title: The biaxial mechanical behaviour of abdominal aortic aneurysm intraluminal thrombus: classification of morphology and the determination of layer and region specific properties.
abstract: Intraluminal thrombus (ILT) is present in 75% of clinically-relevant abdominal aortic aneurysms (AAAs) yet, despite much research effort, its role in AAA biomechanics remains unclear. The aim of this work is to further evaluate the biomechanics of ILT and determine if different ILT morphologies have varying mechanical properties. Biaxial mechanical tests were performed on ILT samples harvested from 19 patients undergoing open surgical repair. ILT were separated into luminal, medial and medial/abluminal layers. A total of 356 tests were performed and the Cauchy stress (σ) and tangential modulus (TM) at a stretch ratio (λ) of 1.14 were recorded for each test in both the circumferential (θ) and longitudinal (L) directions. Our data revealed three distinct types of ILT morphologies, each with a unique set of mechanical properties. All ILT layers were found to be isotropic and inhomogeneous. Type 1 (n=10) was a multi-layered ILT (thick medial/abluminal layer) whose strength and stiffness decreased gradually from the luminal to the medial/abluminal layer. Type 2 (n=6) was a multi-layered ILT (thin/highly degraded medial/abluminal layer) whose strength and stiffness decreased abruptly between the luminal and medial/abluminal layer and Type 3 (n=3) is a single layered ILT with a lower strength and stiffness than Types 1 and 2. In a sub-study, we found the luminal layer to be stronger and stiffer in the posterior than the anterior region. This work provides further insights to the biomechanical behaviour of ILT and the use of our ILT classification may be useful in future studies.
authors.affiliation: Centre for Applied Biomedical Engineering Research, Materials and Surfaces Science Institute, Mechanical, Aeronautical and Biomedical Engineering Department, University of Limerick, Limerick, Ireland.
authors.forename: Siobhan A
authors.initials: SA
authors.lastname: O'Leary
authors.affiliation: Department of Vascular Surgery, HSE Midwestern Regional Hospital, Limerick, Ireland.
authors.forename: Eamon G
authors.initials: EG
authors.lastname: Kavanagh
authors.affiliation: Department of Vascular Surgery, HSE Midwestern Regional Hospital, Limerick, Ireland.
authors.forename: Pierce A
authors.initials: PA
authors.lastname: Grace
authors.affiliation: Centre for Applied Biomedical Engineering Research, Materials and Surfaces Science Institute, Mechanical, Aeronautical and Biomedical Engineering Department, University of Limerick, Limerick, Ireland; Department of Biomedical Engineering, Khalifa University of Science, Technology & Research (KUSTAR), P.O. Box: 127788, Abu Dhabi, UAE.
authors.forename: Tim M
authors.initials: TM
authors.lastname: McGloughlin
authors.affiliation: Intelligent Systems for Medicine Laboratory, School of Mechanical and Chemical Engineering, The University of Western Australia, Australia; Centre for Cardiovascular Science, The University of Edinburgh, United Kingdom. Electronic address: barry.doyle@uwa.edu.au.
authors.forename: Barry J
authors.initials: BJ
authors.lastname: Doyle
mesh_terms: D000368:Aged; D016880:Anisotropy; D017544:Aortic Aneurysm, Abdominal / Q000503:physiopathology*; D001696:Biomechanical Phenomena; D003198:Computer Simulation; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D008962:Models, Theoretical; D013314:Stress, Mechanical; D013718:Tensile Strength; D013927:Thrombosis / Q000503:physiopathology*; D014057:Tomography, X-Ray Computed
keywords: AAA; Abdominal aortic aneurysm; Anisotropy; Biaxial mechanical properties; ILT; ILT morphology; Intraluminal thrombus; Layer properties; Regional properties