Bare Metal Stents
-
Upload
justin-eng -
Category
Documents
-
view
227 -
download
0
Transcript of Bare Metal Stents
Endovascular StentsMark DeAngelis, Hector Baez, Amanda
Johnston, Justin Eng
Background● Developed 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:
○ Coil■ Circular tubes of metallic wire or strips in coil
shape.○ Tubular mesh
■ Wires wound together in a mesh network.○ Slotted tube
■ Metal tubes that have a laser-cut design (Butany et al, 2005).
Materials● Metals 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).
Fabrication● Can 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 Steel● Low 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 Element Percent
Composition
Iron Balance
Carbon <0.03%
Chromium 16-18.5%
Nickel 10-14%
Molybdenum 2-3%
Manganese <2%
Silicon <1%
Phosphorus <0.045%
Sulphur <0.03
Figure 2. A table of the chemical composition of 316L stainless steel (Stainless Steel).
Figure 3. The Medtronic beStent2, a balloon expandable, slotted tube stent made of 316L stainless steel. The arrow is pointing to gold radiopaque marker. (Butany et al, 2005)
UNIMET L-605 Cobalt Chromium● Super-alloy
○ Can withstand high temps and mechanical stress.● Solid strengthened.● Excellent resistance to:
○ Oxidation○ Sulfidation○ Wear○ Galling
● Stronger than steel, better radiopacity (AZoM, Kereiakes et al, 2003).
UNIMET L-605 Cobalt Chromium
Element Percent Composition
Cobalt 46.38-56.95%
Chromium 19-21%
Tungsten 14-16%
Nickel 9-11%
Iron <3%
Other Balance
Figure 4. A table of UNIMET L-605’s chemical composition (AZoM).
Comparison of Metals
Metal
Elastic modulus (GPa)
Yield strength (MPa)
Tensile strength (MPa)
Density (g/cm3)
316L stainless steel (ASTM F138 and F139; annealed) 190 331 586 7.9Cobalt chromium 210 448-648 951-1220 9.2Pure iron 211.4 120-150 180-210 7.87Mg alloy (WE43) 44 162 250 1.84
Figure 4. A comparison of the mechanical properties of metals, including 316L and cobalt chromium (Mani et al, 2007).
Optimizing the Device● Desirable characteristics:
○ Low cross sectional area○ High flexibility○ High biocompatibility○ High radial strength○ Low metallic surface area○ Favorable radiographic properties○ Easy deployment (Butany et al, 2005)
Figure 5. Features of a commercial cobalt chromium stent (Sahajanand Medical Technologies Pvt. Ltd.).
Interaction● Minimal interaction with the host
tissue (blood)● Withstand corrosion
○ Cobalt Chromium○ 316L Stainless Steel
Engineering Solutions● Drug-Eluting stents
○ anti-proliferative drug (Maisel)○ prevents neointima
● Biodegradable stents○ short term support○ absorbed or dissolved○ match the radial strength of traditional
materials
Why Stents?● Treats stenosis,
improving blood flow● High complication rate
(Biomaterials Science 775)○ ~21% within the first
9 months ● Room for improvement
Figure 6. Increase in carotid stenting (Nallamothu)
FDA Approval● First coronary stent 1994● Classification
○ nature of expansion○ stent design
Commercialization● As late as 2004, 16 models were
approved○ 9 different manufacturers
● Prefered treatment for Coronary Artery Disease
● $2.5 billion spent on stents in 2003 (Butany)
Competition● Currently 13
approved coronary stents by FDA
● Growing Market● Overuse debate
Figure 7. Market size and growth for coronary stent devices (Ruchika BBC)
Work Cited● AZoM.com Staff Writers. "UDIMET Alloy L-605 (UNS R30605)." UDIMET Alloy L-605 (UNS R30605).
AZoM, 29 June 2013. Web. 08 Apr. 2014. <http://www.azom.com/article.aspx?ArticleID=9458>.● Butany, J., K. Carmichael, S. W. Leong, and M. J. Collins. "Coronary Artery Stents: Identification and
Evaluation." Journal of Clinical Pathology 58.8 (n.d.): 795-804. US National Library of Medicine. Web.<http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1770873/>.
Gregorich, Daniel, and Jonathan Stinson. Medical Devices and Methods of Making the Same. Boston Scientific Scimed, Inc., assignee. Patent US 20080114449 A1. 23 Jan. 2008. Print. "How Is Coronary Angioplasty Done?" - NHLBI, NIH. NIH, 01 Feb. 2012. Web. 08 Apr. 2014. <http://www.nhlbi.nih.gov/health/health-topics/topics/angioplasty/howdone.html>.Kereiakes, Dean J. "Usefulness of a Cobalt Chromium Coronary Stent Alloy." ScienceDirect. The American Journal of Cardiology, Aug.-Sept. 2003. Web. 8 Apr. 2014.
● Maisel, William H., Dr. "Drug-Eluting Stents." American Heart Association Journals. Circulation, 2017. Web. 30 Apr. 2014.
● Mani, Gopinath, Marc D. Feldman, Devang Patel, and C. Mauli Agrawal. "Coronary Stents: A Materials Perspective." Coronary Stents: A Materials Perspective. Biomaterials Volume 28, Issue 9, Mar. 2007. Web. 08 Apr. 2014. <http://www.sciencedirect.com/science/article/pii/S0142961206010076>.
● Mirizzi, Michael S. Stent Made by Rotational Molding or Centrifugal Casting and Method for Making the Same. Advanced Cardiovascular Systems, Inc., assignee. Patent US 6574851 B1. 31 July 2000. Print.
● Nallamothu, Brahmajee K., Dr., Mingrui Lu, Dr., Mary A. Rogers, Dr., Hitinder S. Gurm, Dr., and John D. Birkmeyer, Dr.
● "Physician Speciality No Effect on Carotid Stenting Outcomes | HeartZine." Physician Speciality No Effect on Carotid Stenting Outcomes | HeartZine. Archives of Internal Medicine, Aug. 2008. Web. 30 Apr. 2014.
● Ratner, Buddy D. Hoffman, Allan S. Schoen, Frederick J. Lemons, Jack E. (2013). Biomaterials Science - An Introduction to Materials in Medicine (3rd Edition). (pp. 773-776). Elsevier.
● Sahajanand Medical Technologies Pvt. Ltd. Design Features of Coronnium. Digital image. SMTPL - Coronnium - Cobalt Chromium Alloy Coronary Stent. Sahajanand Medical Technologies Pvt. Ltd, n.d. Web. 30 Apr. 2014. <http://www.smtpl.com/coronnium.html>.
● "Stainless Steel - Grade 316L - Properties, Fabrication and Applications (UNSS31603)." Stainless Steel - Grade 316L - Properties, Fabrication and Applications (UNS S31603). AZoM, 18 Feb. 2004. Web. 08 Apr. 2014. <http://www.azom.com/article.aspx?ArticleID=2382>.
● "Stent Manufacturing." Stent Manufacturing - Nitinol Stents. Norman Noble, Inc, n.d. Web. 08 Apr. 2014. <http://www.nnoble.com/Stent/Stents.htm>.
Questions?