Toward the understanding of crystallization, mechanical properties and reactivity of multicomponent bioactive glasses

Abstract In this study, we have applied Molecular Dynamics (MD) simulations to obtain reliable structural models of the bulk and surfaces of the 45S5 Bioglass® and three recently designed glasses in the system Na2O-K2O-CaO-MgO-SrO-P2O5-SiO2 and to interpret their different behaviour and properties. In fact, the substitution of sodium oxide with alkaline earth oxides (Ca, Mg and Sr) in the traditional 45S5 Bioglass® has been shown to be beneficial for improving the sinterability and mechanical properties of the glass maintaining optimal biocompatibility. The reduced tendency of crystallization has been associated to the increased chemical disorder around network former cations, the reduced mobility of alkaline earth cations with respect to sodium and the reduced coordination number of magnesium, which hamper the large structural re-organization necessary to the precipitation of the Na2Ca2Si3O9 crystal phase. In all the compositions, fragmented chains dominate the silica network and the network connectivity is similar. However, the increased interconnection of such chains by Mg, Ca and Sr cations makes the substituted glasses stiffer and harder than the 45S5 Bioglass®. The different reactivity of the glasses is due to the different amount of alkali cations and undercoordinated species at the glass surfaces. The approach presented provides deeper insights on the structure-properties relationships in bioactive glasses, and can be used to find precious guidelines for compositional tuning and designing innovative bioactive glass compositions with desired behaviour or property for a specific application.