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research-article

Histology and Biaxial Mechanical Behavior of Abdominal Aortic Aneurysm Tissue Samples

[+] Author and Article Information
Francesco Q. Pancheri

Dept. of Mechanical Engineering Tufts University Medford, MA 02155
fqpvr6@gmail.com

Robert A. Peattie

Dept. of Surgery Tufts Medical Center Boston, MA 02111
robert.peattie@tufts.edu

Nithin D. Reddy

Dept. of Surgery Tufts Medical Center Boston, MA 02111
nithin.reddy@tufts.edu

Touhid Ahamed

Dept. of Civil and Environmental Engineering Tufts University Medford, MA 02155
touhid.ahamed@tufts.edu

Wenjian Lin

Dept. of Civil and Environmental Engineering Tufts University Medford, MA 02155
wenjian.lin@tufts.edu

Timothy D. Ouellette

Dept. of Surgery Tufts Medical Center Boston, MA 02111
timothy.ouellette@tufts.edu

Mark D. Iafrati

Dept. of Surgery Tufts Medical Center Boston, MA 02111
miafrati@tuftsmedicalcenter.org

A. Luis Dorfmann

Dept. of Civil and Environmental Engineering Tufts University Medford, MA 02155Dept. of Biomedical Engineering Tufts University Medford, MA 02155
luis.dorfmann@tufts.edu

1Corresponding author.

ASME doi:10.1115/1.4035261 History: Received December 16, 2015; Revised November 01, 2016

Abstract

Abdominal aortic aneurysms (AAA) represent permanent, localized dilations of the abdominal aorta that can be life-threatening if progressing to rupture. Evaluation of risk of rupture depends on understanding the mechanical behavior of patient AAA walls. In this project, a series of patient AAA wall tissue samples have been evaluated through a combined anamnestic, mechanical and histopathologic approach. Mechanical properties of the samples have been characterized using a novel, strain-controlled, planar biaxial testing protocol emulating the in vivo deformation of the aorta. Histologically, the tissue ultrastructure was highly disrupted. All samples showed pronounced mechanical stiffening with stretch and were notably anisotropic, with greater stiffness in the circumferential than the axial direction. However, there were significant intra-patient variations in wall stiffness and stress. In biaxial tests in which the longitudinal stretch was held constant at 1.1 as the circumferential stretch was extended to 1.1, the maximum average circumferential stress was 330 ± 70 kPa while the maximum average axial stress was 190 ± 30 kPa. A constitutive model considering the wall as anisotropic with two preferred directions fit the measured data well. No statistically significant differences in tissue mechanical properties were found based on patient gender, age, maximum bulge diameter, height, weight, body mass index or smoking history. Although a larger patient cohort is merited to confirm these conclusions, the project provides new insight into the relationships between patient natural history, histopathology and mechanical behavior that may be useful in the development of accurate methods for rupture risk evaluation.

Copyright (c) 2016 by ASME
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