Natural hydroxyapatite—its behaviour during heat treatment

Natural origin hydroxyapatite (HAp) was extracted from animal bones by their treatment with hot NaOH solution. The remaining organic material oxidized in air atmosphere at moderate temperatures. In the material of this kind carbonate groups and small amounts of magnesium were found, usually not present in the synthetic HAp. Ca/P ratio in pig cortical bones was higher than that in the stoichiometric (synthetic) material. Fraction of carbonate groups decreased with temperature and CaO appeared at higher temperatures, but structure of hydroxyapatite became preserved even at 1000 °C, the highest temperature applied in this investigation. At temperatures >700 °C crystallite growth became intensive, specific surface area of the powder decreased and compacts of such powder started to shrink. Biological test showed that CAL-72 (human osteosarcoma) cells growth depended on heat treatment temperature of the natural HAp substrate.