A polymeric film responding in diffusion properties to environmental pH stimuli: a model for a self-regulating drug delivery system.

A new polymeric film, ethylene-vinyl-NN-diethylglycinate random copolymer, has been studied to evaluate possible applications of such a material to produce controlled release dosage forms. Protonation of the substituted amino groups took place to different extents according to environmental pH conditions. The polymeric film proved to be permeable only to uncharged species, the rate of diffusion of which increased with the increasing charge of the membrane. This effect might be related to strong polymer-proton interactions affecting structure and transport properties of the film and enhancing the solvation process. The charged form of a number of barbituric acid derivatives did not diffuse through the membrane. The uncharged forms permeated the polymeric sheeting at rates consistent with their partition coefficients and which increased with the increasing charge of the polymer.