Biomechanical Characterization of Abdominal Aortic Aneurysms

ILT Histological image characterizing the morphology of the thrombus-covered arterial wall.

Unknown Mounted patch of a carotid artery (a) before the peeling test, shown from the side, and (b) during the testing procedure, shown from the top.

An abdominal aortic aneurysm (AAA) is a vascular pathology associated with permanent and localized dilatation (ballooning) of the abdominal aorta. Continuous growth of AAAs may lead to wall rupture, which is a catastrophic event frequently associated with high mortality and serious life-threatening morbidity if not addressed. AAA development is multifactorial and is primarily related to elastolysis. From a pathohistological point of view, aneurysmal degeneration is mainly attributed to loss of elastin and turnover of collagen within the aortic wall. Such structural alterations and excessive aged collagen deposition result in significant changes in the tissue’s mechanical properties. Therefore, investigation of the biomechanical properties of AAA tissues provides an essential insight into growth and remodeling, and advances our understanding of disease progression and intrinsic rupture mechanism.

In our lab we focus on a few fields in AAA research:

  1. mechanical testing of aneurysmal tissues harvested from open surgical repair

  2. microstructural characterization by histology and multiphoton microscopy

  3. biochemical quantification of mass fractions of the main protein components within the tissues

  4. histomechanical characterization of the intraluminal thrombus.

By performing biaxial extension and peeling tests of the intraluminal thrombus (ILT) and the thrombus-covered wall (see figure), the mechanical responses are systematically explored and more appropriate 3D material models developed. The microstructural characterization of ILT samples serves as the basis for the determination of relative thrombus ages. We propose the four age phases: very fresh, young, intermediate and old. Mass fraction analyses determine dry weight percentages of elastin and collagen within the layer-specific aneurysmal aortic structure, which, in turn, affect the mechanical properties at the tissue level. In addition, our effort is also aimed at a refined understanding of the effect of ILT age on AAA wall mechanics and gender differences.

Funding: Graz University of Technology and Medical University of Graz – Clinical Department of Vascular Surgery