Controlled release of antibacterial compounds based on multiparametric analysis of mesoporous silicon carriers

Abstract

Controlled delivery of antibacterial agents remains a topic of widespread significance, given the need for sustained release of therapeutically relevant concentrations. Porous Si (PSi), and the mesoporous form in particular, possesses useful properties relevant to its use in medical therapies such as drug delivery and tissue engineering. For drug delivery, both the biodegradability of mesoporous Si and its ability to nanostructure a given encapsulated substance present marked advantages. In this work we have systematically investigated the influence of the properties of mesoporous silicon on both controlled release and antibacterial assay for the case of the loaded antibacterial drug triclosan and its activity versus Staphylococcus aureus. Specifically, the role of Si porosity, loading method, surface chemistry and particle morphology on the above outcomes are explored.^For long term stabilization of the drug-loaded PSi, preliminary experiments regarding organosilicon and organotitanium surface coatings have also been carried out. The role of PSi porosity on drug delivery has been highlighted by a comparison between the properties of triclosan loaded into porous silicon with high (81%), medium (65-75%), and low porosity (13%). The significant differences in triclosan release behavior are demonstrated in their corresponding antibacterial disk diffusion assays. A remarkable sustained triclosan release beyond 100 days from mesoporous silicon matrices was revealed, combined with an enhanced concentration of released triclosan. Due to the high surface area of these mesoporous materials, surface chemistry is expected to have a significant impact on drug delivery. Since freshly-etched PSi with its hydride-terminated surface possesses a relatively rapid degradation rate in aqueous media, derivatization of PSi by oxidation or chemical modification is needed.^In this study, a relatively long octyl chain is covalently attached to the mesoporous silicon surface, which possesses hydrophobicity and inhibits aqueous dissolution. A combination of thermogravimetric analysis, X-ray diffraction, electron microscopy, and FT IR spectroscopy, in addition to triclosan release and antibacterial assays, are employed for this purpose. A preliminary study involving organosilica and organotitania surface coatings on PSi was also conducted. FT IR spectroscopy, scanning electron microscopy (SEM), energy-dispersive X-ray (EDX) analyses, and subsequent antibacterial assays confirm that the coating is present.