Bioactive glasses undergo dynamic changes in vivo to produce an apatite layer permitting a strong bond with living tissues including both bone and soft tissues, and their compositions can be modified and tailored. The aim of this project was to generate high phosphate low fluoride containing bioactive glasses and explore their bioactivity and biological performances in vitro. Bioactive glasses (0-7% F- content, constant 6.33% P2O5 in Mol.%) were produced and the particles immersed in Tris Buffer solution or cell culture medium (α-MEM) to determine apatite formation and ion (Ca, P, Si and F) release. Bioactive glass conditioned medium was used to treat pre-osteoblasts MC3T3-E1 for cytotoxicity, pre-osteogenic and pro-angiogenic responses, and to human oral fibroblasts and epithelial cells for proliferation. Antibacterial ability was explored by incubating supra- and sub-gingival bacteria with bioactive glass particulates. Rapid apatite formation was observed in F- containing bioactive glasses after only 2 h immersion in Tris buffer solution, while it was not detectable until 72 h in the F- free bioactive glass. Alkaline phosphatase activity, cell number, collagen formation, bone-like mineral nodules and osteogenic gene expression of MC3T3-E1 cells were significantly promoted in low F- bioactive glass (P6.33F1) conditioned medium. MC3T3-E1 VEGF gene expression was increased, and protein production was dose-dependently promoted with F- containing bioactive glass conditioned medium, which also promoted human oral fibroblast proliferation, but suppressed epithelial cell numbers. After incubation with glass particulates, the growth of L. casei, S. mitis, A. actinomycetemcomitans and P. gingivalis, was significantly inhibited; the antibacterial activity being dependent on the F- content of the bioactive glasses. As a potential bone graft substitute in vivo, such novel bioactive glasses would be expected to stimulate bone formation and overcome problems associated with infection and the poor vascularisation in large bone graft sites. Additionally, they could reduce the need for further clinical intervention, and in particular, will be advantageous for the periodontal soft tissue regeneration.

The viscosity of Zr[subscript 41.2]Ti[subscript 13.8]Cu[subscript 12.5]Ni[subscript 10.0]Be[subscript 22.5] (Vit1) has been measured above the liquidus temperature, T[subscript liq]=1026 K, using a high vacuum high temperature rapid annealing furnace equipped with a Couette Concentric Cylinder Rheometer. Steady state measurements have been taken over a temperature range of 1075-1300 K and a shear rate range of 10⁰-10² s⁻¹. It has previously been discovered that there exists a pronounced decrease in viscosity with increasing shear rate which is contrary to the general belief that metallic systems above the liquidus temperature should show Newtonian behavior due to high atomic mobility. This suggests that there is short or medium range order present in the liquid state that can be destroyed by shearing. This current study has discovered that this shear rate dependence of the viscosity of Vit1 decreases with increasing temperature and approaches the Newtonian behavior and viscosities of simple monatomic or binary liquid alloys at 1225 K. Once this state is reached the viscosity will remain Newtonian in the liquid state and no order is reformed until the sample is cooled into the supercooled region. This indicates a strong temperature history dependence of the viscosity. It has also been discovered that initially crystalline Vit1 has an order of magnitude lower viscosity than initially amorphous Vit1 at 1075 K after melting. This difference decreases with increasing temperature until similar viscosities are obtained at 1175 K. The Vogel-Fulcher-Tammann relationship shows decreasing fragility of Vit1 with increasing shear rate and increasing temperature. It was also seen that temperature has a larger and more permanent effect on the fragility than shear rate. The development and results of converting viscosity data to configurational entropy using the Adam-Gibbs entropy model for viscous flow are discussed. This shows that the configurational entropy present after melting is on the order of the entropy of fusion. / Graduation date: 2006

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Binary series CoO-P205 and ternary series CoO-NiO-P205 glasses are prepared. The density, d.c. conductivity, highfield I-V characteristicsr memory switching actiong a.c. electrical conductivity, infra-red absorption and optical absorption edge of the glasses are presented. The historical background and the formation and theory of the glassy state are reviewed. Previous works on the electrical conductivity of phosphate glasses are reviewed in the framework of Mott's theory. In the binary glasses, the glass acquires a more compact structure with increased CoO content whereas for the ternary series the results show otherwise. A polaronic model is shown to be generally applicable to explaining the results of electrical conduction measurements. The pre-exponential factor containing the term exp (-2aR) arising from electron tunnelling should not be ignored; thus the theory of the small polaron hopping is in the non-adiabatic regime. The high-field ohmic behaviour is observed up to a field of about 3x 104 V-cm-l'. Apparentlyt the field dependence is a property of the bulk material. Thin films of glass with 30 Mol % CoO show memory switching phenomena. The results of a.c. measurements characterize hopping conduction as a dominant process in cobalt-phosphate glasses. Results of the infra-red spectra measured in the range 400 cm-1 to 4000 cm-1 show that the phosphate polyhedra dominate the structure of the glasses. Measurements of the optical gap in the binary series show decreasing values with increased CoO content. It is believed that the fundamental absorption arises from indirect transitions.

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