Purpose: Tissue engineering offers new therapeutic perspectives with the possibility of producing cartilage tissue for a large number of patients. These structures are composed of an absorbable synthetic support and competent cells. Two types of cells can be proposed: articular chondrocytes harvested from the peripheral part of the joint, or mesenchymatous stem cells (MSC) present in the bone marrow and possessing chondrogenic potential. The purpose of this study was to determine the optimal cell source and the best supporting material for in vitro production of cartilage.

Material and methods: Isolated rabbit MSC were harvested and amplified with cell culture for 21 days. After this period, 20–40 million cells/ml were combined with polyglycolic acid sponges (3 types of sponges 1x1x0.2 cm2) and cultured in TGFß-enriched medium under specific dynamic conditions allowing gas exchange. The tissue obtained was compared with structures of identical size obtained with differentiated chondrocytes harvested from the same animals. The study included a histological analysis and immunohistochemistry for type I, II, and X collagen and biochemistry for DNA content, glycosaminoglycanes (GAG) and type II collagen.

Results: After 3 weeks in culture, the composites obtained with MSC preserved their size and had the white pearly aspect of hyalin cartilage. The histological analysis and immunohistochemistry tests for type II collagen confirmed the presence of a cartilaginous matrix throughout the thickness of the fragments. The GAG and type II collagen contents were significantly higher with MSC compared with chondrocytes, irrespective of the supporting material.

Discussion: This study demonstrated that cartilaginous tissue fragments can be obtained with MSC cultured on PGA supporting material under very specific conditions. Use of these cells offers the advantage of easy harvesting followed by in vitro amplification, and thus less harvesting morbidity. Complementary studies are needed to evaluate the behaviour of these living materials after implantation in the articulation.

Limited success in regenerating large bone defects has been achieved by bridging them with osteoconductive materials. These substitutes lack the osteogenic and osteoinductive properties of bone autograft. A direct approach would be to stimulate osteogenesis in these biomaterials by the addition of fresh bone-marrow cells (BMC).

We therefore created osteoperiosteal gaps 2 cm wide in the ulna of adult rabbits and either bridged them with coral alone (CC), coral supplemented with BMC, or left them empty. Coral was chosen as a scaffold because of its good biocompatibility and resorbability. In osteoperiosteal gaps bridged with coral only, the coral was invaded chiefly by fibrous tissue. It was insufficient to produce union after two months. In defects filled with coral and BMC an increase in osteogenesis was observed and the bone surface area was significantly higher compared with defects filled with coral alone. Bony union occurred in six out of six defects filled with coral and BMC after two months. An increase in the resorption of coral was also observed, suggesting that resorbing cells or their progenitors were present in bone marrow and survived the grafting procedure. Our findings have shown that supplementation of coral with BMC increased both the resorption of material and osteogenesis in defects of a clinical significance.