A neutron and X-ray diffraction study of bioglass with reverse Monte Carlo modelling

A class of melt-quenched silicate glasses, containing calcium, phosphorus and alkali metals, and having the ability to promote bone regeneration and to fuse to living bone, creating strong implants with less danger of interfacial instability than previous materials, is produced commercially as Bioglass (R) and sold under the brand names of PerioGlas (R), NovaBone (R) and NovaBone-C/M (R). We have collected the first high energy X-ray and neutron diffraction data, on this important material in the hope of providing more direct experimental insight into the glass structure. Similarly, the first solid state MAS (magic angle spinning) Si-29, P-31, and Na-23 NMR data on the material is presented. The diffraction data has been modeled using the reverse Monte Carlo (RMC) method to allow the identification of the atomic-scale structural features present; the solid state NMR data is used explicitly within the model-building process as a constraint on the connectivity of the network. The 29Si NMR suggests that the host silica network primarily consists of chains and rings of Q(2) SiO4 tetrahedra, with some degree of cross linking as represented by the presence of Q(3) units. The diffraction-based RMC model suggests a Na-O distance of 2.35 angstrom and a corresponding coordination of similar to 6; the coordination number is supported by the Na-23 NMR data presented here which reveals that the likely sodium environment is six-coordinate in pseudo-octahedral arrangement. The RMC model provides evidence for the non-uniform distribution of Ca, which is in line with previous molecular dynamics simulation results, and the data is also suggestive of CaO as the associated structural motif within the high calcium content regions of the glass.