title: A transverse isotropic viscoelastic constitutive model for aortic valve tissue.
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 ([Formula: see text]). 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 betweenηand [Formula: see text] 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.
authors.affiliation: The BIONEER centre, Cardiovascular Engineering Research Laboratory (CERL), School of Engineering , University of Portsmouth , Anglesea Road, Portsmouth PO1 3DJ , UK.
authors.forename: Afshin
authors.identifier: 0000-0003-4348-5186
authors.initials: A
authors.lastname: Anssari-Benam
authors.affiliation: The BIONEER centre, Cardiovascular Engineering Research Laboratory (CERL), School of Engineering , University of Portsmouth , Anglesea Road, Portsmouth PO1 3DJ , UK.
authors.forename: Andrea
authors.initials: A
authors.lastname: Bucchi
authors.affiliation: Institute of Bioengineering, School of Engineering and Materials Science, Queen Mary University of London , Mile End Road, London E1 4NS , UK.
authors.forename: Hazel R C
authors.initials: HR
authors.lastname: Screen
authors.affiliation: School of Engineering , Cardiff University , The Parade, Cardiff CF24 3AA , UK.
authors.forename: Sam L
authors.initials: SL
authors.lastname: Evans
keywords: aortic valve; physiological rate; rate dependency; transverse isotropy; uniaxial data; viscoelastic model