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Research Papers

Fluid-Structure Interaction Model of Aortic Valve With Porcine-Specific Collagen Fiber Alignment in the Cusps

[+] Author and Article Information
Gil Marom

e-mail: maromgil@eng.tau.ac.il

Moshe Rosenfeld

School of Mechanical Engineering,
Tel Aviv University,
Ramat Aviv 69978, Israel

Ehud Raanani

Cardiothoracic Surgery Department,
Chaim Sheba Medical Center,
Tel Hashomer 52621, Israel

Ashraf Hamdan

Heart Institute,
Chaim Sheba Medical Center,
Tel Hashomer 52621, Israel

Rami Haj-Ali

School of Mechanical Engineering,
Tel Aviv University,
Ramat Aviv 69978, Israel

1Corresponding author.

Contributed by the Bioengineering Division of ASME for publication in the Journal of Biomechanical Engineering. Manuscript received November 15, 2012; final manuscript received June 3, 2013; accepted manuscript posted June 17, 2013; published online September 13, 2013. Assoc. Editor: Fotis Sotiropoulos.

J Biomech Eng 135(10), 101001 (Sep 13, 2013) (6 pages) Paper No: BIO-12-1560; doi: 10.1115/1.4024824 History: Received November 15, 2012; Revised June 03, 2013; Accepted June 05, 2013

Native aortic valve cusps are composed of collagen fibers embedded in their layers. Each valve cusp has its own distinctive fiber alignment with varying orientations and sizes of its fiber bundles. However, prior mechanical behavior models have not been able to account for the valve-specific collagen fiber networks (CFN) or for their differences between the cusps. This study investigates the influence of this asymmetry on the hemodynamics by employing two fully coupled fluid-structure interaction (FSI) models, one with asymmetric-mapped CFN from measurements of porcine valve and the other with simplified-symmetric CFN. The FSI models are based on coupled structural and fluid dynamic solvers. The partitioned solver has nonconformal meshes and the flow is modeled by employing the Eulerian approach. The collagen in the CFNs, the surrounding elastin matrix, and the aortic sinus tissues have hyperelastic mechanical behavior. The coaptation is modeled with a master-slave contact algorithm. A full cardiac cycle is simulated by imposing the same physiological blood pressure at the upstream and downstream boundaries for both models. The mapped case showed highly asymmetric valve kinematics and hemodynamics even though there were only small differences between the opening areas and cardiac outputs of the two cases. The regions with a less dense fiber network are more prone to damage since they are subjected to higher principal stress in the tissues and a higher level of flow shear stress. This asymmetric flow leeward of the valve might damage not only the valve itself but also the ascending aorta.

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Figures

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Fig. 1

A view of the stretched cusps (left column) and the mapped collagen fiber network on the stretched cusps of the asymmetric model (right column)

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Fig. 2

A schematic view of the aortic valve model showing the compliant region and the added rigid tubes

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Fig. 3

(a) Stress–strain curves for the hyperelastic materials in the root and for the collagen and elastin of the cusps, and (b) a schematic description of the symmetric cusp with the location of the collagen fibers

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Fig. 4

A 3D view from the aortic side on the collagen fiber maps of the mapped-asymmetric and simplified-symmetric models

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Fig. 5

The aortic and left ventricular (LV) pressure as a function of time

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Fig. 6

The valve opening area, of the symmetric and mapped models, as a function of time with maximum principal stress contours plotted on the deformed structure during peak systole and diastole

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Fig. 7

Blood velocity vectors and blood pressure contours plotted on two-dimensional sections of the mapped (first column) and symmetric (second column) models during different instances of the cardiac cycle

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Fig. 8

Blood flow shear stress contours plotted on the deformed cusps of the mapped (first column) and symmetric (second column) models during different instances of the systolic phase

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