Kinetics of drug release from hydrogel matrices

Abstract

The release of water soluble drugs from initially dehydrated hydrogel matrices generally involves the simultaneous absorption of water and desorption of drug via a swelling-controlled diffusion mechanism. Thus, as water penetrates a glassy hydrogel matrix containing dispersed drug, the polymer swells and its glass transition temperature is lowered. At the same time, the dissolved drug diffuses through this swollen rubbery region into the external releasing medium. Such diffusion and swelling generally do not follow a Fickian diffusion mechanism. The existence of some molecular relaxation process in addition to diffusion is believed to be responsible for the observed non-Fickian behavior. In this article, the kinetics of drug release from hydrogel matrices will be examined both experimentally and theoretically. Special emphasis will be placed on the effect of local drug concentration on the swelling behavior of hydrogel drug carriers. A novel approach to constant-rate drug delivery from glassy hydrogel matrices via an immobilized non-uniform drug concentration distribution will also be described.