Glass - Back to the Future!

Presenting Author:
Sam Hollings

article posted 28 April 2016

Sam Hollings graduated from the University of Durham in 2011 with an MPhys in Physics and Astronomy focusing on computational galaxy modelling. He later entered the Doctoral Training Centre in Tissue Engineering and Regenerative Medicine (DTCTERM), a four year program, initially training at the University of Leeds with a year of biology and materials training and laboratory rotations. Now in his 3rd year of the DTCTERM, Sam is now currently doing a PhD project between York and Leeds on the effects of bioactive glasses on Mesenchymal Stromal Cells.

Neutron Diffraction and NMR to determine the short range order of Sr substituted Apatite-Wollastonite bioactive glasses.

Sam Hollings123*, Paul Genever1, David Wood2, Alex C Hannon4, Richard A Martin5

Bioactive glass ceramics are of considerable interest due to their potential for dental and medical applications, the ageing population and associated osteoporosis, fracture and arthritis. The University of Leeds have developed a series of novel sodium free, high phosphate, Apatite-Wollastonite Glass Ceramics (AWGC) containing magnesium oxide. A series with increasing substitution of strontium for calcium has been studied. These materials show promising bioactivity, with human Mesenchymal Stromal Cells (MSCs) seen to readily attach, proliferate and osteogenically differentiate on their surface, most likely associated with the strontium content of the glass.

Neutron diffraction and solid state MAS-NMR were used to explore how the short range order of these materials changes with Sr content. Understanding the short range order of these materials is essential to understanding the dissolution which strongly influences the biological response. 31Si MAS-NMR and 29P MAS-NMR were consistent as a function of glass composition as Sr replaces Ca, typically resulting in a predominantly Q2 silicon network with smaller amounts of Q3 (Figure 1), and orthophosphate (Q0) separate from the glass network (Figure 2). This indicates that the addition of strontium does not significantly change the glass network connectivity. The neutron diffraction data, once deconvoluted with the aid of the MAS-NMR and isomorphic substitution based analysis, indicates that the Ca-O and Sr-O correlations are in good agreement with results previously published for high sodium, low phosphate bioglass. The glass structure is shown in Figure 3. The results will help to model and understand the macroscopic properties of these materials including dissolution rates and therefore bioactivity.

Figure 1 29Si MAS-NMR of AW glasses without (x=0) and with 1:1 Ca-Sr ratio (x=24.9). Both show approximately 2:1 ratio of Q2 and Q3 Silica associated peaks (Q2 and Q3 total fit depicted by dashed line, deconvoluted peaks by dotted lines).

Figure 2 31P MAS-NMR of AW glasses without (x=0) and with 1:1 Ca-Sr ratio (x=24.9). Both show a dominant peak indicative of orthosphosphate (Q0) (dotted line fit). The small sidebands are an artefact of the spinning.

Figure 3: The total neutron diffraction signal from six different compositions of SrAW glass (containing the indicated mol% of SrO, substituting for CaO). The signal was deconvoluted into Si-O, P-O, O-Si-O, O-P-O, Mg-O, Ca-O and Sr-O peaks, though only some component peaks are shown for clarity.

1Department of Biology, University of York, YO10 5DD, UK
2Department of Physics, University of York, YO10 5DD, UK
3Department of Oral Biology, University of Leeds, WTBB, LS9 7TF, UK
4ISIS Facility, Rutherford Appleton Laboratory, Chilton, Didcot, OX11 0QX, UK
5School of Engineering and Applied Science and Aston Research Centre for Health Ageing, University of Aston, B4 7ET, UK