Carbonate apatite derived from Northern region limestone of Malaysia: A preliminary evaluation

Abstract

The global rise in bone reconstructive surgeries necessitates effective artificial bone substitutes, with carbonate apatite (CO₃Ap) being a promising candidate for bone regeneration. However, CO₃Ap cannot be sintered due to thermal decomposition at high sintering temperatures. An alternative method to synthesis CO₃Ap is via dissolution-precipitation reaction of precursor such as calcium carbonate (CaCO₃). This study focuses on the feasibility to synthesis CaCO₃ precursor from natural source material such as limestone. In this study, limestone obtained from the Northern Region of Malaysia were utilized to synthesis CaCO₃. The limestone was subjected to calcination, dissolution in distilled water and dried to produce calcium hydroxide (Ca(OH)₂) powder, which was subsequently carbonated at room temperature and 4 °C to produce calcite and vaterite, polymorphs of CaCO₃, respectively. These were then pressed into pellets and immersed in 1 M sodium hydrogen phosphate (Na₂HPO₄) solution at 80 °C for up to 14 days. Characterization using X-ray Diffraction (XRD), Fourier transform infra-red (FTIR), scanning electron microscope (SEM), particle size analyzer and carbon-hydrogen-nitrogen (CHN) analyzer were conducted to examine the formation of CO₃Ap. FTIR analysis identified the synthesized product as AB-type CO₃Ap. Vaterite precursor treated in 1 M Na₂HPO₄ transform to CO₃Ap within 3 days with 13.5 wt% of carbonate content while for calcite precursor, the transformation to CO₃Ap was within 7 days with 11.8 wt% of carbonate content. This is due to vaterite having higher surface area and solubility when compared to calcite in aqueous solution. These findings suggest the feasibility to obtain high-purity CO₃Ap by utilizing locally available limestone are feasible.