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Article

Improved Prediction of the Collagen Fiber Architecture in the Aortic Heart Valve

[+] Author and Article Information
Niels J. B. Driessen1

 Department of Biomedical Engineering, Eindhoven University of Technology, P.O. Box 513, 5600 MB Eindhoven, The Netherlandsn.j.b.driessen@tue.nl

Carlijn V. C. Bouten, Frank P. T. Baaijens

 Department of Biomedical Engineering, Eindhoven University of Technology, P.O. Box 513, 5600 MB Eindhoven, The Netherlands

1

To whom correspondence should be addressed.

J Biomech Eng 127(2), 329-336 (Sep 16, 2004) (8 pages) doi:10.1115/1.1865187 History: Received August 26, 2003; Revised September 16, 2004

Living tissues show an adaptive response to mechanical loading by changing their internal structure and morphology. Understanding this response is essential for successful tissue engineering of load-bearing structures, such as the aortic valve. In this study, mechanically induced remodeling of the collagen architecture in the aortic valve was investigated. It was hypothesized that, in uniaxially loaded regions, the fibers aligned with the tensile principal stretch direction. For biaxial loading conditions, on the other hand, it was assumed that the collagen fibers aligned with directions situated between the principal stretch directions. This hypothesis has already been applied successfully to study collagen remodeling in arteries. The predicted fiber architecture represented a branching network and resembled the macroscopically visible collagen bundles in the native leaflet. In addition, the complex biaxial mechanical behavior of the native valve could be simulated qualitatively with the predicted fiber directions. The results of the present model might be used to gain further insight into the response of tissue engineered constructs during mechanical conditioning.

FIGURES IN THIS ARTICLE
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Copyright © 2005 by American Society of Mechanical Engineers
Topics: Fibers , Valves
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Figures

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Figure 1

Schematic representation of the preferred fiber direction (e⃗p) in a local coordinate system, spanned by the principal stretch directions (v⃗i)

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Figure 2

Schematic representation of fiber reorientation. The fiber (e⃗fj) is rotated over an angle Δθj toward the preferred fiber direction (e⃗pj), resulting in the fiber direction (e⃗fj′). αj denotes the angle between e⃗fj and e⃗pj.

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Figure 3

Finite element mesh of the stented valve geometry. Because of symmetry only 1∕6 of the valve is used in the finite element computations. This part of the leaflet is subdivided into 147 hexahedral elements with 1893 nodes.

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Figure 4

Maximum principal stretch (λ1) for a node in the commissure region as a function of scaled time (κ0t), obtained with the reference values of the parameters (case 1), a reduced pressure level (case 2), a decreased fiber stiffness (case 3), an increased matrix modulus (case 4), and a more pronounced alignment (case 5). Note that the curves of cases 1 and 5 nearly coincide.

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Figure 5

Fiber configuration after the remodeling process, obtained with the reference values of the parameters (case 1). (a) Total volume fraction ϕftot(=ϕf1+ϕf2) on the aortic side of the leaflet. Note that ϕf1≃ϕf2 because λf1≃λf2. (b) Fiber directions (e⃗f1 and e⃗f2) on the aortic side of the leaflet.

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Figure 6

Value of γ1 (deg) in the belly region on the aortic surface of the leaflet after the remodeling process. (a) is obtained with reference values of the parameters (case 1), (b) with a reduced pressure level (case 2), (c) with a reduced fiber stiffness (case 3), (d) with an increased matrix modulus (case 4), and (e) with a more pronounced alignment (case 5).

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Figure 7

Fiber architecture in a porcine aortic heart valve leaflet [from Sauren (see Ref. 26) with permission]. The macroscopically visible bundles seem to originate at the commissures and run in the circumferential direction. In the central part of the leaflet the bundles branch and the fibers enter the fixed edge radially.

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Figure 8

Schematic representation of hypothetical overall fiber distributions in the leaflet’s belly region, consisting of two local preferred fiber directions (schematically arranged with respect to the circumferential direction). These curves are based on measurements by Sacks and Gloeckner (see Ref. 29), assuming that the overall distribution is the sum of the individual subdistributions (see Ref. 31). The local preferred directions are predicted by our model and are assumed to represent a Gaussian subdistribution. (a) The two fiber populations overlap sufficiently and as a result only one single fiber population is detectable (μ1=−μ2=25°; σ1=σ2=30°). (b) The local subdistributions are less dispersed and the two preferred directions become distinguishable (μ1=−μ2=25°; σ1=σ2=20°).

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Figure 9

Stress-stretch curve of a part of the belly region with a homogenized predicted fiber architecture (γ1=25° and ϕf1=ϕf2=0.07) in an equibiaxial loading protocol.

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