The substructures of an aorta wall in hypertension play a critical mechanical role in aorta damage and possible rupture. The goal is to develop a hypothesis for these invisible dynamic mechanisms in a rupturing wall from the rupture surface morphology. Rupture mechanisms suggested by tensile tests, including histological images of the crack, are explored on a novel pneumatic device to expand ring specimens excised from bovine aorta. This technique elucidates the role in rupture of the medial substructures, the wall thickness and the moisture content of the specimen using images of the rupture surface, weight measures, and measurements of the permanent deformation prior to rupture and also at rupture. In both excised aorta tensile strip specimens and ring specimens, collagen fiber pull-out due to shear is a prerequisite for rupture, and is reflected in local permanent deformation that precedes rupture. Some of this permanent deformation is recovered by rehydrating the specimen. In the specimens loaded parallel to the collagen fibers, the change in crack direction shown in histological images of uniaxial specimens is reflected in rings by the acute rupture angle with the load direction. A hypothesis is proposed for the rupture mechanisms in the aorta wall that involves shear of the connections between fascicle substructures in the media. The results suggest requirements for a mathematical model of the aorta wall in hypertension that is more realistic than the usual hyperelastic models.

Rupture of vascular tissue in the circulatory system under non-impact loading is involved in potentially life threatening events such as Marfan’s syndrome or rupture of small renal veins during shock wave lithotripsy. The rupture mechanisms are not well-understood. The complexity of the artery wall precludes the use of rupture theories invented for metals or for fibered composites with a homogeneous matrix. Artery tissue is composed of ground material, smooth muscle cells, elastin and collagen. The collagen fibers, which are generally circumferentially oriented, are the load carrying material after large deformations. Clark and Glagov [1] propose that the media of an elastic artery is built of musculo-elastic fascicles made up of a layer of circumferentially oriented SMC that lie parallel and between two elastin lamellae. Between the elastin sheets of adjacent elements are interspersed collagen fiber bundles.