Preparation of strontium substituted hydroxyapatite nanoparticles by supercritical fluid drying

Strontium substituted hydroxyapatite (SrCaHAP) nanoparticles were prepared by sol-gel-supercritical fluid drying (SCFD) method. The samples were characterized by the element content analysis, TEM, XRD and FT-IR. And the effects of Sr2+ on crystal structure, particle shape and crystallinity were discussed. Results showed that HAP, SrCaHAP and SrHAP nanoparticles with the molar ratios of Sr/[Sr + Ca], 0, 0.5, 1, respectively, could be made by sot-gel-SCFD. Sr2+ could substitute for Ca2+ and enter the structure of HAP in the predetermined molar ratios of Sr/[Sr + Ca]. The IR wavenumbers of the Sr2+ substituted powders decreased. The morphology of the particle changed from the short rod shaped HAP to the needle shaped SrCaHAP with calcium partially substituted by strontium, at the same time the crystallinity of the sample decreased. After the Ca2+ was totally substituted by Sr2+, the SrHAP particle changed back to the shape of short rod, and the crystallinity increased.