Mesoporous Silica: An Alternative Diffusion Controlled Drug Delivery System

M esoscopically ordered mesoporous silica materials have attracted a wide interest since their discovery in the early 1990’s due to their diverse potential applications areas; including catalysis, filtration and chromatography. Supramolecular surfactant aggregates are used as structure directing agents for inorganics during condensation, leading to mesoscopically ordered surfactant-inorganic composites. Porosity can be induced in the inorganic part by removal of the surfactant portion through thermal or chemical means. By controlling the synthesis conditions and choice of structure directing agents, the system can be engineered to fit numerous functions of preference. As the purely siliceous mesoporous materials have been shown to be biocompatible, or sometimes even bioactive, there is an increasing interest in this class of materials for applications in the field of bioceramics, especially as bone substitute materials. Furthermore, the highly organized porous silica matrix could be used as a potential controlled drug release system. Another attractive advantage is that amorphous silica is degradable in an aqueous solution, and thus problems related to the removal of the material after use can be avoided. In this article, a few of the most common forms of drug delivery mechanism from ceramic drug carrier systems are investigated. Furthermore, some examples are given on different mesoporous silica systems as drug delivery devices and how factors such as pore size, pore connectivity and surface affect the drug loading and the release (diffusion) rate.