion in avascular cartilage conditions. The results encourage further development of such scaffold structures targeted on their best clinical performance rather than trying to imitate the respective original tissue. The authors would like to thank Finnish Agency for Innovation (Tekes) for providing financial support to this project. A.Z. also acknowledges Teknos Foundation (Finland) for the scholarship

Osteoarthritis is a degenerative disease mainly caused by aging, although in younger patients (aged 25 – 50) it can be a consequence of sports-related injuries or trauma. This results in early osteoarthritis with subsequent changes in cartilage extracellular matrix. Cell-based tissue engineering approaches using mesenchymal stem cells (MSCs) are an ideal cell type for the treatment of early osteoarthritc defects. Our group has demonstrated in a clinical study, that interleukin-1β (IL-1β) was expressed in cartilage plugs from patients with early osteoarthritis. In vitro studies have shown that IL-1β inhibits cartilage formation in chondrocytes or MSCs undergoing chondrogenesis. However, these studies show complete inhibition of tissue formation, whereas in the context of early osteoarthritis, cartilage extracellular matrix remains around the defect site. Thus, the present study sought to develop a model mimicking early osteoarthritis using MSCs. Method. Human MSCs (Male donors; aged 18–60 years, n = 6) were isolated from bone marrow and expanded in culture for one passage. 2 × 10. 5. MSCs were aliquoted into wells of a 96-well cell culture plate in the presence of 10ng/ml TGF-β. 1. or in combination with IL-1β administered at a range of concentrations (0.1, 0.5, 1 and 10ng/ml) and centrifuged to form pellets. Pellets were removed from culture on days 7, 14 and 21. Pellets were evaluated for wet weight, pellet area, histological (DMMB staining, collagen type I, II, MMP-13 and TGF-β receptor II) and collagen type II ELISA analysis. Results. Chondrogenic pellets in the presence of IL-1β demonstrated a dose-dependant inhibition in chondrogenesis. Concentrations equal or greater than 0.5ng/ml IL-1β showed significant reduction (p < 0.05) in pellet area and wet weight, with no positive staining for collagen type I, II (including ELISA analysis) and DMMB. However, at 0.1ng/ml IL-1β, despite a slight reduction in pellet area, positive staining for collagen type I, II and DMMB was observed. Furthermore, MMP-13 matrix staining was increased and TGF-b receptor II staining was decreased in pellets at IL-1β concentrations above 0.5ng/ml. Discussion. A dose dependant catabolic response in cartilage extracellular matrix formation was demonstrated for IL-1β treated MSCs undergoing chondrogenesis. At concentrations equal or greater than 0.5ng/ml IL-1β, MMP13 expression was observed in the matrix, indicative of osteoarthritis. Furthermore, there was reduced expression of TGF-β receptor II under these conditions that is required for TGF-b induced chondrogenesis. However, at 0.1ng/ml IL-1β, a reduced catabolic response in extracellular matrix components was observed, whilst showing a moderate expression in MMP-13 and the presence of cellular TGF-β receptor II expression. Therefore, this latter model may be used to develop pro-chondrogenic strategies for the treatment of early osteoarthritic defects

Objectives

Adult mice lacking the transcription factor NFAT1 exhibit osteoarthritis (OA). The precise molecular mechanism for NFAT1 deficiency-induced osteoarthritic cartilage degradation remains to be clarified. This study aimed to investigate if NFAT1 protects articular cartilage (AC) against OA by directly regulating the transcription of specific catabolic and anabolic genes in articular chondrocytes.

Objectives

The role of mechanical stress and transforming growth factor beta 1 (TGF-β1) is important in the initiation and progression of osteoarthritis (OA). However, the underlying molecular mechanisms are not clearly known.

Objectives

After an injury, the biological reattachment of tendon to bone is a challenge because healing takes place between a soft (tendon) and a hard (bone) tissue. Even after healing, the transition zone in the enthesis is not completely regenerated, making it susceptible to re-injury. In this study, we aimed to regenerate Achilles tendon entheses (ATEs) in wounded rats using a combination of kartogenin (KGN) and platelet-rich plasma (PRP).

Objectives

Interleukin 18 (IL-18) is a regulatory cytokine that degrades the disc matrix. Bone morphogenetic protein-2 (BMP-2) stimulates synthesis of the disc extracellular matrix. However, the combined effects of BMP-2 and IL-18 on human intervertebral disc degeneration have not previously been reported. The aim of this study was to investigate the effects of the anabolic cytokine BMP-2 and the catabolic cytokine IL-18 on human nucleus pulposus (NP) and annulus fibrosus (AF) cells and, therefore, to identify potential therapeutic and clinical benefits of recombinant human (rh)BMP-2 in intervertebral disc degeneration.

Objectives

We sought to determine if a durable bilayer implant composed of trabecular metal with autologous periosteum on top would be suitable to reconstitute large osteochondral defects. This design would allow for secure implant fixation, subsequent integration and remodeling.

Objectives

Healing in cancellous metaphyseal bone might be different from midshaft fracture healing due to different access to mesenchymal stem cells, and because metaphyseal bone often heals without a cartilaginous phase. Inflammation plays an important role in the healing of a shaft fracture, but if metaphyseal injury is different, it is important to clarify if the role of inflammation is also different. The biology of fracture healing is also influenced by the degree of mechanical stability. It is unclear if inflammation interacts with stability-related factors.

This study was designed to test the hypothesis that the sensory innervation of bone might play an important role in sensing and responding to low-intensity pulsed ultrasound and explain its effect in promoting fracture healing. In 112 rats a standardised mid-shaft tibial fracture was created, supported with an intramedullary needle and divided into four groups of 28. These either had a sciatic neurectomy or a patellar tendon resection as control, and received the ultrasound or not as a sham treatment. Fracture union, callus mineralisation and remodelling were assessed using plain radiography, peripheral quantitative computed tomography and histomorphology.

Daily ultrasound treatment significantly increased the rate of union and the volumetric bone mineral density in the fracture callus in the neurally intact rats (p = 0.025), but this stimulating effect was absent in the rats with sciatic neurectomy. Histomorphology demonstrated faster maturation of the callus in the group treated with ultrasound when compared with the control group. The results supported the hypothesis that intact innervation plays an important role in allowing low-intensity pulsed ultrasound to promote fracture healing.

Ovine articular chondrocytes were isolated from cartilage biopsy and culture expanded in vitro. Approximately 30 million cells per ml of cultured chondrocytes were incorporated with autologous plasma-derived fibrin to form a three-dimensional construct. Full-thickness punch hole defects were created in the lateral and medial femoral condyles. The defects were implanted with either an autologous ‘chondrocyte-fibrin’ construct (ACFC), autologous chondrocytes (ACI) or fibrin blanks (AF) as controls. Animals were killed after 12 weeks. The gross appearance of the treated defects was inspected and photographed. The repaired tissues were studied histologically and by scanning electron microscopy analysis.

All defects were assessed using the International Cartilage Repair Society (ICRS) classification. Those treated with ACFC, ACI and AF exhibited median scores which correspond to a nearly-normal appearance. On the basis of the modified O’Driscoll histological scoring scale, ACFC implantation significantly enhanced cartilage repair compared to ACI and AF. Using scanning electron microscopy, ACFC and ACI showed characteristic organisation of chondrocytes and matrices, which were relatively similar to the surrounding adjacent cartilage.

Implantation of ACFC resulted in superior hyaline-like cartilage regeneration when compared with ACI. If this result is applicable to humans, a better outcome would be obtained than by using conventional ACI.

The treatment of osteochondral lesions and osteoarthritis remains an ongoing clinical challenge in orthopaedics. This review examines the current research in the fields of cartilage regeneration, osteochondral defect treatment, and biological joint resurfacing, and reports on the results of clinical and pre-clinical studies. We also report on novel treatment strategies and discuss their potential promise or pitfalls. Current focus involves the use of a scaffold providing mechanical support with the addition of chondrocytes or mesenchymal stem cells (MSCs), or the use of cell homing to differentiate the organism’s own endogenous cell sources into cartilage. This method is usually performed with scaffolds that have been coated with a chemotactic agent or with structures that support the sustained release of growth factors or other chondroinductive agents. We also discuss unique methods and designs for cell homing and scaffold production, and improvements in biological joint resurfacing. There have been a number of exciting new studies and techniques developed that aim to repair or restore osteochondral lesions and to treat larger defects or the entire articular surface. The concept of a biological total joint replacement appears to have much potential.

Cite this article: Bone Joint Res 2013;2:193–9.