Covered stent

Stents Polypropylene stent covered with Dacron Elgiloy wire and nylon support band covered with polyester and Teflon cloth... 

Two main US FDA-approved DESs are classified as first generation. The first is the Cypher (Cordis Corp., Miami lakes, FL), which is a sirolimus releasing stent covered with a PEVA and PBMA polymer layer (5 micron thickness) coated on stainless steel struts 140 microns thick. The polymer layer modulates the release of the sirolimus to a release profile of 80% of total drug (140 microgram per square centimeter) within 30 days [31]. 

Metallic stents covered with stem cells were proposed as a plausible solution for preventing in-stent thrombosis and restenosis. Raina et al. published in 2014 in vivo results of 152 implanted hTEC covered stents and compared the outcomes with BMS. The preliminary results showed earlier strut coverage with endothelial cells and no increased neointimal proliferation compared to BMS [92],... 

Stefanadis, C., Toutouzas, K., Tsiamis, E., Kallikazaros, L, Stralos, C., Vlachopoulos, C., Vavuranakis, M., and Toutouzas, P., Implantation of stents covered by autologous arterial grafts in human coronary arteries A new technique, y. Invasive Cardiol., 2CKK)a 12(1) 7-12. 

Cellulose thin films for documents and book recovery fibres (including optical) biodegradable plastics oriented templates liquid crystal displays luminescent materials fuel cell membranes drag delivery stents covering ophthalmic, cardiovascular and neurological prostheses bulletproof materials... 

DESs have been the most recent breakthrough in stent technology. DESs consist of a metal stent covered with a thin polymer coating designed to improve vascular compatibility and elute antiproliferative agents. Drugs such as sirolimus (rapamycin) and paclitaxel serve to reduce restenosis by reducing hyperplasia caused by smooth muscle cell proliferation [37, 38]. 

A number of PTMC-based terpolymers have also been studied. Asplund et al. (2006) reported a three-armed P(TMC-co-CL)-PLLA terpolymer as potential stent cover. Random chain scission and homogenous hydrolysis resulted in a loss in mass and molar mass. After 6 weeks of in vitro hydrolysis the molar mass decreased by 54% and the elongation at break dropped from more than 300 to 90%. A medium free cell seeding study showed that endothelial cells adhered well to the polymeric material. Animal study showed very low levels of inflammation, but pronounced neointimal thickening was observed probably due to the premature failure of the material. 

Fig. 5.12a, b. A 71-year-old male patient with bronchogenic carcinoma invading the mediastinum and brain metastasis. Superior vena cava obstruction syndrome was treated by placement of a Wallstent endoprosthesis in the superior vena cava. At 3 weeks after endoluminal treatment, obstruction symptoms recurred, a Phlebography obtained by a femoral approach and catheterization of the stent lumen showed stent obstruction, and extensive filling of mediastinal veins, b After balloon dilatation at the junction of the stent with the internal jugular vein, a residual stenosis (arrow), due to insufficient stent covering of mediastinal tumor extent was evident... 

There are now various expandable meshed metallic stents used in the ureter such as Wallstents (Schneider, Minneapolis, Minn.), Palmaz-Schatz (Johnson and Johnson Interventional Systems, Warren, N.J.) and Ultraflex (Boston Scientific, Boston, Mass.) stents. The Wallstent consists of multiple stainless steel filaments (0.14 mm in caliber), woven in a crisscross pattern to form a tubular mesh that self-expands to a predetermined diameter and length. The stent is compliant and flexible it moulds to the lumen of the ureter but leaves more than 75% of its surface free of metal. Expandable metal stents have received widespread recognition in the treatment of a variety of occlusive diseases, particularly in the arterial and biliary systems. The advantages over plastic polymers are their larger luminal diameter, the ease of placement, the ability to limit the length of the area the stent covers so that it closely... 

In the initial paper on the self-expanding polyester stent covered with a thin layer of sificone (Polyflex stent), the authors reported treatment of flve esophagorespiratory fistulas with placement of this stent into the trachea (Wassermann et al. 1997). Three patients had a tracheal stent only two patients had additional previously placed esophageal stents. The Polyflex stent sealed the flstula initially in all flve cases, but this success was only transient. Symptoms recurred in four patients after a median of 1 month and required placement of additional tracheal stents. All patients had deceased after a mean survival of 6.6 months (range, 2-11 months). 

Interaction of the metalhc stent and the tracheobronchial wall is expected unlike plastic tube stents. This leads to specific problems. Removal of a metalhc stent, which is incorporated into the mucosa several weeks after deployment is extremely difficult and sometimes requires laser destruction of the stent struts in order to remove the stent piece by piece . Similarly, repositioning of an embedded metal stent is more difficult than relocation of a silicone stent. Covered metal stents exert less problems regarding removal and repositioning than uncovered mesh stents, where the open mesh design can lead to complete inoculation of the small stent wires into the mucosa. 

Aguilar, L.E., Unnithan, A.R., Amarjargal, A., Tiwari, A.P., Hong, S.T., Park, C.H., Kim, C.S., 2015. Electrospun polyurethane/Eudragit LlOO-55 composite mats for the pH dependent release of paclitaxel on duodenal stent cover application. International Journal of Pharmaceutics 478, 1-8. http //dx.doi.Org/10.1016/j.ijpharm.2014.10.057. 

Figure 12.14 Schematic illustration showing the electrospinning procedure for fabricating a stent covered with nanofihers. A high voltage is applied between the needle and the ground to create an electrically charged jet of polymer solution. The polymer solution is jet dried to leave a polymerfiber on the stent. Reprinted with permission from [121]. Copyright 2009 Wiley.

---