In vitro bioactivity of partially crystallised glasses

The influence of crystallinity on the bioactivity of low silica glasses is not fully understood. The bioactivity of three partially crystallised glasses was studied by immersion in a simulated body fluid (SBF) for 24 and 72 h. The glasses contained two different types of crystals namely sodium calcium silicate type crystals or wollastonite crystals or both. In the wollastonite type glasses the glassy phase between crystals and grain boundaries as well as the crystal interfaces were attacked by SBF With the longer immersion time wollastonite crystals began to corrode. A thin layer of silica gel was formed on the glassy phase left on the surface. Calcium phosphate could be identified in the layer. However, the formation of the layer was slower than on samples which had not been heat treated. In the sodium-calcium-silicate type glasses, calcium phosphate was precipitated both on the silica gel formed on the residual glassy phase and on the nanosize sodium-calcium silicate crystals. The crystallisation of the phosphate rich layer to hydroxyapatite was, however, rather slow. The results indicate that both wollastonite and sodium-calcium-silicate crystals retard the bonding of glass to bone, but that bioactivity is not totally lost in the partially crystallised glasses.