Mechanosynthesis and microstructural characterization of F− and CO32− mono- and co-substituted hydroxyapatite

Abstract

An investigation into the microstructural properties and mechanosynthesis mechanisms of three distinct calcium phosphate compounds, namely, carbonate-substituted hydroxyapatite (CHA), fluorapatite (FA), and carbonate- and fluoride-substituted hydroxyapatite (CFHA), was undertaken in this study. Significant insights into the crystalline structures of CHA, FA, and CFHA were revealed through Rietveld refinement analysis. In the CaCO3‒Ca(OH)2‒P2O5 ternary system, the transformation of the biphasic structure composed of CHA and dicalcium phosphate anhydrous (DCPA) into a single-phase A-type CHA was observed as milling duration increased. In the CaO‒Ca(OH)2‒CaF2‒P2O5 quaternary system, the formation of FA was influenced by milling time, and within 1‒5 h, a composite structure was formed. The progression from a composite structure to the formation of fully crystalline nanosized CFHA was also observed over the same milling periods in the CaCO3‒Ca(OH)2‒CaF2‒P2O5 quaternary system. The central finding highlights the substantial influence of milling time on the structural properties of the mechanosynthesized nanopowders, with marked changes in crystallite size, micro-strain, and unit cell volume being observed over different milling durations. The atomic coordinates and displacement parameters of the refined structures were also provided, revealing the presence of apatitic groups. Moreover, a detailed examination of the mechanochemical synthesis processes uncovered intricate sub-reactions that occur during ball milling. This work sets the stage for future investigations, facilitating a better grasp of their distinctive attributes and potential applications across various domains of regenerative medicine.