Effect of material geometry on cartilagenous tissue formation in vitro

The effect of material geometry, as defined by average pore size, on chondrocyte phenotype and cartilagenous tissue formation in vitro was examined. Bovine articular chondrocytes were plated on porous titanium alloy (Ti6Al4V) discs of different average pore sizes (13, 43, and 68 microm) and grown in culture for 4 weeks. Chondrocyte phenotype was maintained as indicated by the synthesis of large proteoglycans (Kav +/- SD: 13 microm = 0.28 +/- 0.01; 43 microm = 0.29 +/- 0.01; 68 microm = 0.27 +/- 0.02) and type II collagen. Light microscopical examination of histological sections of the composites showed that cartilagenous tissue had formed on all discs. The cartilagenous tissue on the discs of the smallest average pore size (13 microm) was significantly thicker than the tissue on the discs of larger average pore sizes and also had greater amounts of proteoglycan [mean glycosaminoglycan content +/- SD microg/disc): 13 microm = 246.9 +/- 7.8; 43 microm = 190.4 +/- 10.2; 68 microm = 156.6 +/- 25.8, p = 0.002] and DNA [mean DNA content +/- SD microg/disc): 13 microm = 12.5 +/- 0.6; 43 microm = 8.3 +/- 0.2; 68 microm = 9.3 +/- 0.9, p = 0.0008]. However, the amount of proteoglycan accumulated per cell was similar in the tissues generated on the discs of different average pore sizes. In contrast, the amount of collagen in the cartilagenous tissues showed no significant differences between the different pore sizes, but the amount of collagen accumulated per cell was less in the tissue formed on the smallest pore size disc (13 microm) as compared with the tissue formed on the discs of the larger pore sizes [mean hydroxyproline content/DNA (microg/microg) +/- SD: 13 microm = 1.56 +/- 0.2; 43 microm = 2.19 +/- 0.2; 68 microm = 2.3 +/- 0.3]. These results suggest that material geometry, as defined by pore size, can affect the amount and composition of the cartilagenous tissue that forms.