The Structure of Bioactive Silicate Glasses:  New Insight from Molecular Dynamics Simulations

The structural properties of three compositions of phosphosilicate glasses are investigated by means of molecular dynamics computer simulations using a new potential model incorporating polarization effects. Structural features of the three compositions are compared in order to highlight the effect of the composition on the different known bioactivities of these materials. Changes in the coordination environment, network connectivity, and ion aggregation with the silica content are discussed, as they enable us to draw a microscopic model of the glasses, which supports the interpretation of experimental data and provides new insight into the special physicochemical behavior of these materials. The transition from highly bioactive to bioinactive compositions is characterized by a marked increase in the connectivity of the silicate network and by an increasing fraction of phosphate groups involved in P−O−Si cross-links. Our analysis also highlights a possible correlation between the loss of bioactivity and a significant aggregation between Ca2+ and PO43- ions, which leads to calcium-phosphate-rich regions for a bioinactive composition containing 65% SiO2.