Multiscale simulations suggest a protective role of neo-adventitia in abdominal aortic aneurysms

A two-scale numerical study on the mechanobiology of abdominal aortic aneurysms

“…The material parameters adopted in the simulations of the three-layered healthy aorta can be found in table 1. Two sets of parameters were employed for the aneurysmatic tissue to account for the different stages of the disease [40,43], as shown in table 2.…”

“…In this section, geometries, boundary conditions and constitutive models for the multi-scale simulations of arterial tissue at the cellular level are described. The methods presented here were previously employed by Dalbosco et al [43]; therefore, only the main features of the multi-scale model are presented. The goal of these simulations is to shed light on possible micro-mechanical cues sensed by vascular cells, especially fibroblasts, since smooth muscle cells are largely absent in AAAs [40,63].…”

“…RVEs, which represent a tissue-level point (figure 2) and consist of two families of collagen fibres embedded in a ground substance of non-collagenous micro-constituents, were constructed for three different stages of AAA pathogenesis, namely: the fibroblast-rich adventitia of a healthy aorta, whose collagen fibres are preferentially aligned in an axial direction [39,43] (figure 2 a );the abluminal side of an early AAA [40,43], in which there is a realignment of collagen fibres towards the circumferential direction (figure 2 b );the abluminal side of a late AAA [40,43], with a stiff neo-adventitia characterized by a highly isotropic distribution of collagen fibres in the circumferential-axial plane (figure 2 c ).

Figure 2The micro-scale model consists of representative volume elements (RVEs) of ( a ) the tunica adventitia of a healthy aorta and AAAs at ( b ) an early and ( c ) late microstructural stage. For each stage, five realizations of the microstructure were created and simulated according to the deformation gradients F of the macro-scale models with different diameters d an .

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“…Given these recent findings, it seems obvious that an answer to the evolution of aneurysms, and in particular to the mechanobiological aspects involved, suggests a multi-scale modelling approach, where simulation and experiment go hand in hand. In this direction, Dalbosco et al [43] recently evaluated the mechano-pathological theory of Niestrawska et al [40] by simulating the equibiaxial loading of representative volume elements (RVEs) of the arterial microstructure in the healthy tissue and in different stages of AAA, with a special focus on the changes in collagen arrangement. However, a major limitation of [43] is that only the micro-scale of the tissue, subjected to an equibiaxial macroscopic deformation of 10%, was modelled.…”

“…First, the healthy abdominal aorta is simulated as a three-layered cylindrical segment under in vivo loading conditions. The deformation of points at the abluminal side of the vessel is then applied to (microscopic) RVEs whose geometry is based on the collagen configuration of the healthy adventitia [39,43]. The resulting deformation fields in the RVEs are then interpreted as the homeostatic mechanical state experienced by vascular cells, particularly fibroblasts, in the healthy non-aneurysmal tissue.…”