Novel synthesis and characterization of an AB‐type carbonate‐substituted hydroxyapatite

Abstract

A novel synthesis route has been developed to produce a high‐purity mixed AB‐type carbonate‐substituted hydroxyapatite (CHA) with a carbonate content that is comparable to the type and level observed in bone mineral. This method involves the aqueous precipitation in the presence of carbonate ions in solution of a calcium phosphate apatite with a Ca/P molar ratio greater than the stoichiometric value of 1.67 for hydroxyapatite (HA). The resulting calcium‐rich carbonate–apatite is sintered/heat‐treated in a carbon dioxide atmosphere to produce a single‐phase, crystalline carbonate‐substituted hydroxyapatite. In contrast to previous methods for producing B‐ or AB‐type carbonate‐substituted hydroxyapatites, no sodium or ammonium ions, which would be present in the reaction mixture from the sodium or ammonium carbonates commonly used as a source of carbonate ions, were present in the final product. The chemical and phase compositions of the carbonate‐substituted hydroxyapatite was characterized by X‐ray fluorescence and X‐ray diffraction, respectively, and the level and nature of the carbonate substitution were studied using C‐H‐N analysis and Fourier transform infrared spectroscopy, respectively. The carbonate substitution improves the densification of hydroxyapatite and reduces the sintering temperature required to achieve near‐full density by approximately 200°C compared to stoichiometric HA. Initial studies have shown that these carbonate‐substituted hydroxyapatites have improved mechanical and biologic properties compared to stoichiometric hydroxyapatite. © 2001 Wiley Periodicals, Inc. J Biomed Mater Res 59: 697–708, 2002