The aim of our group and collaborators is to use tissue engineering methods to develop biomaterial scaffolds for the repair of large articular cartilage defects in the knee joint. Our approach is to use novel non-woven PLDLA felt in combination with human recombinant Collagen II gel as a novel scaffold for autologous chondrocytes. Collagen II is a component of articular cartilage, and applied as a three dimensional gel it presents an interesting scaffold material and a natural environment for chondrocytes and for the development of tissue engineered cartilage. Incorporated PLDLA felt gives additional strength needed in the repair of larger cartilage defects. As hyaline cartilage is difficult to reproduce by tissue engineering methods, our aim is to learn more on chondrocyte behavior and cellular functions during cartilage production in our scaffolds in vitro, in order to discover methods to increase the amount of hyaline cartilage in the forming repair cartilage. We are now studying the effects of cell density, cell state and different growth factor supplements on cell proliferation, differentiation and extra cellular matrix production in the scaffold. However, our in vitro conditions lack many of the natural articular cartilage functions such as mechanical load, oxygen tension and nutrients. Therefore, to study the cartilage forming capacity and the quality of the repair cartilage in the PLDLA and hrCollagen II scaffolds in vivo, experiments with pigs are ongoing.