Effect of pH and ionic strength on the reactivity of Bioglass® 45S5

Bioglass® 45S5 is a silica-based melt-derived glass, used in medical field as a bone regenerative material because of the deposition of a layer of hydroxy carbonate apatite (HCA) on the surface of the glass when immersed in body fluid. The present paper studies the early steps of reaction of 2-μm sized particles of Bioglass®, in solutions buffered with TRIS at different pH, by means of ICP-ES and FTIR spectroscopy. Only at pH 8 could a total reconstruction of the glass be observed, with the formation of both a silica and a calcium phosphate rich layers. At higher pH, selective dissolution of the glass was hindered by the immediate precipitation of a layer of calcium phosphate, whereas at lower pH a total breakdown of the glass occurred and no calcium phosphate precipitation was noted. The use of the ATR-liquid cell allowed the observation of the reaction in real time, and this showed that the process of silica formation is not separable from cation leaching from the glass, as well as the formation of the calcium phosphate rich layer.