Dispersible Microparticles

Abstract

The release of active ingredient from conventional formulations generally follows an exponential decay; that is, the release rate is proportional to the quantity of active ingredient remaining in the formulation. Transport through a polymer membrane or matrix occurs by a solution-diffusion process, where the active ingredient first dissolves in the polymer and then diffuses across the polymer to the external surface, where the concentration is lower. The most common types of controlled-release microparticles are membrane-coated reservoirs and polymeric matrices. A reservoir system consists of a core of pure or saturated active ingredient surrounded by a rate-controlling membrane. The release rate from a given membrane-coated reservoir will remain constant as long as the diffusivity and concentration gradient remain constant. A matrix type of microparticle consists of the active ingredient dispersed or dissolved in a polymeric matrix. Dispersible microparticles include several types of microcapsules, matrix micro-particles, and microporous particles.