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

2. 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

3. 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

4. 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.

5. 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.

6. 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

7. 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

8. Shape Memory Alloys Superelasticity Shape Memory

9. 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)

10. 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.

11. 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

12. Who Makes Nitinol Stents?

13. 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.

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

15. "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
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