Effect of Sulfonic Group and Calcium Content on Apatite-Forming Ability of Polyamide Films in a Solution Mimicking Body Fluid

Apatite-polymer hybrids have attractive features as novel bone substitutes since they may show bone-bonding ability and mechanical performances analogous to those of natural bone. We previously reported that polyamide films containing sulfonic group (-SO₃H) and calcium chloride can effectively deposit apatite on their surfaces in a solution (1.5SBF) mimicking body fluid. 1.5SBF has 1.5 times ion concentrations of a simulated body fluid (SBF). In the present study, the apatite-forming ability of polyamide films with different amounts of sulfonic groups and CaCl₂ was investigated in 1.5SBF. It was found that the polyamide films showed the ability of apatite formation, which was increased with increasing amounts of not only calcium chloride but also sulfonic group. Adhesion of apatite layer to the organic polymer may be enhanced by increasing the amounts of sulfonic group in the polymer. These results indicate that increasing sulfonic groups could accelerate the rate of heterogeneous nucleation of apatite on its surface. The interaction between sulfonic group and apatite crystals constitute a tight attachment.