ABSTRACT
Recently, the study of application of controlled release systems that contain biologically active substances, has grown enormously. In the preparation of these systems, the biologically active substance is immobilized in a carrier, usually a polymeric material. These polymeric systems can be either natural or synthetic, have the right balance of hydrophilicity/hydrophobicity, the right charge character and biocompatibility. Their form (powder, fibre or membrane) is dependent on the application. Cellulose acetate propionate/cellulose acetate butyrate composite membranes were used by Sobral et al.1 to prepare a drug release system. These authors immobilized ketotifen, by entrapment in theses membranes.
