Bare Metal Stents
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Endovascular StentsMark DeAngelis, Hector Baez, Amanda Johnston, Justin Eng
BackgroundDeveloped in late 1980s.Hold open blood vessels at sites of percutaneous transluminal coronary angioplasty (PCTA) or vascular injury.PCTA is a form of percutaneous cardiovascular intervention (PCI), used for patients with atherosclerotic plaque or thrombotic deposits (Ratner et al, 2013).
Diagram of PCTA
Figure 1. A diagram of PCTA: A) the location of the coronary arteries, B) the artery before the balloon is expanded, C) the artery as the balloon is expanding, D) the stent in place. (NIH)
Background (cont.)Can be balloon inflated or self-inflated.Three main types:CoilCircular tubes of metallic wire or strips in coil shape.Tubular meshWires wound together in a mesh network.Slotted tubeMetal tubes that have a laser-cut design (Butany et al, 2005).
MaterialsMetals are ideal for stents.Many choices for grades and alloys.Allows tailoring to different needs.Excellent mechanical properties.Typically bioinert.Fairly inexpensive and easy to fabricate.Can be coated with polymeric coatings (Ratner et al, 2013; Stent Manufacturing).
FabricationCan be laser fabricated using computer numerical control (CNC).Produces slotted tube type.Laser cuts pattern from metal tube.Mask is applied to allow different heat treatment for bands and connectors.Mask is removed after heat treatment (Gregorich).
Fabrication (cont.)Alternative method:Liquid or powder stent material is poured into female mold.Mold is rotated with forces of at least 1G as stent solidifies (Mirizzi).Argon furnaces allow annealing temps of 11oo C for 316L stainless steel.Stents can be electropolished after heat treatment.Inspected for quality control and packaged in clean rooms (Stent Manufacturing).
316L Stainless SteelLow carbon grade of 316 stainless steel.Unaffected by sensitization, the precipitation of carbides at grain boundaries.Contains molybdenum.Provides corrosion resistance in chloride environments.Austenitic structure.Provides excellent strength (Stainless Steel).
316L Stainless Steel ElementPercent CompositionIronBalanceCarbon