Characterization of apatite layer formation on P2O5-CaO, P2O5-CaO-Na2O, and P2O5-CaO-Na2O-Al2O3 glass hydroxyapatite composites.

P2O5-based glass hydroxyapatite (HA) composites denoted HA-2 oxide, HA-3 oxide, and HA-4-oxide, were immersed in Hank's balanced salt solution for a period of 1, 2, 3, and 4 weeks at 37 degrees C in nonagitated condition for in vitro evaluation. A surface layer was precipitated on the composites that was analyzed using scanning electron microscopy (SEM), X-ray photoelecton spectroscopy, and thin film X-ray diffractometry (TF-XRD). SEM micrographs showed complete coverage of the composite surface by crystallites after immersion of 1 week in the solution, which grew thicker with respect to immersion time. The binding energies measured by XPS indicated apatite formation and the presence of carbonate on the composite surface, showing the newly formed layer was a carbonated apatite. Confirmation of the formed apatite layer was obtained by TF-XRD.