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

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 sur face properties, all the glasses showed in vitro bioactivity, as evidenced by the formation of an apatite-like layer on their surface when soaked in a n acellular medium with ionic composition similar to human blood plasma. An increase in the CaO content of the glasses also caused an increase in thei r porosity. Higher porosity facilitated the apatite nucleation on the sampl e surface during the first days of the in vitro test. On the other hand, th ose glasses with higher SiO2 content also showed higher surface area values , as well as higher calcium phosphate layer growth rates. For longer soakin g periods, the grown layer was analyzed, revealing a two-phase composition: apatite and whitlockite. (C) 1999 John Wiley & Sons, Inc.