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Welcome to the 6 th European Bifurcation Club 22-23 October 2010 - BUDAPEST

Welcome to the 6 th European Bifurcation Club 22-23 October 2010 - BUDAPEST. Bifurcation stenting simulation: the stent. Dr. Gabriele Dubini. Laboratory of Biological Structure Mechanics – LaBS Dept. of Structural Engineering Politecnico di Milano Milan, Italy. Idealized bifurcation.

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Welcome to the 6 th European Bifurcation Club 22-23 October 2010 - BUDAPEST

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  1. Welcome to the 6th European Bifurcation Club 22-23 October 2010 - BUDAPEST Bifurcation stenting simulation: the stent

  2. Dr. Gabriele Dubini Laboratory of Biological Structure Mechanics – LaBS Dept. of Structural Engineering Politecnico di Milano Milan, Italy

  3. Idealized bifurcation ADVENTITIA 0.34 0.32 MEDIA INTIMA 0.24 45 °

  4. The grid (‘mesh’) for structural computations • 100,980 hexahedral elements (C3D8R) and 73,856 tetrahedral elements (C3D4)

  5. The wall material properties MEDIA AVVENTITIA Circumferential values after Holzapfel et al. (2005) INTIMA STRESS [MPa] Isotropic hyperelastic constitutive law STRAIN

  6. The plaque material properties (Loree et al. 1994) 800 800 600 600 STRESS [KPa] STRESS [KPa] 400 400 200 200 0 0.3 0.6 0 0.3 0.6 STRAIN STRAIN Isotropic hyperelasto-plastic behaviour

  7. Two stent models Multi-Link Vision (L-602 Co-Cr) Multi-Link Frontier (AISI 316L) Elasto-plastic materials: L-602 Co-Cr E = 233 GPa n = 0.35 σy = 414 MPa σf = 930 MPa AISI 316L E = 193 GPa n = 0.30 σy = 205 MPa σf = 515 MPa Stent mesh: 211,628 C3D8R elements

  8.  The balloon Initial configuration: 3 mm diameter; 2, 2.5 and 2 mm ‘tapered’ PET, semi-compliant, isotropic, linear elastic material (E = 1.455 MPa, n = 0.30)

  9. The ‘Provisional Stenting’ simulation Final Kissing Balloon INSERTION EXPANSION RECOIL Main Branch Stenting Main Branch Stenting

  10. Main Branch Stenting The ‘Dedicated Stent’ simulation Opening of the access site to the Side Branch

  11. Different access to Side Branch CENTRAL ACCESS PROXIMAL ACCESS CENTRAL ACCESS CENTRAL ACCESS PROXIMAL ACCESS PROXIMAL ACCESS PROXIMAL ACCESS CENTRAL ACCESS

  12. Validation vs. in vitro experiments (Gastaldi et al., Biomech Model Mechanobiol. 2010; 9: 551–561)

  13. Local fluid dynamics Radius Flow OSI = OSI = OSI > 0.1 ÷ 0.2 associated with cellular proliferation, intimal thickening, and inflammation WSS < 0.5 Pa • Wall Shear Stress (WSS) and WSS gradients • Oscillatory Shear Index (OSI) T = duration of cardiac cycle and tw = instantaneous wall shear stress vector T = duration of cardiac cycle and tw = instantaneous wall shear stress vector

  14. The grid for fluid dynamic computations Total number of elements: about 2,500,000

  15. The grid for fluid dynamic computations

  16. Boundary conditionsfor fluid dynamic computations • Fluid characteristics:homogeneous, isotropic, non-Newtonian (Carreau) fluid • Boundary conditions: OUTLET i) Steady-state simulations:parabolic velocity profile vmax= 0.266 m/s (after Huo et al. 2009) Inlet ii) Pulsatile simulations:parabolic velocity profile time function after Charonko (2010) Outlet null pressure Walls rigid, no-slip condition INLET OUTLET • Solver: ANSYS FLUENT coupled

  17. Velocity and pathlines C D (FKB) VELOCITY [m/s] 0 0.330 0.165 A

  18. Wall shear stress D E Significant low WSS area at the proximal end of the stent in Model D Model E (tapered balloon) causes a reduced dilation of the proximal end Flow WSS [Pa] 0 0.50 0.25 C WSS < 0.5 Pa close to stent struts

  19. Oscillatory Shear Index (OSI) Flow A B C D OSI 0.5 E 0.4 0.3 0.2 0.1 0

  20. More realistic configurations:the ‘Tryton’-like stent expansion

  21. Drug release t = 0.4 s t = 40 s lumen wall wall

  22. Conclusions Towards (patient-specific) virtual interventional planning - i.e. open problems for engineers: • Material properties of the arterial wall and plaque • Detailed anatomy from routine visualisation techniques – i.e. beyond fluoroscopy • Inlet flow curve and outlet pressure/flow split • Short term prediction • How to smoothly fit in the clinical workflow? gabriele.dubini@polimi.it LABORATORY OF BIOLOGICAL STRUCTURE MECHANICS www.labsmech.polimi.it

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