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Metal–Polymer Composite Biomaterials
Published in Severian Dumitriu, Valentin Popa, Polymeric Biomaterials, 2020
Stents are expandable tubes of metallic mesh that were developed to address the negative sequelae of balloon angioplasty. At the beginning of the twentieth century, glass tubes that became a prototype of stents were implanted into blood vessels of animals. In the next stage, the origin of percutaneous transluminal angioplasty (PTA), the expansion of blood vessels obtained by increasing the diameter of catheter tube, was attempted.38 This trial failed because of migration and the development of thrombus. In 1985, Palmaz and his colleagues developed the first balloon-expanded stent,39 and just 1 year later, Gianturco developed a balloon-expanded coil stent.40 These stents were made of stainless steel. The first self-expandable stent, Wallstent®, made of a Co-Cr alloy (Elgiloy), was clinically applied in 1986.41 Another popular self-expandable stent, SMART®, consists of a superelastic Ni-Ti alloy.42 Since the 1990s, stents have been used in coronary arteries. Typical popular stents for this purpose are the Palmaz-Schatz® stent and the Gianturco-Roubin® stent. New designs and functions of stents have also been developed. Today, for example, the majority of patients undergoing percutaneous transluminal coronary angioplasty (PTCA) receive a stent. Since the mid-1990s, stents have also been applied to the treatment of cerebrovascular disease, and carotid stenting to prevent stroke, recoil, and restenosis has been attempted.43–45 In addition, the first treatment for abdominal aortic aneurysms with stent grafts started in the 1990s.46 Stent grafts are generally constructed of stainless steel or a Ni-Ti alloy and coated with compounds such as expanded polytetrafluoroethylene (ePTFE) that is a metal–polymer composite. Typical bare stent and stent graft are shown in Figure 12.13.
Finite element analysis of braided dense-mesh stents for carotid artery stenosis
Published in Computer Methods in Biomechanics and Biomedical Engineering, 2023
Atherosclerotic stenosis of the carotid artery is a major cause of ischemic stroke, accounting for about 15–20% of all cases (Woo et al. 2017). Carotid endarterectomy (CEA) and carotid stenting (CAS) are effective technical options for the treatment of carotid stenosis, and CAS has been increasingly recognized by physicians and patients for its advantages of less trauma, less patient pain, and shorter hospital stays (Coelho et al. 2019; ACST-2 Collaborative Group, 2021). Many types of vascular stents are in clinical use, among which braided stents have the advantages of high flexibility and good wall adhesion and have received wide attention. Moeri et al. (Moeri et al. 2021) followed 150 patients with post-thrombotic syndrome who were implanted with braided stents and laser-carved stents for 12 months and found a higher rate of patency after implantation of braided stents. Reports on the Casper double-layer braided dense-mesh stent (Microvention, USA) show that the stent exhibits good plaque blockage and a low incidence of adverse events in the treatment of carotid stenosis (Mutzenbach et al. 2020; Imamura et al. 2021).
Procedural embolic protection strategies for carotid artery stenting: current status and future prospects
Published in Expert Review of Medical Devices, 2023
Eligio Miccichè, Francesco Condello, Davide Cao, Alessia Azzano, Anna Maria Ioppolo, Andrea Mangiameli, Alberto Cremonesi
The GORE NeuroProtection System (W.L.Gore & Associates, Inc., Flagstaff, AZ, U.S.A.) is a proximal EPD, which consists of two independent systems: the balloon wire and the 9.5 Fr sheath which has an effective-working channel of 6 Fr and contains an inflatable balloon at its tip. The sheath is positioned in the CCA, and the balloon wire is inserted through the sheath and positioned in the ECA. When both balloons are inflated, the blood flow through the CCA and ECA is blocked. A connection between the proximal part of the sheath and the contralateral femoral vein allows blood flow reversal from the cerebral circulation into the venous system. An extracorporeal filter, with a pore size of 180 μm, interposed between the arterial and venous connection collects debris before the blood reenters circulation through the femoral vein. Consequently, the carotid lesion can be crossed and treated in reverse flow mode. At the end of the procedure, 10–20 mL of blood is actively aspirated from the sheath, and then the balloons are deflated applying an active suction through the sheath to retrieve any particle contiguous to the occluding balloons. The EMPIRE (the Embolic protection with reverse flow study of the GORE neuro Protection system in Carotid Stenting of subjects at high Risk for carotid Endarterectomy) trial was a multicenter, single-arm study including 245 patients at high risk of complication from CEA [38]. At 30 days, the rate of major adverse events including stroke, death, myocardial infarction, or TIA was 4.5% (p = 0.002 compared with an objective performance criterion). No patient had a major ischemic stroke. Intolerance to flow reversal was observed in six patients (2.4%). In a separate series, Nikas et al. reported technical success in 97.5% of the cases and a 1.6% incidence of periprocedural stroke with the use of the GORE system [39]. In a small, randomized trial (n = 40), the GORE flow reversal system compared with filter protection resulted in an increased incidence (47.6% vs 15.8%, p = 0.03), number (2.61 vs 0.73, p = 0.05), and size (2.23 vs 0.81 mm, p = 0.05) of new ischemic brain lesions on DW-MRI. Two patients, one from each group, experienced a TIA at three-month follow-up. There were no major adverse cardiac or cerebrovascular events [40]. This device has been removed from the market.