Joint cartilage regeneration by tissue engineering.

The research field of tissue engineering combines cells biology, biomaterial science, and surgery. Major long-term goals are tissue and organ replacement therapies using the patients' own cells. Our work is focused on the treatment of severe joint defects and on plastic surgery using in vitro engineered cartilage tissues. The practical approaches in cartilage engineering face problems with three-dimensional cell distribution or cell immobilization raising biocompatibility problems. The tissue engineering of cartilage is based on combining biocompatible cell embedding substances such as fibrin, agarose, alginate, hyaluronic acid and fiber fleece scaffolds of poly alpha-hydroxy acids (PLLA/PGLA). Different technical approaches were established: a) three-dimensional in vitro cultures of chondrocytes for the development of vital tissue transplants and b) interacting three-dimensional cultures consisting of different cell populations, such as BMP-transfected mesenchymal cells. The preshaped artificial tissue constructs were cultured in perfusion chambers to maintain a stable diffusion of nutrients during the in vitro pre-formation step. Subsequently, pre-formed tissues were implanted into nude mice and into 4 mm articular joint defects of rabbits. Transplants were found to produce cartilage typic morphological patterns and matrix. 80% of the transplants remained stable in vivo. However, 20% of the tissues are resorbed or replaced by a fibrous tissue. These results demonstrate that current artificial cartilage transplants are already feasible for plastic reconstruction. The treatment of severe joint defects, however, faces additional problems which are addressed in ongoing studies: (a) the fixation of engineered cartilage in joints, (b) the protection against chronic inflammatory degradation, and (c) the required enormous mechanical stability.