Evolution of the magnesium incorporated amorphous calcium phosphate to nano-crystallized hydroxyapatite in alkaline solution

A homogeneous amorphous calcium phosphate (ACP) coating containing magnesium was achieved on titanium substrates by electrochemical deposition (ECD). Its amorphous structure is confirmed by transmission electron microscope (TEM) together with grazing reflection absorption infrared spectroscopy (IR) spectrometer. In the images of high-resolution transmission electron microscope (HRTEM), the ACP spheres are assembled by nano-particles with the diameter of 5–10 nm. In the alkaline environment, nucleation of hydroxyapatite (HAP) occurs on the surfaces of ACP spheres. By consuming the Ca and PO4 ions inside the ACP spheres, the HAP nuclei grow outward. Confirmed by TEM, the ACP spheres converse to hollow HAP spheres composed of HAP nano-needles. The coating is finally constructed by the HAP nano-needles, which are themselves aggregated by numerous nano-particles.

► The amorphous structure of the coating was confirmed by the results of TEM and IR.
► Nonapatitic layer on ACP sphere containing high mobility ions was identified by TEM.
► ACP sphere provided the nutrition for the growth of HAP nuclei on its surfaces.
► HAP needle covers the surface of hollow ACP whose spherical morphology was preserved.
► HAP crystallized via assembling of nano-particles randomly and their rearrangment.