Differential scanning calorimetry and NMR study of water confined in a mesoporous bioactive glass

The emergence of a new generation of nanostructured materials opened a wide range of new potential applications for Bioglasses such as DNA vaccination, cellular treatment or drug delivery with a well-controlled loading and release of (bio)active molecules. In this study we compare structural, dynamic and thermal properties of water confined in two CaO–SiO2–P2O5 mesoporous bioactive glasses (MBGs). One of the MBGs is prepared by standard sol-gel methods and the other by microfluidic procedures, therefore both MBGs have the same molar compositions (92% SiO2, 6% CaO, and 2% P2O5) but different textural properties (surface areas, porous volume and grain architecture). These materials are intended to interact with body fluids which are essentially composed of water, it is therefore crucial to understand the water-MBG interaction. With this objective, we apply a complementary approach based on 1H field-cycling NMR relaxometry, 1H magic-angle spinning NMR spectroscopy and differential scanning calorimetry (DSC). With low-field relaxometry we observe that adsorbed water has the same behavior in the mesoporous channels of both systems, but that the escaping of water molecules towards the bulk is slightly faster in the microfluidic material. By combining 1H MAS NMR and DSC to study a series of MBG samples at variable temperature and water content, we observe that for low temperature and low water content, pooling of water molecules is less pronounced in the case of the microfluidic MBG. All our results therefore point towards a microcapsule organization of the microfluidic MBG that provides better water access to the full porous volume.