Novel Halide Containing Bioactive Glasses
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Bioactive glasses (BG) are widely used in dentistry and medicine due to the ability to form a hydroxyapatite layer to bond to bone. Fluoride has been introduced into BG to provide additional effects, such as inhibition at enamel and dentine demineralisation, reduction of glass melting temperature and facilitating an acid durable fluorapatite formation etc.. Therefore, fluoride containing BG are attractive for remineralising toothpaste application. However, excessive fluoride is problematic. Chlorine is thought to behave like fluorine in terms of glass structure and properties. As the chloride ion is larger than fluoride ion, the incorporation of chloride could expand the glass volume that might result in a more open structure and a more degradable glass. These glasses are of interest for resorbable bone grafts and remineralising toothpastes. In this thesis, the investigation of chloride as an alternative to fluoride in the silicate BG was carried out for the first time. Sodium free BG based on SiO2-P2O5-CaO-CaF2/CaCl2 or SiO2-CaO-CaF2/CaCl2 with varying calcium halide content were synthesised via a melt-derived route and characterised by various advanced techniques. The glass bioactivity was estimated in Tris and SBF. Ion release measurements were carried out by using ICP-OES and ion selective electrodes. The apatite formation was characterised by FTIR, XRD and MASNMR. The crystallisation events of the glasses were explored by heat treatment. This study reveals that the majority of chloride is successfully retained in the Q2 type silicate BG. Glass transition temperature and density decrease with increasing halide content. The studied high phosphate containing BG are highly dissolvable and formed apatite-like phases within 3h in Tris. The glass dissolution rate was found to increase with CaCl2 content but not with CaF2. On heat treatment, fluorapatite or chlorapatite is the main crystalline phase in phosphate containing glasses, while CaF2/CaCl2 is likely the one for the glasses without phosphate. This is the first time to our knowledge that chlorapatite has been shown to crystallise from a glass.
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