ABSTRACT
A new controlled release matrix that is beginning to receive broad commercial acceptance is an ultramicroporous open-celled form of cellulose triacetate. Sustained release from ultramicroporous cellulose triacetate is basically diffusion-controlled, in which respect it differs from microencapsulation which depends primarily on rupture or dissolving of a thin shell for release. When an internal liquid, such as water, is partially or wholly removed, shrinkage appears to occur initially with a collapse of the smallest pores, and eventually, it also includes the larger pores. Thus, liquids or solids can initially be diffused into the Poroplastic® matrix; and then by a drying and shrinkage process, the pores can be partially collapsed so as to entrap or reduce the rate of active agent diffusion to the surface of the matrix. Cellulose triacetate is generally considered to have very good solvent resistant properties, and the solvent resistance of Poroplastic® film and Sustrelle® powder are accordingly quite good.
