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Influence of zinc and magnesium substitution on ion release from Bioglass 45S5 at physiological and acidic pH

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Blochberger M., Hupa L., Brauer D. S.
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Ion release of Mg- and Zn-substituted Bioglass 45S5 (46.1 SiO2-2.6 P2O5-26.9 CaO-24.3Na2O; mol%; with 0, 25, 50, 75 or 100% of calcium replaced bymagnesium/zinc) was investigated at pH 7.4 (Tris buffer) and pH 4 (acetic acid/sodium acetate buffer) in static and dynamic dissolution experiments. Despite Mg2+ and Zn2+ having the same charge and comparable ionic radii, they influenced the dissolution behaviour in very different ways. In Tris, Mgsubstituted glasses showed similar ion release as 45S5, while Zn-substituted glasses showed negligible ion release. At low pH, however, release behaviour was similar, with all glasses releasing large percentages of ions within a few minutes. Precipitation of crystalline phases also varied, as Mg- and Zn-substitution inhibited apatite formation, and Zn-substitution resulted in formation of zinc phosphate phases at low pH. These results are relevant for glasses used in aluminium-free glass ionomer bone cements, as they show that Zn/Mg-substituted glasses release ions similarly fast as glasses containing no Zn/Mg, suggesting that these ions are no prerequisite for ionomer glasses. Zn-substituted glasses may potentially be used as controlled-release materials, which release antibacterial zinc ions when needed only, i.e. at low pH conditions (e.g. bacterial infection), but not at normal physiological pH conditions.
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Novel Highly Degradable Chloride Containing Bioactive Glasses

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Chen X., Karpukhina N., Brauer D. S., Hill R. G.
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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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Dissolution behavior and cell compatibility of alkali-free MgO-CaO-SrO-TiO2-P2O5glasses for biomedical applications

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Lee S., Obata A., Brauer D. S., Kasuga T.
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Owing to their controlled solubility, phosphate invert glasses are of interest for use as temporary implant materials or tissue engineering scaffolds for controlled ion release.MgO-CaO-SrO-TiO2-P2O5 invert glasses were prepared and their dissolution behavior and cell response were examined.MgO addition to the phosphate invert glass system improved glass formation, owing to the relatively large field strength of Mg2+ ions. In osteoblastlike MC3T3-E1 cell culture tests, cell numbers on the invert glasses were significantly larger compared with the control, possibly caused by the release of Mg2+ ions promoting enhanced cell adhesion and proliferation. Alkaline phosphatase (ALP) activity varied with glass composition, with higher strontium for calcium substitution (33 to 100%) showing highest ALP activity. This effect may be caused by the release of strontium ions from the glasses.
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