STUDY OF STENT DEFORMATION AND STRESS DEVELOPED AT DIFFERENT STENT DEPLOYMENT PRESSURES

Transcription

1 STUDY OF STENT DEFORMATION AND STRESS DEVELOPED AT DIFFERENT STENT DEPLOYMENT PRESSURES KRISTI BASU PRANAB GHOSH DR. ABHIJIT CHANDA SCHOOL OF BIOSCIENCE AND ENGINEERING JADAVPUR UNIVERSITY KOLKATA: W.B, INDIA

2 What is coronary artery disease (CAD)? A narrowing of the coronary arteries that is usually caused by atherosclerosis, it may progress to the point where the heart muscle is damaged due to lack of blood supply. Such damage may result in infarction, arrhythmias, and heart failure.

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4 WHAT IS A STENT? A stent is an artificial 'tube' inserted into a natural passage/conduit in the body to prevent, or counteract, a disease-induced, localized flow constriction. The term may also refer to a tube used to temporarily hold such a natural conduit open to allow access for surgery.

5 STENT CLASSIFICATION Material Area of Usage Drug Eluting/ Non Eluting Balloon Expanding/ Self Expanding

6 Stalwarts of Cardiology Andreas Gruentzig Julio Palmaz

7 BALLOON ANGIOPLASTY?? STENT???

8 Design aspect Stents possess deformation regions that behave differently according to the type of load applied With a stent with a link structure, a deformable (link) region and rigid (cell) region are arranged in an alternate fashion. Therefore, the bending test should be performed with uniform bending moment without radial deformation.

9 Stent Designs 1. Coil Stents High stenosis rates Tissue collapse between widely spaced struts Gianturco- Roubin II 2. Open- Cell Modular Stents Superior flexibility Some areas more susceptible to corrosion and fatigue 3. Multi-Cell Closed Cell Structure Rigid High radial strength NIR & NIROYAL Bx Velocity

10 Problems Vessel Wall injury In Stent Restenosis Target Lesion Failure Stent under/ over expansion Stent Malapposition Stent Fracture

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12 Material Elastic Modulas (GPa) msi Tensile Strength (MPa) ksi Ultimate Tensile Strength (MPa) ksi Poisson s Ratio Yield Strength (MPa) 316L-SS Tantalum Nitinol to Elgiloy

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14 PALMAZ- SCHATZ STENT GEOMETRY A SINGLE SEGMENT OF PS STENT (Cordis, USA) (Cordis, USA)

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16 COMSOL Multiphysics v4.2a Structural Mechanics Module Parametric Solver Solver Equation: Load_max*((para<=1)*para+(para>1)*(2-para)) Physics Controlled Triangular Mesh 3 different Deployment Pressures

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21 Von Mises Stress (MPa) Von Mises Stress at 2 atm Deployment Pressure Series SS Tantalum NiTinol Elgiloy Material

22 Displacement (mm) Displacement at 2 atm Deployment Pressure Series SS Tantalum NiTinol Elgiloy

23 Von Mises Stress (MPa) Von Mises Stress at 7 atm Deployment Pressure Series SS Tantalum NiTinol Elgiloy

24 Displacement (mm) Displacement at 2 atm Deployment Pressure Series SS Tantalum NiTinol Elgiloy

25 Von Mises Stress (MPa) Von Mises Stress (MPa) Von Mises Stress at 12 atm Pressure Deployment at Clinically Significant Deployment Pressure Series1 Von Mises Stress at 17 atm Pressure SS Tantalum Series NiTinol Elgiloy

26 Displacement (mm) Displacement (mm) Deployment at Clinically Significant Deployment Pressure Displacement at 12 atm pressure Series1 Displacement at 17 atm Pressure 0 316L-SS Tantalum Series1 0 NiTinol Elgiloy

27 Change design Decrease deployment pressure New mechanism to dissipate the high stresses formed

28 A preliminary study to make a realistic assessment on the effect of deployment pressure on the mechanical performance of cardiac stents. Deployment pressure in the range of atm. generates higher stress and deformation in SS 316L and Tantalum in Comparison with Nitinol and Elgiloy. Evident that SS 316L and Tantalum were likely to be more prone to fracture under In Situ condition. Higher deformation and stress associated with these stents can cause endothelial cell denudation of the arterial wall.

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31 Documentation, COMSOL Multiphysics, Structural Mechanics Module, V3.5a C. Lally et.al, Cardiovascular stent design and vessel stresses: a finite element analysis, Journal of biomechanics, 2005 Gerard A. Holzapfel et.al, Changes in the mechanical environment of stenotic arteries during interaction with stents Frank J. H. Gijsen et.al., Simulation of stent deployment in a realistic human coronary artery, Biomedical Engineering Online, August 2008 Koji Mori and Takashi Saito, Effects of Stent Structure on Stent Flexibility Measurements, Annals of Biomedical Engineering, June 2005 Azadeh Farnoush and Qing Li, Three Dimensional Nonlinear Finite Element Analysis of a newly designed Cardiovascular Stent, Australasian Congress on Applied Mechanics, 2007 Linxia Gu et.al, The relation between the arterial stress and restenosis rate after coronary stenting, Mechanical Engineering, department of DigitalCommons, University of Nebraska-Lincoln, 2010

32 C. Lally et.al, Stents, Wiley Encyclopedia of Biomedical Engineering, 2006 J. Theodore Dodge Jr. et.al., Lumen Diameter of Normal Human Coronary Arteries: Influence of Age, Sex, Anatomic Variation, and Left Ventricular Hypertrophy or Dialation, EJ Topol et.al, Caveats about coronary stent, N Engl J MED, 1994 Stoeckel et. al., Self-Expanding Nitinol Stents - Material and Design Considerations, European Radiology, 2003 J. Levesque et. al., Materials And Properties For Coronary Stents, Advanced Materials & Processes, September, 2004 Fernando Alfonso et.al., A randomized comparison of repeat stenting with balloon angioplasty in patients with In Stent Restenosis, journal of American College of cardiology, 2003 Adrian James Ling, Stenting for carotid artery stenosis: Fractures, proposed etiology and the need for surveillance, Journal of Vascular Surgery, (2008)