Drug entrapment in silica microspheres through a single step sol-gel process and in vitro release behavior

A single step sol-gel process was used to precipitate silica microspheres containing ibuprofen or naproxen for controlled drug delivery applications. The drug release behavior from these systems was analyzed in vitro. Pure ibuprofen and naproxen exhibited linear release with time, while sol-gel silica entrapped drugs were released with a logarithmic time dependence starting with an initial burst effect followed by a gradual decrease. Microscopic analysis combined with gravimety and infrared spectroscopy indicated that some of the drug is entrapped as large crystals attached to silica microspheres while the rest is encapsulated inside the microspheres. Drug-loaded silica microspheres with no open porosity and with a narrow particle size distribution were obtained. Both erosion of the microspheres and diffusion through them contributed to drug release. Sol-gel precipitation of silica microspheres is a promising method for drug entrapment and controlled release.