AMORPHOUS-PRECURSOR MEDIATED FORMATION OF MAGNESIUM-FREE WHITLOCKITE

Calcium phosphates (CPs) were widely used as synthetic bone graft substitutes. However, the control of particle size and morphology of CP materials have not been achieved substantially, even though these factors would influence the physicochemical properties. Recent studies revealed that a uniform nanostructured Mg-free whitlockite (WH), which was structurally similar to a high temperature polymorph of β-tricalcium phosphate, was synthesized by precipitation in organic solvents of N,N-dimethylformamide (DMF) and ethylene glycol (EG). The present study therefore aims to synthesize WH particles in the DMF-EG binary solvents by a solvothermal reaction to investigate the formation mechanism of the WH particles. The nucleation of the amorphous precursor, which occurred at 3 h, was dominated by the slow hydrolysis of organophosphate, which retarded reaching critical supersaturation and hindered the fast nucleation. The investigation on the effect of reaction time on WH formation revealed that the amorphous-precursor mediated WH formation via a solid-solid phase transformation occurred between 4 and 9 h of reaction time. (Received Mar 19, 2021; Accepted Apr 13, 2021)