Characterization of macroporous carbonate-substituted hydroxyapatite bodies prepared in different phosphate solutions

Abstract

Bone mineral of human is different in composition from the stoichiometric hydroxyapatite (Ca10(PO4)6(OH)2) in that it contains additional ions, of which CO 3 2− is the most abundant species. Carbonate-substituted hydroxyapatite (CHA) bodies were prepared by the hydrothermal treatment of highly porous calcium carbonate (CaCO3) body at 120 °C in 1 M M2HPO4 and M3PO4 solutions (M = NH4 or K). It was found that CaCO3 body was almost transformed into CHA body after hydrothermal treatment for 24 h irrespective of type of phosphate solution. However, a small amount of CaCO3 still remained after the treatment in K3PO4 for 48 h. Crystal shape of CHA bodies prepared in those solutions except for K2HPO4 was flake-like, which was different from that (stick-like) of original CaCO3 body used for the preparation of CHA body. CHA prepared in the K2HPO4 showed globule-like crystal. Average pore size and hole size of the CHA bodies were 150, 70 μm and their porosities were about 89% irrespective of the solution. Carbonate content was slightly higher in the CHA bodies obtained from potassium phosphate solutions than in those obtained from ammonium phosphate solutions. Mostly B-type CHA was obtained after the hydrothermal treatment in the potassium phosphate solutions. On the other hand, mixed A- and B-type CHA (ca. 1–2 in molar ratio) was obtained in the ammonium phosphate solutions. The content of CO 3 2− in the CHA body depended on the type of phosphate solution and was slightly larger in the potassium phosphate solutions.