Surface chemistry and pore size affect carrier properties of mesoporous silicon microparticles.

Six different types of mesoporous silicon microparticles were prepared to evaluate the effect of surface treatment and pore sizes on their properties as drug carriers. The studied porous silicon particles were as-anodized, thermally carbonized (TCPSi) and thermally oxidized (TOPSi) in addition to three novel ones: annealed TCPSi, annealed TOPSi and thermally hydrocarbonized porous silicon (THCPSi). Drug dissolution at pH 5.5 and physical and chemical stabilities after 3 months of storage were used as experimental models to investigate the loaded particles. Loading degrees of ibuprofen in the particles were determined by several methods before and after storage, and the results were in good agreement with each other. Loading improved the dissolution rate of ibuprofen in all the studied cases, while the hydrophilic TCPSi material resulted in the fastest dissolution and the most stable mesoporous microparticles. The release profiles of ibuprofen did not change markedly during storage. The effect of storage on the loading degrees of the other PSi microparticles than the unstable (easily oxidized) as-anodized porous silicon was not notable.