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1 Journal of the Korean Ceramic Society Vol. 44, No. 7, pp. 362~367, Material Design and Analysis of Coronary Artery Stents JoongGwun Park, TaeWon Kang, Kee Sung Lee, and Tae-Woo Kim School of Mechanical and Automotive Engineering, Kookmin University, Seoul , Korea (Received June 19, 2007; Accepted July 23, 2007) x lp w «Á k Á» Á½k w» œw ( ; ) ABSTRACT Stent is a tiny structure made with either ceramic coating and/or bare metal. Being approximately 1 ~ 2 mm in diameter, it consists of holes, slots, or void space and is designed to cover entire medical lesions. Stent implantation into patients arteries has been practiced for a little more than a decade in order to widen the blocked artery. The adoption of the stent has significantly improved the efficacy when compared with the previous medical practice by balloon angioplasty alone. Yet better biomedical performance of the stent is being demanded in order to eliminate the still existing problem of artery restenosis, which means the artery becomes narrowed again. Recent literature survey shows researches on ceramic coatings onto the stent surface, or material design to improve the mechanical response of the stent. This study focuses more on the material design and mechanical analysis. The results showed that the void configuration within the stent affects the mechanical response significantly. The rectangular shape was found to yield expansion at a relatively lower pressure than the elliptical slot for a slotted tube stent. The present results, when combined with research on coating at the stent surface, may provide stents with improved bio-medical performance. Key words : Stent, Finite element, Material design, Ceramic coating, Stainless steel 1. y w w ƒ w ƒ x y š. w w 1) s³ 50 ù w x l. 2) ù 2006 m w šx / y w ƒ 70% w., w / ye w x ƒ w š, 3) p / t w d ƒ š., x, šx x y x ü š w x» w. 4) ù x x» w 20 t w. t y x x y» w x l Corresponding author : Tae-Woo Kim twkim@kookmin.ac.kr Tel : Fax : p w e wù. lp w ü w 2 q w» ù, l p t p j» w z w ƒ w š. ù, lp q k, lp t x ü w w ƒw x x x x w., w w q w lp x w ƒ»., lp t ù»œ gqw z w y e w ù, x j lp t gq w ƒ w š. w x t lp p w. 5), p w w gq y ù, w w w w w ky³ 6) l (316L) 2 ù p x lp 362

2 gq z š. Gerickens q 7) ù»œ ù w gq w ƒ šw. y (IRO X ) 8) w š yw» lp t gq z, gq w x lp ü xsƒ x šw. Windecker q 9) pk - y- y l lp gqw gq w z šw. lp ƒ ü w l ù f-j, t ù f, j,» y w x» pk - y- y (TINO X ) gqƒ 10) ƒ š. wr, Maguire q e (DLC)gq 11) w w, Huang q 12) Ti-O/Ti-N gq, š Liu q 13) lp l TiN TaN gq w šw. w gq ƒ w š, w gq wì gq w lp x sww» w lp w z. wr, lp j»ƒ ƒ q w» w ( ) x r w x sƒ ww w», lp w» p ful w w ƒ v w. lp d w. k Migliavacca q 14) 2002 w» (FEM) w w w. m¼ w œ ( ) p x lp w w x w šw. Chua(2002 ) q 15) FEM w Migliavacca q 14), m¼ w œ ( ) lp w w šw, p lp ü ƒ lp y, y w. w, Chua q 16) ƒ x p lp w w w šw. x š ƒx ù p x» w, p ü x y k lp w» p w» (FEM) w ww. œ w y p x lp w w w x y» p w. lp x lp w 363 s y x y j» w š w, w lp t gq ƒ ù w ³» w lp w w w w. 2. w 2.1. lp 316L l p ƒ w. k 190 GPa, s 0.3, w 315 MPa, w 616 MPa ƒ w. k w w e Ramberg-Osgood 17) w w lp lp ü w w q» w, m ¼ w œ w. x š x lp j 2ƒ xk. œ w y s x p x lp w œ y x / j x lp, s x w w. x p x lp ƒx lp» w, w t w wš k x yw ƒƒ C-1, C-2 lp w. w w C-1, C-2 lp 2 x Fig. 1. C-1 C-2 ƒƒ ƒx k x. C-1 xk lp x x. 0.7 mm m w ¼ (L) 8.06 mm ¼ / ƒ v w 2 š, 3 x. Fig. 1. Plane views of stent (a) C-1 and (b) C-2. 44«7y(2007)

3 364 «Á k Á» Á½k Fig. 2. Typical mesh configuration for C-1 and C-2. CATIA V5 w, w w v ABAQUS 18) w. ü ƒw m» z w» w θ w š wš, w ³ w q j» w t m t (r, θ, z) w. t y lp 2 q w x k- w. w lp ü t w y 5~10 atm q. w t lp ü w w w w wù, ª lp» t w š x š. Fig. 1 2 ƒ lp (C-1, C-2) 2, r s x 3 x ùkù. Fig. 3 3 w w w ƒ lp 8-6 ù. 2 x w 3 x. t lp ³ w ü ƒw w q w. w lp p t 24, 32, 40, 48 ƒ j t,, w œ m w ƒ» e w w ww. 3. š 3 s x lp 2 ü ƒw θ w z, r w ³ w q j» w m t w. lp x 2 y x š. 0.7 mm lpƒ 2 q w ¾ ƒw. Fig. 3 2 ¾ q g lp q q z.(q w ) Fig. 3, s x lp q z x yƒ (Dog bone) xk ó w q w. š ó ó» ƒ ó x w. x w q g, lp ó x. x É»ƒ x ù x w š š. lp x q j» x x p w, wz lp w ƒ. Fig. 3. Expanded shape with internal pressure (a) C-1 stent and (b) C-2 stent. Fig. 4. Von Mises Stress distribution of (a) C-1 stent and (b) C- 2 stent with internal pressure. w wz

4 x lp w 365 Fig. 5. Radial displacements of C-1 and C-2 stents with internal pressure. Fig. 4 lpƒ q z Von Mises s ùkü. s x lp w w, e g. g w q» w w. wr, t ( ) xx w. C-1 C-2 2 q j» w v w w. C-1 w k x C-2 ƒx z p ƒ w, w ¾ q k. Fig. 5 C-1 C-2 ƒƒ 1.5 mmƒ ¾ ƒ lp w y ù Fig. 7. Tube configurations with number of slots. kü. 0.4 MPa l x w w ƒ w MPa, C mmƒ, C mm. C-1 ƒ x š, C-2 k x. C-1 y j. ƒx ƒ C-1 w ¾ q k. Fig. 6 ü g, C-1 C-2 ¼ w. ü g q k z, w ¼ y ùkü, ¼ w w. C-2 ó q,, ó ƒ ƒ ¼ w ƒ w. Fig. 7 lp ( ) ƒw ùkü, Fig. 8 ƒ,, w. lp x» w v Fig. 8 w, x ƒ { w ƒw ùkû. w, Fig. 6. Axial displacements of C-1 and C-2 stents with internal pressure. Fig. 8. Comparision of mechanical response with the surface area as a function of total number of slots in tube slotted stent. 44«7y(2007)

5 366 «Á k Á» Á½k ƒ jš w lp» w ƒ w lp t w w», t gq mw w., lp w q w w ƒ j ( ) xk x s w w q w x ƒ w w lp w ƒ v w. š ü ƒ x y e w t y, z e. w œw w, lp k e š. 19) w, w lp x y x» j» w lp t gq w x w x lp w ƒ w š. lp t gq ƒ š», gq sww,», /p, w w / w 19) lp. 4. s x lp x y» p sƒw., k x ƒx w ¾ q k w. ù, ƒx lpƒ ¼ w ùkû.. w q w, ¼ w w lp x w ƒ wz w š w. lp ( )x ƒx wwš ƒw x { w ƒw ùkû., w q w w ƒ j ( ) xk x s w w q w x, ƒ w lp w ƒ v w. lp w z ƒ j» w, l p w w, gq w wz w w. Acknowledgments 2005 ( ) w w w (KRF D00004). REFERENCES 1. A. D. Callow, Cariovascular Disease 2005-the Global Picture, Vascular Pharmacology, (2006). 2. C. L. Athanasuleas, G. D. Buckberg, B. S. Allen, F. Beyersdorf, and M. M. Kirsh, Sudden Cardiac Death: Directing the Scope of Resuscitation Towards the Heart and Brain, Resuscitation, (2006). 3. J. A. Suwaidi and P. B. Berger, Do Stents Reduce Mortality Compared with Balloon Angioplasty? A Cirtical Review of all the Evidence, Am. Heart J., 150 [1] 7-10 (2005). 4. D. L. Fischman, M. B. Leon, and D. S. Baim, A Randomized Comparison of Coronary Stent Placement and Balloon Angioplasty in the Treatment of Coronary Artery Disease, N. Engl. J. Med., (1994). 5. R. Hoffmann, G. Mintz, P. K. Haager, T. Bozoglu, E. Grube, M. Gross, C. Beythien, H. Mudra, J. Dahl, and P. Hanrath, Relation of Stent Design and Stent Surface Material and to Subsequent in Stent Intimal Hyperplasia in Coronary Arteries Determined by Intravascular Ultrasound, The American J. of Cardiology, (2002). 6. M. Unverdorben, B. Sippel, R. Degenhardt, K. Sattler, R. Fries, B. Abt, E. Wagner, H. Koeher, G. Daemgen, M. Scholz, H. Ibrahim, K. Tews, B. Hennen, H. Berthold, and C. Vallbracht, Comparison of a Silicon Carbide Coated Stent versus a Noncoated Stent in Human Beings: The Tenax versus Nir Stent Study s Long-term Outcome, Am. Heart J., G1-G8 (2003). 7. U. Gerckens, L. Buellesfeld, D. Horstkotte, R. Mueller, M. Staberock, G. Sellbach, T. Schmidt, and E. Grube, Evaluation of a Tacrolimus-Eluting Coronary Stent with Nanoporous Ceramic Coating in Treatment of Native Coronary Artery Lesions, Angiography and interventional cardiology, 41 [6] 7A (2003). 8. C. D. Mario, E. Grube, Y. Nisanci, N. Reifart, A. Colombo, J. Rodermann, R. Muller, S. Ulmman, F. Liistro, M. Montorfano, and E. Alt, MOONLIGHT: a Controlled Registry of an Iridium Oxide coated Stent with Angiographic Followup, Int. J. Cardiology, (2004). 9. S. Windecker, R. Simon, M. Lins, V. Klauss, F. R. Eberli, M. Roffi, G. Pedrazzini, T. Moccetti, P. Wenaweser, M. Togni, D. Tüller, R. Zbinden, C. Seiler, J. Mehilli, A. Kastrati, B. Meier, and O. M. Hess, Randomized Comparison of a Titanium-Nitride-Oxide- coated Stent with a Stainless steel Stent for coronary Revasculations: The TiNOX Trial, ACC Current J. Review, 14 [9] 43 (2005). 10. M. Mosseri, I. Tamari, M. Plich, Y. Hasin, M. Brizines, A. Frimerman, H. Miller, J. Jafari, V. Guetta, M Solomon, and C. Lotan, Short and Long Term Outcome of the Titanium- NO stent Registry, Cardiovascular Revascularization Medicine, (2005). 11. P. D. Maguire, J. A. McLaughlin, T. I. T. Okpalugo, P. Lemoine, P. Papakonstantinou, E. T. McAdams, M. Needham, A. w wz

6 x lp w 367 A. Ogwu, M. Ball, and G. A. Abbas, Mechanical Stability, Corrosion Performance and Bioresponse of Amorphous Diamond-Like Carbon for Medical Stents and Guidewires, Diamond Related Materials, (2005). 12. N. Huang, Y. X. Leng, P. Yang, J. Y.Chen, H. Sun, J. Wang, G. J. Wan, A. S. Zhao, and P. D. Ding, Surface Modification of Coronary Artery Stent by Ti-O/Ti-N Complex Film Coating Prepared with Plasma Immersion Ion Implantation and Deposition, Nuclear Inst. Methods in Phy. Research B., (2006). 13. C. L. Liu, P. K. Chu, G. Q. Lin, and M. Qi, Anti-corrosion Chacteristics of Nitride-coated AISI 316L Stainless steel Coronary Stent, Surface & coating Technology, (2006). 14. F. Migliavacca, L. Petrini, M. Colombo, F. Auricchio, and R. Pietravissa, Mechanical Behavior of Coronary Stents Investigated through the Finite Element Method, J. Biomechanics, (2002). 15. N. David Chua, B. J. MacDonald, and M. S. J. Hashmi, Finite Element Simulation of Stent Expansion, J. of Materials Processing Technology, (2002). 16. S. N. D. Chua, B. J. MacDonald, M. S. J. Hashmi, Effects of Varying Slotted Stent Geometry on its Expansion Behaviour using Finite Element Method, J. of Mat. Processing Technology, (2004). 17. KIM, J. R. Rasmussen, 2001, Full-range Stress-Strain Curves for Stainless Steel Alloys, J. Constuctional Steel Research, 59, (2003). 18. ABAQUS user s manual, HKS, U.S.A. (2006). 19. H. M. Burt and W. L. Hunter, Drug-eluting Stents: A Multidisciplinary Success Story, Adv. Drug Delivery Review, (2006). 44«7y(2007)