Surface modifications of hydroxyapatite ceramics in aqueous media

Hydroxyapatite (HA) surfaces exposed, at room temperature, to various aqueous media of different compositions (distilled water, saline solution, cell culture media, saturated HA solution) have been studied by X-ray photoelectron spectroscopy (XPS) angular analysis and IR reflectance spectroscopy. An important decrease of the Ca/P atomic ratio of the surface layer was seen on all exposed surfaces, reaching 1, the Ca/P ratio of dicalcium phosphate dihydrate (DCPD) for the uppermost surface layer. Furthermore, HPO 4 2− ions were observed by XPS and IR. These chemical changes seem to be related to an equilibration process of the surface independent of the dissolution mechanism. Despite the Ca/P ratio observed, no specific phosphate ion environments, such as that of DCPD, were seen by IR.