A novel approach on the preparation of biphasic calcium phosphate bioceramics under physiological conditions. The effect of the starting material

Biphasic Calcium Phosphate (BCP) bioceramics were prepared in physiological pH. Salts of Calcium and Phosphate with initial molar ratio of Ca/P=1.67, similar to Hydroxyapatite (HA) stoichiometry, were precipitated by the addition of NH4HCO3 1 M. XRD results of the as prepared materials show that high crystalline CaHPO4·2H2O (DCPD) was produced, resulting a decrease of the initial Ca/P ratio. However ageing of the slurry under continuous stirring for 1 and 2 days time, lead to the gradual hydrolysis of dicalcium phosphate dihydrate (DCPD) to low crystalline HA producing biphasic HA/DCPD particles. Ageing time affects also the morphology of the materials. SEM images show that the initial lath-like DCPD particles with HA during the ageing were transformed firstly into bigger particles and flake like particles afterwards. The above mentioned are in accordance to the results of TG/DTA analysis. The morphology and the phase composition of the yielding materials depend on the initial concentration of HCO3− and ageing time. Hydrolysis of NH4HCO3, affects the precipitation of both Ca2+ and PO43− on the starting material, under physiological pH and thus has to be manipulated properly in order to achieve the desirable results in a possible hard tissue evaluation of in vitro bioactivity.