Addition of CaF2 to a silicate bioactive glass favours formation of fluorapatite, which is less soluble in acidic environment than hydroxyapatite. However, excess CaF2 in the glass is problematic, owing to the formation of crystalline calcium fluoride rather than fluorapatite on immersion. In this paper we investigate chloride as an alternative to fluoride in bioactive silicate glasses and in particular their bioactivity for the first time. Meltderived bioactive glasses based on SiO2-P2O5-CaO-CaCl2 with varying CaCl2 contents were synthesised and characterised by DSC. Chemical analysis of the chloride content was performed by using an ion selective electrode. Glass density was determined using Helium Pycnometry. The glass bioactivity was investigated in Tris buffer. Ion release measurements were carried out by using ICP-OES. The chemical analysis results indicated that the majority of the chloride is retained in the Q2 type silicate glasses during synthesis. Tg and glass density reduced with increasing CaCl2 content. Apatite-like phase formation was confirmed by FITR, XRD and 31P MAS-NMR. The results of the in vitro studies demonstrated that the chloride containing bioactive glasses are highly degradable and form apatite-like phase within three hours in Tris buffer and, therefore, are certainly suitable for use in remineralising toothpastes. The dissolution rate of the glass was found to increase with CaCl2 content. Faster dissolving bioactive glasses may be attractive for more resorbable bone grafts and scaffolds.
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