Tissue-engineered growth of cartilage: the effect of varying the concentration of chondrocytes seeded onto synthetic polymer matrices.

Ninety-six synthetic bioresorbable cell-delivery devices (10 x 10 x 0.5 mm) were seeded, varying the concentrations of living chondrocytes (2, 10, 20, 100 million cells/cc) isolated from shoulders of freshly killed calves and implanted subcutaneously on the dorsum of nude mice after 1 week of in vitro culture. This resulted in the formation of new cartilage in 95.6% of the implants. Twenty-four control implants (0 cells seeded) did not show cartilage formation. During 12 weeks of in vivo implantation, the wet weight and the thickness of the specimens (10, 20, 100 million cells/cc) increased significantly. Histologic analysis revealed cells appearing in their own lacunar structures surrounded by basophilic matrix. The increase in sulfated glycosaminoglycan content indicated the maturation of the extracellular matrix. The ability to manipulate the growth of new cartilage on biocompatible polymer scaffolds by varying the cell density before in vivo implantation will allow engineering to optimize the utilization of chondrocytes in relation to the desired shape, thickness, and quality of the new cartilage.