Surface composition of calcium hydroxyapatite modified with metal ions

Colloidal calcium hydroxyapatite (CaHAP) particles were modified with Ni2+, Cu2+, Co2+ and Cr3+ ions by ion-exchange and coprecipitation. The CaHAPs doped with these ions were characterized by various methods including FTIR, XPS, TEM and ICP. The atomic ratio, metal/(Ca + metal), of the surface phase (X-s) of the particles modified with Ni2+ and Cu2+ by coprecipitation was much less than the atomic ratio of the whole particle (X-w), while X-s of the particles modified with Cr3+ approximated to their X-w. In the modification by ion-exchange, X-s was larger than X-w except for the Ni2+-substituted samples where X-s was identical to X-w. The surface P-OH groups were decreased by cation-exchange of the protons of the P-OH groups with Ni2+, Cu2+ and Co2+ in both the modification methods. On the other hand, Cr3+ ions were doped in the surface phase by anion-exchange of the surface phosphate ions with hydrated chromium hydroxide anions. (C) 1998 Elsevier Science B.V. All rights reserved.