Multinuclear Solid-State NMR Studies of Ordered Mesoporous Bioactive Glasses

The local structures of highly ordered mesoporous bioactive CaO−SiO 2 −P 2 O 5 glasses were investigated for variable Ca contents. 1 H 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 29 Si and 31 P 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 1 H− 29 Si and 1 H− 31 P hetero-nuclear two-dimensional correlation spectroscopy. The results are consistent with SiO 2 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.