Effect of Carbonate to Phosphate Molar Ratios on the Physico-Chemical Properties of Carbonated Hydroxyapatite Nanopowder

The aim of this study was to incorporate carbonate ions (CO3 2–) into the hydroxyapatite (HA) crystal structure followed by investigation on the effect of different carbonate to phosphate (CO3 2–/PO4 3–) ratios on the phase purity, crystal structure as well as CO3 2– content present in the apatite structure. CO3 2– substitution has been proposed to enhance the performance of HA-based material, particularly on the physico-chemical properties. Three different compositions of carbonated hydroxyapatite (CHA) powder with different CO3 2–/ PO4 3– ratios (namely, CHA 1:1, CHA 2:1 and CHA 4:1) were chemically synthesised by nanoemulsion method at 37°C and characterised for their physico-chemical properties. Results demonstrated that all as-synthesised powders formed single phase B-type CHA without any additional phases. Interestingly, an increasing amount of CO3 2– substituted into the apatite structure gives rise to the formation of CHA structure with a variation on their cell parameters and the degree of crystallinity. An increase in the CO3 2–/ PO4 3– ratio was also found to lead a higher amount of CO3 2– content present in the as-synthesised powder (in a range of 4 wt % to 10 wt %), which is comparable to the CO3 2– content found in the human bone mineral.