An Application of the Pipette Technique to the Measurement of Local Mechanical Properties of Aortic Walls

Abstract

Local elastic moduli in the wall of bovine and porcine thoracic aortas were measured in the axial, circumferential, and radial directions by the pipette aspiration method. Comparing the relationship between aspiration pressure and aspirated length in experiments with that of the finite element analysis, we can calculate an elastic modulus of soft tissue. In experiments a glass pipette was placed perpendicular to the surface of specimen and a negative pressure was applied to aspirate the surface. The moduli in three directions obtained for bovine aortas were found to decrease significantly and monotonously from the inner to the outer walls. No directional differences were statistically found among the moduli at any radial positions in the wall. In contrast with the bovine aorta, the elastic moduli in the porcine thoracic aortas were almost equal in any radial positions in the cross section. From the histological point of view, there were quite distinguishable differences between the bovine and the porcine aortas. Bovine aortas have a heterogeneous structure, that is, large clusters of smooth muscle cells exist in the adventitial side. In porcine aortic walls, a regularly layered structure is found. These aortic walls were stained with Azan-Mallory and Resorcin-Fuchsin, and the histological image analysis was performed to quantitatively asses the correlation between the elastic moduli and the distribution of the structural components. The results suggested that the intramural distributions of elastic moduli were closely correlated with the histological structure.