Investigating the structure-diffusion-bioactivity relationship of strontium containing bioactive glasses using molecular dynamics based computer simulations

Molecular dynamics simulations have been used to study the effect of SrO/CaO substitution and composition on the glass structure and ionic diffusion behaviors of bioactive glasses. The glass compositions studied include three bioactive glass compositions with silica content ranging from 46 to 65 mol% that covers a wide range of bioactivity. The local environments around modifier cations such as strontium, calcium and sodium and the network structures such as Qn distribution and network connectivity of these glasses were determined as a function of composition. Ionic diffusion was studied by calculating the mean square displacement (MSD) to obtain self-diffusion coefficients and studying diffusion at different temperatures to obtain diffusion energy barriers. The ionic diffusion properties, together with the glass structure features, were used to understand the difference in dissolution and bioactivities of these glasses. It was found that sodium ions had a much higher diffusion coefficient and lower diffusion energy barrier than calcium and strontium ions and the diffusion coefficient of modifier cations decreases by several orders of magnitude with increasing silica content and decreasing bioactivity. The preexponential factor was found to dominate the values of cation diffusion coefficients while diffusion energy barriers are relatively insensitive to composition change in the glasses studied.