Dissolution properties of calcium phosphate granules with different compositions in simulated body fluid

Calcium phosphate granules were produced through the calcination of three hydroxyapatites (HAs) at 1150 degrees C: nearly-stoichiometric (NS-HA), calcium-deficient (CD-HA), and carbonated (Carb-HA). The characterization using scanning electron microscope (SEM), X-ray diffraction (XRD), and Fourier-transformed infrared spectroscopy (FT-IR) showed that those granules exhibit strong differences in chemical composition, surface texture, and dissolution behavior. Sample dissolution in a simulated body fluid (SBF) and precipitation of a calcium phosphate layer on the granule surface were followed up for 7 days by chemical analysis of calcium content in SBF. After 80-min reaction, precipitation of new calcium phosphate phases predominates over the dissolution of original granules. Comparison between SEM images and XRD/FT-IR analysis revealed that the composition of the calcium phosphate layer and its precipitation rate depend on the HA composition and its heat treatment. Calcined carbonated apatite induces the precipitation of an octacalcium phosphate (OPC) layer, whereas a carbonated apatite layer is formed from calcined-deficient HA. The calcined nearly-stoichiometric HA exhibits low efficiency in producing carbonated apatite layer.