Metallic stent strut

BMSs are usually well covered by an intimal hyperplasia. But, with drug-eluting stents, because of the potency of the drug being eluted, sometimes struts are found that are thinly or barely covered by intimal hyperplasia. Hence, the concern is actually a vulnerable stent strut. The polymer around the metal of the strut is usually quite thin and usually next to the blood stream, providing the potential for some of the metal strut to be exposed to the blood stream. 

The stent struts are comprised of the metal and the polymer, and, overtime, the drug disappears (e.g., with the Cypher stent) or some drug will remain (e.g., with the Taxus stent). Thus, there is the potential for some metal, polymer, and drug to remain exposed to the blood stream. Using high-resolution imaging techniques, intimal hyperplasia is seen when looking at BMS in vivo. 

This led to the introduction of a stronger metal alloy that has better X-ray attenuation properties, thus enabling the development of balloon-expanding metallic stents with thinner struts. The metal alloy was a cobalt-chromium alloy (Co-Cr) that was already used for stents [10]. 

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],... 

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. 

Fig. 16.2a,b. In-stent lumen imaging, a Imaging of a stent phantom acquired on a conventional 16-detector-row scanner with a voxel size of 1 mm. A conventional cobalt-chromium alloy bare metal stent (Multi-Link Vision Rx Coronary Stent System, Boston Scientific, Gatwick, Mass.) with thin struts (0.08 mm) is used, b The same stent as in a is visualized with a fourfold-better spatial resolution (voxel size of 0.25 mm), utilizing a flat-panel detector. (Modified according to Mahnken et al. 2005)... 

The high elastic modulus of the metal alloy allowed the creation of the self-expandable WaUstent (Boston Scientific Corp., Natick, MA), while one of the first balloon-expandable stents made of Co-Cr alloy was the Multi-Link Vision coronary stent (Abbott Laboratories, Abbott Park, IL) made of L605 allot (Co-20Cr-15W-10Ni) that provided both strength and increased X-ray attenuation compared to stainless steel, thus allowing for thinner struts [11]. 

In this section, second generation drug eluting stents are described, the first of which is the Endeavor (Medtronic Vascular, Santa Rosa, CA). This stent s metallic mesh is made up of cobalt-chromium with strut thickness of 91 microns, coated with zotarolimus drug (10 pg zotarolimus per 1 mm stent length) with 70% released after 30 days, blended with phosphorylcholine (a synthetic copy of the most common phospholipid in the outer membrane of RBCs and has high... 

Raina, T., Arnold, N., Moore, H., et al. 152 Stem cell coated metallic coronary stents show accelerated strut coverage without excessive neointimal proliferation in a porcine model. Heart 100, A88-A89 (2014)... 

Recent developments of plastic stents have aimed to improve the resistance of plastic stents to external compression forces. Therefore, metal has been incorporated into the plastic material of the stent. One of the latest developments is the dynamic bifurcation stent made of silicone (Freitag et al. 1994). This Dynamic stent (Riisch, Kernen, Germany) is reinforced with horseshoe-shaped steel struts. A posteriorly located flexible membrane allows dynamic compression of the stent during coughing, whereas the steel struts prevent airway compression from external forces. Theoretically, this stent mimics the mechanical dynamics of the normal trachea. The distal end is a Y shape which rides on the carina to prevent distal migration. 

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