ARUP; ISBN: 978-0-9562121-5-3 - CMBBE 2012 - Cardiff University

fatigue behaviour of Nitinol peripheral stents using finite element analyses.
3. MATERIAL AND METHODS
The Finite Element Method (FEM) was used to simulate the deployment of selfexpandable
Nitinol stent in a peripheral artery and subsequent in vivo loading
conditions. The commercial finite element code ANSYS (Ansys Inc., Canonsburg, PA,
USA) was used to run the simulations.
The stent geometry resembling Medtronic-Invatec Maris Plus peripheral stent was
deduced from images obtained by optical microscopy of the devices; the dimensions
were derived from the same images and from the values defined by the manufacturers.
The stent had an external diameter of 8 mm, a length of 45.8 mm and a strut thickness
of 0.17 mm. The Nitinol material properties required for the ANSYS material model,
were obtained averaging typical values taken from literature. The reconstructed
peripheral stent is depicted in Fig. 1.
Figure 1. 3D model of the studied peripheral stent, which consist of open cell design, peak to peak
connections and 3 links for each crown.
A parametric model of stenotic artery was developed, described by vessel inner
diameter, obstruction ratio, length, asymmetry and sharpness. The distal SFA-proximal
PA segment was considered. It was modelled as a hollow cylinder with an inner
diameter of 5.6 mm, a thickness of 0.56 mm and a length of 100 mm.
The plaque shape was modeled according to the Hicks-Henne function 4 (Fig. 2):
Figure 2. Hicks-Henne function used to model the plaque shape.
This function presents 4 parameters: DV (vessel diameter), RS (residual stenosis), LP
(plaque length), S (shapeness of the peak).
Varying the values of these parameters, different plaque geometries having the same
maximum stenosis rate (80% of the healthy vessel lumen) and the same length (45.8
mm), were made: a concentric plaque with a single peak (Fig. 3a), an eccentric one with
a single peak (Fig. 3b), and a concentric plaque with a double peak (Fig. 3c).
Figure 3. Vessel and plaque models.