Physicochemical degradation studies of calcium phosphate glass ceramic in the CaO–P2O5–MgO–TiO2 system

The aim of this work was to evaluate the in vitro degradation behaviour of a 45CaO–37P2O5–5MgO–13TiO2 (mol.%) glass ceramic, under two different simulated physiological conditions: normal physiological pH 7.4, and pH 3.0, which was designed to simulate the acidic conditions produced by osteoclast cells. The in vitro testing was carried out at 37 °C for up to 42 days for the pH 7.4 solution and for up to 1 day for the pH 3.0 solution. The incorporation of TiO2 into the glass structure leads to the precipitation of specific crystalline phases in the glass matrix, namely α- and β-Ca2P2O7, TiP2O7 and CaTi4(PO4)6. The degradation testing at pH 3.0 showed a higher weight loss compared with degradation testing at pH 7.4; the weight loss under the acidic condition after 1 day (24 h) was about 10 times higher than the weight loss after 42 days of immersion at pH 7.4. The ionic release profile of Ca2+, PO 4 3 - , Mg2+ and Ti4+ showed a continuous increase in concentration over all immersion times for both testing solutions. After 1 day of immersion at pH 3.0, the concentration levels of Mg2+, Ca2+, PO 4 3 - were about six times higher than the levels achieved after 42 days of immersion at pH 7.4. The glass ceramic showed similar degradation to hydroxyapatite, and therefore has potential to be used in certain clinical applications where relatively slow resorption of the implant and replacement by bone is required, e.g. cranioplasty.