Porosity-Controlled Ethylcellulose Film Coating. IV. Evaluation of Mechanical Strength of Porous Ethylcellulose Film.

Abstract

The mechanical characteristics of porous ethylcellulose (EC) film as a barrier in a controlled release dosage form were investigated. Sprayed EC films with various porosities were prepared by changing the ethanolic concentrations in the EC spraying solution, and their film porosities (ε) and tensile strength (Ts) were measured. It was found that the Ts of EC films decreased with an increase in ε, and that the quantitative relationship between both parameters was considerably adapted to the equation proposed by Bal'shin. By using the permeability-ε and Ts-ε relations, the mechanical strength of two EC films with different porosities were estimated under the assumption that the drug permeation rate through the two films was equal. The result suggested that, when the permeation rate was equal, a film with higher porosity would have higher mechanical strength. This was also proved by a high-shear dissolution test for theophylline beads coated with EC film. The in vivo drug release behavior from porous EC film-coated beads agreed well with the in vitro drug release, indicating that the porous EC film-coated beads had sufficient strength to withstand the mechanical stress of the gastrointestinal tract, and that the porous EC film coating could be used as a barrier for controlled release preparations.