Cytotoxicity of stoichiometric hydroxyapatites with different crystallite sizes

Hydroxyapatite (HAp) samples were synthesized by a solution reaction method followed by heat-treatments at three different temperatures. Special attention was given to optimizing the processing parameters to obtain the chemical composition near to the stoichiometry of HAp. No trace of secondary crystalline phase was found from powder X-ray diffraction in all samples. X-ray fluorescence measurements found that the Ca/P ratio was 1.68 ± 0.02, which is close to the stoichiometry of HAp, i.e., 1.67. Electron microscope observations revealed that the grain size was uniform within a sample, which was dependent on the heat treatment temperature. Dissolution rates in acid solution and cytotoxicity of the samples were measured. Tendency to decrease both the dissolution rates and the cytotoxicity with increasing crystallite size was observed. After heat-treatment at 1000 °C, the cytotoxicity of the sample was found to be minimal, which had uniaxial and faceted grains with a mean diameter of 200 nm.