stent ansys
DESCRIPTION
Stent simulation methodsTRANSCRIPT
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2011 ANSYS, Inc. May 7, 20121
Finite Element Modeling of Traditional and Innovative Biomedical Stents
Davide Fugazza, ANSYS Belgium
Vinay Carpenter, ANSYS India
Marc Horner, ANSYS, Inc.
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2011 ANSYS, Inc. May 7, 20122
1. What is a stent?
2. Motivation
3. Stent geometry
4. Material properties
5. Finite element mesh
6. Boundary/Loading conditions
7. Selected results
8. Solution process
9. Innovative materials
Overview
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2011 ANSYS, Inc. May 7, 20123
A stent is a tiny tube placed into an artery, blood vessel, or
other duct, partially occluded by a plaque, to restore the
original width and then re-establish a correct blood flow.
1. What is a stent?
1
2
3
1 stent mounted on a balloon catheter
2 balloon is inflated and stent expands
3 balloon is removed and stent is implanted in the vessel
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2011 ANSYS, Inc. May 7, 20124
2. Motivation
Need of highly reliable numerical tools to simulate
biomedical devices
Numerical analyses allow investigating both
material behavior and structures
Possibility of improving design
Experimental testing is complex and costly
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2011 ANSYS, Inc. May 7, 20125
3. Stent geometry(*)
Outer diameter = 0.058 (~ 1.47 mm)
Radial thickness = 0.0006 (~ 0.15 mm)
OD
RT
(*) courtesy ASTM Endovascular Devices Test Methods Task Group (F04.30.06)
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2011 ANSYS, Inc. May 7, 20126
3. Stent geometry (contd)
234 bodies
Create an hexahedral mesh
Take advantage of symmetries
and/or repetitive patterns
Localize slicing locations
Model decomposition
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s
S
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slicing planes
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4. Material properties
Material : stainless steel (E = 200000 MPa, = 0.3)
Constitutive model : elasto-plastic with multilinear hardening
Yielding value,y ~ 300 MPa
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2011 ANSYS, Inc. May 7, 20128
5. Finite element mesh
SOLID 185, 3D 8-Node Structural Solid
SOLID 186, 3D 20-Node Structural Solid
Outer diameter ~ 1.47 mm
Radial thickness ~ 0.15 mm
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2011 ANSYS, Inc. May 7, 20129
6. Boundary/Loading conditions
Deformation Stage Objectives
Load Step 1
Radial expansion of the stentSimulate balloon inflation
Load Step 2
Recoil of the stentSimulate balloon deflation
We focus on the stent behavior only therefore the balloon will not be
modelled. Expansion and recoil are simulated by imposing target
displacements to a rigid cylinder.
Output quantities of interest :
1. Stresses after radial expansion
2. Residual stresses and plastic strains after recoil
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2011 ANSYS, Inc. May 7, 201210
6. Boundary/Loading conditions (contd)
Load Step 1
Radial expansion of 0.875 mm
Balloon modelled as rigid
target in contact with stent
Load Step 2
Radial recoil to 0.7 mm
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2011 ANSYS, Inc. May 7, 201211
7. Solution process
Complex behavior :
Non-linear material : elasto-plastic constitutive model
Non-linear BCs : contact between stents and balloon
Geometric non-linearities : large deflections
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8. Selected results
max~ 1.8 y
inflation deflation
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2011 ANSYS, Inc. May 7, 201213
8. Selected results (contd)
inflation deflation
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2011 ANSYS, Inc. May 7, 201214
9. Innovative materials
Question: any alternatives to steel? I believe so
Shape-memory alloys (SMAs) : materials with intrinsic ability to remember
an original shape featuring at the macroscopic level two uncommon
characteristics not present in materials typically used in engineering.
Superelasticity (SE) : upon loading and unloading cycles an SMA can
undergo large deformations without showing residual strains.
Shape-memory effect (SME) : the SMA can recover its original shape
through thermal cycles.
SE SME
New in R14!
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2011 ANSYS, Inc. May 7, 201215
9. Innovative materials (contd)
An example of SMA material: Nitinol (Nickel Titanium Naval Ordinance Lab.)
Nitinol is a compound of Nickel and Titanium. Due to its unique properties,
which depend upon temperature and processing history, it has found
widespread acceptance as a material of choice for medical implants and
other engineering devices.
Biomechanics : orthodontics, orthopedics, eyeglasses, etc.
Mechanics : actuators, thermal valves, connectors, etc.
Structural : vibration control systems, dissipation devices, etc.
Macroscopic effects not available in traditional materials
Innovative and commercially valuable applications
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2011 ANSYS, Inc. May 7, 201216
9. Innovative materials (contd)
Can we use/simulate shape-memory alloy stents? I would feel confident
SMA stents are manufactured with a diameter larger than that of the target
vessel. They are then crimped at or below room temperature and placed in
a delivery system. At the treatment site the stent is released from the
delivery system and expands until it hits the vessel wall and conforms to it.
Then, at body temperature, the stent shows a superelastic behavior.
Nitinol vs. Steel
Nitinol Steel
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2011 ANSYS, Inc. May 7, 201217
Thank you!