Chemical durability and microstructural analysis of glasses soaked in water and in biological fluids

A new glass, obtained from Bioglass® BG45S5 original composition by substituting CaO with MgO, was produced and its chemical durability and microstructural characteristics were compared with that of Bioglass®. The two glasses (labelled as BG45 and MG45) were soaked up to 4 weeks at physiological temperature in different solutions, i.e. bi-distilled water, Hankʹs Buffered Salt Solution 61200 (labelled as HBSS+), Hankʹs Buffered Salt Solution 14170 (labelled as HBSS−), and Kokuboʹs SBF. Moreover, the influence of either flat or flake surfaces was analysed for both glasses. Results showed that the chemical durability of a glass in saline at 37 °C, evaluated through pH and ICP-AES chemical analysis of the leached components, depended mainly on the chemical composition of the soaking solution. Moreover, the MG45 glass never exhibited hydroxyapatite crystal formation on its surface also after soaking in calcium-containing solutions. The apatite crystallisation and deposition mechanism, typical of a bioactive glass, was induced only if the glass itself contained calcium. The contemporaneous presence of calcium in the glass and in the soaking solution improved the reactivity of the glass, as apatite crystals nucleated in a shorter time and grew more quickly. As regards the morphology of the glass surface, rougher surfaces favoured the formation of hydroxyapatite crystals on glasses containing calcium.