Static and dynamic in vitro study of a sol–gel glass bioactivity

A comparative study of in vitro bioactivity of a sol–gel glass with composition 55% SiO2–41% CaO–4%P2O5 has been carried out by soaking it in a simulated body fluid (SBF) with and without exchange of this solution. When SBF is kept constant (static assay) the solution composition changes, increasing the Ca2+ concentration and pH as a function of soaking time while these parameters remain nearly constant and very close to human conditions in dynamic conditions. Glass surface is studied by FTIR, XRD and SEM in order to compare the behaviour in the two procedures, revealing that in both cases an apatite-like layer is formed on the glass surface, although there are differences in rate and morphology in this formation. In addition, a study of porosity was carried out by Hg intrusion pointing out the pore distribution and changes in porosity with time for both procedures. A similar behaviour in mesopore region was detected, while macropores remain nearly constant in static conditions, decreasing from 0.48 to 0.12 μm in just 3 h of soaking in dynamic assay.