Precipitation of biocompatible hydroxyapatite whiskers from moderately acid solution

Hydroxyapatite (HA) whiskers with uniform morphology and good crystallinity were successfully prepared by a precipitation-hydrolysis method in moderately acid solutions at 85-95 °C for 48-120 h. A proper precipitation agent was selected to control the growth of HA crystal in a desired way. The lengths of HA whiskers were in the range of 50-150 μm and aspect ratios (length/diameter) in the range of 40-100. The precipitates formed at each stage of the synthesis were characterized by XRD, FTIR, TG-DSC and SEM techniques. It is revealed that the morphology and crystallinity of the precipitates depended on the synthesis temperature and time as well as the concentrations of soluble calcium and phosphate ions. The HA whiskers obtained were morphologically stable at elevated temperatures below 1200 °C. They were formed by the hydrolysis of precursors produced during the reactions and took over the morphology of fibrous octacalcium phosphate [Ca₈H₂(PO₄)₆·5H₂O, OCP]. The stoichiometric HA whiskers were improved with the increase of the synthetic temperature and the duration.