CHONDROCYTES IN CULTURE PRODUCE A MECHANICALLY FUNCTIONAL TISSUE

A mechanically testable tissue was grown in vitro from rabbit chondroc ytes that were initially plated at high density (approximately 80,000 cells/cm(2)). The DNA, collagen, and proteoglycan content, as well as the tissue thickness, tensile stiffness, and synthesis rates, were mea sured at 4, 6, and g weeks. The biochemical properties were similar to those for immature cartilage, with predominantly type-II collagen pro duced; this indicated that the cells retained their chondrocytic pheno type. The tissue formed a coherent mechanical layer with testable tens ile stiffness as early as 4 weeks. The tensile elastic modulus reached 1.3 MPa at 8 weeks, which is in the range of values for native cartil age from the midzone. Collagen density was approximately 24 mg/ml at 8 weeks, which is about one-half the value for native cartilage, and th e collagen fibril diameters were smaller. Chondrocytes in culture resp onded to culture conditions and were stimulated by cytokine interleuki n-1 beta. When culture conditions were varied to RPMI nutrient medium with lower fetal bovine serum and higher ascorbic acid concentrations, the thickness decreased and the modulus increased significantly. Inte rleukin-1 beta, added to the 8-week culture for 2 weeks, caused a decr ease of 60% in thickness, a decrease of 81% in proteoglycan content, a nd a decrease of 31% in collagen content; this is similar to the respo nse of cartilage explants to interleukin-1 beta. This cartilage analog may be useful as a model system to study structure-function relations hips in cartilage or as cartilage-replacement tissue.