Abstract
We review the benefits of using 29Si and 1H magic angle spinning (MAS) nuclear magnetic resonance (NMR) spectroscopy for probing the local structures of both bulk and surface portions of mesoporous bioactive glasses (MBGs) of the CaO–SiO2−(P2O5) system. These mesoporous materials exhibit an ordered pore arrangement, and are promising candidates for improved bone and tooth implants. We discuss experimental MAS NMR results from three MBGs displaying different Ca, Si and P contents: the 29Si NMR spectra were recorded either directly by employing radio-frequency pulses to 29Si, or by magnetization transfers from neighbouring protons using cross polarization, thereby providing quantitative information about the silicate speciation present in the pore wall and at the MBG surface, respectively. The surface modifications were monitored for the three MBGs during their immersion in a simulated body fluid (SBF) for intervals between 30 min and one week. The results were formulated as a reaction sequence describing the interconversions between the distinct silicate species. We generally observed a depletion of Ca2+ ions at the MBG surface, and a minor condensation of the silicate-surface network over one week of SBF soaking.
Highlights
Silica-based melt-prepared bioactive glasses (MPBGs) [1,2,3,4] are in clinical use for repairing fractures and filling voids in bone and tooth
We have focused on the mesoporous bioactive glasses (MBGs) surface reactions during simulated body fluid (SBF) treatment, as inferred from the silicate speciations derived from 1H→29Si CPMAS nuclear magnetic resonance (NMR)
The key experimental tools of this work consisted of solid-state 29Si and 1H NMR [30,31], whose utilities were reviewed and illustrated for quantitatively monitoring the silicate speciation of both the MBG pore-wall interior and its surface for three MBG specimens of different Ca, Si and P contents
Summary
Silica-based melt-prepared bioactive glasses (MPBGs) [1,2,3,4] are in clinical use for repairing fractures and filling voids in bone and tooth. The precise molecular mechanism underlying the HM presumably varies slightly depending on the structural, textural and compositional properties of the biomaterial [14] and the exact external conditions of its surrounding medium Such issues are important to settle in view of the currently rapid developments of improved bioactive glasses (BGs), notably those prepared by using structure-directing agents, e.g. mesoporous bioactive glasses (MBGs) of the CaO–SiO2−P2O5 system [13,20,21,22,23,24]. The resulting homogeneous membranes were heated at 700◦C for 6 h to remove organic species and nitrate ions This procedure was employed to prepare three MBG specimens of nominal molar compositions 10CaO–90SiO2, 10CaO–85SiO2−5P2O5 and 37CaO–58SiO2−5P2O5, labelled ‘S90’, ‘S85’ and ‘S58’, respectively, according to their mol% of SiO2.
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