Chondrocyte interactions with porous titanium alloy and calcium polyphosphate substrates

Chondrocytes maintain their phenotype and form cartilagenous tissue when cultured on calcium polyphosphate (CPP) or titanium alloy (Ti alloy), porous three-dimensional materials. To understand how these materials may influence chondrocyte phenotype and matrix synthesis, the early interactions of cultured cells with CPP and titanium alloy were examined. These were compared to chondrocytes grown in monolayer culture on tissue culture polystyrene, conditions in which cultured chondrocytes dedifferentiate and do not form cartilagenous tissue. Scanning electron microscopy of cells up to 72 h in culture showed that bovine chondrocytes on CPP, Ti alloy, and polystyrene were an admixture of round and spread cells. The spread cells on CPP and titanium alloy were not entirely flattened but maintained a polygonal shape. In contrast, spread chondrocytes in monolayer culture were flatter and significantly larger, a difference that was maintained even in the absence of serum. All cells cultured on CPP and Ti alloy exhibited subcortical ring-like distribution of actin filaments whereas the flattened cells on polystyrene showed actin filaments distributed throughout the cytoplasm. Cells on CPP and Ti alloy synthesized significantly less collagen and proteoglycans than cells cultured on polystyrene at 72 h of culture. In summary the cells on the porous three-dimensional materials differed from those on polystyrene in terms of cell morphology and size, actin cytoskeleton organization, and synthesis of selected matrix macromolecules. The data suggests that CPP and titanium alloy may mediate their effect by limiting cell spreading in part by favoring the maintenance of a ring-like actin distribution.