Dynamical descriptors of bioactivity: a correlation between chemical durability and ion migration in biodegradable glasses.

Ion migration in two fluorinated bioactive glasses of significantly different durability was modeled through molecular dynamics simulations. Whereas the very different biodegradation of these glasses cannot be explained on the basis of their structural features alone, the analysis of the diffusive data highlights a strong connection between the glass durability determined experimentally and the activation barriers for ion diffusion extracted by the simulations, clarifying the source of the different solubility and suggesting that "dynamical" descriptors of bioactivity could represent a key tool to predict the macroscopic behavior of a biomaterial, in some cases more effectively than with the current structural descriptors.

Influence of Calcium on the Initial Stages of the Sol-Gel Synthesis of Bioactive Glasses.

Understanding how calcium interacts with silica sources and influences their polycondensation in aqueous solutions is of central importance for the development of more effective biomaterials by sol-gel approaches. For this purpose, the atomic-scale evolutions of a calcium-containing precursor solution corresponding to a typical sol-gel bioactive glass and of a corresponding Ca-free solution were compared using reactive molecular dynamics simulations. The simulations highlight a significantly faster rate of condensation when calcium is present in the initial solution, resulting in the formation of large and ramified silica clusters within 5 ns, which are absent in the Ca-free system.

Structure-solubility relationships in fluoride-containing phosphate based bioactive glasses.

The dissolution of fluoride-containing bioactive glasses critically affects their biomedical applications. Most commercial fluoride-releasing bioactive glasses have been designed in the soda-lime-silica system. However, their relatively slow chemical dissolution and the adverse effect of fluoride on their bioactivity are stimulating the study of alternative biodegradable materials with higher biodegradability, such as biodegradable phosphate-based bioactive glasses, which can be a good candidate for applications where a fast release of active ions is sought.

Atomic-scale models of early-stage alkali depletion and SiO2-rich gel formation in bioactive glasses.

Molecular dynamics simulations of Na(+)/H(+)-exchanged 45S5 Bioglass® models reveal that a large fraction of the hydroxyl groups introduced into the proton-exchanged, hydrated glass structure do not initially form covalent bonds with Si and P network formers but remain free and stabilised by the modifier metal cations, whereas substantial Si-OH and P-OH bonding is observed only at higher Na(+)/H(+) exchange levels. The strong affinity between free OH groups and modifier cations in the highly fragmented 45S5 glass structure appears to represent the main driving force for this effect. This suggests an alternative direct route for the formation of a repolymerised silica-rich gel in the early stages of the bioactive mechanism, not considered before, which does not require sequential repeated breakings of Si-O-Si bonds and silanol condensations.

Role of glass structure in defining the chemical dissolution behavior, bioactivity and antioxidant properties of zinc and strontium co-doped alkali-free phosphosilicate glasses.

We investigated the structure-property relationships in a series of alkali-free phosphosilicate glass compositions co-doped with Zn(2+) and Sr(2+). The emphasis was laid on understanding the structural role of Sr(2+) and Zn(2+) co-doping on the chemical dissolution behavior of glasses and its impact on their in vitro bioactivity. The structure of glasses was studied using molecular dynamics simulations in combination with solid state nuclear magnetic resonance spectroscopy.