Polyethylene stent

Introduced in 1994, the Tannenbaum stent was designed to overcome some of the limitations of the polyethylene stent Four flaps positioned at each end of the stent and the notable absence of sideholes characterize this Teflon stent (Trotteur et al. 2000) (Fig. 1.9). Several randomized trials have compared the Tarmenbaum stent to conventional Cotton-Leung stents. No significant difference in duration of patency or survival was found (Seitz et la. 1994 Terruzzi et... 

Five randomized, prospective, controlled trials have compared plastic (polyethylene) stents and SEMS (Wallstent, BSC, Natick, MA). While SEMS... 

Burcharth F (1978) A new endoprosthesis for nonoperative intubation of the biliary tract in malignant obstructive jaundice. Surg Gynecol Obstet 146 76 Catalano MF, Geenen JE, Lehman GA et al (2002) Tannen-baum Teflon stents versus traditional polyethylene stents for treatment of malignant biliary stricture. Gastrointest Endosc 55 354-358... 

Sheth S, Dev V Jacobs H, et al. Prevention of subacute stent thrombosis by polymer-polyethylene oxide-heparin coating in rabbit carotid artery [abstr]. J Am Coll Cardiol 1995 25 348A. 

The CYPHER stent employs two nonerodible polymers polyethylene-co-vinyl acetate (PEVA) and poly-n-butyl methacrylate (PBMA), The combination of sirolimus and these two polymers constitutes the basecoat formulation that is applied to a stent treated with paryleneC. In addition, a drug-free topcoat of PBMA polymer is applied to control the release kinetics of sirolimus (59), making this a diffusion-controlled reservoir device. The chemical structure of the polymers used in the CYPHER stent is shown in Figure 4,... 

Polymers used in the CYPHER sirolimus-eluting stent. Abbreviations PBMA, poly-n-butyl methacrylate PEVA, polyethylene-co-vinyl acetate. 

Antithrombonic esters, including co-poly-(A,A -sebacoyl-bis-(L-leucine)-l,6-hexylene diester), (III), and polyethylene glycol derivatives, (IV), were prepared by Pacetti [3] and Hossainy [4], respectively, and used as bio-absorbable stent coatings. 

Hie reen polyethylene if transformed in final products in the tanne unitief alreai exi stents... 

Polymeric materials that have been used in the cardiovascular system include polytetrafluorethy-lene, polyethylene terephthalate, polyurethane, polyvinyl chloride, etc. Textiles bas on polytetra-fluorethylene and polyethylene terephthalate are us extensively as fabrics for repair of vasculature and larger-vessel replacement (greater than 6 mm in diameter). Stent-grafts are hybrid stent grafts placed by catheter to treat aortic aneurysms nonsurgically and are fabricated of the same metallic alloys used in stents and textiles similar to those used in vascular grafts. Table 14.1 lists many of the biomaterials currently used in the cardiovascular system. 

The Nellix device from Endologix is a novel approach to EVAR. It uses endobags that are inflated with liquid polyethylene glycol, to fill the aneurysmal sac. The stents themselves are cobalt chromium and can be delivered through a low profile sheath. 

Despite intensive efforts to improve plastic endoscopic stents, few modifications have proved advantageous. Plastic stents are simple single lumen devices designed to function as an aqueduct for bile. Conventional plastic Cotton-Leung biliary stents, composed of polyethylene, have single flaps at both ends of the stent The stents are available in varied lengths from 3 to 20 cm ranging in diameters from 7 to 11 F. (Fig. 1.8)... 

England RE, Martin DF, Morris J et al (2000) A prospective randomised multicentre trial comparing 10 Fr Teflon Tan-nenbaum stents with 10 Fr polyethylene Cotton-Leung stents in patients with malignant common duct strictures. Gut 46 395-400... 

This stainless steel device consists of several Z stents joined in series and completely covered by polyethylene (Fig. 2.6). There are several versions of this endoprosthesis available around the world, e.g., the Song stent. Some devices have barbs to assist fixation and... 

The Gianturco and Rosch-Z stents are much stiffer in the longitudinal axis and are also available in a non-covered and a polyethylene-covered version (Fig. 3.3). The non-covered types are cylindrical or flared at each end and available in diameters of 15-35 mm (Fig. 3.3a). The covered oesophageal Z-stent is flared at each end to increase local stability and reduce the risk of migration. The diameter in its mid-portion measures 18 mm and 25 mm at each end (Fig. 3.3b, c). The stent is dehvered through a 28- F (outer diameter) sheath. 

Using medical devices such as catheters, angioplasty balloons, pacemaker leads, and cardiovascular stents usually involves insertion of such devices into urinal tracts or blood vessels. During insertion, high surface lubricity of Ihe devices helps to facilitate the insertion process and reduce insertion-associated tissue damage, which benefits both the patient and the surgeon. Early approaches to decrease insertion friction involve using lubricants such as olive oil and silicon oil, or low friction materials like polyethylene. Due to the superior mechanical properties, polyurethane is extensively used in catheters/baUoons and it is desirable to improve the lubricity of polyurethane materials. 

Biomaterials have played a vital role in the treatment of cardiovascular diseases, examples of applications including heart valve prostheses, vascular grafts, stents, indwelling catheters, ventricular assist devices, total implantable artificial heart, pacemakers, automatic internal cardioverter defibrillator, intraaortic balloon pump, and more. A key requirement for materials in cardiovascular applications, particularly blood-contacting devices, is blood compatibility, that is, nonthrombogenic. Additional requirements include mechanical and surface properties that are application specific. Surveying the field of polymers used in cardiovascular applications reveals that PUs, polyethylene terephthalate (PET), and expanded PTFE (ePTFE) are the most commonly used. This section will review each of the three polymers followed by a brief introduction of other emerging polymers for use in the cardiovascular area. 

The Medtronic Endurant bifurcated stent graft was approved for commercial use by the FDA in December 2010 (FDA, 2013). It consists of two components, the main bifurcated body and the contralateral limb (Fig. 21.10). The main body consists of a multifilament polyester fabric coupled with laser-cut nitinol stents, sewn together using polyester sutures. A bare nitinol stent is affixed to the proximal end of the main body using ultra-high molecular weight polyethylene sutures. This stent allows the device to be fixed above the renal arteries without preventing arterial blood flow to the kidneys, and is referred to as the suprarenal stent. There are barbs on the top of... 

Cypher is a first-generation DES that releases the immxmosuppressive agent siroli-mus (brand name Rapamxme) which is bound to polymers embedded in this stent. The Cypher system has a stainless steel base which is cut into a sinusoid shape and is coated with a blend of two polymers. The blended polymers are polyethylene-co-vinyl acetate (PEVA) and poly n-butyl methacrylate (PBMA). A combination of the two polymers mixed with sirolimus (67%/33%) makes up the basecoat formulation. Another coat of... 

Among the most used synthetic polymers as cover materials for stent devices within the vasculature we can find polytetrafluoroethylene (PTFE), polyethylene terephthalate (PET), and polyurethane. PTFE is a synthetic polymer of tetrafluoroethylene (C F ) composed of a carbon chain saturated with fluorine. This polymer has hydrophobic properties conferred by the presence of electronegative fluorine atoms. This characteristic which results in unfavorable reactions that enhance platelet adhesion, activation and thrombus formation [123], consists of ethylene glycol and terephthaHc add. 

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