Structural Characterisation of Bioactive Glasses

Melt-quenched glasses containing SiO2, CaO, Na2O and P2O5, and sol-gel

derived glasses containing SiO2 and CaO are known to have bioactive properties.

Foaming of binary sol-gel derived bioactive glasses containing SiO2 and CaO can be

used to produce 3D porous scaffolds which mimic the structure of trabecular bone,

increasing the potential for these glasses to be used as bioactive bone-regenerative

materials.

A range of experimental techniques have been used to investigate the atomic

scale structure of these materials, and also to observe the reaction mechanisms which

occur when these materials are immersed in a simulated physiological solution

(simulated body fluid, SBF) and a standard cell culture medium (tris buffer solution,

TBS).

A robust structural model of the most bioactive of the melt-quenched glasses,

namely Bioglass®, has been produced by combining high energy X-ray and neutron

diffraction data, magic angle spinning nuclear magnetic resonance (MAS NMR) and

reverse Monte Carlo (RMC) modelling. It has been shown that Ca clustering occurs

in the glass, which is of direct relevance to the understanding of the facile nature of

calcium within such glasses giving rise to its relatively rapid diffusion from the solid

into solution.

Hydroxyapatite has been confirmed as the calcium phosphate phase which

grows on the surface of Bioglass® when immersed in the standard cell culture

medium, TBS.

A new method which can be used for in-situ time resolved high-energy X-ray

diffraction studies of reaction mechanisms, such as those involved when a bioactive

glass is immersed in a simulated physiological solution, is decribed in this thesis.

Small-angle X-ray scattering has enabled the growth of mesopores to be

observed during the foamed sol-gel stabilisation process. In-situ simultaneous small

and wide angle X-ray scattering measurements of a foam in SBF have shown that the

mesoporous network facilitates the rapid growth of relatively high-density HCA,

which will therefore eventually replace the initial silicate glass as the material

bounding the macropores.

The data presented herein reveal the structure of highly important materials in

the field of biomaterials and enable a link to be made between the atomic scale

structure of the materials and their bioactive properties.