Multinuclear Solid-State NMR Studies of Ordered Mesoporous Bioactive Glasses

Abstract

The local structures of highly ordered mesoporous bioactive CaO−SiO2−P2O5 glasses were investigated for variable Ca contents. 1H NMR revealed a diversity of hydrogen-bonded and “isolated” surface silanols as well as adsorbed water molecules. The structural roles of Si and P were explored using a combination of 29Si and 31P magic-angle spinning (MAS) nuclear magnetic resonance (NMR) techniques; the proximities of Si and P to protons were studied through cross-polarization-based experiments, including 1H−29Si and 1H−31P hetero-nuclear two-dimensional correlation spectroscopy. The results are consistent with SiO2 being the main pore-wall component, whereas P is present as a separate amorphous calcium orthophosphate phase, which is dispersed over the pore wall as nanometer-sized clusters. The excess Ca that is not consumed in the phosphate phase modifies the silica glass network where it associates at/near the mesoporous surface. This biphasic structural model of the pore wall leads to the high accessibility of both Ca and P to body fluids, and its relation to the experimentally demonstrated high in vitro bioactivities of these materials is discussed.

PDMS-SiO2-TiO2-CaO hybrid materials – Cytocompatibility and nanoscale surface features

“…Also, from the observation of 1 H MAS NMR spectra ( Figure 3), and as explained in section 3.2, sample K presents a higher amount of physisorbed water than sample I. As reported by other authors for bioglass compositions [43,44] this difference in the amount of physisorbed water are related to the Ca 2+ concentration in the surface. Thus, one can conclude that sample K presents a higher concentration of calcium ions at its surface when compared to sample I, in agreement with the ICP results.…”

“…A sharp peak at ca. 4.8 ppm is assigned to physisorbed water molecules [41,43], probably related to the inclusion of Ca into the composition of the hybrids. No physisorbed water was detected in our previous studies [12] were the structure of PDMS-SiO 2 hybrids without Ca was also analysed by 1 H MAS-NMR.…”

“…Leonova et al [43] and Gunawidjaja et al [44] reported the presence of physisorbed water due to the presence of Ca in bioglass compositions.…”

Recent technique developments and applications of solid state NMR in characterising inorganic materials

“…Another example of the use of a combined methodology was a study on some mesoporous CaO-SiO 2 -P 2 O 5 glasses that combined 1D 1 H, 29 Si and 31 P MAS NMR with CP, DQ 1 H-1 H experiments and heteronuclear correlation experiments. The combination allowed the spatial distribution of the different elements to be understood and a biphasic model of the structure to be proposed [85]. The pore wall is mainly SiO 2 with a nanoscale amorphous calcium orthophosphate phase that is distributed heterogeneously on the inner surface.…”

The influence of phosphorus precursor on the structure and properties of SiO 2 –P 2 O 5 –CaO bioactive glass

“…Similar 1 NMR signals had sometimes been suggested to attribute to pyrophosphates (i.e., P-O-P bonds) 34 . On the other hand, it has been suggested that in CaO-SiO2-P2O5 glasses this signal might represent P-O-Si moieties 35 . For TEP-BG and BP-BG, three resonances at approximately 2, -8 and24ppm were present on the 31 P NMR spectra.…”