Dissolution characteristics of bioactive glasses

The formation of hydroxycarbonate apatite (HCA) layer on the surface of bioactive glasses and glass ceramics involves an ion exchange reaction, which increases the pH and causes cytotoxicity in the surrounding environment. Investigations into the in-vitro cell behaviour of bioactive glasses use a preconditioning step to reduce this pH excursion. This technique involves the immersion of the glass in either simulated body fluid (SBF) or culture medium for a pre-determined time period. Preconditioning of two types of bioactive glass particulates (melt-derived 45S5 Bioglass(R), and 58S gel-glass) were examined to evaluate the effect on glass dissolution and subsequent HCA formation. This was achieved by immersing the glass powders in SBF for periods ranging from 30 minutes to 48 hours. The samples were evaluated using inductive coupled plasma atomic emission spectroscopy (ICP) and infrared spectroscopy (FTIR) to analyse the dissolution rates and HCA layer formation on the surface of the particles. Preconditioning was found to reduce the rate of dissolution for both glasses for calcium (by 20ppm for 45S5 and 75ppm for 58S). Sodium release from 45S5 was also diminished by 100ppm, whereas silica release was not affected for either glass. Results obtained from FTIR indicate that the rate of HCA layer formation was not significantly changed for either of the glass powders, implying that bioactivity has not been adversely influenced by the preconditioning step.