Chondrocytes Differentiation- Biological and Biomaterial Perspectives

Abstract: Articular cartilage is an avascular tissue and once injured it does not heal spontaneously. A successful tissue engineering approach for cartilage reconstruction is autolougus chondrocyte implantation (ACI). In ACI a biopsy is harvested from the knee joint and the chondrocytes are isolated, expanded in vitro and subsequently implanted into the defect to regenerate new hyaline tissue. During the ACI procedure the chondrocytes undergo a process of de- and re-differentiation. To improve cartilage cell therapy, knowledge of how we can control and modulate the chondrocytes behavior is essential. The general aim of this thesis was to give insight in how we can influence the differentiation of chondrocytes. To accomplish this we examined whether and to what extent the redifferentiation capacity of articular chondrocytes was affected by the cell source, in vitro cultivation, and the scaffolds used. We found that human chondrocytes behaviour in vitro was depending on the harvesting site in the knee joint. The chondrocytes from femur had a better attachment, proliferation and post-expansion redifferentiation capacity than chondrocytes from tibia. Focusing on the cell source we further found that some degree of dedifferentiation is needed to obtain high quality redifferentiation in vitro. To further study how we could affect the behavior of in vitro expanded chondrocytes the cells were cultured in scaffolds with defined architecture during the redifferentiation. The effect of scaffolds with varied pore size as well as fiber size was examined. The results revealed that the pore size of the scaffold influenced the redifferentiation capacity whereas the size of the fibers did not. The size of the fiber showed to affect the proliferation of the cells and thus different biological processes can be manipulated by the design of the scaffolds. Furthermore, we found that scaffold mediated chondrogenesis in vitro is a process mimicking the fetal cartilage development. Moreover, we found that that redifferentiation of in vitro expanded articular chondrocytes is needed at the time of implantation for neocartilage formation to take place in vivo. The result presented in this thesis thus show that the outcome of articular cartilage tissue engineering in cartilage reconstruction will depend on harvesting site, degree of differentiation of the chondrocytes as well as the scaffold architecture. This information adds additional knowledge into the field of cartilage tissue engineering to be used for further improvement of the treatment of cartilage repair.