On the Compressibility of Arterial Tissue

Abstract

Arterial tissue is commonly assumed to be incompressible. While this assumption is convenient for both experimentalists and theorists, the compressibility of arterial tissue has not been rigorously investigated. In the current study we present an experimental-computational methodology to determine the compressibility of aortic tissue and we demonstrate that specimens excised from an ovine descending aorta are significantly compressible. Specimens are stretched in the radial direction in order to fully characterise the mechanical behaviour of the tissue ground matrix. Additionally biaxial testing is performed to fully characterise the anisotropic contribution of reinforcing fibres. Due to the complexity of the experimental tests, which entail non-uniform finite deformation of a non-linear anisotropic material, it is necessary to implement an inverse finite element analysis scheme to characterise the mechanical behaviour of the arterial tissue. Results reveal that ovine aortic tissue is highly compressible; an effective Poisson's ratio of 0.44 is determined for the ground matrix component of the tissue. It is also demonstrated that correct characterisation of material compressibility has important implications for the calibration of anisotropic fibre properties using biaxial tests. Finally it is demonstrated that correct treatment of material compressibility has significant implications for the accurate prediction of the stress state in an artery under in vivo type loading.

Compressibility and Anisotropy of the Ventricular Myocardium: Experimental Analysis and Microstructural Modeling

“…Tissue specimens are excised from porcine hearts, sourced from a certified abattoir (Brady's, Athenry, Ireland). The organs are stored at À80 C until required, and thawed in phosphate buffer solution at room temperature, in accordance with previous protocols [6]. The atria are removed and a transmural base-apex cut is taken between the posterior and the anterior papillary muscles from the lateral left ventricular wall ( Fig.…”

“…Volume change during stretching is tracked using the quasi-3D methodology proposed by Nolan and McGarry [6]. A series of images from the orthogonal video-extensometer cameras are imported to and digitized in MATLAB (R2017b, The Mathworks, Natick, MA).…”

“…Incompressibility is commonly assumed in the computational modeling of some soft tissues (primarily due to the fluid content within cells and interstitial components), though recent investigations have challenged such assumptions [6,7]. The incompressible condition for myocardium is supported by a study from Vossoughi and Patel [8].…”

Improving the experimental protocol for a more accurate identification of a given mechanical behaviour in a single assay: Application to skin

“…For example, the measures are sensitive to the fine positioning (spacing and alignment) of suture attachment points, which may induce stress concentrations in the specimen . In the work of Jacobs et al and Nolan and McGarry, finite element simulations of a biaxial clamp experiment were performed to quantify stress shielding and to create a correction factor. An illustration of the dependence on sample geometry and material anisotropy was shown in the same paper.…”

An investigation of damage mechanisms in mechanobiological models of in-stent restenosis

“…Additionally, residual stresses which exist in the artery wall at a zero pressure state should be included in future FE models [40]. Finally, both VSMCs and ECs are idealised and represented by circles, despite the fact that ECs are squamous epithelial cells and VSMCs are more spindle like in form, particularly contractile VSMCs [41,42].…”