PubMed · 15217650
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Abdalla Hassan. 2004. Symptomatic persistent sciatic artery.. https://doi.org/10.1016/j.jamcollsurg.2004.02.020
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A method of encasing cardiovascular stents with an expandable polyurethane coating has been developed to provide a smooth homogeneous inner wall allowing for a confluent growth of endothelial cells. In this design, the metal wire stent structure is completely covered by the polyurethane film, minimizing biocorrosion of the metal (stainless steel or nitinol), and providing a homogeneous surface for surface treatment and incorporation of various eluting drugs to prevent platelet aggregation while supporting endothelialization. The polyurethane surface was treated with a helium plasma for sterilization and promotes growth of cells. The article details the performance of the coated film to expand with the metal stent up to 225% during deployment. Stress/strain behavior of polyurethane films, subsequent plasma treatment of the surface, and the adhesion of the coating to the stent structure upon expansion are presented. A film of less than 25 microm was found to be sufficient for corrosion resistance and flexibility without producing any excess stress on the stent structure. Straining the film to 225% and plasma modification did not affect the mechanical and surface properties, but allowed for improved biocompatibility as determined by the critical surface tension, surface chemistry, and roughness.
Cardiovascular stents are small cylindrical devices introduced in stenosed arteries to reopen the lumen and restore blood flow. However, this treatment presents complications, including restenosis, which is the reclosing of the artery's diameter after the insertion of a stent. The structure of the prosthesis penetrates into and injures the walls of the patient's artery. There then follows a proliferation of cells and the formation of scar tissue around the injury, similar to the scarring of other organic tissues. This reaction to the trauma subjects the artery to close. The proposed solution is to develop a Nitinol stent with a progressive expansion device made of polyethylene, allowing smooth and gradual contact between the stent and the artery's wall by creep effect. The purpose of this paper is to describe the technology and methodology for the numerical study of this kind of stent through the finite element method. ANSYS 8.0 software is used to perform the analysis. The Nitinol is modeled with a superelastic law and the polyethylene with a yield hardening law. A first simulation determines the final geometry of the stent laser cut from a small tube. A second simulation examines the behavior of the prosthesis during surgery and over the 4 weeks following the operation. The results demonstrate that a compromise can be reached between a limited expansion prior the inflation of the expandable balloon and a significant expansion by creep of the polymer rings.
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