Synthesis of biomimetic Ca-hydroxyapatite powders at 37°C in synthetic body fluids

An important inorganic phase for synthetic bone applications, calcium hydroxyapatite (HA, Ca10(PO4)6(OH)2), was prepared as a nano-sized ( 50 nm), homogeneous and high-purity ceramic powder from calcium nitrate tetrahydrate and diammonium hydrogen phosphate salts dissolved in modified synthetic body fluid (SBF) solutions at 37°C and pH of 7.4 using a novel chemical precipitation technique. The synthesized precursors were found to easily reach a phase purity >99% after 6 h of calcination in air atmosphere at 900°C, following oven drying at 80°C. There was observed, surprisingly, no decomposition of HA into the undesired β-TCP phase even after heating at 1600°C in air for 6 h. This observation showed the superior high-temperature stability of such ‘biomimetic’ HA powders as compared to those reported in previous studies. The former powders were also found to contain trace amounts of Na and Mg ions, originating from the use of SBF solutions instead of pure water during their synthesis. Characterization and chemical analaysis of the synthesized powders were performed by X-ray powder diffraction, energy-dispersive X-ray spectroscopy, Fourier-transform infra-red spectroscopy, scanning electron microscopy, and inductively coupled plasma atomic emission spectroscopy.