Self-Expandable Nitinol Coronary Stent Yasemin YAR MASE 542 BIOMATERIALS Spring 2012

Coronary Artery Disease Narrowing or blockage of 1 or more of the arteries that supply blood and oxygen to the heart. Caused by buildup of plaque in the arteries. Normal Early Fatty Deposition Fatty Deposition Progresses Severe Narrowing

What Is A Stent? Used at various sites: A hollow cylinder that is used to treat narrowed arteries in the body. Used at various sites: Coronary, carotid, renal, ureteral stents etc. Ureteral Stent Renal Stent http://www.vascularspecialist.com

Critical Stent Requirements Corrosion Resistant Inhibits Hyperplasia & Restenosis Durable Radiopaque Flexible The Ideal Coronary Stent Drug Delivery Capacity Thromboresistive Radial Strength MRI Compatible Manufacturable Biocompatible G. Mani, M.D. Feldman, D. Patel and M. Agrawal, “Coronary stents: A material perspective,” Biomaterials, vol. 28, pp. 1689–1710, 2006.

Coronary Stents Implantation of 1st coronary stent by Jacques Puel & Ulrich Sigwart (1986) Each year in the world more than one million stents are implanted. Principal advantage: No open heart surgery. Metallic Drug-Eluting Stents Polymeric Stainless Steel Pt-Ir Tantalum Nitinol Co-Cr Ti Biodegradable metallic stents pure Fe Mg alloys Heparin-coated stents Sirolimus-coated stents Paclitaxel-coated stents Biostable polymers PET Biodegradable polymers PLLA G. Mani, M.D. Feldman, D. Patel and M. Agrawal, “Coronary stents: A material perspective,” Biomaterials, vol. 28, pp. 1689–1710, 2006.

Nitinol-Material with Unusual Properties What is it? Equiatomic or near-equiatomic alloy of Ni and Ti Where does it get its name? Nickel Titanium Naval Ordnance Laboratory (1962). Where is nitinol used? Dental Braces Glass Frame a) b) c) d) Stone Basket Fabrics Grasper Bone Staples & Drill Catherer

Mechanical properties of two phases of nitinol Shape Memory Alloys What is it? Shape memory  “remembering” their original shape Superelasticity  enormous elasticity Based on phase transformation of the crystal structure Twinned Martensite (unstressed) Detwinned Martensite (stressed - deformed) Austenite (undeformed) Mechanical properties of two phases of nitinol Shape-memory materials: a review of technology and applications", Assembly Automation, Vol. 29 Iss: 3, pp.214 - 219

Shape Memory Alloys Superelasticity Shape Memory http://c2i2.digithalamus.com/autumn2004/Metallurgical_principles_of_Nitinol.asp

Nitinol remembers its original shape What Smart Material! Nitinol remembers its original shape Thermal deployment of Bard® Luminexx™ stent. (a) Stent loading into delivery system; (b) and (c) Stent deployment at body temperature. A. Biscarini, G. Mazzolai, and A. Tuissi, “Enhanced nitinol properties for biomedical applications,” Recent Patents on Biomedical Engineering, vol. 1, pp. 180–196, 2008. a) b) c) a) b) c) d)

Problems with Metallic Stents Limitations: SS: Biocompatibility, non-MRI compatible, radiolucent Ta : High recoiling % and breaking during deployment Ti : Low ductility Co-Cr: Problems related to manufacturing G. Mani, M.D. Feldman, D. Patel and M. Agrawal, “Coronary stents: A material perspective,” Biomaterials, vol. 28, pp. 1689–1710, 2006.

Advantageous Features of Nitinol Elastic & thermal deployment Easy to sterilize Very flexible Biocompatible Corrosion & fatigue resistant Kink resistance Constant stress & no recoil MRI compatibility Shape-memory materials: a review of technology and applications", Assembly Automation, Vol. 29 Iss: 3, pp.214 – 219

Who Makes Nitinol Stents?

State of the Art Joner et al., “Polymer-free immobilization of a cylic RGD peptide on a nitinol stent promotes integrin-dependt endothelial coverage of strut surfaces,” J. Biomed. Mater. Res. Part B, vol. 28, pp. 637–645, 2012.

The “perfect” stent does not exist, and it will probably never exist.

"The human body is a series of tubes just waiting to be stented" Cerebro Carotid Esophagus Trachea Cornary Biliary Aorta "The human body is a series of tubes just waiting to be stented" Dr. Paul S. Teirstein, 1998 Iliac Colon Urinary Tract Femoral Popitieal