Repair Of Articular Cartilage Defects With Tissue-engineered Osteochondral Composites

Background: Tissue engineering has become a promising strategy for cartilage regeneration, which has preliminary clinical success. There are some problems need to be solved in applying tissue engineering cartilage to repair cartilage defect, especially tissue engineered cartilage are difficult to fix onto the recipient site. The shearing force encountered during joint motion will lead to dehiscence of cartilage graft from the underlying bone. Additionally, interface between tissue engineering cartilage and host bone was poor. The clinical success of mosaicplasty brings the idea of engineering osteochondral composites for cartilage repair. Several groups have generated osteochondral composite in vitro. In vivo repair of animal articular cartilage defects with osteochondral composites have acquired well result. Those studies had some limitations; specifically, the experimental defect area was too small to mimic the clinical cartilage defect. We believe that small defects can"auto-repair"by chondrocytes migrating from the periphery. The defects in the studies described above were newly formed, and many defects were located in non-weightbearing regions, which is not in accordance with the clinical defects. In addition, it has not been reported if the outcome of repair of articular cartilage defects with osteochondral composites is better than that of tissue-engineered cartilage.Objective: To compare the results of repair of knee cartilage defects with tissue-engineered osteochondral composites and tissue-engineered cartilage in pigs.Methods: Experiment is divided into three parts. Part I: Chondrocytes were isolated from the distal non-weight bearing place of pig femoral condyle and expanded in vitro, immunocytochemistry staining was used to evaluate type II collagen expression. Osteoblasts were isolated from the cancellous bone in medial condyle of the femur, cytochemical staining was used to evaluate alkaline phosphatase expression. Part II: Autologous chondrocytes and osteoblasts were isolated and cultured in vitro. They were then seeded on scaffolds of PLGA (diameter, 8 mm; height, 2 mm) and TCP (diameter, 8 mm; height, 6 mm ) to generate tissue-engineered cartilage and tissue-engineered bone, respectively. The tissue-engineered osteochondral composite was formed by a chondrocyte-PLGA construct sutured to a osteoblast-TCP construct with an absorbable suture. The resulting composites were implanted under the dorsum of nude mice and remained there for up to 8 weeks. Cell-free biphasic scaffold served as control. Specimens were harvested at 8 weeks after implantation and subjected to histological examination, GAG content of the cartilage was also assessed. Part III: Cartilage defects were surgically created at the weightbearing surface of the bilateral femoral medial condyles of 12 mini-pigs(6 males and 6 females). Thus, after 4 weeks 24 defects in 12 pigs were randomly assigned to three treatment groups: tissue-engineered osteochondral composite group, tissue-engineered cartilage group, and blank control group. Six months after surgery, the regenerated cartilage was scored macroscopically and histologically. The compressive properties and GAG content of the cartilage were also assessed.Results: Part I: Chondrocytes were successfully isolated from the pig femoral condyle, type II collagen expression was detected by immunocytochemistry staining. Osteoblasts were also isolated and alkaline phosphatase expression was detected by cytochemical staining. Part II: Cartilaginous tissue and bone tissue were detected in the composites. Cartilage tissue integrated well to bone tissue in tissue-engineered osteochondral composites at 8 weeks after implantation. Part III: A lot of neocartilage formed in the defects of the tissue-engineered osteochondral composite group. The gross grading scale indicated that the mean scores of the tissue-engineered osteochondral composite group were significantly higher than those of the tissue-engineered cartilage group(P<0.05). Histological evaluation indicated that the defects were repaired by newly generated hyaline cartilage in the osteochondral composite group. The round cells in the neocartilage were distributed more evenly and appeared essentially as individual cells. According to the International Cartilage Repair Society (ICRS) Visual Histological Assessment Scale, the scores of the osteochondral composite group were significantly better than those of the tissue-engineered cartilage group and blank bilayered scaffold group(P<0.05). Assessment of compressive properties and GAG content showed better repair results in the osteochondral composite group than those of the tissue-engineered cartilage group(P<0.05).Conclusion: Using tissue-engineered osteochondral composites to repair cartilage defects was better than that of tissue-engineered cartilage.