Re-examination of the mechanical anisotropy of porcine thoracic aorta by uniaxial tensile tests.

Qiang Chen,Zhi-Yong Li,Yan Wang

doi:10.1186/s12938-016-0279-6

Abstract

ObjectiveConsidering past studies on the orthotropic anisotropy of arteries in the circumferential and axial directions, this work aims to experimentally study the anisotropic behaviour of arteries by tensioning multi-directional strips of porcine thoracic aorta.MethodsHistology is first analyzed by staining arterial sections of three orthotropic (axial, circumferential, and radial) planes. 168 stripped samples from 21 aortas are categorized into three loading-rate groups to investigate the influence of loading rates on the Young’s modulus and ultimate stress. Basing on the Young’s modulus and ultimate stress, the degree of anisotropy is calculated. Moreover, 24 stripped samples from 3 aortas are tested to study the relaxation anisotropy of arteries by fitting the experimental data with a five-parameter Maxwell reduced relaxation function.ResultsHistological analysis shows the parallel orientation of crimpled collagen and elastin fibres. The Young’s modulus and ultimate stress reach the greatest in the circumferential direction, and the smallest in the axial direction, respectively, and the values in the other directions are in-between; moreover, the two parameters monotonously increase as the samples orientate from the axial to circumferential directions. The Young’s modulus is more sensitive to the loading rate than the ultimate stress. The degree of anisotropy calculated by the Young's modulus is similar to that by the ultimate stress, and it is independent of loading rates. Stress-relaxation also exhibits anisotropy, whose variation is consistent with those of the two parameters.ConclusionsDue to the stress-growth rule, fibre preferably orientates in the circumferential direction, and the preferable orientation results in great mechanical parameters, anisotropy, and small relaxation behaviour of arteries. The work extends the studies on the arterial anisotropy instead of only the circumferential and axial directions, and could be useful to comprehensively understand the anisotropy of arteries.

Highlights

Artery is composed of three layers, i.e., adventitia, media, intima, and is a composite mainly containing three components, i.e., collagen fibre, elastin fibre, and arterial smooth muscle, which determine the mechanical behaviour of arteries
Work experimentally measured the mechanical anisotropy of arteries by different methods [1], such as the uniaxial [2] and biaxial tensile tests [3], physiologically-simulated test, digital image correlation (DIC) technology [5]
Compared to the ultimate stress, the loading rate produces a greater effect on the Young’s modulus, in other words, the Young’s modulus is loading-rate-dependent, but generally they are in the range of 0.1–0.4 MPa, and this is comparable to the value (~0.4 MPa at 10% strain level) obtained by the inflation method [25]

Summary

Introduction

Artery is composed of three layers, i.e., adventitia, media, intima, and is a composite mainly containing three components, i.e., collagen fibre, elastin fibre, and arterial smooth muscle, which determine the mechanical behaviour of arteries. Chen et al BioMed Eng OnLine 2016, 15(Suppl 2):167 of literature on the biomechanics of arteries, and the mechanical anisotropy of arteries is one of the classical and fundamental issues. Work experimentally measured the mechanical anisotropy of arteries by different methods [1], such as the uniaxial [2] and biaxial tensile tests [3], physiologically-simulated test (cylindrical arterial segments subjected to an internal pressure and axial prestretch without torsion and shear [4]), digital image correlation (DIC) technology [5]. The uniaxial tensile method only obtains the mechanical behaviour of arteries in one direction at a time, and the biaxial obtains those in two directions interested, the residual stress is released and neglected due to the opening of arterial samples. The uniaxial tensile test as a simple and effective method, it has some disadvantages, it is still widely employed to study the relevant mechanical issues including the anisotropy of arteries [7,8,9]

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Results

Conclusion