A series of ordered mesoporous SiO 2 -CaO-P 2 O 5 sol-gel glasses which are highly bioactive has been synthesized through evaporation-induced self-assembly in the presence of a nonionic triblock copolymer, EO 20 PO 70 EO 20 (P123), template. By keeping constant the SiO 2 + P 2 O 5 /P123 ratio, the influence of the CaO precursor, Ca(NO 3 ) 2 ‚4H 2 O, on the mesostructure has been determined. After calcination at 700°C, ordered mesoporous glasses are obtained, showing structures that evolve from 3D-cubic to 2D-hexagonal when the CaO content increases. The mesoporous glasses are highly bioactive compared with conventional ones, due to the increased textural characteristics supplied by the template. The bioactivity tests point out that the surface area, porosity, and 3D-structure become more important than chemical composition during the apatite crystallization stage in these materials, due to the very high textural parameters obtained. IntroductionSince 1991, when scientists of Mobil Oil Corporation synthesized the silica-based MCM-41 molecular sieve, 1-2 highly ordered mesoporous materials have attracted the attention of many scientists, mainly due to their potential technological applications. Mesoporous materials are characterized as having high surface area, pore volume, and pore size, with narrow pore diameter distribution. For this reason, applications in the field of catalysis, lasers, sensors, solar cells, etc. have been proposed and/or developed. [3][4][5][6][7][8] Recently, these materials have been proposed for their application in biomaterials science. 9 Due to their textural properties of surface and porosity, ordered mesoporous materials have shown to be excellent candidates for two biomedical applications: local drug delivery systems 10-12 and bone tissue regeneration. 13-15 Actually, silica-based mesoporous materials are able to incorporate high dosages of drugs into the mesopores. On the other side, mesoporous materials can be synthesized with analogous chemical composition to highly bioactive sol-gel glasses. These materials are able to bond to living bone when implanted through the formation of a nonstoichiometric carbonated hydroxyapatite of nanometrical size (CHA). 16,17 This bioactiVe bond ensures the implant osteo-integration, and its degradation products promote the bone tissue regeneration.Increasing the specific surface area and pore volume of bioactive glasses greatly accelerates the CHA formation and therefore enhances the bioactive behavior. 18 In this sense, highly ordered mesoporous materials provide very promising possibilities in the field of bone tissue regeneration. Moreover, these materials can be loaded with osteogenic agents promoting the new bone formation in vivo and can also be applied as scaffolds for bone tissue engineering. 19,20 Nonionic block copolymers are an interesting class of structure-directing agents whose self-assembly characteristics lead to ordered mesostructures. 21-25 They have the advantage that their ordering properties can be tuned by adjusting * Corres...
This manuscript reviews the recent progress on mesoporous silica nanoparticles as drug delivery systems. Their intrinsic structural, textural and chemical features permit to design versatile multifunctional nanosystems with the capability to target the diseased tissue and release the cargo on demand upon exposition to internal or external stimuli. The degradation rate of these nanocarriers in diverse physiological fluids is overviewed obeying their significance for their potential translation towards clinical applications. To conclude, the balance between the benefits and downsides of this revolutionary nanotechnological tool is also discussed.
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.
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