Abstract
Classical molecular dynamics (MD) simulations were used to study the structural changes in the surfaces of biocompatible phosphate glasses with compositions (P2O5)0.45(CaO)x(Na2O)0.55−x (x=30, 35, 40) to evaluate their effect on the solubility of the material. Direct comparison of the data for the three compositions highlighted the critical role that an enhancement in Na+ concentration plays in the hydrolysis of the material, which is responsible for the release of network components into solution. The calculations also confirm that the most soluble material is (P2O5)0.45(CaO)0.30(Na2O)0.25, has the lowest calcium coordination number, thereby causing fewer cross links to phosphate chains.
Highlights
Phosphate-based glasses (PBGs) in the CaO–Na2O–P2O5 system have a number of biomedical applications [1,2]
We found that the decrease in coordination is at the expense of Me-nonbridging oxygens (NBOs) coordination with the two extreme calcium compositions (N25, N15) the most significantly affected for calcium coordination, while the sodium experiences the same drop in NBO coordination compared to the bulk values for the three compositions, showing the lowest coordination number in N25
In N20 sodium has a preference to aggregate more in a region just below the interface, and there are not as many Na+ ions exposed at the interface, i.e. closer to the solvent, as in other compositions
Summary
Phosphate-based glasses (PBGs) in the CaO–Na2O–P2O5 system have a number of biomedical applications [1,2]. Their ionic compositions mimic the mineral constituent of hard tissue, and they can act as a template to repair soft tissue [3]. Based on their controlled ion release capabilities, they can temporarily replace hard tissues whereas metal-doped PBGs are used in veterinary medicine to treat trace element deficiencies [1,4,5]. The same authors proposed that the clustering of modifier cations, which affect the solubility of these bioactive glasses by strengthening the glass network, should be considered [14]
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