Preparation and bioactivity evaluation of bone-like hydroxyapatite nanopowder

Calcium phosphate ceramic such as hydroxyapatite (HA) is good candidate for bone substitutes due to their chemical and structural similarity to bone minerals. The bone mineral consists of tiny hydroxyapatite crystals in the nanoregime. Nanostructured hydroxyapatite is also expected to have better bioactivity than coarser crystals. This paper reports on the preparation and in vitro evaluation of bone-like hydroxyapatite nanopowder. The sol-gel prepared hydroxyapatite nanopowder was characterized for its phase purity, chemical homogeneity and bioactivity. Fourier transform infrared (FTIR) spectroscopy was used to identify the functional groups. X-ray diffraction (XRD) analysis was carried out to study the phase composition, crystallinity and the crystallite size of hydroxyapatite nanopowders that were sintered at different temperatures. The in vitro test was performed in a Stimulated body fluid (SBF) medium. The changes of the pH of SBF medium were measured at pre-determined time intervals using a pH meter. The dissolution of calcium ions in SBF medium was determined by an atomic absorption spectrometer (AAS). FTIR result combined with the X-ray diffraction exhibited single phase of hydroxyapatite with carbonate peaks in the FTIR spectrum. The results indicate that increasing the sintering temperature increases the crystallinity and the crystallite size of hydroxyapatite nanopowders. Photomicrograph of transmission electron microscopy (TEM) showed that the obtained powder after sintering at 600 degrees C is composed of hydroxyapatite nanoparticles (20-30 nm). Dissolution rate of hydroxyapatite nanopowders was higher than conventional hydroxyapatite powders and closer to biological apatite due to its nanostructure dimensions. It was concluded that sol-gel prepared hydroxyapatite nanopowders had superior bioresorption and similar chemical and crystal structure to natural bone apatite. (C) 2007 Elsevier B.V. All rights reserved.