A type of esophageal stent coating composed of one 5-fluorouracil-containing EVA layer and one drug-free protective layer: In vitro release, permeation and mechanical properties

A type of esophageal stent coating was investigated, which consists of one 5-fluorouracil (5-FU)-containing ethylene-vinyl acetate (EVA) copolymer layer and one drug-free EVA protective layer. The amount of 5-FU permeated through the protective layer (100 mu m) is thousands of times lower than that of 5-FU released from the drug-loaded layer, indicating that the coating releases drug molecules in a unidirectional fashion. The barrier of the protective layer can be attributed to a tiny flux of 5-FU through the EVA film. In vitro release profiles of the stent coatings with various drug contents were investigated in pH 6.5 phosphate buffer solution. The results show that, the burst effect is not obvious for the coatings with 20-50% of 5-FU and the release profiles can be characterized by a first faster release rate phase followed by a decrease in release rate. The release data in the early and late stages can all be well fitted with zero-order kinetics, and the possible reasons for the release profiles were discussed. The rate of 5-FU permeation through porcine esophageal mucosa from the coatings can be adjusted by changing drug content of the coatings. The increase of drug content of the coatings significantly leads to the decrease of the maximum elongation, maximum tensible strength and maximum tear strength, and the increase of the modulus of elasticity. The coatings with 20-60% of drug attached to a stent can endure repeated binding and liberation via a stent introducer. (c) 2007 Elsevier B.V. All rights reserved.