Behavior of hydroxyapatite crystals in a simulated body fluid: effects of crystal face

Abstract

Control of calcification behaviors in osteoconductive ceramics is important for development of novel materials. Calcification behaviors of osteoconductive materials in bony defects can be assessed using a simulated body fluid (SBF). Previous studies of hydroxyapatite (HAp) ceramics have not found a clear relationship between calcification behaviors and morphology, in particular the crystal face, of HAp. In this study we have investigated calcification behaviors of rod-shaped HAp crystals with controlled crystal face in a SBF. The aspect ratios of the rod-shaped HAp was taken to be the area ratio of (the a face)/(the c face) in HAp crystals. HAp with aspect ratios ranging between approximately 10 and 17 was synthesized under hydrothermal conditions. Scale-like precipitates, which should be nonstoichiometric HAp referred to as bone-like apatite, were formed on the HAp crystals soaked in the SBF. The formation rate of bone-like apatite was estimated by measuring decreases in calcium and phosphate ion concentrations of the SBF. The formation rate increased with increasing aspect ratios of the HAp crystals. The results show that bone-like apatite was preferentially formed on the a face of the HAp crystals and that the calcification behaviors of HAp crystals in a SBF can be controlled using the aspect ratio of the HAp crystal, that is, by controlling the crystal face of HAp.