Delia S. Brauer is Professor of Bioactive Glasses at the Otto Schott Institute of Materials Research, University of Jena, Germany. After finishing her studies in environmental chemistry she completed her doctoral studies on phosphate glasses at the University of Jena. She worked as a postdoctoral researcher at the University of California, San Francisco, Nagoya Institute of Technology, Japan, and Imperial College and Queen Mary University of London, UK, before returning to Jena in 2012. Her research focuses on the structure-property relationship in glasses, with a focus on degradable and highly disrupted glass systems including phosphate glasses and phospho-silicate glasses. She is Chair of Technical Committee 04 (Bioglasses) of the International Commission on Glass, member of the Basic Sciences and Technology Committee of the Society of Glass Technology, Associate Editor of a new journal “Biomedical Glasses” and winner of the Gottardi Prize of the ICG in 2015.
Delia S. Brauer
Dahiana A. Avila Salazar, Peter Bellstedt, Delia S. Brauer*
Friedrich Schiller University Jena
Structural changes in phosphate glasses tune their degradation rate in aqueous media, which is of interest for potential therapeutic applications such as drug delivery. Therefore, getting insight into the mechanism of degradation is of great interest to tailor glass dissolution. In this study, structural characterisation by P-31 MAS NMR of the glass system 45 P2O5–(x-y) CaO–(55-x) Na2O–y CoO (x: 25 to 40, y: 0 to 10 mol%) was correlated with dissolution kinetics in various immersion media: deionised water, Tris (pH: 7.4, 7.9) and EDTA (pH: 10.0) studied by time-dependent P-31 NMR, pH and ICP-OES measurements. For P-31 NMR studies in solution, the paramagnetic nature of Co2+ was exploited to obtain information about complexing of metal cations by phosphate species. Paramagnetic centres, such as Co2+, broaden the P-31 resonance, providing direct information about the role of metal complexes in the hydrolysis process. The trimetaphosphate ring and orthophosphate as predominant structures in solution, except in EDTA, indicated fast hydrolysis of chains and exhibited paramagnetic broadening, thus suggesting that the phosphate group may be directly coordinated to Co2+. The rate of hydrolysis was proportional to the stability of the respective phosphate complex, with stronger complexes for the phosphate chains than for the rings. A competition between the solvent and phosphate species for the metal ion occurred following the trend: EDTA>Tris (pH: 7.9)> Tris (pH: 7.4) > deionised water. In conclusion, the catalytic effect of the metal ions may consist in turning the phosphorus atom into a suitable electrophile, for a subsequent nucleophilic attack by water.