Tunability of pore diameter and particle size of amorphous microporous silica for diffusive controlled release of drug compounds

Amorphous microporous silica (AMS) materials with variation in microporosity were prepared using an acidcatalyzed sol-gel procedure departing from tetraethylorthosilicate. The silicas were fined to specific particle sizes by crushing and sieving. AMS materials were loaded with 10 wt% ibuprofen either by uptake of molten ibuprofen or by adsorption of ibuprofen from a methylene chloride solution. DSC analysis of ibuprofenloaded AMS confirmed the molecular dispersion of ibuprofen on the silica material. In vitro ibuprofen release from AMS carrier was investigated in simulated intestinal fluid and in a dissolution medium simulating the gastrointestinal tract with simulated gastric fluid followed by simulated intestinal fluid. The release of ibuprofen molecules from the AMS silica carrier is governed by diffusion. The diffusivity of ibuprofen in the investigated series of AMS samples was in the range 10(-14)-10(-11) m(2) s(-1). By adapting the porosity and particle size of AMS, the release could be evenly spread over periods from 3 to 100 h. This flexibility of AMS opens perspectives for designing tailor-made controlled release formulations.