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Research Papers

# Determination of Coefficient of Friction for Self-Expanding Stent-Grafts

[+] Author and Article Information

Department of Aerospace and Mechanical Engineering, University of Arizona, Tucson, AZ 85721

Amanda Eskinazi

Department of Agricultural and Biosystems Engineering, University of Arizona, Tucson, AZ 85721

Timothy Corbett, Tim McGloughlin

Center for Applied Biomedical Engineering Research (CABER), MSSi, and Department of Aerospace and Mechanical Engineering, University of Limerick, Ireland

Jonathan P. Vande Geest1

Department of Aerospace and Mechanical Engineering, Department of Biomedical Engineering, and BIO5 Institute for Collaborative Research, University of Arizona, Tucson, AZ 85721jpv1@email.arizona.edu

1

Corresponding author.

J Biomech Eng 132(12), 121007 (Nov 08, 2010) (10 pages) doi:10.1115/1.4002798 History: Received March 25, 2010; Revised September 12, 2010; Posted October 15, 2010; Published November 08, 2010; Online November 08, 2010

## Abstract

Migration of stent-grafts (SGs) after endovascular aneurysm repair of abdominal aortic aneurysms is a serious complication that may require secondary intervention. Experimental, analytical, and computational studies have been carried out in the past to understand the factors responsible for migration. In an experimental setting, it can be very challenging to correctly capture and understand the interaction between a SG and an artery. Quantities such as coefficient of friction (COF) and contact pressures that characterize this interaction are difficult to measure using an experimental approach. This behavior can be investigated with good accuracy using finite element modeling. Although finite element models are able to incorporate frictional behavior of SGs, the absence of reliable values of coefficient of friction make these simulations unreliable. The aim of this paper is to demonstrate a method for determining the coefficients of friction of a self-expanding endovascular stent-graft. The methodology is demonstrated by considering three commercially available self-expanding SGs, labeled as $A$, $B$, and $C$. The SGs were compressed, expanded, and pulled out of polymeric cylinders of varying diameters and the pullout force was recorded in each case. The SG geometries were recreated using computer-aided design modeling and the entire experiment was simulated in ABAQUS 6.8/STANDARD . An optimization procedure was carried out for each SG oversize configuration to determine the COF that generated a frictional force corresponding to that measured in the experiment. The experimental pullout force and analytically determined COF for SGs $A$, $B$, and $C$ were in the range of 6–9 N, 3–12 N, and 3–9 N and 0.08–0.16, 0.22–0.46, and 0.012–0.018, respectively. The computational model predicted COFs in the range of 0.00025–0.0055, 0.025–0.07, and 0.00025–0.006 for SGs $A$, $B$, and $C$, respectively. Our results suggest that for SGs $A$ and $B$, which are exoskeleton based devices, the pullout forces increase upto a particular oversize beyond which they plateau, while pullout forces showed a continuous increase with oversize for SG $C$, which is an endoskeleton based device. The COF decreased with oversizing for both types of SGs. The proposed methodology will be useful for determining the COF between self-expanding stent-grafts from pullout tests on human arterial tissue.

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## Figures

Figure 1

Material properties of polymeric cylinder derived from uniaxial testing and second order polynomial fit

Figure 2

(a) Pullout force experimental setup for SG C. (b) Stent-grafts A, B, and C considered for the pullout force experiment.

Figure 3

Procedures for calculating experimental contact pressure and coefficient of friction

Figure 4

Geometry and typical mesh structure of SGs A, B, and C

Figure 5

Compression, expansion, equilibrium, and pullout steps for SG C

Figure 6

Plot of experimental and simulated pullout forces recorded against cylinder diameter for SGs A, B, and C

Figure 7

Plot showing influence of diameter oversize on the experimental and simulated pullout forces for SGs A, B, and C

Figure 8

Plot showing influence of diameter oversize on the experimental and simulated coefficient of friction for SGs A, B, and C

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