Engineering a joint: a chimeric construct with bovine chondrocytes in a devitalized chick knee

This study assessed the feasibility of a devitalized knee as a scaffold for an engineered chimeric joint. Embryonic chick knees (19 days old), devitalized by lyophilization or multiple freeze-thaw cycles, were tested as scaffolds for repopulation with bovine articular chondrocytes (bACs). bACs were seeded into porous three-dimensional collagen sponges and were cultured for 1 day before fabrication of chimeric constructs. A pair of cell-seeded sponges was inserted into the joint space to contact preshaved articular surfaces. In some constructs, a sterile membrane of expanded polytetrafluoroethylene (ePTFE) was inserted between the collagen sponges. Histologic analysis showed that at 1 week, sponges with bACs were adherent to the shaved articular surfaces of the joint with accumulation of metachromatic extracellular matrix. Penetration of bACs and neomatrix into the devitalized matrix appeared to begin in preexistent epiphyseal canals and was observed to some extent in all specimens. Membranes of ePTFE maintained a joint space at 2 and 3 weeks, whereas there was fusion across the two sponges in many specimens lacking the membrane. Gene expression analysis demonstrated that lyophilization, but not multiple freeze-thaw cycles, completely devitalized the chick knees. These studies identified several design parameters crucial for successful engineering of a chimeric joint.