Articular Cartilage Tissue-engineering Based On MSCs And Biodegradable Porous Bioceramics

Tissue engineering is an interdisciplinary field that applies the principles of engineering and life sciences to develop biological substitutes that restore, maintain, or improve tissue function. With the development of biomaterial science and tissue-engineering techniques, various tissue-engineered cartilage has been made in animal models in recent years. A tissue-engineered cartilage product has been approved clinical application by FDA. Significant progresses have been made in China in articular cartelage issue-engineering with great hope in development of tissue-engineered articular cartelage product.Articular cartilage is of great importance but limited self-repair capacity.For decades, scientists have been engaged in finding out a proper way to repair cartilage injuries. However, the advance is very slow. Autologous rib cartilage is widely used due to the remaining transplant viability and only minor resorption phenomena. Unfortunately, there is rarely enough material. In addition, the risks of a second operation have to be considered. Furthermore, calcification mainly of rib cartilage would have a negative influence on mechanical characteristics.Allogeneic transplants must be conserved to prevent autolysis. At the same time, antigenic characteristics and the chance of transmitting infection are eliminated or at least reduced. However, no definite consensus exists regarding whether transmission of infective chemicals. Xenogeneic transplants needto be treated for conservation as well, which results in frequent resorption, moreover, the risk of infectiousness cannot be excluded completely. The poor healing potential of cartilage tissue has been ascribed in part to a paucity of chondrogenic cells available for repair. Tissue-engineering technique brings hope for the functional and biological replacement of articular cartilage injuries.In recent years, cartilage tissue-engineering goes far from smoothly due to thedeficiency of ideal seed cell and proper scaffold bio-materials. For seed cells,autologous and allogenic chondrocytes are not ideal for above reasons. Human bone marrow-derived mesenchymal stem cells (MSCs) are a population of pluripotent cells , which can be induced to differentiate into cells of osteogenic, chondrogenic, tendonogenic, adipogenic and myogenic lineages. Besides, MSCs can be expanded in vitro without loss of phenotypic characteristics. With these regards, MSCs are potential origin of seed cells for tissue engineering, especially cartilage tissue engineering. For cell scaffold, polymers, collagens and some other oganic biomaterials have been widely used in cartilage tissue-engineering. However, problems are obvious in bad bio-compatibility and mechanical intensity. Recently, a French team has just developed a macrostructure controllable porous β-tricalcium phosphate (β-TCP).This material has been proved an ideal cell scaffold for bone tissue-engineering due to its good bio-compatibility, mechanical intensity and adjustable in vivo degradation time. However, application of this material in cartilage tissue-engineering has not been reported.In this study, we investigate the possibility of generating tissue-engineered articular cartilage using β-TCP as scaffold and autologous MSCs as seed cells, and thus pave the way for the commercialization of tissue-engineered articular cartilage.The first part of this study is about the seed cells for cartilage tissue-engineering. Human MSCs were isolated from bone marrow aspirates by density gradient centrifugation. Then the cells were culture-expanded for phenotypic identification, biological activity analysis and in vitro chondrogenic differentiation. The results showed that density gradient centrifugation with Percoll at a density of 1.073g/ml can isolate MSCs with a purity of no less than 97%. The isolated cells demonstrated chondrogenic differentiation and biological characteristics of MSCs in histo-chemical examinations and growth curve analysis.In the second part, we studied the in vitro construction and in vivo application of tissue-engineered cartilage. Cell migration and proliferation were detected in β-TCP slices seeded with chondrocytes after incubation in vitro for 3 to 9 days, indicating the good biocompatibility of this material. On the basis of this, we constructed MSCs/β-TCP complexes and implanted the complexes to repair sheep articular cartilage defects.3 months post-operation, the defects were partially repaired and 6 months post-operation, the defects were completely replaced by new cartilage.To sum up, MSCs, which can generate articular cartilage in in vivo environment, can be used as seed cell for cartilage tissue-engineering. β-TCP is an ideal cell scaffold for articular cartilage tissue- engineering. Tissue-engineered articular based on MSCs and β-TCP is promising in clinical application and commercialization.