The Quasi-Static Failure Properties of the Abdominal Aortic Aneurysm Wall Estimated by a Mixed Experimental-Numerical Approach

• Published in: Annals of biomedical engineering 2013-07, Vol.41 (7), p.1554-1566
• Main Authors: Forsell, Caroline, Swedenborg, Jesper, Roy, Joy, Gasser, T. Christian
• Format: Article
• Language: English
• Subjects: Aged; Aneurysm rupture; Aorta, Abdominal - pathology; Aorta, Abdominal - physiopathology; Aortic Aneurysm, Abdominal - complications; Aortic Aneurysm, Abdominal - pathology; Aortic Aneurysm, Abdominal - physiopathology; Aortic Rupture - physiopathology; Biochemistry; Biological and Medical Physics; Biomechanical Phenomena; Biomechanics; Biomedical and Life Sciences; Biomedical Engineering and Bioengineering; Biomedicine; Biophysics; Chronic obstructive pulmonary disease; Classical Mechanics; Collagen; Collagen - physiology; Constitutive modeling; Damage; Female; Fibers; Finite Element Analysis; Humans; Male; Medicin och hälsovetenskap; Middle Aged; Models, Cardiovascular; Plasticity; Pulmonary Disease, Chronic Obstructive - complications; Pulmonary Disease, Chronic Obstructive - pathology; Pulmonary Disease, Chronic Obstructive - physiopathology; Risk Assessment; Tensile Strength
• ISSN: 0090-6964; 1573-9686; 1573-9686
• DOI: 10.1007/s10439-012-0711-4

Assessing the risk for abdominal aortic aneurysm (AAA) rupture is critical in the management of aneurysm patients and an individual assessment is possible with the biomechanical rupture risk assessment. Such an assessment could potentially be improved by a constitutive AAA wall model that accounts for irreversible damage-related deformations. Because of that the present study estimated the elastic and inelastic properties of the AAA wall through a mixed experimental-numerical approach. Specifically, finite element (FE) models of bone-shaped tensile specimens were used to merge data from failure testing of the AAA wall with their measured collagen orientation distribution. A histo-mechanical constitutive model for collagen fibers was employed, where plastic fibril sliding determined not only remaining deformations but also weakening of the fiber. The developed FE models were able to replicate the experimentally recorded load–displacement property of all 16 AAA wall specimens that were investigated in the study. Tensile testing in longitudinal direction of the AAA defined a Cauchy strength of 569(SD 411) kPa that was reached at a stretch of 1.436(SD 0.118). The stiffness and strength of specimens decreased with the wall thickness and were elevated ( p  = 0.018; p  = 0.030) in patients with chronic obstructive pulmonary disease (COPD). Smoking affected the tissue parameters that were related to the irreversible deformation response, and no correlation with gender and age was found. The observed effects on the biomechanical properties of the AAA wall could have long-term consequences for the management of aneurysm patients, i.e., specifically they might influence future AAA rupture risk assessments. However, in order to design appropriate clinical validation studies our findings should firstly be verified in a larger patient cohort.