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MODELING MECHANICAL PROPERTIES OF ENDOVASCULAR STENTS IN THEIR EXPANDED STATE

This study aims to determine the radial force a stent can sustain based on its mechanical and geometrical parameters. It also investigates the pressure-displacement relationship for stents of arbitrary geometry. The research includes mathematical theory, custom finite element method-based software, and experimental validation results. The influence of non-uniform geometry on stent behavior is explored, and the response of different stent designs to compression and bending forces is analyzed.

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MODELING MECHANICAL PROPERTIES OF ENDOVASCULAR STENTS IN THEIR EXPANDED STATE

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  1. MODELING MECHANICAL PROPERTIES OF ENDOVASCULAR STENTS IN THEIR EXPANDED STATE • determine radial force that a stent can sustain depending on the • mechanical and geometrical stent parameters: • Youngs modulus and shear modulus of strut material • Number of stent struts in the circumferential and axial direction • Reference radius and length of stent in expanded state • Width and thickness of stent struts • determine pressure-displacement relationship (radial and axial) for • a stent with given mechanical and geometrical characteristics • stents of arbitrary geometry, for example:

  2. METHODS • MATHEMATICAL THEORY OF SLENDER • CURVED RODS TO APPROXIMATE STENT STRUTS • DEVELOPMENT OF IN-HOUSE CUSTOM MADE • FINITE ELEMENT METHOD-BASED SOFTWARE • (1000 times faster than commercial software using 3D approx) • EXPERIMENTAL VALIDATION

  3. RESULTS • NON-UNIFORM GEOMETRY INFLUENCES STENTS’ • MECHANICAL RESPONSE: SMALLER DIAMONDS • IMPLY HIGHER STIFFNESS pressure=0.5 atm pressure=0.5 atm pressure=5 atm

  4. MAXIMALLY EXPANDED STENTS ARE STIFFER Colored by radial displacement Colored by longitudinal displacement R = 1cm Deformation (15 %) R = 0.8cm Larger deformation (23.5 %)

  5. STENTS PLACED IN A SMOOTH, UNIFORM LUMEN CAN SUPPORT LARGER UNIFORM PRESSURE • if radial force is not uniformly applied to a stent due to, • for example, non-axially symmetric lumen cross-section, • or a plaque deposit that has not been uniformly pushed • against the wall during balloon angioplasty, a stent is • less stiff than when it is applied to a “uniform” lumen • surface.

  6. A STUDY OF CORONARY STENT RESPONSE TO COMPRESSION AND TO BENDING FORCES STENTS CONSIDERED: • Express-like stent • (Express stent by Boston Scientific) • Cypher-like stent • (Cypher stent by Cordis) • Xience-like stent • (Xience stent by Abbott) COMPRESSION (MOVIES) BENDING (MOVIES)

  7. CONCLUSIONS • open-cell design provides more flexibility to bending • Express-like stent has high flexibility (bending) while keeping • high radial strength (radial displacement: 0.24%) • Xience-like stent is very flexible but it is also soft to • radial force (compression) (radial displacement: 2%) • Xience-like stent has the smallest longitudinal extension • under cyclic loading (struts “in phase”) • New design: more flexibility than Express with higher • radial strength…..Cypher-like stent with open-cell design

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