Non-linear viscoelastic behavior of abdominal aortic aneurysm thrombus

The objective of this work was to determine the linear and non-linear viscoelastic behavior of abdominal aortic aneurysm thrombus and to study the changes in mechanical properties throughout the thickness of the thrombus. Samples are gathered from thrombi of seven patients. Linear viscoelastic data from oscillatory shear experiments show that the change of properties throughout the thrombus is different for each thrombus. Furthermore the variations found within one thrombus are of the same order of magnitude as the variation between patients. To study the non-linear regime, stress relaxation experiments are performed. To describe the phenomena observed experimentally, a non-linear multimode model is presented. The parameters for this model are obtained by fitting this model successfully to the experiments. The model cannot only describe the average stress response for all thrombus samples but also the highest and lowest stress responses. To determine the influence on the wall stress of the behavior observed the model proposed needs to implemented in the finite element wall stress analysis

Computational modelling of endoleak after endovascular repair of abdominal aortic aneurysms

To better understand the effects of endoleak on the aneurysm intrasac pressure, previously, in a small number of studies, numerical models have been developed for the simulation of endoleak based on coupled fluid-structure interaction (FSI). Although such models can provide useful information on the fluid dynamics and structural deformations in aneurysms after endovascular repair (EVAR), they may computationally be too expensive if one is solely interested in the effects of endoleak on the risk of aneurysm rupture. To assess the value of computationally more efficient lumped parameter models in the simulation of endoleak, in the current study, a lumped parameter-based computational model of an incompletely excluded abdominal aortic aneurysm is developed as well as one based on coupled FSI. Both models are used to study the aneurysm intrasac pressure as a function of the degree of endoleak and the stent-graft compliance. Based on the agreement of the results of the two models it is concluded that the lumped parameter modelling method provides a useful alternative to coupled FSI for modelling the aneurysm intrasac pressure in the presence of endoleak. The modelled pressure could be used as a boundary condition for solid stress analyses to predict the risk of aneurysm rupture after EVAR