Failure properties of abdominal aortic aneurysm tissue are orientation dependent

Abstract

Introduction: Biomechanical rupture risk assessment of abdominal aortic aneurysm (AAA) requires information about failure properties of aneurysmal tissue. There are large differences between reported values. Among others, studies vary in using either axially or circumferentially oriented samples. This study investigates the effect of sample orientation on failure properties.

Methods: Aneurysmal tissues from 45 patients (11 females) were harvested during open AAA repair, cut into uniaxial samples (90) and tested mechanically within 3 h. If possible, the samples were cut in both axial (49 samples) and circumferential (41 samples) directions. Wall thickness, First Piola-Kirchhoff strength P-ult and ultimate tension T-ult were recorded. Influence of sample orientation and other clinical parameters were investigated using non parametric tests.

Results: Medians of Pull (values 1100 kPa for circumferential vs. 715 kPa for axial direction, p < 10(-4)) and T-ult (17.4 N/cm in circumferential vs. 11.2 N/cm in axial direction, p < 10(-4)) were significantly higher in circumferential direction. For paired data, the median of difference was 411 kPa (p < 10(-3)) in P-ult, and 7.4 N/cm < 10(-4)) in T-ult in favor of circumferential direction.

Conclusions: In this first study of anisotropy in AAA wall failure properties using paired comparisons, the strength in circumferential orientation was found to be higher than in axial orientation.