Cross-linked films of gelatin (Gel), casein (Cas) and their (1:1, m/m) mixture (Gel/Cas) were studied in terms of their thermal, morphological and water absorption properties and the permeation profile of p-hydroxyacetanilide (p-HAA) as a model drug. The degrees of cross-linking by 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide hydrochloride (EDC) were 90.6% for Gel films and approximately 70% for Cas and Gel/Cas films. The totally soluble non cross-linked films achieved only 21 - 22% of solubility after cross-linking with EDC. Despite the high cross-linking degree, the swelling of Gel films (87.2%) was practically twice that determined for Gel/Cas and Cas films. The permeation rate of p-HAA followed the order Gel>Gel/Cas ≅ Cas for cross-linked films, which is consistent with the Gel film showing a greater swelling than the other two systems studied. Lower permeation rates were observed for Cas and Gel/Cas films, suggesting that these could be used as rate-controlling systems for drug permeation. For the different mathematical models applied, the systems studied did not show a good fit with the first-order equation and only a partial fit with the zero-order equation and Higuchi's model. However, good correlations (r² > 0.99) were obtained using the power law equation (n = 0.70 - 0.87), indicating that the p-HAA permeation through the films was mainly controlled by a diffusion mechanism.
gelatin; casein; films; cross-linking; drug permeation
