Three-dimensional analysis of the thoracic aorta microscopic deformation during intraluminal pressurization

The aorta is composed of various constituents with different mechanical properties. This heterogeneous structure implies non-uniform deformation in the aorta, which could affect local cell functions. The present study investigates 3D strains of the aorta at a cell scale induced by intraluminal pressurization. After resected mouse, thoracic aortas were stretched to their in vivo length, and the aortas were pressurized at 15, 40, 80, 120, and 160 mmHg. Images of autofluorescent light of elastin were captured under a two-photon microscope. From the movement of markers in elastic laminas (ELs) created by photo-bleaching, 3D strains (epsilon(theta theta), epsilon(zz), epsilon(rr), epsilon(r theta), epsilon(rz), epsilon(theta z)) between two neighboring ELs in the circumferential (theta), longitudinal (z), and radial (r) directions with reference to the dimensions at 15 mmHg were calculated. The results demonstrated that the average of shear strain epsilon(r theta) was almost 0 in a physiological pressure range (from 80 to 120 mmHg) with an absolute value |epsilon(r theta)| changing approximately by 5%. This indicates that ELs experience radial-circumferential shear at the cell scale, but not at the whole tissue scale. The normal strains in the circumferential epsilon(theta theta) and longitudinal direction epsilon(zz) were positive but that in the radial direction epsilon(rr) was almost 0, which demonstrates that aortic tissue is not an incompressible material. The first principal direction in the radial-circumferential plane was 29 degrees +/- 13 degrees from the circumferential direction. We show that the aorta is not simply stretched in the circumferential direction during pressurization and that cells in the aorta undergo complex deformations by nature.