Atomic structure of biodegradable Mg-based bulk metallic glass

We have used highly accurate first-principles molecular dynamics simulations to elucidate the structure of Mg60Zn35Ca5 and Mg72Zn23Ca5 bulk metallic glasses, which are candidate materials for biomedical implants; these two compositions exhibit different behaviours when implanted. The environments of each species are different, and average coordination numbers are [similar]13 for Mg, [similar]11 for Zn and [similar]18–19 for Ca. A wide range of local environments were found and icosahedral motifs, often seen in bulk metallic glasses, were among the most common for both Mg and Zn. Through the computation of a chemical short-range order parameter, a moderate avoidance of Zn–Zn bonding over Zn–Mg or Zn–Ca was observed. No statistically significant difference in structure was observed between the two compositions

Atomic structure and dissolution properties of yttrium-containing phosphate glasses

We have conducted classical molecular dynamics simulations of three compositions of yttrium-containing phosphate glasses, to study the atomic structure around yttrium, and understand how yttrium incorporation will affect the glass dissolution rate. The Y-O bond length is about 2.2 Å and the coordination number is 6.3. To avoid effects due to different network connectivities, our compositions were chosen to keep the Qn distribution and network connectivity roughly constant, which was confirmed through direct calculation. For these compositions, the structure of the phosphate network is comprised of finite-length chains of PO4 tetrahedra bound to the network modifiers. We showed that yttrium bonds to 4.2-4.3 of these chains, compared to 3.8 for calcium, and 3.1-3.2 for sodium. This implies that yttrium will bond more parts of the glass to the same place, and therefore, that yttrium incorporation will strengthen phosphate glass against dissolution, making it potentially suitable for radiotherapy applications where a durable glass is required

The role of fluoride in the nano-heterogeneity of bioactive glasses

Fluoride-containing bioactive phospho‐silicate glasses have recently attracted interest for dental applications, particularly as remineralising additives in dentifrices, and are potentially attractive for bone regeneration, particularly in patients suffering from osteoporosis. The incorporation of fluoride into phospho­‐silicate glasses is also attractive from a structural viewpoint: Fluoride complexes modifier ions rather than binding to the silicate network, and it thereby adds a significant ionic contribution to the average character of chemical bonds in the system. Molecular dynamics simulations have suggested that this also results in the formation of nano-­eterogeneities. In this paper, we review the current knowledge on the structural role of fluoride in bioactive glasses, with a particular focus on inhomogeneities on a nano-­‐scale

Effect of strontium inclusion on the bioactivity of phosphate-based glasses

We have conducted first-principles and classical molecular dynamics simulations of various compositions of strontium-containing phosphate glasses, to understand how strontium incorporation will change the glasses’ activity when implanted into the body (bioactivity). To perform the classical simulations, we have developed a new interatomic potential, which takes account of the polarizability of the oxygen ions. The Sr-O bond length is ∼ 2.44 − 2.49Å, and the coordination number is 7.5 – 7.8. The Qn distribution and network connectivity were roughly constant for these compositions. Sr bonds to a similar number of phosphate chains as Ca does; based on our previous work [J. K. Christie et al., J. Phys. Chem. B 117, 10652 (2013)], this implies that SrO ↔ CaO substitution will barely change the dissolution rate of these glasses, and that the bioactivity will remain essentially constant. Strontium could therefore be incorporated into phosphate glass for biomedical applications

Atomic-scale clustering inhibits the bioactivity of fluoridated phosphate glasses

© 2019 Adja B. R. Touré et al. Here, molecular dynamics simulations have been carried out on phosphate glasses to clarify the previously debated influence of fluoride on the bioactivity of these glasses. We developed a computationally advanced inter-atomic force field including polarisation effects of the fluorine and oxygen atoms. Structural characterisations of the simulated systems showed that fluoride ions exclusively bond to the calcium modifier cations creating clusters within the glass structure and therefore decreasing the bioactivity of fluoridated phosphate glasses, making them less suitable for biomedical applications

A new potential for radiation studies of borosilicate glass

Borosilicate glass containing 70 mol% SiO2 and 30 mol% B2O3 is investigated theoretically using fixed charge potentials. An existing potential parameterisation for borosilicate glass is found to give good agreement for the bond angle and bond length distributions compared to experimental values but the optimal density is 30% higher than experiment. Therefore the potential parameters are refitted to give an optimal density of 2.1 g=cm3, in line with experiment. To determine the optimal density, a series of random initial structures are quenched at a rate of 5 1012 K/s using constant volume molecular dynamics. An average of 10 such quenches is carried out for each fixed volume. For each quenched structure, the bond angles, bond lengths, mechanical properties and melting points are determined. The new parameterisation is found to give the density, bond angles, bond lengths and Young’s modulus comparable with experimental data, however, the melting points and Poisson’s ratio are higher than the reported experimental values. The displacement energy thresholds are computed to be similar to those determined with the earlier parameterisation, which is lower than those for ionic crystalline materials

Implementing a structured education program for children with diabetes: lessons learnt from an integrated process evaluation

There is recognition of an urgent need for clinic-based interventions for young people with type 1 diabetes mellitus that improve glycemic control and quality of life. The Child and Adolescent Structured Competencies Approach to Diabetes Education (CASCADE) is a structured educational group program, using psychological techniques, delivered primarily by diabetes nurses. Composed of four modules, it is designed for children with poor diabetic control and their parents. A mixed methods process evaluation, embedded within a cluster randomized control trial, aimed to assess the feasibility, acceptability, fidelity, and perceived impact of CASCADE

Structures and properties of phosphate-based bioactive glasses from computer simulation: a review

Phosphate-based bioactive glasses (PBGs) dissolve harmlessly in the body with a dissolution rate which depends sensitively on composition. This makes them proposed vectors for e.g. drug delivery, or other applications where an active component needs to be delivered at a therapeutically appropriate rate. Molecular dynamics (MD) simulations provide atomic-level structural information about PBG compositions. We review recent work to show that MD is an excellent tool to unravel the connections between the PBG glass composition, its atomic structure, and its dissolution rate, which can help to optimise PBGs for specific medical applications

Bioactive sol-gel glasses at the atomic scale: the complementary use of advanced probe and computer modelling methods

Sol-gel synthesised bioactive glasses may be formed via a hydrolysis condensation reaction, silica being introduced in the form of tetraethyl orthosilicate (TEOS) and calcium is typically added in the form of calcium nitrate. The synthesis reaction proceeds in an aqueous environment; the resultant gel is dried, before stabilisation by heat treatment. These materials, being amorphous, are complex at the level of their atomic-scale structure, but their bulk properties may only be properly understood on the basis of that structural insight. Thus, a full understanding of their structure : property relationship may only be achieved through the application of a coherent suite of leading-edge experimental probes, coupled with the cogent use of advanced computer simulation methods. Using as an exemplar a calcia-silica sol-gel glass of the kind developed by Larry Hench, to whose memory this paper is dedicated, we illustrate the successful use of high-energy x-ray and neutron scattering (diffraction) methods, magic-angle spinning solid state NMR, and molecular dynamics simulation as components to a powerful methodology for the study of amorphous materials