Role of Strontium Incorporation on the Structural Network of 45S5 Bioactive Glass: A Molecular Dynamics Investigation

This study investigated the short- and medium-range structures of 45S5 bioactive glasses (BGs) containing 0–20 mol% SrO using molecular dynamics (MD) simulations and experimental analysis. The sample density increased from 2.674 g/cm³ (45-S0) to 2.947 g/cm³ (45-S20) in simulation, while experimentally measured densities for selected compositions were within 1–3% of these values, confirming the accuracy of the MD approach. The cross-linking Si–O (1.61 Å) and P–O (1.49 Å) bond lengths remained constant in both simulation and experiment, and these values are closely aligned with reported experimental bond lengths for these species. The Sr–O bond length (2.60 Å in simulation; reported experimental values ~2.59–2.61 Å) and coordination number of 7.01 indicated greater network discontinuity than in Ca, in agreement with structural studies. The Qⁿ distribution revealed that Q² was the dominant species (36–42%), again consistent with trends derived from experimental NMR data, suggesting increased solubility and a relative decrease in network connectivity (NC). R-factor analysis showed that 45-S5 exhibited the highest cationic uniformity and the lowest aggregation. Simulated body fluid (SBF) tests confirmed increased ion release, rapid pH elevation, and hydroxyapatite layer formation in the 45-S5 sample, with measured Si 4+ and Sr 2+ ion release matching the higher solubility predicted by MD within experimental error. The addition of 5 mol% SrO resulted in controlled network expansion, enhanced solubility, and bioactivity, identifying 45-S5 as the optimal composition. This quantitative agreement between simulation and experiment strengthens the validity of the structural and property trends observed. • Strontium widens the 45S5 network, enhancing dissolution and bioactivity. • Optimal 5 mol% SrO improves structural uniformity and ion-release behavior. • Sr–O bonds increase network expansion without altering key Si–O/P–O linkages. • Q²-rich structures in Sr-doped glass promote higher solubility and reactivity. • MD and experiments confirm 5% SrO as the most bioactive 45S5 composition.