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 (ε_θθ, ε_zz, ε_rr, ε_rθ, ε_rz, ε_θz) between two neighboring ELs in the circumferential (θ), 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 ε_rθ was almost 0 in a physiological pressure range (from 80 to 120 mmHg) with an absolute value |ε_rθ| 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 ε_θθ and longitudinal direction ε_zz were positive but that in the radial direction ε_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° ± 13° 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.