Cartilage Sheets Research Articles

Injectable Cartilage Microtissue Regenerated by Autologous Chondrocytes for Nasal Augmentation: A 5-Year Follow-Up Study.

A lack of ideal filling materials is a critical limitation in current rhinoplasty. Cartilage sheet regeneration by autologous chondrocytes is expected to provide an ideal source of material. However, the inability to perform minimally invasive transplantation of cartilage sheets has greatly limited the clinical application of this material. In this article, the authors propose the concept of injectable cartilage microtissue (ICM) based on cartilage sheet technology, with the aim of achieving minimally invasive augmentation rhinoplasty in clinical practice. Approximately 1.0 cm2 of posterior auricular cartilage was collected from 28 patients. Isolated chondrocytes were expanded, then used to construct autologous cartilage sheets by high-density seeding and in vitro culture in chondrogenic medium with cytokines (eg, transforming growth factor beta-1 and insulin-like growth factor-1) for 3 weeks. Next, ICM was prepared by granulation of the cartilage sheets; it was then injected into a subcutaneous pocket for rhinoplasty. ICM was successfully prepared in all patients, and its implantation efficiently raised the nasal dorsum. Magnetic resonance imaging confirmed that regenerative tissue was present at the injection site; histologic examinations demonstrated mature cartilage formation with typical cartilage lacunae and abundant cartilage-specific deposition of extracellular matrix. Excellent or good postoperative patient satisfaction results were achieved in 83.3% of patients over 5 years of follow-up. Obvious absorption of grafts occurred in only two patients (8.3%). These results demonstrated that ICM could facilitate stable cartilage regeneration and long-term maintenance in the human body; the implantation of ICM enabled natural augmentation of the depressed nasal dorsum. Therapeutic, IV.

Tracheal Reconstruction with the Scaffolded Cartilage Sheets in an Orthotopic Animal Model.

Tracheal reconstruction remains challenged in clinical. We aimed to fabricate scaffolded cartilage sheets with rigid and elastic supports for tracheal reconstruction. The chondrocyte cell infiltration activity was examined in poly-caprolactone sheet scaffolds with various thicknesses and pore sizes after seeding cells on the top surface of the sheet scaffolds. The expression of cartilage-related genes and accumulation of sulfated glycosaminoglycans were elevated in the cell-scaffold composites upon chondrogenic induction. The thicker cartilage sheets represented stronger mechanical properties than the thinner cartilage sheets. Two different cartilage sheets were orthotopically implanted into a trachea in a rabbit model for 2, 4, and 16 weeks. Cartilage-related sulfated glycosaminoglycans and type II collagen macromolecules were stably expressed in the tracheal implants. However, the invasive migration of fibrous tissue and profibrotic collagen fibers into cartilage implants and the peripheral space surrounding the implants were elevated in a time-dependent manner. At week 16 postimplantation, airway stenosis was noticed under the thicker sheet implants, but not the thinner implants, suggesting that the thinner (1 mm thick) scaffolded cartilage sheet was an optimal candidate for tracheal reconstruction in this study. Finally, cartilage sheets could be a reconstructive therapy candidate applied to reconstruct defects in the trachea and other tissues composed of cartilage. Impact statement Tissue engineering is a promising approach to generate biological substitutes. We aimed to develop cartilage sheets as tracheal prosthesis used in tracheal reconstruction or regional repairing in the animal model. The formation of microvessels and the dynamics of reepithelialization were monitored for 16 weeks in tracheal implants of the engineered cartilage sheets. In this study, it was demonstrated that the tissue-engineered cartilage sheets are potential substitutes applied in the reconstruction of the trachea and other tissues composed of cartilage tissue. The cartilage sheets were thought of as biomaterials for personalized regenerative medicine since the dimensions, thickness, and pore sizes of cartilage sheets were tunable to fit the lesions that need to be reconstructed.

Cartilage Regeneration Characteristics of Human and Goat Auricular Chondrocytes.

Although cartilage regeneration technology has achieved clinical breakthroughs, whether auricular chondrocytes (AUCs) represent optimal seed cells to achieve stable cartilage regeneration is not clear. In this study, we systematically explore biological behaviors of human- and goat-derived AUCs during in vitro expansion as well as cartilage regeneration in vitro and in vivo. To eliminate material interference, a cell sheet model was used to evaluate the feasibility of dedifferentiated AUCs to re-differentiate and regenerate cartilage in vitro and in vivo. We found that the dedifferentiated AUCs could re-differentiate and regenerate cartilage sheets under the chondrogenic medium system, and the generated chondrocyte sheets gradually matured with increased in vitro culture time (2, 4, and 8 weeks). After the implantation of cartilage sheets with different in vitro culture times in nude mice, optimal neocartilage was formed in the group with 2 weeks in vitro cultivation. After in vivo implantation, ossification only occurred in the group with goat-regenerated cartilage sheet of 8 weeks in vitro cultivation. These results, which were confirmed in human and goat AUCs, suggest that AUCs are ideal seed cells for the clinical translation of cartilage regeneration under the appropriate culture system and culture condition.

Dominant role of in situ native cartilage niche for determining the cartilage type regenerated by BMSCs

Tissue-engineered cartilage regeneration by bone marrow stromal cells (BMSCs) is considered an ideal method. However, how to regulate BMSCs to regenerate specific types of cartilage remains unclear, which significantly limits its clinical translation and leads to suboptimal clinical effects. Herein, we systematically explored the role of native ear and articular cartilage niches on the differentiation fate of BMSCs and the type of regenerated cartilage. First, we prepared two types of acellular cartilage sheets (ACSs) and two types of chondrocytes. Then green fluorescent protein-labeled BMSCs were seeded on two types of ACSs with or without corresponding types of chondrocytes using a sandwich model and directed or cross-implanted them into native cartilage niches. After one year of in vivo culture, cell tracking and the results of histological results showed that the native cartilage niches were capable of regulating BMSCs regeneration into specific types of cartilage that were consistent with the cartilage types of the implanted sites. Furthermore, even when the type of niche formed by ACSs or the biomimetic cartilage niche constructed by specific types of ACSs and specific types of chondrocytes did not match with the native cartilage niche, the native cartilage niche continued to determine the type of cartilage regenerated by implanted BMSCs and chondrocytes. All our results provide sufficient evidence for specific types of cartilage regeneration using chondrogenic potential cells, such as mesenchymal stem cells and chondrocytes.

Physioxia Stimulates Extracellular Matrix Deposition and Increases Mechanical Properties of Human Chondrocyte-Derived Tissue-Engineered Cartilage.

Cartilage tissue has been recalcitrant to tissue engineering approaches. In this study, human chondrocytes were formed into self-assembled cartilage sheets, cultured in physiologic (5%) and atmospheric (20%) oxygen conditions and underwent biochemical, histological and biomechanical analysis at 1- and 2-months. The results indicated that sheets formed at physiological oxygen tension were thicker, contained greater amounts of glycosaminoglycans (GAGs) and type II collagen, and had greater compressive and tensile properties than those cultured in atmospheric oxygen. In all cases, cartilage sheets stained throughout for extracellular matrix components. Type II-IX-XI collagen heteropolymer formed in the neo-cartilage and fibrils were stabilized by trivalent pyridinoline cross-links. Collagen cross-links were not significantly affected by oxygen tension but increased with time in culture. Physiological oxygen tension and longer culture periods both served to increase extracellular matrix components. The foremost correlation was found between compressive stiffness and the GAG to collagen ratio.

Repair of articular cartilage defects with acellular cartilage sheets in a swine model

Acellular cartilage sheets (ACSs) have been demonstrated as a good biomaterial for cartilage regeneration as a result of their natural cartilage matrix components, cartilage-specific structures, and good biocompatibility. However, it remains unknown whether allogeneic ACSs could promote cartilage regeneration and repair cartilage defects in a large animal model. The current study explored the feasibility of repairing articular cartilage defects using ACS scaffold with or without autologous bone marrow stromal cells (BMSCs) in a swine model. According to the current results, ACSs retained natural cartilage structure, primary cartilage matrices, and cartilage-specific growth factors. After cell seeding, ACSs presented good biocompatibility with BMSCs, which produced abundant extracellular matrix (ECM) proteins to cover the lacuna structures. In vivo results indicated that ACSs alone could induce endogenous host cells to regenerate cartilage and achieve generally satisfactory repair of cartilage defects at 6 months post-operation, including good interface integration and cartilage-specific ECM deposition. After combination with autologous BMSCs, BMSC-ACS constructs achieved more satisfactory repair of cartilage defects even without in vitro pre-induction of chondrogenesis. More importantly, all defects in both BMSC-ACS and ACS-only groups showed enhanced cartilage regeneration compared with BMSC–polyglycolic acid and blank groups, which mainly exhibited fibrogenesis in defect areas. Collectively, the current results indicate that ACSs can efficiently repair articular cartilage defects by promoting chondrogenic differentiation of BMSCs or inducing endogenous chondrogenesis in situ, thus serving as a good cartilage regeneration scaffold for recovery of articular function.

Tissue engineering of a composite trachea construct using autologous rabbit chondrocytes.

The repair of large tracheal segmental defects remains an unsolved problem. The goal of this study is to apply tissue engineering principles for the fabrication of large segmental trachea replacements. Engineered tracheal replacements composed of autologous cells (neotracheas) were tested in a New Zealand White rabbit model. Neotracheas were formed in the rabbit neck by wrapping a silicone tube with consecutive layers of skin epithelium, platysma muscle, and an engineered cartilage sheet and allowing the construct to mature for 8-12weeks. In total, 28 rabbits were implanted and the neotracheas assessed for tissue morphology. In 11 cases, neotracheas deemed sufficiently strong were used to repair segmental tracheal defects. Initially, the success rate of producing structurally sound neotracheas was impeded by physical disruption of the cartilage sheets during animal handling, but by the end of the study, 15 of 18 neotracheas (83.3%) were structurally sound. Of the 15 structurally sound neotracheas, 11 were used for segmental reconstruction and were left in place for up to 21days. Histological examination showed the presence of variable amounts of viable epithelium, a vascularized platysma flap, and a layer of safranin O-positive cartilage along with evidence of endochondral ossification. Rabbits that had undergone segmental reconstruction showed good tracheal integration, had a viable epithelium with vascular support, and the cartilage was sufficiently strong to maintain a lumen when palpated. The results demonstrated that viable, trilayered, scaffold-free neotracheas could be constructed from autologous cells and could be integrated into native trachea to repair a segmental defect.

Scaffolds Derived from ECM Produced by Chondrogenically Induced Human MSC Condensates Support Human MSC Chondrogenesis.

Osteoarthritis is a leading cause of disability affecting an increasing number of individuals. However, cartilage replacement therapies are inadequate, and better cartilage regeneration products must be developed. In this work, we describe a human mesenchymal stem cell (hMSC)-based approach for fabricating extracellular matrix (ECM) scaffolds from tissue-engineered cartilage sheets and then for inducing chondrogenesis of reseeded hMSCs within the ECM scaffolds. Two types of ECM scaffolds were fabricated: one from high-density hMSC sheets cultured with media-supplemented transforming growth factor beta-1 (TGF-β1; -MS) and the other from high-density hMSC sheets incorporated with TGF-β1-laden gelatin microspheres (+MS), which significantly enhance chondrogenesis within the sheet system. Interestingly, when scaffolds were reseeded with hMSCs, -MS scaffolds lead to significantly more glycosaminoglycan (GAG) accumulation than +MS scaffolds. Importantly, ECM scaffolds could be soak loaded with TGF-β1 to produce cartilage of similar quality as that of constructs cultured with TGF-β1 in the media, thereby removing the need for supplementing the media with the growth factor. Lastly, tissues formed with the scaffolds were larger with more uniform cartilage matrix elaboration compared to scaffold-free groups making this strategy a clinically promising auto- or allogeneic therapy.

Magnetic field application or mechanical stimulation via magnetic microparticles does not enhance chondrogenesis in mesenchymal stem cell sheets.

Using a novel magnetic field bioreactor, this work evaluated the chondrogenesis of scaffold-free human mesenchymal stem cell sheets in response to static and variable magnetic fields, as well as mechanical stimulation via 4.4 μm magnetic particles. Neither static nor variable magnetic fields generated by 1.44-1.45 T permanent magnets affected cartilage formation. Notably, magnetic field-induced mechanical stimulation by magnetic particles, which applied forces to the cells and ECM statically (4.39 pN) or cyclically (1.06-63.6 pN; 16.7 mHz), also did not affect cartilage formation.

Corneal Stroma Regeneration with Acellular Corneal Stroma Sheets and Keratocytes in a Rabbit Model.

Acellular corneal stroma matrix has been used for corneal stroma engineering. However, because of its compact tissue structure, regrowth of keratocytes into the scaffold is difficult. Previously, we developed a sandwich model for cartilage engineering using acellular cartilage sheets. In the present study, we tested this model for corneal stroma regeneration using acellular porcine corneal stroma (APCS) sheets and keratocytes. Porcine corneas were decellularized by NaCl treatment, and the APCS was cut into 20-μm-thick sheets. A rabbit corneal stroma defect model was created by lamellar keratoplasty and repaired by transplantation of five pieces of APCS sheets with keratocytes. Six months after transplantation, transparent corneas were present in the experimental group, which were confirmed by anterior segment optical coherence tomography examination and transmittance examination. The biomechanical properties in the experimental group were similar to those of normal cornea. Histological analyses showed an even distribution of keratocytes and well-oriented matrix in the stroma layer in the experimental group. Together, these results demonstrated that the sandwich model using acellular corneal stroma sheets and keratocytes could be potentially useful for corneal stroma regeneration.

Engineering ear-shaped cartilage using electrospun fibrous membranes of gelatin/polycaprolactone

Tissue engineering approach continuously requires for emerging strategies to improve the efficacy in repairing and regeneration of tissue defects. Previously, we developed a sandwich model strategy for cartilage engineering, using the combination of acellular cartilage sheets (ACSs) and chondrocytes. However, the process for the preparation of ACSs is complicated, and it is also difficult to obtain large ACSs. The aim of this study was to engineer cartilage with precise three-dimensional (3-D) structures by applying electrospun fibrous membranes of gelatin/polycaprolactone (GT/PCL). We first prepared the electrospun GT/PCL membranes into rounded shape, and then seeded chondrocytes in the sandwich model. After in vitro and in vivo cultivation, the newly formed cartilage-like tissues were harvested. Macroscopic observations and histological analysis confirmed that the engineering of cartilage using the electrospun GT/PCL membranes was feasible. An ear-shaped cartilage was then constructed in the sandwich model, with the help of an ear-shaped titanium alloy mold. After 2 weeks of culture in vitro and 6 weeks of subcutaneous incubation in vivo, the ear-shaped cartilage largely maintained their original shape, with a shape similarity up to 91.41% of the titanium mold. In addition, the engineered cartilage showed good elasticity and impressive mechanical strength. These results demonstrated that the engineering of 3-D cartilage in a sandwich model using electrospun fibrous membranes was a facile and effective approach, which has the potential to be applied for the engineering of other tissues with complicated 3-D structures.

Methods for Producing Scaffold-Free Engineered Cartilage Sheets from Auricular and Articular Chondrocyte Cell Sources and Attachment to Porous Tantalum

Scaffold-free cartilage engineering techniques may provide a simple alternative to traditional methods employing scaffolds. We previously reported auricular chondrocyte-derived constructs for use in an engineered trachea model; however, the construct generation methods were not reported in detail. In this study, methods for cartilage construct generation from auricular and articular cell sources are described in detail, and the resulting constructs are compared for use in a joint resurfacing model. Attachment of cartilage sheets to porous tantalum is also investigated as a potential vehicle for future attachment to subchondral bone. Large scaffold-free cartilage constructs were produced from culture-expanded chondrocytes from skeletally mature rabbits, and redifferentiated in a chemically-defined culture medium. Auricular constructs contained more glycosaminoglycan (39.6±12.7 vs. 9.7±1.9 μg/mg wet weight, mean and standard deviation) and collagen (2.7±0.45 vs. 1.1±0.2 μg/mg wet weight, mean and standard deviation) than articular constructs. Aggregate modulus was also higher for auricular constructs vs. articular constructs (0.23±0.07 vs. 0.12±0.03 MPa, mean and standard deviation). Attachment of constructs to porous tantalum was achieved by neocartilage ingrowth into tantalum pores. These results demonstrate that large scaffold-free neocartilage constructs can be produced from mature culture-expanded chondrocytes in a chemically-defined medium, and that these constructs can be attached to porous tantalum.

Chondrogenic differentiation of bone marrow-derived mesenchymal stem cells induced by acellular cartilage sheets

Acellular cartilage sheets (ACSs) have been used as scaffolds for engineering cartilage with mature chondrocytes. In this study we investigated whether ACSs possess a chondrogenic induction activity that may benefit cartilage engineering with multipotent stem cells. Bone marrow-derived mesenchymal stem cells (BMSCs) isolated from newborn pigs were expanded in vitro and seeded on ACSs that were then stacked layer-by-layer to form BMSC-ACS constructs. Cells seeded on polyglycolic acid/polylactic acid (PGA/PLA) scaffolds served as a control. After 4 weeks of culture with or without additional chondrogenic factors, constructs were subcutaneously implanted into nude mice for another 4 weeks. Cartilage-like tissues were formed after 4 weeks of culture. However, formation of cartilage with a typical lacunar structure was only observed in induced groups. RT-PCR showed that aggrecan, COMP, type II collagen and Sox9 were expressed in all groups except the non-induced BMSC-PGA/PLA group. At 4 weeks post-implantation, cartilage formation was achieved in the induced BMSC-ACS group and partial cartilage formation was achieved in the non-induced BMSC-ACS group, confirmed by safranin O staining, toluidine blue staining and type II collagen immunostaining. In addition, enzyme-linked immunosorbent assay demonstrated the presence of transforming growth factor-β1, insulin-like growth factor-1 and bone morphogenic protein-2 in ACSs. These results indicate that ACSs possess a chondrogenic induction activity that promotes BMSC differentiation.

A sandwich model for engineering cartilage with acellular cartilage sheets and chondrocytes

Acellular cartilage can provide a native extracellular matrix for cartilage engineering. However, it is difficult for cells to migrate into acellular cartilage because of its non-porous structure. The aim of this study is to establish a sandwich model for engineering cartilage with acellular cartilage sheets and chondrocytes. Cartilage from adult pig ear was cut into a circular cylinder with a diameter of approximately 6 mm and freeze-sectioned at thicknesses of 10 μm and 30 μm. The sheets were then decellularized and lyophilized. Chondrocytes isolated from newborn pig ear were expanded for 2 passages. The acellular sheets and chondrocytes were then stacked layer-by-layer, in a sandwich model, and cultured in dishes. After 4 weeks of cultivation, the constructs were then either maintained in culture for another 12 weeks or implanted subcutaneously in nude mouse. Histological analysis showed that cells were completely removed from cartilage sheets after decellularization. By re-seeding cells and stacking 20 layers of sheets together, a cylinder-shaped cell sheet was achieved. Cartilage-like tissues formed after 4 weeks of culture. Histological analyses showed the formation of cartilage with a typical lacunar structure. Cartilage formation was more efficient with 10 μm-thick sheets than with 30 μm sheets. Mature cartilage was achieved after 12 weeks of implantation, which was demonstrated by histology and confirmed by Safranin O, Toluidine blue and anti-type II collagen antibody staining. Furthermore, we achieved cartilage with a designed shape by pre-shaping the sheets prior to implantation. These results indicate that the sandwich model could be a useful model for engineering cartilage in vitro and in vivo.

Scaffold‐free tissue‐engineered cartilage implants for laryngotracheal reconstruction

Donor site morbidity, including pneumothorax, can be a considerable problem when harvesting cartilage grafts for laryngotracheal reconstruction (LTR). Tissue engineered cartilage may offer a solution to this problem. This study investigated the feasibility of using autologous chondrocytes to tissue-engineer scaffold-free cartilage grafts for LTR in rabbits to avoid degradation that often arises from an inflammatory reaction to scaffold carrier matrix. Animal study. Auricular cartilage was harvested from seven New Zealand white rabbits, the chondrocytes expanded and loaded onto a custom-made bioreactor for 7 to 8 weeks to fabricate autologous scaffold-free cartilage sheets. The sheets were cut to size and used for LTR, and the rabbits were sacrificed 4, 8, and 12 weeks after the LTR and prepared for histology. None of the seven rabbits showed signs of respiratory distress. A smooth, noninflammatory scar was visible intraluminally; the remainder of the tracheal lumen was unremarkable. Histologically, the grafts showed no signs of degradation or inflammatory reaction, were covered with mucosal epithelium, but did show signs of mechanical failure at the implantation site. These results show that autologous chondrocytes can be used to fabricate an implantable sheet of cartilage that retains a cartilage phenotype, becomes integrated, and does not produce a significant inflammatory reaction. These findings suggest that with the design of stronger implants, these implants can be successfully used as a graft for LTR.

Tissue‐engineered trachea for airway reconstruction

Scaffold-free cartilage has been used to engineer biocompatible and mechanically stable neotracheas in vivo. The purpose of this animal study was to determine if neotracheal constructs, implanted paratracheally, could successfully be used for segmental tracheal reconstruction. Animal study. Culture-expanded auricular rabbit chondrocytes were used to engineer scaffold-free cartilage sheets. Cartilage and a strap muscle flap were wrapped around a tube and implanted paratracheally. At 12 to 14 weeks postimplantation neotracheas were used to reconstruct 20 mm tracheal defects. Surgical technique was modified several times in an attempt to decrease the amount of neotracheal obstruction and fibrosis. In one of the six rabbits, neotrachea with its intact strap muscle flap was dropped into the defect followed by an end-to-end anastomosis; in two animals the muscle flap was partially, and in one rabbit completely removed. In two animals the muscle flap was partially removed, the tube reinserted, and the construct reimplanted for 5 weeks to allow formation of a fibrous lining over the exposed cartilage followed by tracheal reconstruction. All implants developed into vascularized and mechanically sound neotracheas. Following reconstruction, none of the animals showed immediate signs of respiratory distress; however, one died after 24 hours due to extensive endotracheal muscle flap edema, whereas rabbits who had undergone partial or complete muscle flap removal survived up to 39 days before developing cicatricial stenosis. Tissue-engineered neotracheas proved to have excellent biocompatibility and stability to function under physiologic conditions, but lacked adequate endotracheal lining resulting in neotracheal stenosis.

Fabrication of a Neotrachea Using Engineered Cartilage

Surgical management of long-segment tracheal stenosis is an ongoing problem. Many types of tracheal prostheses have been tried but with limited success because of immune rejection, graft ischemia, or restenosis. Tissue engineered cartilage may offer a solution to this problem, although scaffolds, which are currently often used for support, can lead to biocompatibility problems. This study investigated the feasibility of scaffold-free cartilage to tissue engineer a vascularized neotrachea in rabbits. Animal study. Autologous neotracheal constructs were implanted in the abdomen of six New Zealand white rabbits. Auricular chondrocytes were used to engineer scaffold-free cartilage sheets. A muscle flap raised from the external abdominal oblique muscle and the engineered cartilage were wrapped around a silicone stent to fabricate a vascularized neotrachea in vivo. In two of the six rabbits, a full thickness skin graft was used to create an epithelial lining. The constructs were harvested after either 6 or 10 weeks. All neotracheal constructs were healthy with well-vascularized and integrated layers. The implanted engineered cartilage underwent a remodeling process, forming a solid tracheal framework. Constructs harvested after 10 weeks proved to have significantly better mechanical properties than after 6 weeks and were comparable with the rabbit's native trachea. Scaffold-free engineered cartilage can successfully fabricate a well-vascularized, autologous neotrachea with excellent mechanical properties. The results suggest that this approach can be used to reconstruct tracheal defects in rabbits.

Automatic shape model building based on principal geodesic analysis bootstrapping

We present a novel method for automatic shape model building from a collection of training shapes. The result is a shape model consisting of the mean model and the major modes of variation with a dense correspondence map between individual shapes. The framework consists of iterations where a medial shape representation is deformed into the training shapes followed by computation of the shape mean and modes of shape variation. In the first iteration, a generic shape model is used as starting point - in the following iterations in the bootstrap method, the resulting mean and modes from the previous iteration are used. Thereby, we gradually capture the shape variation in the training collection better and better. Convergence of the method is explicitly enforced. The method is evaluated on collections of artificial training shapes where the expected shape mean and modes of variation are known by design. Furthermore, collections of real prostates and cartilage sheets are used in the evaluation. The evaluation shows that the method is able to capture the training shapes close to the attainable accuracy already in the first iteration. Furthermore, the correspondence properties measured by generality, specificity, and compactness are improved during the shape model building iterations.

Thinning of articular cartilage in the domestic fowl

Thinning of articular cartilage was identified in pelvic limb joints of broiler and Leghorn-type fowls. Almost all of 100 fowls examined showed cartilage thinning or loss in hip and knee joints. Particular attention was paid to proximal femora; in these, the principal mechanism of cartilage loss involved processes described as “peripheral remodelling”. From the edge of cartilage sheets, fibrovascular tissue removed articular cartilage by two mechanisms. Either a pannus of fibrovascular tissue covered the articular surface or non-osseous tissue invaded through discontinuities in the bone plate. As in man, peripheral remodelling appears to be age-related and unrelated to regressive or destructive cartilage loss.

Cartilage morphogenesis in vitro

The morphogenetic capacity of prechondrogenic mesenchyme from two developmentally distinct sources was investigated in high density micromass cultures. We confirmed an earlier report (Weiss & Moscona, 1958) that scleral mesenchyme formed cartilage sheets whilst limb bud mesenchyme formed distinct cartilage nodules. It was thus suggested by these authors that this morphogenesis was tissue type specific. However, by varying cell density at inoculation (which controls cell configuration) and by varying the relative amount of prechondrogenic mesenchyme present in cultures we found that dramatic changes in morphogenesis could be brought about. Viewed in these terms we suggest that cartilage morphogenesis in vitro is dependent on cell configuration and the presence of non-chondrogenic cell types and hence is not necessarily a function of an intrinsic morphogenetic potential of the constituent cells.