Investigation of process/formulation parameters on Inulin-Eudragit RS film properties: correlation between microstructure and film permeability.

Coatings made up of Inulin (Inu) and Eudragit RS (ERS) have been used in the past in colon specific drug delivery systems. In the present study, we investigated the correlation between manufacturing conditions (spraying process and solid content of the film-forming system) and the permeability and the microstructure of Inu-ERS films. The solid content of the polymer dispersion, atomization air pressure, feed rate and bed temperature were investigated by a full factorial design. The solid content of the dispersion was the dominant factor affecting the structure of the film and its permeability for the model drug caffeine. Atomization air pressure and bed temperature were of secondary importance. Within the set parameter range, the lower the solid content of the spraying dispersion, the lower the atomization air pressure and the lower the bed temperature, the higher the permeability of the obtained film. The permeability of the film mainly depends on the kinetics of polymer phase separation and the resulting dispersivity as well as connectivity of the Inu phase. Casted films displayed slower phase separation kinetics resulting in higher permeability. Increased curing time and residual moisture in the film favored the coalescence of polymer particles, leading to films with lower permeability. The results show that there was a strong association between manufacturing conditions, the microstructure and permeability of the films, providing insights to guide the rational design of film coatings.