Impact of solution pH (5–9) and dissolution products on in vitro behaviour of the bioactive glass S53P4

The impact of dissolution products on the reaction behaviour of bioactive glasses was explored. Bioactive glass S53P4 particles were immersed in solutions with initial pH of 5–9. After 24 and 72 h, the solution extracts were used for testing unreacted particles. The pH, ion concentrations, and glass surfaces were analysed as functions of immersion time. More Ca, Na, and P dissolved at lower pH (5) than at higher pH (7.4 or 9). The dissolution changed from an incongruent to an apparent congruent with increasing pH. Dissolution products in extracts changed the reaction layer structure on glass particles and led to lower ion release at pH 7.4 and 9. Dissolution increased almost linearly with time in acidic solutions. Silica-rich layer and calcium phosphate were identified on the particles after immersion in all solutions except at pH 9. Local ion concentration variations affected dissolution, leading to nonuniform ion release rates.