Importance of material model in wall stress prediction in abdominal aortic aneurysms

journal article - other

English

Background. Results of biomechanical simulation of the abdominal aortic aneurysm (AAA) depend on the constitutive description of the wall. Based on in-vitro and in-vivo experimental data several constitutive models for the AAA wall have been proposed in literature. Those models differ strongly from each other and their impact on the computed stress in biomechanical simulation is not clearly understood. Methods. Finite Element (FE) models of AAAs from 7 patients who underwent elective surgical repair were used to compute wall stresses. AAA geometry was reconstructed from CT angiography (CTA) data and patient-specific constitutive descriptions of the wall were derived from planar biaxial testing of anterior wall tissue samples. In total 28 FE models were used, where the wall was described either by patient-specific or previously reported study-average properties. This data was derived from either uniaxial or biaxial in-vitro testing. Computed wall stress fields were compared on node-by-node basis. Results. Different constitutive models for the AAA wall cause significantly different predictions of wall stress. While study-average data from biaxial testing gives globally the same stress field as the patient-specific wall properties, the material model based on uniaxial test data overestimates the wall stress on average by 30kPa or about 67% of the mean stress. A quasi-linear description based on the in-vivo measured distensibility of the AAA wall leads to a completely altered stress field and overestimates the wall stress by about 75kPa or about 167% of the mean stress. Conclusion. The present study demonstrated that the constitutive description of the wall is crucial for AAA wall stress prediction. Consequently, results obtained using different models should not be mutually compared unless different stress gradients across the wall are not taken into account. Highly nonlinear material models should be preferred when the response of AAA to increased blood pressure is investigated, while the quasi-linear model with high initial stiffness produces negligible stress gradients across the wall and thus, it is more appropriate when response to mean blood pressure is calculated.

material model, pre-stressing, abdominal aneurysm, wall stress, FE analysis

POLZER, S.; GASSER, T.; BURŠA, J.; STAFFA, R.; VLACHOVSKÝ, J.; MAN, V.; SKÁCEL, P.

2013

27. 1. 2013

Elsevier

1350-4533

MEDICAL ENGINEERING & PHYSICS

35

4

United Kingdom of Great Britain and Northern Ireland

1282

1289

8