Silk fibroin as a novel coating material for controlled release of theophylline

The aim of this study was to explore potential use of the silk fibroin (SF) as an aqueous coating material for theophylline tablets. We have examined the film forming and coating properties of heat-treated fibroin, SF solution having different amounts of polyethylene glycol (PEG) and 1-ethyl-3-(3-dimethyl aminopropyl)carbodiimide (EDC) cross-linked SF. Heat-treated SF material possessed a brittle structure, which resulted in poor film forming and coating properties. The optimum PEG amount in SF solution was determined as 17% (by weight) for an acceptable film forming and zero order release profile. EDC cross-linked SF has shown a very good film forming and coating property with a potential for sustaining the drug release from coated theophylline tablets. Dissolution data for coated theophylline tablets were analyzed using Ritger and Peppas equation to describe the mechanism of drug release. Drug release from the EDC coated tablets followed zero-order kinetics. Release rate constants were found to be 0.26, 0.19, 0.16% min(-1) for single-coated, double coated, and triple coated tablets, respectively. These results clearly demonstrated that silk fibroin has high utility as a novel aqueous coating material for controlled release products. (c) 2005 Elsevier B.V. All rights reserved.