Structural study of Cu1+ and Cu2+ ions in phosphate-based bioactive glasses using classical molecular dynamics simulations

Abstract

Copper oxide-containing bioactive glasses have gained attention as potential candidates for biomedical applications due to their unique properties when compared to their crystalline counterparts. This study aims to elucidate the impact of copper (Cu) ions on the molecular structure of bioactive phosphate glasses. Molecular dynamics simulations were employed to analyse the molecular structures of phosphate bioactive glasses composed of SiO₂ (2.6 mol%), CaO (26.9 mol%), Na${}_2$O (24.4 mol%), and P${}_2$O${}_5$ (46.1 mol%). The study systematically introduced CuO, at concentrations of 10, 15, and 20 mol%, gradually substituting Na${}_2$O. To facilitate this investigation, a polarizable interatomic potential, previously developed for Cu${}^{1+}$-O and Cu${}^{2+}$-O interactions in silicate glasses, was tested and found to represent the structure of Cu-containing phosphate glass well. Our research sought to understand the relationship between structural alterations in the glasses and their bioactivity following the addition of Cu${}^{1+}$ and Cu${}^{2+}$ ions. Key factors such as the quantity of non-bridging oxygens and the overall network connectivity of the glass were examined as predictive metrics for bioactivity. The results indicate that both Cu${}^{1+}$ ions (with three-fold coordination) and Cu${}^{2+}$ ions (coordinated by six oxygen atoms) act as network modifiers in the glass structure. The influence of Cu${}^{1+}$ and Cu${}^{2+}$ ions on the glass network’s connectivity is minimal, as they have field strengths similar to calcium.