P5.3 CHARACTERIZATION OF THE BIOMECHANICS OF THE RAT XENOGRAFT MODEL OF ABDOMINAL AORTIC ANEURYSM BY RING TEST

Abstract

Setting up new strategies to prevent the growth and fatal rupture of aneurysms remains a challenge. The rat xenograft model of abdominal aortic aneurysm (AAA) has been used to develop gene and cell therapies with the aim of countering the expansion of the diseased arterial wall. It is of primary importance to characterize the mechanical behavior of this model before studying the effects of those therapies. Ring tests were performed on 34 samples extracted at several locations along rat AAAs and 8 samples from native healthy rat aortas (NA). The circumferential ultimate strength and extensibility were measured. Material parameters from an exponential isotropic hyperelastic strain energy density function were identified by a finite-element inverse approach. The changes of mechanical properties along the axial direction of AAA were analyzed through the correlation between parameters and external radius. AAAs display significantly higher radius and thickness than NAs and appear weaker, with circumferential ultimate strength and extensibility significantly lower. Best-fit values for material parameters show significant differences between both groups. We reveal strong correlations between ultimate strength and external radius (r=−0.58, p<0.001). As well as between the material parameter accounting for non-collagenous matrix response and external radius (r=−0.79, p<0.001). These associations are explained by the degradation and loss elastin, which are more important as we get closer to the zone of maximal dilatation. These results indicate that the most dilated parts are the most prone to rupture. Further studies should evaluate stress distributions within the arterial wall in order to better predict rupture risk.