Effect of static compression on proteoglycan biosynthesis by chondrocytes transplanted to articular cartilage in vitro

Transplantation of chondrocytes by injection or within carrier matrices has shown promise for augmenting the repair of articular cartilage defects. In vivo, transplanted chondrocytes are exposed to mechanical forces. This in vitro study examined the effect of a step application of compressive load to chondrocytes after the cells had been seeded onto a cartilage surface. Bovine chondrocytes were transplanted onto bovine cartilage disks, allowed to attach for 1 hour or 4 days, and subjected to compression through overlying cartilage disks in a confined compression configuration. Before use, the disks were lyophilized to lyse the endogenous chondrocytes and thereby allow assessment of the metabolic activity of the transplanted cells. During a 16-hour application of compressive stress of 0.24-0.72 MPa, proteoglycan synthesis, assessed as [S-35]sulfate incorporation into macromolecules, was inhibited by approximately 68% after the 1-hour attachment and by approximately 45% after the 4-day attachment. Cell retention after the application of load was assessed by use of [H-3]thymidine-tagged chondrocytes and quantitation of the displacement of radioactivity. After the 1-hour seeding period, loading induced a dose-dependent dislodgment of [H-3]radioactivity (as much as 35%) from the tissue bilayer. In contrast, after the 1-day seeding period, there was no detectable effect of loading on chondrocyte dislodgment with an 8-12% release of radioactivity. The inhibitory effect of a 16-hour compression of 0.48 MPa applied after the 4-day seeding period was studied further. This protocol did not appear to have an irreversible effect on chondrocyte metabolism; at 2 days after the release of load, proteoglycan synthesis by the loaded cells was stimulated by 41% compared with transplanted cells that were not subjected to loading. These results suggest that the application of static compressive stress to chondrocytes at a cartilage surface may affect biosynthesis by these cells and thus subsequent integrative cartilage repair. Such an effect may have implications for optimization of the tightness of the press fit of a cell-laden cartilaginous construct into an articular defect.