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Biomechanics and Modeling in Mechanobiology

, Volume 13, Issue 4, pp 813–826 | Cite as

Interlayer micromechanics of the aortic heart valve leaflet

  • Rachel M. Buchanan
  • Michael S. SacksEmail author
Original Paper

Abstract

While the mechanical behaviors of the fibrosa and ventricularis layers of the aortic valve (AV) leaflet are understood, little information exists on their mechanical interactions mediated by the GAG-rich central spongiosa layer. Parametric simulations of the interlayer interactions of the AV leaflets in flexure utilized a tri-layered finite element (FE) model of circumferentially oriented tissue sections to investigate inter-layer sliding hypothesized to occur. Simulation results indicated that the leaflet tissue functions as a tightly bonded structure when the spongiosa effective modulus was at least 25 % that of the fibrosa and ventricularis layers. Novel studies that directly measured transmural strain in flexure of AV leaflet tissue specimens validated these findings. Interestingly, a smooth transmural strain distribution indicated that the layers of the leaflet indeed act as a bonded unit, consistent with our previous observations (Stella and Sacks in J Biomech Eng 129:757–766, 2007) of a large number of transverse collagen fibers interconnecting the fibrosa and ventricularis layers. Additionally, when the tri-layered FE model was refined to match the transmural deformations, a layer-specific bimodular material model (resulting in four total moduli) accurately matched the transmural strain and moment-curvature relations simultaneously. Collectively, these results provide evidence, contrary to previous assumptions, that the valve layers function as a bonded structure in the low-strain flexure deformation mode. Most likely, this results directly from the transverse collagen fibers that bind the layers together to disable physical sliding and maintain layer residual stresses. Further, the spongiosa may function as a general dampening layer while the AV leaflets deforms as a homogenous structure despite its heterogeneous architecture.

Keywords

Aortic valve Flexure Hyperelastic Interlayer Micromechanics Bimodular 

List of symbols

AV

Aortic valve

AC

Flexure direction directed against the natural curvature of the leaflet

ECM

Extracellular matrix

FE

Finite element

GAG

Glycosaminoglycans

I

Second moment of inertia

\(\Delta \kappa \)

Change in valve leaflet curvature during flexure testing

M

Applied bending moment

PG

Proteoglycan

\(\mu \)

Shear modulus

TE

Tissue engineering

W

Strain energy function

WC

Flexure direction directed with the natural curvature of the leaflet

Notes

Acknowledgments

This research was supported by NIH Grants HL-068816, HL-089750, HL-070969, and HL-108330. The authors would like to thank Thanh V. Lam for the development of the flexure-testing device and Brett Zubiate for the later improvements made to the transmural strain system. Also, recognition goes to Kristen Feaver for her contribution of the bimodular schematic (Fig. 8).

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Copyright information

© Springer-Verlag Berlin Heidelberg 2013

Authors and Affiliations

  1. 1.Center for Cardiovascular Simulation, Institute for Computational Engineering and Sciences, Department of Biomedical EngineeringThe University of Texas at AustinAustinUSA
  2. 2.W.A. “Tex” Moncrief, Jr. Simulation-Based Engineering Science Chair 1AustinUSA

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