Mature full-thickness articular cartilage explants attached to bone are physiologically stable over long-term culture in serum-free media.

Mature tissue explants containing the entire depth of articular cartilage, calcified and uncalcified, attached to a thin layer of subchondral bone were isolated from bovine humeral heads of 1-2-year-old steers. These explants were placed in defined serum-free culture medium for a period of 3 weeks to investigate their biological and mechanical stability and thus to determine their potential utility in studies of cartilage physiology. Tissue mass remained constant over the culture period and no evident tissue swelling or distortion was observed. Chondrocytes were viable in all zones at the time of tissue isolation and throughout the culture period, with the exception of a thin layer of cells at the articular surface and the cut radial edge of the disks. Proteoglycan metabolism attained a steady state after 5 days of culture when the rate of loss of proteoglycan to culture media was compensated by new synthesis to maintain a stable proteoglycan content. Collagen metabolism was also stable with a constant content of type II collagen and a constant content of denatured collagen II throughout culture; the content of the C-propeptide of type II procollagen as a measure of procollagen synthesis, dropped slightly during the first week to attain a steady state after that time. Dynamic and equilibrium mechanical properties of these explant disks were also stable confirming maintenance of these tissue properties during long-term culture. In addition, the disk geometry of the system, with the cut surface in the bone parallel to the intact articular surface, is well-suited to study tissue regulation by mechanical load. Taken together, the stability of these indicators of tissue physiology indicates the maintenance in serum-free conditions of normal metabolism for organ cultures containing full-depth mature articular cartilage attached to bone.