Surface and Chemical Study of SiO2·P2O5·CaO·(MgO) Bioactive Glasses

Glasses in SiO2·CaO·P2O5 and SiO2·CaO·P2O5·MgO systems have been prepared by a sol−gel synthesis procedure. The calcined glasses have been characterized by XRD, N2 adsorption, Hg porosimetry, XPS and TEM and have been also subjected to in vitro tests (immersion in a simulated body fluid) to evaluate their bioactivity. The presence of magnesium in the glasses increases the surface area and porosity, but it retards the formation of an apatite layer on the surface of glasses in the in vitro test. The XPS reveals that the surfaces of the glasses are richer in phosphorus and poorer in calcium than the bulk, whereas the magnesium, if present, associates preferentially to phosphorus at the glass surface. The TEM shows the presence of apatite-like calcium phosphate domains in the magnesium-free glasses, which are barely detected in the glasses, which contain this element. These apatitic domains are proposed to be the nucleation centers for the crystallization of apatite in the in vitro tests.