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TECHNICAL PAPERS: Soft Tissue

3D Mechanical Properties of the Layered Esophagus: Experiment and Constitutive Model

[+] Author and Article Information
W. Yang, T. C. Fung

School of Civil and Environmental Engineering, Nanyang Technological University, Singapore, 639798 Singapore

K. S. Chian

School of Mechanical and Aerospace Engineering, Nanyang Technological University, Singapore, 639798 Singapore

C. K. Chong

School of Chemical and Biomedical Engineering, Nanyang Technological University, Singapore, 639798 Singapore

J Biomech Eng 128(6), 899-908 (May 11, 2006) (10 pages) doi:10.1115/1.2354206 History: Received January 07, 2006; Revised May 11, 2006

The identification of a three dimensional constitutive model is useful for describing the complex mechanical behavior of a nonlinear and anisotropic biological tissue such as the esophagus. The inflation tests at the fixed axial extension of 1, 1.125, and 1.25 were conducted on the muscle and mucosa layer of a porcine esophagus separately and the pressure-radius-axial force was recorded. The experimental data were fitted with the constitutive model to obtain the structure-related parameters, including the collagen amount and fiber orientation. Results showed that a bilinear strain energy function (SEF) with four parameters could fit the inflation data at an individual extension very well while a six-parameter model had to be used to capture the inflation behaviors at all three extensions simultaneously. It was found that the collagen distribution was axial preferred in both layers and the mucosa contained more collagen, which were in agreement with the findings through a pair of uniaxial tensile test in our previous study. The model was expected to be used for the prediction of stress distribution within the esophageal wall under the physiological state and provide some useful information in the clinical studies of the esophageal diseases.

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Copyright © 2006 by American Society of Mechanical Engineers
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Figures

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Figure 1

Procedure used to obtain the true zero-stress state and definition of three states: (1) bonded no-load state; (2) separated no-load state; and (3) true zero-stress state

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Figure 2

Schematic diagram of the inflation test

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Figure 3

Illustration of the experimental protocol

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Figure 4

Plots of the outer radius and axial force as functions of internal pressure for (a) the muscle and (b) mucosa layer. Values are mean ±SD.

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Figure 5

The mean stress-stretch curves at the pressure of 0.5–5kPa for (a) the muscle and (b) mucosa layer. Values are mean ±SD.

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Figure 6

Response functions ψθ(=∂ψ∕∂Eθ) and ψz(=∂ψ∕∂Ez) as function of the Green strain Eθ for (a) the muscle (b) mucosa of the Specimen-1125

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Figure 7

Pressure-radius (“∙” and “-”) and axial force-radius (“*” and “- -”) at λz=1, 1.125, and 1.25 with symbols denoting the experimental data (Specimen-1122-muscle) and lines denoting the modeling curves predicted by the bilinear model (upper row) and the modified exponential model (lower row)

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Figure 8

Plots of the three material parameters fel, fcoll, and α for the muscle (filled symbols) and mucosal (unfilled symbols) layer. Red symbols indicate that fcoll or α does not increase with λz.

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Figure 9

Fittings of the radius-pressure-axial force at three extensions (Specimen-1122-muscle) with (a) the bilinear model and (b) the new model. ∙ and - represent the radius-pressure curve measured from the experiment and predicted by the model while * and - - denote the corresponding radius-force curve.

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Figure 10

Stress distributions within the wall of (a) the muscle, (c) mucosa, and (e) bilayered esophagus under the pressure of 5kPa and λz=1, 1.125, and 1.25 (correspond to the three groups of curves from right to left in each figure) without considering the residual strains. The stresses predicted by taking the residual strains into account are plotted in (b), (d), and (f) correspondingly.

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