Synthesis and characterization of hydroxyapatite-based nanocomposites by the functionalization of hydroxyapatite nanoparticles with phosphonic acids A Physicochemical and engineering aspects

Understanding phosphonates-CaHAp structure interaction and its role in the control of CaHAp particles properties is of interest for the development of biomaterials able for repairing the skeletal system. In this work, the direct synthesis by hydrothermal method of calcium hydroxyapatite (CaHAp)-phosphonic acids (PA) nanocomposites was carried out in the presence of increasing contents of methylphosphonic (MPA) and vinylphosphonic (VPA) acids in the solution. The new CaHAp-PA composite formation was confirmed by IR, Raman and NMR-MAS spectroscopy, and by chemical and thermal analyses. PA amount in composites increased with their added content and MPA showed a greater affinity for CaHAp. A part of PA substituted phosphate groups in CaHAp structure and another was grafted on its surface via Ca-OH sites. X-ray powder diffraction showed that the presence of the PA did not inhibit CaHAp nucleation, but reduced the growth of their crystals and affected their crystallinity. TEM observations revealed nanosized crystallites and confirmed the dimension reduction, which is in agreement with the increase of the surface area up to 250m²g⁻¹. Taken together, the characteristics of the obtained CaHAp-PA nanocomposites suggest their usefulness for the preparation of biomaterials for bone replacement.