Microscopic Residual Stress Caused by the Mechanical Heterogeneity in the Lamellar Unit of the Porcine Thoracic Aortic Wall

Abstract

The opened-up configuration of the artery wall has long been assumed to be stress-free. This is questionable at a microscopic level: The aortic media has a laminated structure consisting of an elastic lamina (EL) and a smooth muscle-rich layer (SML). The ELs are corrugated in the opened-up configuration, suggesting their buckling. We found that the ELs were much stiffer than the SMLs from a radial compression test of the porcine aortas. Such mechanical heterogeneity may cause microscopic residual stress, which is hardly released by the radial cutting except in the area close to the cut surface, where the release may cause hills and valleys. To check this hypothesis, we measured the topography and the stiffness distribution of the cut surface of the aortas with a scanning micro indentation tester to find stiff hills (EL) and soft valleys (SML). Residual stress estimated from the measurements was almost comparable to the conventionally estimated values and was large enough to cause the buckling. Fairly large stress may still reside in the opened-up aortic wall.