Polyurethane-coated, self-expandable biliary stent: An experimental study

Abstract

We describe a self-expanding metallic biliary Gianturco-Rösch stent coated with polymeric material. The coating was designed to prevent the growth of neoplastic and reactive tissue within the biliary ducts. The stents were coated with a solvent-casting technique, which consists of dissolving polyurethane (polyether urethane or polycarbonate urethane) pellets in a solvent (dimethylacetamide), dipping the stent in the solution, and completely evaporating the solvent. In vitro mechanical characterization of the stent was performed to determine the adhesion of the coating to the metallic cage, the best introducer caliber for implantation of the device, and the relationship between the stent's diameter and radial stress. Reports in the literature on the biostability of polycarbonate urethane compared with polyether urethane prompted us to use the former material to coat the stents. The solvent technique gives a smooth internal surface of the stent wall, leaving in relief the coated structure of the stent on the external surface. The functional tests demonstrated that the coating did not compromise the original characteristics of the stent in terms of self-expandability, axial flexibility, and increased radial rigidity of the device. Functional tests verified coating stability and device handling, which are the first steps toward in vivo experimentation.