| Articular cartilage functions as a highly wear-resistant and low-friction weight bearing cushion in the diarthrodial joint (1, 2). When damaged, cartilage has very poor self-healing capacity and often degenerates further, leading to pain and loss of function. This dissertation focuses on optimization of two repair strategies for articular cartilage, which are cartilage allograft transplantation and tissue engineering of articular cartilage grafts, respectively. Cartilage allograft transplantation is currently used clinically to repair cartilage defects as the diarthrodial joint is considered immunoprivileged. However, allograft transplantation is limited by the insufficient supply of suitable donor tissue to meet clinical demand. To increase the clinical impact of allogeneic cartilage tissue, allogeneic chondrocytes can be isolated, expanded and serve as a cell source for tissue engineered articular cartilage grafts in quantities much greater than the donor tissue from which the cells were obtained. Tissue engineering of cartilage is an area of intensive research and it holds the promise of being a more efficient and effective form of treatment for osteoarthritis in the near future. The research presented in this dissertation aims to answer the following critical problems associated with these two treatment strategies: (1) Can tissue culture strategies be developed that can extend the shelf life of native cartilage grafts thereby increasing their availability for clinical use? (2) Can material properties of engineered tissue be increased by remedying the spatial inhomogeneity in tissue properties that develop during in vitro culture due to nutrient diffusion limitations? (3) Can collagen content of tissue-engineered cartilage be increased with controlled enzymatic digestion of the developing glycosaminoglycan (GAG) tissue matrix? (4) Can mechanical loading, shown previously by our laboratory to foster development of functional engineered cartilage in tissue constructs seeded with immature chondrocytes, lead to more functional tissue properties in engineered cartilage fabricated using more clinically-relevant mature chondrocytes?;The results presented in this dissertation indicate that chondral and osteochondral explants can be maintained in tissue culture (serum-free chondrogenic medium at 37°C) without decrease in Young's modulus and dynamic modulus, GAG content and cell concentration from initial "fresh" levels for up to 6 weeks. Findings also demonstrate that more homogeneous tissue engineered cartilage constructs with improved mechanical properties can be achieved by reducing their thickness or through incorporation of macroscopic nutrient channels. It was also found that the collagen content of tissue engineered cartilage constructs can be improved by enzymatically suppressing the GAG content temporarily through either continuous or transient application of chondroitinase ABC. Lastly, applied dynamic deformational loading (unconfined compression, 10% peak-to-peak strain, 1 Hz, 3 hours/daily) was shown to significantly enhance the functional properties of mature chondrocyte-seeded tissue-engineered cartilage in vitro. Overall, we anticipate that these findings will help to increase the clinical impact of native and engineered cartilage grafts in cartilage repair. |
