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A transverse isotropic viscoelastic constitutive model for aortic valve tissue

Anssari-Benam, Afshin, Bucchi, Andrea, Screen, Hazel R. C. and Evans, Samuel Lewin 2017. A transverse isotropic viscoelastic constitutive model for aortic valve tissue. Royal Society Open Science 4 (1) , 160585. 10.1098/rsos.160585

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Abstract

A new anisotropic viscoelastic model is developed for application to the aortic valve (AV). The directional dependency in the mechanical properties of the valve, arising from the predominantly circumferential alignment of collagen fibres, is accounted for in the form of transverse isotropy. The rate dependency of the valve's mechanical behaviour is considered to stem from the viscous (η) dissipative effects of the AV matrix, and is incorporated as an explicit function of the deformation rate (λ˙). Model (material) parameters were determined from uniaxial tensile deformation tests of porcine AV specimens at various deformation rates, by fitting the model to each experimental dataset. It is shown that the model provides an excellent fit to the experimental data across all different rates and satisfies the condition of strict local convexity. Based on the fitting results, a nonlinear relationship between η and λ˙ is established, highlighting a ‘shear-thinning’ behaviour for the AV with increase in the deformation rate. Using the model and these outcomes, the stress–deformation curves of the AV tissue under physiological deformation rates in both the circumferential and radial directions are predicted and presented. To verify the predictive capabilities of the model, the stress–deformation curves of AV specimens at an intermediate deformation rate were estimated and validated against the experimental data at that rate, showing an excellent agreement. While the model is primarily developed for application to the AV, it may be applied without the loss of generality to other collagenous soft tissues possessing a similar structure, with a single preferred direction of embedded collagen fibres.

Item Type: Article
Date Type: Publication
Status: Published
Schools: Engineering
Subjects: T Technology > TA Engineering (General). Civil engineering (General)
Uncontrolled Keywords: aortic valve; transverse isotropy; rate dependency; viscoelastic model; uniaxial data; physiological rate
Publisher: The Royal Society
ISSN: 2054-5703
Date of First Compliant Deposit: 11 January 2017
Date of Acceptance: 14 November 2016
Last Modified: 04 Jun 2017 09:36
URI: http://orca.cf.ac.uk/id/eprint/97364

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