Role of elastin anisotropy in structural strain energy functions of arterial tissue

Abstract

The vascular wall exhibits nonlinear anisotropic mechanical properties. The identification of a strain energy function (SEF) is the preferred method to describe its complex nonlinear elastic properties. Earlier constituent-based SEF models, where elastin is modeled as an isotropic material, failed in describing accurately the tissue response to inflation-extension loading. We hypothesized that these shortcomings are partly due to unaccounted anisotropic properties of elastin. We performed inflation-extension tests on common carotid of rabbits before and after enzymatic degradation of elastin and applied constituent-based SEFs, with both an isotropic and an anisotropic elastin part, on the experimental data. We used transmission electron microscopy (TEM) and serial block-face scanning electron microscopy (SBFSEM) to provide direct structural evidence of the assumed anisotropy. In intact arteries, the SEF including anisotropic elastin with one family of fibers in the circumferential direction fitted better the inflation-extension data than the isotropic SEF. This was supported by TEM and SBFSEM imaging, which showed interlamellar elastin fibers in the circumferential direction. In elastin-degraded arteries, both SEFs succeeded equally well in predicting anisotropic wall behavior. In elastase-treated arteries fitted with the anisotropic SEF for elastin, collagen engaged later than in intact arteries. We conclude that constituent-based models with an anisotropic elastin part characterize more accurately the mechanical properties of the arterial wall when compared to models with simply an isotropic elastin. Microstructural imaging based on electron microscopy techniques provided evidence for elastin anisotropy. Finally, the model suggests a later and less abrupt collagen engagement after elastase treatment.

Age-Related Changes in the Elastic Tissue of the Human Aorta

“…Several groups analyzed biomechanical properties of arteries after selective elimination of elastin and collagen [32,33,34,35]. They reported the existence of significant elastin-dependent compressive pre-stresses (also termed residual stress [36]) within the aortic wall. Interlaminar elastic structures could be responsible for this prestress.…”

Mechanical Testing of Mouse Carotid Arteries: from Newborn to Adult

“…The opening angle measurement is necessary for calculating stress and strain distributions through the wall thickness 12 . The complete set of six test protocols and the opening angle can be used to fit constitutive equations and fully characterize the mechanical behavior of each artery [13][14][15][16] .…”

“…The protocol takes more time and effort than a single pressure-diameter or contractility protocol, but provides enough information to compare the behavior for any loading condition and may highlight subtle differences in mechanical behavior that are not apparent in traditional pressure myograph experiments. Microstructurally-based constitutive equations can be used to correlate the mechanical behavior with measured differences in matrix protein amounts or organization [13][14][15][16] .…”

Energy harvesting through arterial wall deformation: design considerations for a magneto-hydrodynamic generator

“…In a first approximation, we consider the arterial wall as a linear elastic isotropic material, although it is known that the arterial tissue has a nonlinear stress-strain relation [3], behaves viscoelastically [4,40] and has anisotropic properties [26]. These limitations will be addressed in the discussion in Sect.…”

“…Because this effect is apparently of minor importance, it was neglected. (c) Rezakhaniha et al [26] showed that both collagen and elastin, which are the main constituents of the arterial wall together with smooth muscle cells, exhibit anisotropic properties. The authors achieved an excellent agreement between theory and inflationextension experiments by accounting for this behaviour in the modelling of arterial wall mechanics.…”