Effects of Surface Modification Induced by Sterilization Processes on the Thrombogenicity of Nickel-Titanium Stents

Abstract

Based on promising reports from international randomized trials such as BENESTENT, vascular stent implantation has been increasingly used - with more than 500,000 implantations per year worldwide - and has become a procedure of choice in the treatment of atherosclerotic vascular disease [1,2]. Since the first implantation in 1986, many devices, mostly balloon expandable stainless steel stents, have been approved by regulatory agencies, for both peripheral and coronary revascularization. In the early 90’s, many studies have reported experimental temporary or permanent use of NiTi stents [3,4]. Due to the thermoelastic properties of the alloy, optimal deployment of NiTi self expanding stents can be easily achieved with high expansion ratio and less longitudinal shortening than most common stainless steel devices. In addition, their flexibility and radiopacity along with their good biocompatibility and resistance to corrosion have contributed to their increasing use in cardiovascular applications [5-7]. Despite its good biocompatibility, like all metallic materials NiTi is prone to adsorption of plasma protein such as fibrinogen, which is a potent promoter of platelet adhesion [8]. In a recent study, Makkar et al. have shown that surface topography significantly affects the thrombogenicity of NiTi stents, which may in turn have an effect on complications observed much after implantation [9]. Indeed, platelets adhesion is the first step of thrombus formation which may lead to acute and sub-acute thrombosis. Stent thrombosis still represents a major complication after stent implantation, especially for small vessels, thrombus containing lesions and bifurcation stenoses [10]. Moreover, through the release of growth factor by activated platelets, thrombus formation is expected to participate to the restenosis process initiation [11]. Many strategies have been developed to reduce stents thrombogenicity such as improvement of surface characteristics or coating with pharmacological drugs and polymers [9,12,13].