Effect of Strontium Substitution on the Structure of 45S5 Bioglasses

Strontium substitution has been found to have a beneficial effect on tissue growth in traditional bioglasses. In this paper, we have studied the effect of SrO/CaO substitution on the structure of 45S5 bioglasses in the series of 46.1SiO(2)center dot 24.4Na(2)O center dot (26.9-x)CaO2 center dot 6P(2)O(5)center dot xSrO (x = 0, 1, 5, 10, 15) compositions using molecular dynamics (MD) simulations with effective partial charge potentials and a combination of constant temperature and pressure (NPT) and microcanomical (NVE) ensembles. The calculated neutron structure factor and neutron broadened total correlation function of the 45S5 glass were compared with experimental diffraction data and the two were found to be in reasonable agreement with each other. The SrO/CaO substitution effects on cation local environments were analyzed by studying the partial pair distribution functions, bond angle distributions, coordination number and its distribution. Change of the medium-range structures were characterized by distributions and network connectivity, cation cation distributions and their aggregation, as well as the preference of modifiers around the glass former cations. It was found that strontium substitution leads to a linear increase of both molar volume and density. The Sr-O bond distance is found to be around 2.59 angstrom, and the average strontium coordination number is around 7.0 in the substitution series. The glass network structures such as Q(n) distribution and network connectivity does not change much with SrO/CaO substitution. Calcium and strontium ions were found to preferentially distribute around phosphorus ions. These structural and property changes were correlated to observed glass dissolution behavior and bioactivity of strontium-containing bioactive glasses.