Culture surfaces coated with various implant materials affect chondrocyte growth and metabolism

Abstract

The effect on chondrocyte metabolism of culture surfaces sputter‐coated with various materials used for orthopaedic implants was studied and correlated with the stage of cartilage cell maturation. Confluent, fourth‐passage chondrocyts from the costochondral resting zone and growth zone of rats were cultured for 6 or 9 days on 24‐well plates sputter‐coated with ultrathin films of titanium, titanium dioxide, aluminum oxide, zirconium oxide, and calcium phosphate (1.67:1). Corona‐discharged tissue culture plastic served as the control. The effect of surface material was examined with regard to cell morphology; cell proliferation (cell number) and DNA synthesis ([³H]thymidine incorporation); RNA synthesis ([³H]uridine incorporation); collagenase‐digestible protein, noncollagenase‐digestible protein, and percentage of collagen production; and alkaline phosphatase‐specific activity, both in the cell layer and in trypsinized chondrocytes. Cell morphology was dependent on surface material; only cells cultured on titanium had an appearance similar to that of cells cultured on plastic. While titanium or titanium dioxide surfaces had no effect on cell number or [³H]thymidine incorporation, aluminum oxide, calcium phosphate, and zirconium oxide surfaces inhibited both parameters. Cells cultured on aluminum oxide, calcium phosphate, zirconium oxide, and titanium dioxide exhibited decreased collagenase‐digestible protein, noncollagenase‐digestible protein, and percentage of collagen production, but [³H]uridine incorporation was decreased only in those chondrocytes cultured on aluminum oxide, calcium phosphate, or zirconium oxide. Chondrocytes cultured on titanium had greater alkaline phosphatase‐specific activity than did cells cultured on plastic, but the incorporation of [³H]uridine and production of collagenase‐digestible protein, noncollagenase‐digestible protein, and percentage of collagen was comparable. The response of chrondrocytes from the growth zone and resting zone to culture surface was comparable, differing primarily in magnitude. Cell maturation‐dependent effects were evident when enzyme activity in trypsinized and scraped cells was compared. These results indicate that different surface materials affect chondrocyte metabolism and phenotypic expression in vitro and suggest that implant materials may modulate the phenotypic expression of cells in vivo.