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TECHNICAL PAPERS: Fluids/Heat/Transport

# Dynamic Simulation Pericardial Bioprosthetic Heart Valve Function

[+] Author and Article Information
Hyunggun Kim

Department of Biomedical Engineering, University of Iowa, Iowa City, IA 52242

Jia Lu

Department of Mechanical and Industrial Engineering, University of Iowa, Iowa City, IA 52242

Michael S. Sacks

Engineered Tissue Mechanics Laboratory, Department of Bioengineering, University of Pittsburgh, Pittsburgh, PA

Krishnan B. Chandran

Departments of Biomedical and Mechanical and Industrial Engineering, University of Iowa, Iowa City, IA IIHR-Hydroscience and Engineering, Iowa City, IA 52242chandran@engineering.uiowa.edu

J Biomech Eng 128(5), 717-724 (Apr 20, 2006) (8 pages) doi:10.1115/1.2244578 History: Received October 06, 2005; Revised April 20, 2006

## Abstract

While providing nearly trouble-free function for 10–12 years, current bioprosthetic heart valves (BHV) continue to suffer from limited long-term durability. This is usually a result of leaflet calcification and/or structural degeneration, which may be related to regions of stress concentration associated with complex leaflet deformations. In the current work, a dynamic three-dimensional finite element analysis of a pericardial BHV was performed with a recently developed FE implementation of the generalized nonlinear anisotropic Fung-type elastic constitutive model for pericardial BHV tissues (W. Sun and M.S. Sacks, 2005, [Biomech. Model. Mechanobiol., 4(2-3), pp. 190–199]). The pericardial BHV was subjected to time-varying physiological pressure loading to compute the deformation and stress distribution during the opening phase of the valve function. A dynamic sequence of the displacements revealed that the free edge of the leaflet reached the fully open position earlier and the belly region followed. Asymmetry was observed in the resulting displacement and stress distribution due to the fiber direction and the anisotropic characteristics of the Fung-type elastic constitutive material model. The computed stress distribution indicated relatively high magnitudes near the free edge of the leaflet with local bending deformation and subsequently at the leaflet attachment boundary. The maximum computed von Mises stress during the opening phase was $33.8kPa$. The dynamic analysis indicated that the free edge regions of the leaflets were subjected to significant flexural deformation that may potentially lead to structural degeneration after millions of cycles of valve function. The regions subjected to time varying flexural deformation and high stresses of the present study also correspond to regions of tissue valve calcification and structural failure reported from explanted valves. In addition, the present simulation also demonstrated the importance of including the bending component together with the in-plane material behavior of the leaflets towards physiologically realistic deformation of the leaflets. Dynamic simulations with experimentally determined leaflet material specification can be potentially used to modify the valve towards an optimal design to minimize regions of stress concentration and structural failure.

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## Figures

Figure 1

(a) FE model of the pericardial BHV. (b) Subdivision of the leaflet geometry into three regions of interest. (c) Representative data (61) showing a uniform 45deg preferred fiber orientation throughout the pericardial BHV leaflet.

Figure 4

Sequence of the displacements of the BHV model during the opening phase shown from an oblique and top view of the valve

Figure 5

Time-varying von Mises stress distribution of the BHV model with the same color scale for all the plots

Figure 6

Regional stress distribution of the normal and shear components of the BHV model at t=0.13s

Figure 7

Comparison of the displacement of the BHV leaflet with and without the inclusion of the bending stiffness in the dynamic FE analysis

Figure 8

Comparison of the von Mises stresses distribution between the Fung-type elastic (nonlinear anisotropic) model and Saint Venant (isotropic) model at the fully open position

Figure 2

Time-varying pressures for the complete human cardiac cycle: (a) Left ventricular and aortic pressure pulses. (b) Pressure difference between left ventricle and aorta, adapted from Hole’s human anatomy and physiology (62).

Figure 3

Comparison between the FE simulation and experimental data for the equi-biaxial protocol: (a) normal components and (b) shear component

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