Heterogeneity in Microscopic Residual Stress in the Aortic Wall

Abstract

Aortic wall has a concentric layered structure which is a pair of relatively stiff elastic lamina (EL) and a relatively soft smooth muscle cell (SMC)-rich layer. If soft and stiff layers bear the same stress in a loaded state, tensile and compressive residual stress should appear in the soft and stiff layer, respectively, in an unloaded state. In fact, ELs are corrugated and SMCs remain stretched in an unloaded aortic wall, and ELs become straight and SMCs shrink upon isolation from the surrounding tissues. As an index of compressive residual stress, a waviness W, defined as the length along its corrugation divided by its straight length, was calculated in the sections of porcine thoracic aortas. The waviness varied widely, ranging from 1.00 to 1.35. The variation of the waviness caused wide variation of the stress borne by the ELs. For example, estimated stress was as high as 150 kPa for the ELs with W = 1.00, and was 0 kPa for the ELs with W = 1.35. The reason for the large difference in the stress in the ELs is unclear at this stage. This may be caused by local activities of the smooth muscle cells such as wall remodeling and cell division.