Matrix-induced autologous chondrocyte implantation in sheep: objective assessments including confocal arthroscopy

Cartilage Integrity: A Review of Mechanical and Frictional Properties and Repair Approaches in Osteoarthritis

Osteoarthritis (OA) is one of the most common causes of disability around the globe, especially in aging populations. The main symptoms of OA are pain and loss of motion and function of the affected joint. Hyaline cartilage has limited ability for regeneration due to its avascularity, lack of nerve endings, and very slow metabolism. Total joint replacement (TJR) has to date been used as the treatment of end-stage disease. Various joint-sparing alternatives, including conservative and surgical treatment, have been proposed in the literature; however, no treatment to date has been fully successful in restoring hyaline cartilage. The mechanical and frictional properties of the cartilage are of paramount importance in terms of cartilage resistance to continuous loading. OA causes numerous changes in the macro- and microstructure of cartilage, affecting its mechanical properties. Increased friction and reduced load-bearing capability of the cartilage accelerate further degradation of tissue by exerting increased loads on the healthy surrounding tissues. Cartilage repair techniques aim to restore function and reduce pain in the affected joint. Numerous studies have investigated the biological aspects of OA progression and cartilage repair techniques. However, the mechanical properties of cartilage repair techniques are of vital importance and must be addressed too. This review, therefore, addresses the mechanical and frictional properties of articular cartilage and its changes during OA, and it summarizes the mechanical outcomes of cartilage repair techniques.

Translation of cell therapies to treat autoimmune disorders

Autoimmune diseases are a diverse and complex set of chronic disorders with a substantial impact on patient quality of life and a significant global healthcare burden. Current approaches to autoimmune disease treatment comprise broadly acting immunosuppressive drugs that lack disease specificity, possess limited efficacy, and confer undesirable side effects. Additionally, there are limited treatments available to restore organs and tissues damaged during the course of autoimmune disease progression. Cell therapies are an emergent area of therapeutics with the potential to address both autoimmune disease immune dysfunction as well as autoimmune disease-damaged tissue and organ systems. In this review, we discuss the pathogenesis of common autoimmune disorders and the state-of-the-art in cell therapy approaches to (1) regenerate or replace autoimmune disease-damaged tissue and (2) eliminate pathological immune responses in autoimmunity. Finally, we discuss critical considerations for the translation of cell products to the clinic.

Cartilage Tissue Engineering in Practice: Preclinical Trials, Clinical Applications, and Prospects

Articular cartilage defects significantly compromise the quality of life in the global population. Although many strategies are needed to repair articular cartilage, including microfracture, autologous osteochondral transplantation, and osteochondral allograft, the therapeutic effects remain suboptimal. In recent years, with the development of cartilage tissue engineering, scientists have continuously improved the formulations of therapeutic cells, biomaterial-based scaffolds, and biological factors, which have opened new avenues for better therapeutics of cartilage lesions. This review focuses on advances in cartilage tissue engineering, particularly in preclinical trials and clinical applications, prospects, and challenges.

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.

Thickness of the Stifle Joint Articular Cartilage in Different Large Animal Models of Cartilage Repair and Regeneration

OBJECTIVE

Regulatory guidelines for preclinical cartilage repair studies suggest large animal models (e.g., sheep, goat, [mini]-pig, or horse) to obtain results representative for humans. However, information about the 3-dimensional thickness of articular cartilage at different implantation sites in these models is limited.

DESIGN

To identify the most suitable site for experimental surgery, cartilage thickness at the medial femoral condyle (MFC), lateral femoral condyle (LFC), and trochlea in ovine, caprine, and porcine cadaver stifle joints was systematically measured using hematoxylin-eosin staining of 6 µm paraffin sections and software-based image analysis.

RESULTS

Regarding all ventral-dorsal regions of the MFC, goat showed the thickest articular cartilage (maximal mean thickness: 1299 µm), followed by sheep (1096 µm) and mini-pig (604 µm), with the highest values in the most ventral and dorsal regions. Also for the LFC, the most ventral regions showed the thickest cartilage in goat (maximal mean thickness: 1118 µm), followed by sheep (678 µm) and mini-pig (607 µm). Except for the mini-pig, however, the cartilage thickness on the LFC was consistently lower than that on the MFC. The 3 species also differed along the transversal measuring points on the MFC and LFC. In contrast, there were no consistent differences for the regional cartilage thickness of the trochlea among goat and sheep (≥780 µm) and mini-pig (≤500 µm).

CONCLUSIONS

Based on their cartilage thickness, experimental defects on goat and sheep MFC may be viable options for preclinical cartilage repair studies, in addition to well-established horse models.

A multiscale study of morphological changes in tendons following repeated cyclic loading

The response of white New Zealand rabbit Achilles tendons to load was assessed using mechanical measures and confocal arthroscopy (CA). The progression of fatigue-loading-induced damage of the macro- (tenocyte morphology, fiber anisotropy and waviness), as well as the mechanical profile, were assessed within the same non-viable intact tendon in response to prolonged cyclic and static loading (up to four hours) at different strain levels (3%, 6% and 9%). Strain-mediated repeated loading induced a significant decline in mechanical function (p < 0.05) with increased strain and cycles. Mechanical and structural resilience was lost with repeated loading (p < 0.05) at macroscales. The lengthening of D-periodicity correlated strongly with the overall tendon mechanical changes and loss of spindle shape in tenocytes. This is the first study to provide a clear concurrent assessment of form (morphology) and function (mechanics) of tendons undergoing different strain-mediated repeated loading at multiple-scale assessments. This study identifies a variety of multiscale properties that may contribute to the understanding of mechanisms of tendon pathology.

Operative treatments for osteochondral lesions of the talus in adults: A systematic review and meta-analysis

PURPOSE

This systematic review aimed to identify the available evidence regarding the comparative effectiveness and safety of various operative treatments in adult patients with osteochondral lesions of the talus (OLT).

MATERIALS AND METHODS

The PubMed, Embase, ISI Web of Knowledge, and the Cochrane Controlled Trial Register of Controlled Trials were searched from their inception date to September 2019. Two reviewers selected the randomized controlled trials (RCTs) and non-RCTs assessing the comparative effectiveness and safety of various operative treatments for OLT. The meta-analysis was performed using Revman 5.3.

RESULTS

Eight studies (1 RCT and 7 non-RCTs) with 375 patients were included in this review. The difference in the American Orthopaedic Foot and Ankle Society (AOFAS) score between the cartilage repair and replacement was not significant. The cartilage regeneration with or without cartilage repair had significant superiority in improving the AOFAS score compared with the cartilage repair. The difference in the magnetic resonance observation of cartilage repair tissue score between the cartilage repair and replacement and between cartilage repair and cartilage repair plus regeneration was significant.

CONCLUSIONS

Cartilage regeneration and cartilage repair plus regeneration had significant superiority in improving the ankle function and radiological evaluation of OLT, although the trials included did not have high-level evidence. Moreover, which treatment between the 2 was safer could not be addressed in this review as most of the trials did not report the safety outcome. Further studies are needed to define the best surgical option for treating OLT.

Trends in Articular Cartilage Tissue Engineering: 3D Mesenchymal Stem Cell Sheets as Candidates for Engineered Hyaline-Like Cartilage

Articular cartilage defects represent an inciting factor for future osteoarthritis (OA) and degenerative joint disease progression. Despite multiple clinically available therapies that succeed in providing short term pain reduction and restoration of limited mobility, current treatments do not reliably regenerate native hyaline cartilage or halt cartilage degeneration at these defect sites. Novel therapeutics aimed at addressing limitations of current clinical cartilage regeneration therapies increasingly focus on allogeneic cells, specifically mesenchymal stem cells (MSCs), as potent, banked, and available cell sources that express chondrogenic lineage commitment capabilities. Innovative tissue engineering approaches employing allogeneic MSCs aim to develop three-dimensional (3D), chondrogenically differentiated constructs for direct and immediate replacement of hyaline cartilage, improve local site tissue integration, and optimize treatment outcomes. Among emerging tissue engineering technologies, advancements in cell sheet tissue engineering offer promising capabilities for achieving both in vitro hyaline-like differentiation and effective transplantation, based on controlled 3D cellular interactions and retained cellular adhesion molecules. This review focuses on 3D MSC-based tissue engineering approaches for fabricating “ready-to-use” hyaline-like cartilage constructs for future rapid in vivo regenerative cartilage therapies. We highlight current approaches and future directions regarding development of MSC-derived cartilage therapies, emphasizing cell sheet tissue engineering, with specific focus on regulating 3D cellular interactions for controlled chondrogenic differentiation and post-differentiation transplantation capabilities.

Characterisation of ovine bone marrow-derived stromal cells (oBMSC) and evaluation of chondrogenically induced micro-pellets for cartilage tissue repair in vivo

Abstract

Bone marrow stromal cells (BMSC) show promise in cartilage repair, and sheep are the most common large animal pre-clinical model.

Objective

The objective of this study was to characterise ovine BMSC (oBMSC) in vitro, and to evaluate the capacity of chondrogenic micro-pellets manufactured from oBMSC or ovine articular chondrocytes (oACh) to repair osteochondral defects in sheep.

Design

oBMSC were characterised for surface marker expression using flow cytometry and evaluated for tri-lineage differentiation capacity. oBMSC micro-pellets were manufactured in a microwell platform, and chondrogenesis was compared at 2%, 5%, and 20% O₂. The capacity of cartilage micro-pellets manufactured from oBMSC or oACh to repair osteochondral defects in adult sheep was evaluated in an 8-week pilot study.

Results

Expanded oBMSC were positive for CD44 and CD146 and negative for CD45. The common adipogenic induction ingredient, 3-Isobutyl-1-methylxanthine (IBMX), was toxic to oBMSC, but adipogenesis could be restored by excluding IBMX from the medium. BMSC chondrogenesis was optimal in a 2% O₂ atmosphere. Micro-pellets formed from oBMSC or oACh appeared morphologically similar, but hypertrophic genes were elevated in oBMSC micro-pellets. While oACh micro-pellets formed cartilage-like repair tissue in sheep, oBMSC micro-pellets did not.

Conclusion

The sensitivity of oBMSC, compared to human BMSC, to IBMX in standard adipogenic assays highlights species-associated differences. Micro-pellets manufactured from oACh were more effective than micro-pellets manufactured from oBMSC in the repair of osteochondral defects in sheep. While oBMSC can be driven to form cartilage-like tissue in vitro, the effective use of these cells in cartilage repair will depend on the successful mitigation of hypertrophy and tissue integration.

Supplementary information

The online version contains supplementary material available at 10.1186/s13287-020-02045-3.

Modeling and Staging of Osteoarthritis Progression Using Serial CT Imaging and Arthroscopy

OBJECTIVE

The objective of this study was to describe in life methods by which osteoarthritis can be staged in order to time therapeutic interventions that are relevant to osteoarthritis (OA) clinical trials.

METHODS

Twenty-two sheep underwent arthroscopic meniscal destabilization to induce OA. Serial computed tomography (CT) imaging and arthroscopy were used to monitor osteoarthritis progression at 3-month intervals over 9 months. Eleven sheep received 1 intra-articular injection of hyaluronate 3 months after OA induction and another group of 11 received saline. A linear mixed model was used to define the trajectory of shape change in the medial joint compartment. Ordinal logistic regression was used to investigate the association between morphological changes and sclerosis.

RESULTS

Three months after meniscal destabilization there were early bipolar chondral lesions in the medial compartment of the knee, as well as osteophytes and bone remodeling. Superficial fissures and cartilage cracks progressed to discrete areas of cartilage thinning and fibrillation on the medial tibial plateau by 6 months that became cartilage erosions by nine months. A linear mixed effect model demonstrated significant change in medial compartment length and width with over time (P < 0.05) for both groups. A significant association between severity of sclerosis and medial compartment morphology was also observed.

CONCLUSIONS

The induction of osteoarthritic lesions with meniscal release model can be followed using noninvasive and minimally invasive procedures allowing for real-time decisions about redosing therapies, or other changes such as extending trial timelines without sacrificing animals to conduct assessments.

A preclinical large-animal model for the assessment of critical-size load-bearing bone defect reconstruction

Critical-size bone defects, which require large-volume tissue reconstruction, remain a clinical challenge. Bone engineering has the potential to provide new treatment concepts, yet clinical translation requires anatomically and physiologically relevant preclinical models. The ovine critical-size long-bone defect model has been validated in numerous studies as a preclinical tool for evaluating both conventional and novel bone-engineering concepts. With sufficient training and experience in large-animal studies, it is a technically feasible procedure with a high level of reproducibility when appropriate preoperative and postoperative management protocols are followed. The model can be established by following a procedure that includes the following stages: (i) preoperative planning and preparation, (ii) the surgical approach, (iii) postoperative management, and (iv) postmortem analysis. Using this model, full results for peer-reviewed publication can be attained within 2 years. In this protocol, we comprehensively describe how to establish proficiency using the preclinical model for the evaluation of a range of bone defect reconstruction options.

Report on a large animal study with Göttingen Minipigs where regenerates and controls for articular cartilage were created in a large number. Focus on the conditions of the operated stifle joints and suggestions for standardized procedures

The characterization of regenerated articular cartilage (AC) can be based on various methods, as there is an unambiguous accepted criterion neither for the natural cartilage tissue nor for regenerates. Biomechanical aspects should be considered as well, leading to the need for more equivalent samples. The aim of the study was to describe a large animal model where 8 specimens of regenerated AC can be created in one animal plus the impact of two surgeries on the welfare of the animals. The usefulness of the inclusion of a group of untreated animals (NAT) was to analyzed. Based on the histological results the conditions of the regenerates were to be described and the impact on knee joints were to be explored in terms of degenerative changes of the cartilage. The usefulness of the statistical term “effect size” (ES) will be explained with histological results. We analyzed an animal model where 8 AC regenerates were obtained from one Göttingen Minipig, on both sides of the trochleae. 60 animals were divided into 6 groups of 10 each, where the partial thickness defects in the trochlea were filled with matrices made of Collagen I with or without autologous chondrocytes or left empty over the healing periods of 24 and 48 weeks. One additional control group consisting of 10 untreated animals was used to provide untouched “external” cartilage. We harvested 560 samples of regenerated tissue and “external” controls, besides that, twice the number of further samples from other parts of the joints referred to as “internal” controls were also harvested. The animals recovered faster after the 1^st operation when the defects were set compared to the 2^nd operation when the defects were treated. 9% of all animals were lost. Other complications were for example superficial infections, seroma, diarrhea, febrile state and an injury of a claw. The histological results of the treatments proved the robustness of the study design where we included an “external” control group (NAT) in which the animals were not operated. Comparable significant differences between treated groups and the NAT group were detected both after ½ year and after 1 year. Spontaneous regenerated AC as control revealed differences after an observation time of nearly 1 year. The impact of the treatment on cartilage adjacent to the defect as well as the remaining knee joint was low. The ES was helpful for planning the study as it is shown that the power of a statistical comparison seems to be more influenced by the ES than by the sample size. The ranking of the ES was done exemplarily, listing the results according to their magnitude, thus making the results comparable. We were able to follow the 3 R requirements also in terms of a numerical reduction of animals due to the introduction of a group of untreated animals. This makes the model cost effective. The presented study may contribute as an improvement of the standardization of large animal models for research and regulatory requirements for regenerative therapies of AC.

Quantification of solute diffusivity in osteoarthritic human femoral cartilage using correlation spectroscopy

Osteoarthritis is a chronic joint disease characterized by articular cartilage degeneration, pain, and disability. As an avascular tissue, the movement of water and solutes through the tissue is critical to cartilage health and function, and early changes in solute diffusivity due to micro-scale changes in the properties of cartilage's extracellular matrix might precede clinical symptoms. A diagnostic technique for quantifying alteration to the diffusive environment of cartilage that precedes macroscopic changes may allow for the earlier identification of osteoarthritic disease, facilitating earlier intervention strategies. Toward this end, we used two confocal microscopy-based correlation spectroscopy techniques, fluorescence correlation spectroscopy and raster image correlation spectroscopy, to quantify the diffusion of two small solutes, fluorescein and 3k dextran, within human osteoarthritic articular cartilage. Our goal was to determine if these relatively simple optical correlation spectroscopy techniques could detect changes in solute diffusivity associated with increasing cartilage damage as assessed by International Cartilage Repair Society scoring guidelines, and if these measures are correlated with mechanical and compositional measures of cartilage health. Our data show a modest, yet significant increase in solute diffusivity and cartilage permeability with increasing osteoarthritis score (grades 0-2), with a strong correlation between diffusion coefficients, permeability, and cartilage composition. The described correlation spectroscopy techniques are quick, simple, and easily adapted to existing laboratory workflow and equipment. Furthermore, the minimal solute concentrations and laser powers required for analysis, combined with recent advances in arthroscopic microscopy, suggest correlation spectroscopy techniques as translational candidates for development into early OA diagnosis tools. © 2018 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 36:3256-3267, 2018.

Orthopedic Surgical Options for Joint Cartilage Repair and Restoration

The limited natural capacity for articular cartilage to regenerate has led to a continuously broadening array of surgical interventions. Used once patients' symptoms are not relieved by nonoperative management, these share the goals of joint preservation and restoration. Techniques include bone marrow stimulation, whole-tissue transplantation, and cell-based strategies, each with its own variations. Many of these interventions are performed arthroscopically or with extended-portal techniques. Indications, operative techniques, unique benefits, and limitations are presented.

Large Animal Models for Osteochondral Regeneration

Namely, in the last two decades, large animal models - small ruminants (sheep and goats), pigs, dogs and horses - have been used to study the physiopathology and to develop new therapeutic procedures to treat human clinical osteoarthritis. For that purpose, cartilage and/or osteochondral defects are generally performed in the stifle joint of selected large animal models at the condylar and trochlear femoral areas where spontaneous regeneration should be excluded. Experimental animal care and protection legislation and guideline documents of the US Food and Drug Administration, the American Society for Testing and Materials and the International Cartilage Repair Society should be followed, and also the specificities of the animal species used for these studies must be taken into account, such as the cartilage thickness of the selected defect localization, the defined cartilage critical size defect and the joint anatomy in view of the post-operative techniques to be performed to evaluate the chondral/osteochondral repair. In particular, in the articular cartilage regeneration and repair studies with animal models, the subchondral bone plate should always be taken into consideration. Pilot studies for chondral and osteochondral bone tissue engineering could apply short observational periods for evaluation of the cartilage regeneration up to 12 weeks post-operatively, but generally a 6- to 12-month follow-up period is used for these types of studies.

Matrix-Induced Autologous Chondrocyte Implantation (MACI) Using a Cell-Seeded Collagen Membrane Improves Cartilage Healing in the Equine Model

BACKGROUND

Autologous chondrocyte implantation (ACI) using a collagen scaffold (matrix-induced ACI; MACI) is a next-generation approach to traditional ACI that provides the benefit of autologous cells and guided tissue regeneration using a biocompatible collagen scaffold. The MACI implant also has inherent advantages including surgical implantation via arthroscopy or miniarthrotomy, the elimination of periosteal harvest, and the use of tissue adhesive in lieu of sutures. This study evaluated the efficacy of the MACI implant in an equine full-thickness cartilage defect model at 1 year.

METHODS

Autologous chondrocytes were seeded onto a collagen type-I/III membrane and implanted into one of two 15-mm defects in the femoral trochlear ridge of 24 horses. Control defects either were implanted with cell-free collagen type-I/III membrane (12 horses) or were left ungrafted as empty defects (12 horses). An additional 3 horses had both 15-mm defects remain empty as nonimplanted joints. The repair was scored by second-look arthroscopy (12 weeks), and necropsy examination (53 weeks). Healing was assessed by arthroscopic scoring, gross assessment, histology and immunohistology, cartilage matrix component assay, and gene expression determination. Toxicity was examined by prostaglandin E2 formation in joint fluid, and lymph node morphology combined with histologic screening of organs.

RESULTS

MACI-implanted defects had improved gross healing and composite histologic scores, as well as increases in chondrocyte predominance, toluidine blue-stained matrix, and collagen type-II content compared with scaffold-only implanted or empty defects. There was minimal evidence of reaction to the implant in the synovial membrane (minor perivascular cuffing), subchondral bone, or cartilage. There were no adverse clinical effects, signs of organ toxicity, or evidence of chondrocytes or collagen type-I/III membrane in draining lymph nodes.

CONCLUSIONS

The MACI implant appeared to improve cartilage healing in a critical-sized defect in the equine model compared with collagen matrix alone.

CLINICAL RELEVANCE

These results indicate that the MACI implant is quick to insert, provides chondrocyte security in the defect, and improves cartilage healing compared with ACI.

Ex vivo model unravelling cell distribution effect in hydrogels for cartilage repair

The implantation of chondrocyte-laden hydrogels is a promising cartilage repair strategy. Chondrocytes can be spatially positioned in hydrogels and thus in defects, while current clinical cell therapies introduce chondrocytes in the defect depth. The main aim of this study was to evaluate the effect of spatial chondrocyte distribution on the reparative process. To reduce animal experiments, an ex vivo osteochondral plug model was used and evaluated. The role of the delivered and endogenous cells in the repair process was investigated.

Full thickness cartilage defects were created in equine osteochondral plugs. Defects were filled with (A) chondrocytes at the bottom of the defect, covered with a cell-free hydrogel, (B) chondrocytes homogeneously encapsulated in a hydrogel, and (C, D) combinations of A and B with different cell densities. Plugs were cultured for up to 57 days, after which the cartilage and repair tissues were characterized and compared to baseline samples. Additionally, at day 21, the origin of cells in the repair tissue was evaluated.

Best outcomes were obtained with conditions C and D, which resulted in well-integrated cartilage-like tissue that completely filled the defect, regardless of the initial cell density. A critical role of the spatial chondrocyte distribution in the repair process was observed. Moreover, the osteochondral plugs stimulated cartilage formation in the hydrogels when cultured in the defects. The resulting repair tissue originated from the delivered cells.

These findings confirm the potential of the osteochondral plug model for the optimization of the composition of cartilage implants and for studying repair mechanisms.

Construction and biocompatibility of a thin type I/II collagen composite scaffold

Articular cartilage injury is a common type of damage observed in clinical practice. A matrix-induced autologous chondrocyte implant was developed to repair articular cartilage as an advancement on the autologous chondrocyte implant procedure. Here, we establish a thin double layer of collagen as a novel and effective bioscaffold for the regeneration of cartilaginous lesions. We created a collagen membrane with double layers using a cover slip, a cover slip, and the collagen was then freeze-dried under vacuum. Carbodiimide as a crosslinking agent was used to obtain a relatively stable collagen construction. The thickness of the knee joint cartilage from grown rabbits was measured from a frozen section. Both type I and type II collagens were characterized using Sodium dodecylsulfate/polyacrylamide gel electrophoresis (SDS-PAGE) and ultraviolet absorption peaks. The aperture size of the scaffold was observed using a scanning electron microscope (SEM). The degradation of the scaffolds in vitro was tested through digestion using collagenase solution. The mechanical capacity of the scaffolds was assessed under dynamic compression. The influence of the scaffold on chondrocyte proliferation was assessed using the methyl thiazolyl tetrazolium (MTT) colourimetric assay and scanning electron microscopy. The frozen sections of the rabbit femoral condyle showed that the thickness of the weight-bearing area of the articular cartilage was less than 1 mm. The results of the SDS-PAGE and ultraviolet absorption peaks of the collagens were in agreement with the standard photographs in the references. SEM showed that the aperture size of the cross-linked scaffold was 82.14 ± 15.70 μm. The in vitro degradation studies indicated that Carbodiimide cross-linking can effectively enhance the biostability of the scaffolds. The Carbodiimide cross-linking protocol resulted in a mean value for the samples that ranged from 8.72 to 15.95 MPa for the compressive strength. The results of the MTT demonstrated that the scaffold had promoted chondrocyte proliferation and SEM observations showed that the scaffold was a good adhesive and growth material for chondrocytes. Thin type I/II collagen composite scaffold can meet the demands of cartilage tissue engineering and have good biocompatibility.

Single-stage cell-based cartilage repair in a rabbit model: cell tracking and in vivo chondrogenesis of human umbilical cord blood-derived mesenchymal stem cells and hyaluronic acid hydrogel composite

OBJECTIVE

Human umbilical cord blood-derived mesenchymal stem cells (hUCB-MSCs) have gained popularity as a promising cell source for regenerative medicine, but limited in vivo studies have reported cartilage repair. In addition, the roles of MSCs in cartilage repair are not well-understood. The purpose of this study was to investigate the feasibility of transplanting hUCB-MSCs and hyaluronic acid (HA) hydrogel composite to repair articular cartilage defects in a rabbit model and determine whether the transplanted cells persisted or disappeared from the defect site.

DESIGN

Osteochondral defects were created in the trochlear grooves of the knees. The hUCB-MSCs and HA composite was transplanted into the defect of experimental knees. Control knees were transplanted by HA or left untreated. Animals were sacrificed at 8 and 16 weeks post-transplantation and additionally at 2 and 4 weeks to evaluate the fate of transplanted cells. The repair tissues were evaluated by gross, histological and immunohistochemical analysis.

RESULTS

Transplanting hUCB-MSCs and HA composite resulted in overall superior cartilage repair tissue with better quality than HA alone or no treatment. Cellular architecture and collagen arrangement at 16 weeks were similar to those of surrounding normal articular cartilage tissue. Histological scores also revealed that cartilage repair in experimental knees was better than that in control knees. Immunohistochemical analysis with anti-human nuclear antibody confirmed that the transplanted MSCs disappeared gradually over time.

CONCLUSION

Transplanting hUCB-MSCs and HA composite promote cartilage repair and interactions between hUCB-MSCs and host cells initiated by paracrine action may play an important role in cartilage repair.

Perivascular Mesenchymal Stem Cells in Sheep: Characterization and Autologous Transplantation in a Model of Articular Cartilage Repair

Previous research has indicated that purified perivascular stem cells (PSCs) have increased chondrogenic potential compared to conventional mesenchymal stem cells (MSCs) derived in culture. This study aimed to develop an autologous large animal model for PSC transplantation and to specifically determine if implanted cells are retained in articular cartilage defects. Immunohistochemistry and fluorescence-activated cell sorting were used to ascertain the reactivity of anti-human and anti-ovine antibodies, which were combined and used to identify and isolate pericytes (CD34^-CD45^-CD146⁺) and adventitial cells (CD34⁺CD45^-CD146^-). The purified cells demonstrated osteogenic, adipogenic, and chondrogenic potential in culture. Autologous ovine PSCs (oPSCs) were isolated, cultured, and efficiently transfected using a green fluorescence protein (GFP) encoding lentivirus. The cells were implanted into articular cartilage defects on the medial femoral condyle using hydrogel and collagen membranes. Four weeks following implantation, the condyle was explanted and confocal laser scanning microscopy demonstrated the presence of oPSCs in the defect repaired with the hydrogel. These data suggest the testability in a large animal of native MSC autologous grafting, thus avoiding possible biases associated with xenotransplantation. Such a setting will be used in priority for indications in orthopedics, at first to model articular cartilage repair.

Articular cartilage repair with recombinant human type II collagen/polylactide scaffold in a preliminary porcine study

The purpose of this study was to investigate the potential of a novel recombinant human type II collagen/polylactide scaffold (rhCo-PLA) in the repair of full-thickness cartilage lesions with autologous chondrocyte implantation technique (ACI). The forming repair tissue was compared to spontaneous healing (spontaneous) and repair with a commercial porcine type I/III collagen membrane (pCo). Domestic pigs (4-month-old, n = 20) were randomized into three study groups and a circular full-thickness chondral lesion with a diameter of 8 mm was created in the right medial femoral condyle. After 3 weeks, the chondral lesions were repaired with either rhCo-PLA or pCo together with autologous chondrocytes, or the lesion was only debrided and left untreated for spontaneous repair. The repair tissue was evaluated 4 months after the second operation. Hyaline cartilage formed most frequently in the rhCo-PLA treatment group. Biomechanically, there was a trend that both treatment groups resulted in better repair tissue than spontaneous healing. Adverse subchondral bone reactions developed less frequently in the spontaneous group (40%) and the rhCo-PLA treated group (50%) than in the pCo control group (100%). However, no statistically significant differences were found between the groups. The novel rhCo-PLA biomaterial showed promising results in this proof-of-concept study, but further studies will be needed in order to determine its effectiveness in articular cartilage repair. © 2015 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 34:745-753, 2016.

Hydrogels based on collagen and fibrin – frontiers and applications

Hydrogels are a versatile tool for a multitude of applications in biomedical research and clinical practice. Especially collagen and fibrin hydrogels are distinguished by their excellent biocompatibility, natural capacity for cell adhesion and low immunogenicity. In many ways, collagen and fibrin represent an ideal biomaterial, as they can serve as a scaffold for tissue regeneration and promote the migration of cells, as well as the ingrowth of tissues. On the other hand, pure collagen and fibrin materials are marked by poor mechanical properties and rapid degradation, which limits their use in practice. This paper will review methods of modification of natural collagen and fibrin materials to next-generation materials with enhanced stability. A special focus is placed on biomedical products from fibrin and collagen already on the market. In addition, recent research on the in vivo applications of collagen and fibrin-based materials will be showcased.

Non-clinical assessment design of autologous chondrocyte implantation products

The aims of this study were to investigate the premarket assessment of autologous chondrocyte implantation (ACI) products especially regarding the non-clinical assessment by surveying the guidelines and review reports of authorized ACI products in detail and to provide information regarding the non-clinical assessment of the safety and efficacy for the future development of regenerative medicine products to design effective premarket assessment. The non-clinical assessment plays a role in justifying the testing of investigational products in humans. Effective non-clinical assessments minimize the risk of clinical trials and achieve prompt product development. In this study, we focused on authorized ACI products that remain in the body of patients for a long time and often contain extrinsic components such as animal tissue-derived collagen. We summarized the details of the characteristics of each ACI product, non-clinical assessment design and related guidelines. To design effective non-clinical assessments, we discussed the evaluation method (particularly the validation of clinical assessment and mechanical property testing), the employed animal models, and the differences in the assessment of the safety and efficacy of the products. Based on these investigations, we provide the details of satisfactory non-clinical assessment of ACI products and indicate the possibility of more effective non-clinical assessment of ACI products and other future regenerative medicine products.

A chondrocyte infiltrated collagen type I/III membrane (MACI® implant) improves cartilage healing in the equine patellofemoral joint model

Autologous chondrocyte implantation (ACI) has improved outcome in long-term studies of joint repair in man. However, ACI requires sutured periosteal flaps to secure the cells, which precludes minimally-invasive implantation, and introduces complications with arthrofibrosis and graft hypertrophy. This study evaluated ACI on a collagen type I/III scaffold (matrix-induced autologous chondrocyte implantation; MACI(®)) in critical sized defects in the equine model.

METHODS

Chondrocytes were isolated from horses, expanded and seeded onto a collagen I/III membrane (ACI-Maix™) and implanted into one of two 15-mm defects in the femoral trochlear ridge of six horses. Control defects remained empty as ungrafted debrided defects. The animals were examined daily, scored by second look arthroscopy at 12 weeks, and necropsy examination 6 months after implantation. Reaction to the implant was determined by lameness, and synovial fluid constituents and synovial membrane histology. Cartilage healing was assessed by arthroscopic scores, gross assessment, repair tissue histology and immunohistochemistry, cartilage glycosaminoglycan (GAG) and DNA assay, and mechanical testing.

RESULTS

MACI(®) implanted defects had improved arthroscopic second-look, gross healing, and composite histologic scores, compared to spontaneously healing empty defects. Cartilage GAG and DNA content in the defects repaired by MACI implant were significantly improved compared to controls. Mechanical properties were improved but remained inferior to normal cartilage. There was minimal evidence of reaction to the implant in the synovial fluid, synovial membrane, subchondral bone, or cartilage.

CONCLUSIONS

The MACI(®) implant appeared to improve cartilage healing in a critical sized defect in the equine model evaluated over 6 months.

An educational review of cartilage repair: precepts & practice--myths & misconceptions--progress & prospects

OBJECTIVE

The repair of cartilaginous lesions within synovial joints is still an unresolved and weighty clinical problem. Although research activity in this area has been indefatigably sustained, no significant progress has been made during the past decade. The aim of this educational review is to heighten the awareness amongst students and scientists of the basic issues that must be tackled and resolved before we can hope to escape from the whirlpool of stagnation into which we have fallen: cartilage repair redivivus!

DESIGN

Articular-cartilage lesions may be induced traumatically (e.g., by sports injuries and occupational accidents) or pathologically during the course of a degenerative disease (e.g., osteoarthritis). This review addresses the biological basis of cartilage repair and surveys current trends in treatment strategies, focussing on those that are most widely adopted by orthopaedic surgeons [viz., abrasive chondroplasty, microfracturing/microdrilling, osteochondral grafting and autologous-chondrocyte implantation (ACI)]. Also described are current research activities in the field of cartilage-tissue engineering, which, as a therapeutic principle, holds more promise for success than any other experimental approach.

RESULTS AND CONCLUSIONS

Tissue engineering aims to reconstitute a tissue both structurally and functionally. This process can be conducted entirely in vitro, initially in vitro and then in vivo (in situ), or entirely in vivo. Three key constituents usually form the building blocks of such an approach: a matrix scaffold, cells, and signalling molecules. Of the proposed approaches, none have yet advanced beyond the phase of experimental development to the level of clinical induction. The hurdles that need to be surmounted for ultimate success are discussed.

Viability of chondrocytes seeded onto a collagen I/III membrane for matrix-induced autologous chondrocyte implantation

Cell viability is crucial for effective cell-based cartilage repair. The aim of this study was to determine the effect of handling the membrane during matrix-induced autologous chondrocyte implantation surgery on the viability of implanted chondrocytes. Images were acquired under five conditions: (i) Pre-operative; (ii) Handled during surgery; (iii) Cut edge; (iv) Thumb pressure applied; (v) Heavily grasped with forceps. Live and dead cell stains were used. Images were obtained for cell counting and morphology. Mean cell density was 6.60 × 10(5) cells/cm(2) (5.74-7.11 × 10(5) ) in specimens that did not have significant trauma decreasing significantly in specimens that had been grasped with forceps (p < 0.001) or cut (p = 0.004). Cell viability on delivery grade membrane was 75.1%(72.4-77.8%). This dropped to 67.4%(64.1-69.7%) after handling (p = 0.002), 56.3%(51.5-61.6%) after being thumbed (p < 0.001) and 28.8%(24.7-31.2%) after crushing with forceps (p < 0.001). When cut with scissors there was a band of cell death approximately 275 µm in width where cell viability decreased to 13.7%(10.2-18.2%, p < 0.001). Higher magnification revealed cells without the typical rounded appearance of chondrocytes. We found that confocal laser-scanning microscope (CLSM) can be used to quantify and image the fine morphology of cells on a matrix-induced autologous chondrocyte implantation (MACI) membrane. Careful handling of the membrane is essential to minimise chondrocyte death during surgery.

In vivo evaluation of biomechanical properties in the patellofemoral joint after matrix-associated autologous chondrocyte transplantation by means of quantitative T2 MRI

PURPOSE

To determine in vivo biomechanical properties of articular cartilage and cartilage repair tissue of the patella, using biochemical MRI by means of quantitative T2 mapping.

METHODS

Twenty MR scans were achieved at 3T MRI, using a new 8-channel multi-function coil allowing controlled bending of the knee. Multi-echo spin-echo T2 mapping was prepared in healthy volunteers and in age- and sex-matched patients after matrix-associated autologous chondrocyte transplantation (MACT) of the patella. MRI was performed at 0° and 45° of flexion of the knee after 0 min and after 1 h. A semi-automatic region-of-interest analysis was performed for the whole patella cartilage. To allow stratification with regard to the anatomical (collagen) structure, further subregional analysis was carried out (deep-middle-superficial cartilage layer). Statistical analysis of variance was performed.

RESULTS

During 0° flexion (decompression), full-thickness T2 values showed no significant difference between volunteers (43 ms) and patients (41 ms). Stratification was more pronounced for healthy cartilage compared to cartilage repair tissue. During 45° flexion (compression), full-thickness T2 values within volunteers were significantly increased (54 ms) compared to patients (44 ms) (p < 0.001). Again, stratification was more pronounced in volunteers compared to patients. The volunteer group showed no significant increase in T2 values measured in straight position and in bended position. There was no significant difference between the 0- and the 60-min MRI examination. T2 values in the patient group increased between the 0- and the 60-min examination. However, the increase was only significant in the superior cartilage layer of the straight position (p = 0.021).

CONCLUSION

During compression (at 45° flexion), healthy patellar cartilage showed a significant increase in T2-values, indicating adaptations of water content and collagen fibril orientation to mechanical load. This could not be observed within the patella cartilage after cartilage repair (MACT) of the patella, most obvious due to a lack of biomechanical adjustment.

LEVEL OF EVIDENCE

III.

High-resolution measurements of the multilayer ultra-structure of articular cartilage and their translational potential

Current musculoskeletal imaging techniques usually target the macro-morphology of articular cartilage or use histological analysis. These techniques are able to reveal advanced osteoarthritic changes in articular cartilage but fail to give detailed information to distinguish early osteoarthritis from healthy cartilage, and this necessitates high-resolution imaging techniques measuring cells and the extracellular matrix within the multilayer structure of articular cartilage. This review provides a comprehensive exploration of the cellular components and extracellular matrix of articular cartilage as well as high-resolution imaging techniques, including magnetic resonance image, electron microscopy, confocal laser scanning microscopy, second harmonic generation microscopy, and laser scanning confocal arthroscopy, in the measurement of multilayer ultra-structures of articular cartilage. This review also provides an overview for micro-structural analysis of the main components of normal or osteoarthritic cartilage and discusses the potential and challenges associated with developing non-invasive high-resolution imaging techniques for both research and clinical diagnosis of early to late osteoarthritis.

Utilizing tissue-engineered cartilage or BMNC-PLGA composites to fill empty spaces during autologous osteochondral mosaicplasty in porcine knees

The potential empty spaces between cylindrical plugs remaining after autologous osteochondral mosaicplasty rely on fibrous repair, which may constrain the quality and integrity of the repair. Thus, the empty spaces should be repaired, and how to fill the empty spaces is still a problem. In the present study, a standardized full-thickness defect (diameter, 6 mm) was created in the weight-bearing area of each medial femoral condyle in both knees of 18 miniature pigs. The 36 knees were randomly assigned to four groups with nine in each group. The defects were initially repaired by autologous osteochondral mosaicplasty. Simultaneously, any empty spaces between the multiple plugs were filled with cell-free poly(lactide-co-glycolide) (PLGA) scaffolds (the scaffold group), tissue-engineered cartilage (the TE group) or bone marrow mononuclear cell (BMNC)-PLGA composites (the composite group). The empty spaces were left untreated as control (the control group). Six months after surgery, the repair results were assessed via macroscopic observation, histological evaluation, magnetic resonance imaging, biomechanical assessment and glycosaminoglycan content. The results demonstrated that mosaicplasty combined with the treatment of the empty spaces could improve cartilage regeneration. The filling of empty spaces by tissue-engineered cartilage produced the best result in all the four groups. Meanwhile, utilizing BMNC-PLGA composites achieved a similar repair result. Considering the cost-effective, time-saving and convenient performance, the BMNC-PLGA composite could be an alternative option to fill the empty spaces combined with mosaicplasty. Copyright © 2014 John Wiley & Sons, Ltd.

[Defect models for the regeneration of articular cartilage in large animals]

BACKGROUND

Several animal models are available for the analysis of regeneration of articular cartilage in large animals, such as sheep, pigs, goats, dogs and horses. The subchondral bone lamella must be considered when ACT and MACT techniques are examined in order to protect the implant against migration of cells from the bone marrow, although recruitment of cells is often desirable in the regeneration of human cartilage.

MATERIAL AND METHODS

The defects are mainly positioned at the condyles and the trochlea often bilaterally and spontaneous healing should be excluded. The follow-up period for assessment of the effectiveness of cartilage regeneration is 6-12 months. Shorter observation times up to 12 weeks can be used for pilot studies. Scores based on histological, immunohistological and biochemical staining are mostly used for assessing the regenerated tissue. Biomechanical tests with destructive features need isolated specimens from the animal but modern slice imaging techniques can reflect the progression of the healing processes over the time span of the study in vivo.

CONCLUSION

Approaches to standardize the evaluation of the regeneration of articular cartilage have been sporadically described whereas they are required from the point of view of the approval of new concepts for therapy and the protection of animals.

Improved repair of chondral and osteochondral defects in the ovine trochlea compared with the medial condyle

Associations between topographic location and articular cartilage repair in preclinical animal models are unknown. Based on clinical investigations, we hypothesized that lesions in the ovine femoral condyle repair better than in the trochlea. Full-thickness chondral and osteochondral defects were simultaneously established in the weightbearing area of the medial femoral condyle and the lateral trochlear facet in sheep, with chondral defects subjected to subchondral drilling. After 6 months in vivo, cartilage repair and osteoarthritis development was evaluated by macroscopic, histological, immunohistochemical, and biochemical analyses. Macroscopic and histological articular cartilage repair and type-II collagen immunoreactivity were better in the femoral trochlea, regardless of the defect type. Location-independently, osteochondral defects induced more osteoarthritic degeneration of the adjacent cartilage than drilled chondral lesions. DNA and proteoglycan contents of chondral defects were higher in the condyle, reflecting physiological topographical differences. The results indicate that topographic location dictates the structural patterns and biochemical composition of the repair tissue in sheep. These findings suggest that repair of cartilage defects at different anatomical sites of the ovine stifle joint needs to be assessed independently and that the sheep trochlea exhibits cartilage repair patterns reflective of the human medial femoral condyle.

Bone marrow stimulation of the medial femoral condyle produces inferior cartilage and bone repair compared to the trochlea in a rabbit surgical model

The influence of the location of cartilage lesions on cartilage repair outcome is incompletely understood. This study compared cartilage and bone repair in medial femoral condylar (MFC) versus femoral trochlear (TR) defects 3 months after bone marrow stimulation in mature rabbits. Intact femurs from adult rabbits served as controls. Results from quantitative histomorphometry and histological scoring showed that bone marrow stimulation produced inferior soft tissue repair in MFC versus TR defects, as indicated by significantly lower % Fill (p = 0.03), a significant increase in collagen type I immunostaining (p < 0.00001) and lower O'Driscoll scores (p < 0.05). 3D micro-CT analysis showed that repaired TR defects regained normal un-operated values of bone volume fraction, trabecular thickness, and trabecular number, whereas in MFC defects the repaired bone architecture appeared immature and less dense compared to intact un-operated MFC controls (p < 0.0001). Severe medial meniscal damage was found in 28% of operated animals and was strongly correlated with (i) low cartilage defect fill, (ii) incomplete bone repair in MFC, and (iii) with a more posterior defect placement in the weight-bearing region. We conclude that the location of cartilage lesions influences cartilage repair, with better outcome in TR versus MFC defects in rabbits. Meniscal degeneration is associated with cartilage damage.

Operative treatment of osteochondral lesions of the talus

➤ Osteochondral lesions of the talus are common injuries in recreational and professional athletes, with up to 50% of acute ankle sprains and fractures developing some form of chondral injury. Surgical treatment paradigms aim to restore the articular surface with a repair tissue similar to native cartilage and to provide long-term symptomatic relief.➤ Arthroscopic bone-marrow stimulation techniques, such as microfracture and drilling, perforate the subchondral plate with multiple openings to recruit mesenchymal stem cells from the underlying bone marrow to stimulate the differentiation of fibrocartilaginous repair tissue in the defect site. The ability of fibrocartilage to withstand mechanical loading and protect the subchondral bone over time is a concern.➤ Autologous osteochondral transplantation techniques replace the defect with a tubular unit of viable hyaline cartilage and bone from a donor site in the ipsilateral knee. In rare cases, a graft can also be harvested from the ipsilateral talus or contralateral knee. The limitations of donor site morbidity and the potential need for an osteotomy about the ankle should be considered. Some anterior or far posterior talar lesions can be accessed without arthrotomy or with a plafondplasty.➤ Osteochondral allograft transplantation allows an osteochondral lesion with a large surface area to be replaced with a single unit of viable articular cartilage and subchondral bone from a donor that is matched to size, shape, and surface curvature. The best available evidence suggests that this procedure should be limited to large-volume cystic lesions or salvage procedures.➤ Autologous chondrocyte implantation techniques require a two-stage procedure, the first for chondrocyte harvest and the second for implantation in a periosteum-covered or matrix-induced form after in vivo culture expansion. Theoretically, the transplantation of chondrocyte-like cells into the defect will result in hyaline-like repair tissue.

A low morbidity surgical approach to the sheep femoral trochlea

BACKGROUND

The ovine stifle joint is an important location for investigations on the repair of articular cartilage defects in preclinical large animals. The classical medial parapatellar approach to the femoral trochlea is hazardous because of the high risk of postoperative patellar luxation. Here, we describe a low morbidity surgical exposure of the ovine trochlea without the necessity for intraoperative patellar luxation.

METHODS

Bilateral surgical exposure of the femoral trochlea of the sheep stifle joint was performed using the classical medial parapatellar approach with intraoperative lateral patellar luxation and transection of the medial patellar retinaculum in 28 ovine stifle joints. A low morbidity approach was performed bilaterally in 116 joints through a mini-arthrotomy without the need to transect the medial patellar retinaculum or the oblique medial vastus muscle nor surgical patellar luxation. Postoperatively, all 72 animals were monitored to exclude patellar luxations and deep wound infections.

RESULTS

The novel approach could be performed easily in all joints and safely exposed the distal two-thirds of the medial and lateral trochlear facet. No postoperative patellar luxations were observed compared to a postoperative patellar luxation rate of 25% experienced with the classical medial parapatellar approach and a re-luxation rate of 80% following revision surgery. No signs of lameness, wound infections, or empyema were observed for both approaches.

CONCLUSIONS

The mini-arthrotomy presented here yields good exposure of the distal ovine femoral trochlea with a lower postoperative morbidity than the classical medial parapatellar approach. It is therefore suitable to create articular cartilage defects on the femoral trochlea without the risk of postoperative patellar luxation.

Experimental scoring systems for macroscopic articular cartilage repair correlate with the MOCART score assessed by a high-field MRI at 9.4 T--comparative evaluation of five macroscopic scoring systems in a large animal cartilage defect model

OBJECTIVE

To develop a new macroscopic scoring system which allows for an overall judgment of experimental articular cartilage repair and compare it with four existing scoring systems and high-field magnetic resonance imaging (MRI).

METHODS

A new macroscopic scoring system was developed to assess the repair of cartilage defects. Cartilage repair was graded by three observers with different experience in cartilage research at 2-3 time points and compared with the protocol A of the international cartilage repair society (ICRS) cartilage repair assessment score, the Oswestry arthroscopy score, and macroscopic grading systems designed by Jung and O'Driscoll. Parameters were correlated with the two-dimensional (2D) magnetic resonance observation of cartilage repair tissue (MOCART) score based on a 9.4 T MRI as an external reference standard.

RESULTS

All macroscopic scores exhibited high intra- and interobserver reliability and high internal correlation. The newly developed macroscopic scoring system had the highest intraobserver [0.866 ≤ intraclass correlation (ICC) ≤ 0.895] and the highest interobserver reliability (ICC = 0.905) for "total points". Here, Cronbach's alpha indicated good homogeneity and functioning of the items (mean = 0.782). "Total points" of the 2D MOCART score correlated with all macroscopic scores (all P < 0.0001). The newly developed macroscopic scoring system yielded the highest correlation for the MRI parameter "defect fill" (rho = 0.765; all P < 0.0001).

CONCLUSIONS

"Total points" and "defect fill", two clinically relevant indicators of cartilage repair, can be reliably and directly assessed by macroscopic evaluation, using either system. These data support the use of macroscopic assessment to precisely judge cartilage repair in preclinical large animal models.

High mesenchymal stem cell seeding densities in hyaluronic acid hydrogels produce engineered cartilage with native tissue properties

Engineered cartilage based on adult mesenchymal stem cells (MSCs) is an alluring goal for the repair of articular defects. However, efforts to date have failed to generate constructs with sufficient mechanical properties to function in the demanding environment of the joint. Our findings with a novel photocrosslinked hyaluronic acid (HA) hydrogel suggest that stiff gels (high HA concentration, 5% w/v) foster chondrogenic differentiation and matrix production, but limit overall functional maturation due to the inability of the formed matrix to diffuse away from the point of production and form a contiguous network. In the current study, we hypothesized that increasing the MSC seeding density would decrease the required diffusional distance, and so expedite the development of functional properties. To test this hypothesis bovine MSCs were encapsulated at seeding densities of either 20,000,000 or 60,000,000 cells ml(-1) in 1%, 3%, and 5% (w/v) HA hydrogels. Counter to our hypothesis the higher concentration HA gels (3% and 5%) did not develop more rapidly with increased MSC seeding density. However, the biomechanical properties of the low concentration (1%) HA constructs increased markedly (nearly 3-fold with a 3-fold increase in seeding density). To ensure that optimal nutrient access was delivered, we next cultured these constructs under dynamic culture conditions (with orbital shaking) for 9 weeks. Under these conditions 1% HA seeded at 60,000,000 MSCs ml(-1) reached a compressive modulus in excess of 1 MPa (compared with 0.3-0.4 MPa for free swelling constructs). This is the highest level we have reported to date in this HA hydrogel system, and represents a significant advance towards functional stem cell-based tissue engineered cartilage.

Implantation of orthobiologic, biodegradable scaffolds in osteochondral repair

The treatment of articular cartilage lesions is complicated, but novel tissue engineering approaches seem to improve the outcome. A tissue engineering approach is less invasive and reduces surgical time, periosteal hypertrophy, and morbidity. Cell-based therapies using scaffolds have advantages compared with microfracture techniques, but the efficacy and cost-effectiveness need to be investigated. Second-generation cell-based therapies have lower morbidity and the ease of the technique is not significantly different from that of first-generation autologous chondrocyte implantation techniques. Third-generation cell-based therapies such as the use of tissue engineered scaffolds need to be studied in more detail.

A review of the treatment methods for cartilage defects

The purpose of this article is to provide a broad review of the literature related to the treatment of cartilage defects and degenerated cartilage in animals with some inferences to the treatment in humans. Methods range from the insertion of osteochondral tissue or cells to the application of radio frequency or insertion of scaffolds and growth factors alone or in combination. Debridement, microfracture, radio frequency, and chondrocyte implantation are all methods normally utilized when treating smaller articular cartilage defects. Scaffolds and mosaicplasty are examples of methods to treat larger defects. This review will cover all major treatment methods currently used to treat articular cartilage defects.

Preclinical Studies for Cartilage Repair: Recommendations from the International Cartilage Repair Society

Investigational devices for articular cartilage repair or replacement are considered to be significant risk devices by regulatory bodies. Therefore animal models are needed to provide proof of efficacy and safety prior to clinical testing. The financial commitment and regulatory steps needed to bring a new technology to clinical use can be major obstacles, so the implementation of highly predictive animal models is a pressing issue. Until recently, a reductionist approach using acute chondral defects in immature laboratory species, particularly the rabbit, was considered adequate; however, if successful and timely translation from animal models to regulatory approval and clinical use is the goal, a step-wise development using laboratory animals for screening and early development work followed by larger species such as the goat, sheep and horse for late development and pivotal studies is recommended. Such animals must have fully organized and mature cartilage. Both acute and chronic chondral defects can be used but the later are more like the lesions found in patients and may be more predictive. Quantitative and qualitative outcome measures such as macroscopic appearance, histology, biochemistry, functional imaging, and biomechanical testing of cartilage, provide reliable data to support investment decisions and subsequent applications to regulatory bodies for clinical trials. No one model or species can be considered ideal for pivotal studies, but the larger animal species are recommended for pivotal studies. Larger species such as the horse, goat and pig also allow arthroscopic delivery, and press-fit or sutured implant fixation in thick cartilage as well as second look arthroscopies and biopsy procedures.

Membrane bioreactors enhance microenvironmental conditioning and tissue development

In membrane bioreactors the cells are isolated from the bulk medium through a semipermeable membrane. This concept, which is analogous to how the circulatory system supplies solid tissues with nutrients, allows the maintenance of cells at much higher densities than is possible in traditional cultures. The membrane-based microbioreactor described herein is easy to operate, requiring only a pipette to load and harvest cells. A 10 microL culture volume was isolated from 1 mL of bulk medium through a semipermeable membrane having a molecular weight cutoff of 10 kDa. Here we describe the benefits regarding the retention of both cells and their secretions within this small culture volume using the following two model systems: hematopoietic stem cell expansion and mesenchymal stem cell-derived cartilage matrix accumulation.

Cell carriers as the next generation of cell therapy for cartilage repair: a review of the matrix-induced autologous chondrocyte implantation procedure

BACKGROUND

Since the first patient was implanted with autologous cultured chondrocytes more than 20 years ago, new variations of cell therapies for cartilage repair have appeared. Autologous chondrocyte implantation, a first-generation cell therapy, uses suspended autologous cultured chondrocytes in combination with a periosteal patch. Collagen-covered autologous cultured chondrocyte implantation, a second-generation cell therapy, uses suspended cultured chondrocytes with a collagen type I/III membrane. Today's demand for transarthroscopic procedures has resulted in the development of third-generation cell therapies that deliver autologous cultured chondrocytes using cell carriers or cell-seeded scaffolds.

PURPOSE

To review the current evidence of the matrix-induced autologous chondrocyte implantation procedure, the most widely used carrier system to date. Also discussed are the characteristics of type I/III collagen membranes, behavior of cells associated with the membrane, surgical technique, rehabilitation, clinical outcomes, and quality of repair tissue.

STUDY DESIGN

Systematic review.

METHODS

Relevant publications were identified by searching Medline from its inception (1949) to December 2007; peer-reviewed publications of preclinical and clinical cell behavior, manufacturing process, surgical technique, and rehabilitation protocols were identified. Preclinical and clinical studies were included if they contained primary data and used a type I/III collagen membrane.

RESULTS

Data from these studies demonstrate that patients treated with matrix-induced autologous chondrocyte implantation have an overall improvement in clinical outcomes. Reduced visual analog scale pain levels (range, 1.7-5.32 points) and improvements in the modified Cincinnati (range, 3.8-34.2 points), Lysholm-Gillquist (range, 23.09-47.6 points), Tegner-Lysholm (range, 1.39-3.9 points), and International Knee Documentation Classification scale (P <.05) were observed. Patients had good-quality (hyaline-like) repair tissue as assessed by arthroscopic evaluation (including International Cartilage Repair Society score), magnetic resonance imaging, and histology, as well as a low incidence of postoperative complications.

CONCLUSION

The findings suggest that matrix-induced autologous chondrocyte implantation is a promising third-generation cell therapy for the repair of symptomatic, full-thickness articular cartilage defects.

Management of articular cartilage defects of the knee

Articular cartilage has a poor intrinsic capacity for healing. The goal of surgical techniques to repair articular cartilage injuries is to achieve the regeneration of organized hyaline cartilage. Microfracture and other bone marrow stimulation techniques involve penetration of the subchondral plate in order to recruit mesenchymal stem cells into the chondral defect. The formation of a stable clot that fills the lesion is of paramount importance to achieve a successful outcome. Mosaicplasty is a viable option with which to address osteochondral lesions of the knee and offers the advantage of transplanting hyaline cartilage. However, limited graft availability and donor site morbidity are concerns. Transplantation of an osteochondral allograft consisting of intact, viable articular cartilage and its underlying subchondral bone offers the ability to address large osteochondral defects of the knee, including those involving an entire compartment. The primary theoretical advantage of autologous chondrocyte implantation is the development of hyaline-like cartilage rather than fibrocartilage in the defect, which presumably leads to better long-term outcomes and longevity of the healing tissue. Use of synthetic scaffolds is a potentially attractive alternative to traditional cartilage procedures as they are readily available and, unlike allogeneic tissue transplants, are associated with no risk of disease transmission. Their efficacy, however, has not been proven clinically.

The elusive path to cartilage regeneration

Numerous attempts have been made to develop an efficacious strategy for the repair of articular cartilage. These endeavours have been undaunted, if not spurred, by the challenge of the task and by the largely disappointing outcomes in animal models. Of the strategies that have been lately applied in a clinical setting, the autologous-chondrocyte-transplantation technique is the most notorious example. This methodology, which was prematurely launched on the clinical scene, was greeted with enthusiasm and has been widely adopted. However, a recent prospective and randomized clinical trial has revealed the approach to confer no advantage over conventional microfracturing. Why is the repair of articular cartilage such a seemingly intractable problem? The root of the evil undoubtedly lies in the tissue's poor intrinsic healing capacity. But the failure of investigators to tackle the biological stumbling blocks systematically rather than empirically is hardly a less inauspicious circumstance. Moreover, it is a common misbelief that the formation of hyaline cartilage per se suffices, whereas to be durable and functionally competent, the tissue must be fully mature. An appreciation of this necessity, coupled with a thorough understanding of the postnatal development of articular cartilage, would help to steer investigators clear of biological cul-de-sacs.

Clinical application of scaffolds for cartilage tissue engineering

The purpose of this paper is to review the basic science and clinical literature on scaffolds clinically available for the treatment of articular cartilage injuries. The use of tissue-engineered grafts based on scaffolds seems to be as effective as conventional ACI clinically. However, there is limited evidence that scaffold techniques result in homogeneous distribution of cells. Similarly, few studies exist on the maintenance of the chondrocyte phenotype in scaffolds. Both of which would be potential advantages over the first generation ACI. The mean clinical score in all of the clinical literature on scaffold techniques significantly improved compared with preoperative values. More than 80% of patients had an excellent or good outcome. None of the short- or mid-term clinical and histological results of these tissue-engineering techniques with scaffolds were reported to be better than conventional ACI. However, some studies suggest that these methods may reduce surgical time, morbidity, and risks of periosteal hypertrophy and post-operative adhesions. Based on the available literature, we were not able to rank the scaffolds available for clinical use. Firm recommendations on which cartilage repair procedure is to be preferred is currently not known on the basis of these studies. Randomized clinical trials and longer follow-up periods are needed for more widespread information regarding the clinical effectiveness of scaffold-based, tissue-engineered cartilage repair.