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Asymmetric membrane tablet coatings for controlled-release of drugs
Most of the controlled release systems developed for drug delivery applications dependon membrane technology. The dense structure of the membrane in conventional controlled release systems prolongs the release of drug. To eliminate this disadvantage while maintaining the benefits of dense membrane systems, an asymmetric type of coating was applied on tablets. Coatings were prepared from cellulose acetate, acetone, water solution by phase inversion technique. To determine the release rate of drug, dissolution studies on tablets were performed according to United States of Pharmacopeia (USP). In these studies, the effects of composition of the polymer/solvent/nonsolvent, coating time, number of coating layers, evaporation conditions and the nonsolvent type on the release rate of the drug and the structure of membrane were investigated. Experiments were designed using commercial software package Design-Expert and a quadratic model equation was obtained to predict the effect of composition of cellulose acetate, acetone and water on the release rate of drug. The advantage of asymmetric type coating over the conventional dense type coating was further demonstrated by measuring the permeabilities of both type of coatings. In addition, the structures of membranes were analyzed using scanning electron microscope (SEM) micrographs.