Mature articular cartilage maintains tissue-scale biomechanical and biochemical properties and composition-function relationships that allow joints to function as load-bearing, wear-resistant, low-friction material during use. The objectives of this thesis were to determine these properties and relationships for articular cartilage of the fetus and early post-natal bovine knee joint.

The biomechanical properties of articular cartilage improved during growth between fetal, calf, and adult stages. With articular cartilage development and growth from the fetal to adult stages the compressive modulus increased, permeability decreased, and tensile modulus and strength increased. Concurrent with changes in cartilage biomechanical properties were changes in biochemical composition, particularly the concentration of collagen and pyridinoline cross-link increased. Changes in tensile properties and collagen network components were more marked in the intermittently loaded cartilage of the patellofemoral groove than in the constantly-loaded cartilage of the femoral condyle. Growth-associated changes in cartilage compressive and tensile biomechanical function were associated primarily with changes in the collagen network components.

To examine the basis for these growth-associated changes, the effects of free-swelling culture of immature cartilage explants on the function, composition, and function-composition relationships were studied. During up to 6 weeks of culture, immature cartilage explants grew, increasing in both solid and fluid components. While the overall cell, GAG, collagen, and pyridinoline content increased, the concentration of GAG remained constant, and that of collagen and pyridinoline decreased. During the first three weeks of culture, the tensile modulus and strength of immature cartilage explants fell to similarly low levels, and remained at these levels during subsequent growth. Explant tensile properties exhibited relationships with composition similar to those determined above, further implicating collagen network components as critical for cartilage tensile properties.

Thus, the findings described here indicate that articular cartilage matures in mechanical function and composition during development and growth in vivo, and that changes in compressive and tensile properties during growth in vivo and in vitro appear determined primarily by changes in the collagen network. The results described here may be useful for further probing mechanical and chemical regulators of articular cartilage growth and degeneration, and for tissue engineering therapies that recapitulate normal growth.