Glass - Back to the Future!

Presenting Author:
Jamieson Christie

article posted 22 March 2016

Dr Jamieson Christie is a lecturer in the Department of Materials at Loughborough University, a post he took up in 2015 after research positions at University College London and The Abdus Salam International Centre for Theoretical Physics in Trieste, and a PhD at the University of Cambridge. His research interests are in the computer simulation of glass, particularly biomedically relevant compositions. Much of a particular composition's suitability for biomedical implantation can be understood from a characterization of its atomic structure and Jamie has used a range of computational techniques to improve our understanding of these connections.

Understanding the solubility of phosphate-based glass from computer simulation

J. K. Christie*,1, R. I. Ainsworth2, D. Di Tommaso3 & N. H. de Leeuw4
1 Department of Materials, Loughborough University

Phosphate-based glasses (PBG) have wide application as biomaterials because they dissolve when implanted into the body, with a composition-dependent dissolution rate that varies over several orders of magnitude. They can be synthesised containing different substances or materials, making them useful for controlled delivery of therapeutically relevant substances. In order to optimise PBGs for these applications, it is vital to understand the dependence of their dissolution rate on the glass composition and structure.
In traditional silicate-based bioactive glasses, the network connectivity (NC) is often used as a reliable parameter correlating with the glass dissolution rate. In phosphate-based glass, we have shown that the NC does not capture many effects of the structure on the dissolution. We have used molecular dynamics (MD) simulations to show that for biomedically relevant compositions (<50 mol % P2O5, and some Na2O and CaO) where the dissolution rate substantially decreases with increasing CaO content, Ca binds together more phosphate chains (3.9) than Na does (3.2) (see Fig. 1), strengthening the glass network and making it less prone to dissolution [1], even for compositions with identical network connectivities.

The inclusion of therapeutic ions alters the glass structure and properties in non-trivial ways, but we have successfully used this characterisation of the atomic structure to identify trends in the dissolution of PBGs containing various ions, including fluorine [2], silver [3], and strontium [4], among others. I will discuss the extent to which this network modifier to phosphate bonding affects the solubility, and outline steps toward a quantitative understanding of PBG dissolution rate with composition.

[1] J. K. Christie, R. I. Ainsworth, D. Di Tommaso, N. H. de Leeuw, J. Phys. Chem. B 117, 10652 (2013).
[2] J. K. Christie, R. I. Ainsworth, N. H. de Leeuw, Biomaterials 35, 6164 (2014).
[3] R. I. Ainsworth, J. K. Christie, N. H. de Leeuw, Phys. Chem. Chem. Phys. 16, 21135 (2014).
[4] J. K. Christie, N. H. de Leeuw, submitted.

2 Department of Chemistry and Biochemistry, University of California, San Diego
3 School of Biological and Chemical Sciences, Queen Mary, University of London
4 Department of Chemistry, University of Cardiff