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, HPO42- 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.