Compositional dependence of bioactivity of glasses in the system Na2O-K2O-MgO-CaO-B2O3-P2O5-SiO2.

The bioactivity, i.e., bone-bonding ability, of 26 glasses in the system Na2O-K2O-MgO-CaO-B2O3-P2O5-SiO2 was studied in vivo. This investigation of bioactivity was performed to establish the compositional dependence of bioactivity, and enabled a model to be developed that describes the relation between reactions in vivo and glass composition. Reactions in vivo were investigated by inserting glass implants into rabbit tibia for 8 weeks. The glasses and the surrounding tissue were examined using scanning electron microscopy (SEM), light microscopy, and energy-dispersive X-ray analysis (EDXA). For most of the glasses containing < 59 mol % SiO2, SEM and EDXA showed two distinct layers at the glass surface after implantation, one silica-rich and another containing calcium phosphate. The build-up of these layers in vivo was taken as a sign of bioactivity. The in vivo experiments showed that glasses in the investigated system are bioactive when they contain 14-30 mol % alkali oxides, 14-30 mol % alkaline earth oxides, and < 59 mol % SiO2. Glasses containing potassium and magnesium bonded to bone in a similar way as bioactive glasses developed so far.