Influence of composition and surface characteristics on the in vitro bioactivity of SiO2-CaO-P2O5-MgO sol-gel glasses

Abstract

Glasses in the system SiO2-CaO-P2O5-MgO were prepared by the sol-gel method. These glasses featured SiO2 contents in the range 60-80 mol %, 4 mol % of P2O5, and a CaO/MgO molar ratio of 4. Because of their composition and surface properties, all the glasses showed in vitro bioactivity as evidenced by the formation of an apatite-like layer on their surface when soaked in an acellular medium with ionic composition similar to human blood plasma. An increase in the CaO content of the glasses also caused an increase in their porosity. Higher porosity facilitated the apatite nucleation on the sample surface during the first days of the in vitro test. On the other hand, those glasses with higher SiO2 content also showed higher surface area values, as well as higher calcium phosphate layer growth rates. For longer soaking periods, the grown layer was analyzed, revealing a two-phase composition: apatite and whitlockite.