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. 31
Si MAS-NMR and 29
P 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 – 29
Si 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
Silica associated peaks (Q2
fit depicted by dashed line, deconvoluted peaks by dotted lines).
Figure 2 – 31
P 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.
Department of Biology, University of York, YO10 5DD, UK
Department of Physics, University of York, YO10 5DD, UK
Department of Oral Biology, University of Leeds, WTBB, LS9 7TF, UK
ISIS Facility, Rutherford Appleton Laboratory, Chilton, Didcot, OX11 0QX, UK
School of Engineering and Applied Science and Aston Research Centre for Health Ageing, University of Aston, B4 7ET, UK