Stent nitinol

Figure 21.1. Stents are used to open arteries of the heart blocked by atherosclerotic plaques (A) a balloon and stent are placed across the plaque (B) the balloon is expanded, leaving the stent to prop open the artery (C) restenosis is the process wherein scar tissue builds up around the stent, again causing a flow restriction. A balloon is required for stainless steel, whereas a nitinol stent will expand on its own, due to the shape memory property of nitinol. (From Ref. 11, with permission.)...

In an optical micrograph of a commercially available nitinol stent s surface examined prior to implantation, surface craters can readily be discerned. These large surface defects are on the order of 1 to 10 p.m and are probably formed secondary to surface heating during laser cutting. As mentioned above, these defects link the macro and micro scales because crevices promote electrochemical corrosion as well as mechanical instability, each of which is linked to the other. Once implanted, as the nitinol is stressed and bent, the region around the pits experiences tremendous, disproportionate strain. It is here that the titanium oxide layer can fracture and expose the underlying surface to corrosion (9). 

Dev Y Eigler N, Sheth S, et al. Kinetics of drug delivery to the arterial wall via polyurethane-coated removable nitinol stent comparative study of two drugs. Cathet Cardiovasc Diagn 1995 34 272-278. 

Post balloon angioplasty and nitinol stent placement at distal end of graft. 

Reconstruction of anterior tibial artery with balloon angioplasty and nitinol stent in the proximal segment of anterior tibial artery,... 

Ansel GM, Silver MJ, Botti CFJr, et al. Functional and clinical outcomes of nitinol stenting with and without abeiximab for complex superficial femoral artery disease a randomized trial. Catheter Cardiovasc Interv 2006 67(2) 288-297. 

Peluso JP, van Rooij WJ, Sluzewski M, Beute GN. A new self-expandable nitinol stent for the treatment of wide-neck aneurysms initial clinical experience. AJNR Am J Neuroradiol. 2008 29 1405-1408... 

Cejna M, Loewe C, Schoder M, et al (2002) MR angiography vs CT angiography in the follow-up of Nitinol stent grafts in the endoluminally treated aortic aneurysms. Eur Radiology 12 2443-2450... 

Duda SH, Bosiers M, Lammer J, Scheinert D, Zeller T, Oliva V, et al. Drug-eluting and bare nitinol stents for the treatment of atherosclerotic lesions in the superficial femoral artery long-term results from the SIROCCO trial. J Endovasc Titer 2006 13(6) 701-10. 

The Medtronic Talent device is a stent graft constructed from a plain woven polyester fabric and a nitinol stent frame. The bifurcated device for the abdominal aorta has a bare suprarenal stent, but no hooks or barbs. The thoracic stent graft has been replaced by the Valiant device (see below). Early Talent devices had a rigid longitudinal bar that was meant to provide columnar support. However, this component signihcantly decreased the flexibility of the device, and so has been discontinued in more recent models. 

The Incraft device from Cordis is a modular, low-profile system using nitinol stent rings and a tubular polyester graft fabric. It uses active suprarenal fixation and an active locking mechanism between components. It has the ability to increase its length in situ. 

The Fortevo device from Aptus capitalizes on Aptus experience with their endovascular Helifx anchoring device, which is similar to the helical tacks used to fix meshes in laparoscopic hernia repair. The Fortevo is a modular device made from nitinol stents and a woven polyester graft. This device uses separate endoanchors to secure the proximal fixation zone. 

The Ultraflex nitinol stent comes in both covered and uncovered versions (Fig. 3.4). It has a significantly lower radial expansile force than the other stents but the covered version is much more flexible than any of the other covered stents and may therefore be placed across acutely angled stenoses (Repici et al. 2000). The stent is available with a 23-mm mid diameter and a 28-mm funnel-shaped proximal end and is mounted on a 16-F delivery catheter. The stent consists of a nitinol wire mesh with a polyurethane external membrane which leaves both stent ends bare for 1.5 cm for better fixation. 

Fig. 3.4a, b. Ultraflex nitinol stents, a Uncovered version with flare at proximal end. b Covered stent with uncoated proximal and distal end... 

Other types of stents such as the Strecker tantalum stent (SoLT and Papp 1993), the Strecker Nitinol stent (Strecker et al. 1995) or modified and covered Gianturco stents (Song et al. 1993) have been used only occasionally and not much experience exists with these stents. Recently, however, two series of 19 and 24 patients have been published advocating covered metallic expandable stents for prevention of tumour ingrowth after stenting for gastroduodenal obstruction (Jung et al. 2000 Park et al. 2001). 

Stent fracture in the colon and rectum seems to be a rare event and has only been described in connection with one particular stent design. Odurny et al. (2001) described three cases in which Memotherm nitinol stents were found to be fractured after 3,6 and 7 months. All patients had originally been treated for recurrent anastomotic strictures, one of which was due to local tumour recurrence. This type of nitinol stent does seem unsuitable for long-term management of strictures in the gastrointestinal tract since fracture of Memotherm stents has also been reported in the biliary tract (Peck and Wattam 2000). 

Song et al. (1996) treated three patients with esophagorespiratory fistulas with their own covered (potentially retrievable) self-expanding nitinol stent. All three fistulas were successfully sealed off by stent insertion. In one patient the stent was initially malpositioned with coverage of the right main stem bronchus, but this problem was successfully solved with repositioning. Two patients died after 2 and 3 weeks one patient was alive at 24 weeks with good respiratory status. 

In the series of Strecker stent placement in 21 patients, complications were reported in two. One stent compression and one stent dislocation occurred in two patients. Both stents were removed without problems (WiTT et al. 1997). In a smaller trial, one Strecker stent out of five dislocated 6 days after placement (ScHMiDT et al. 1999). In the series of Hauck et al. (1997), tumor ingrowth through the stent was seen in nine of 51 patients treated with Strecker or nitinol stents. Stent deformation occurred only with Strecker stents ( =12), but not in nitinol stents. Mucus retention was a frequent problem within the first 7 days after stent placement (39%). 

Colreavy MP, Keogh 1, Hone S, Lacy PD, Gaffney RJ, Walsh MA (2000) Nitinol stents their value in tracheobronchial obstruction. Clin Otolarynology 25 233-239 Colt HG, Dumon JF (1995) Airway stents. Present and future. 

Miyayama S, Matsui O, Kamimura R, Kakuta K, Takashima T (1997) Partially covered Gianturco stent for tracheobronchial stricture caused by intraluminal tumor. Cardiovasc Intervent Radiol 20 60-62 Miyazawa T, Yamakido M, Ikeda S, Furukawa K, Takiguchi Y, Tada H, Shirakusa T (2000) Implantation of Ultraflex nitinol stents in malignant tracheobronchial stenoses. Chest 118 959-965... 

Bakhshi, R., Darbyshire, A., Evans, J.E., You, Z., Lu, J., Seifalian, A.M., 2011. Polymeric coating of surface modified nitinol stent with POSS-nanocomposite polymer. Colloids and Surfaces B Biointerfaces 86, 93-105. 

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... 

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