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TECHNICAL PAPERS: Soft Tissue

Directional, Regional, and Layer Variations of Mechanical Properties of Esophageal Tissue and its Interpretation Using a Structure-Based 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(3), 409-418 (Nov 16, 2005) (10 pages) doi:10.1115/1.2187033 History: Received February 05, 2005; Revised November 16, 2005

The esophagus, like other soft tissues, exhibits nonlinear and anisotropic mechanical properties. As a composite structure, the properties of the outer muscle and inner mucosal layer are different. It is expected that the complex mechanical properties will induce nonhomogeneous stress distributions in the wall and nonuniform tissue remodeling. Both are important factors which influence the function of mechanosensitive receptor located in various layers of the wall. Hence, the characterization of the mechanical properties is essential to understand the neuromuscular motion of the esophagus. In this study, the uniaxial tensile tests were conducted along two mutually orthogonal directions of porcine esophageal tissue to identify the directional (circumferential and axial), regional (abdominal, thoracic, and cervical), and layer (muscle and mucosa) variations of the mechanical properties. A structure-based constitutive model, which took the architectures of the tissue’s microstructures into account, was applied to describe the mechanical behavior of the esophagus. Results showed that the constitutive model successfully described the mechanical behavior and provided robust estimates of the material parameters. In conclusion, the model was demonstrated to be a good descriptor of the mechanical properties of the esophagus and it was able to facilitate the directional, layer, and regional comparisons of the mechanical properties in terms of the associated material parameters.

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Copyright © 2006 by American Society of Mechanical Engineers
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Figures

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Figure 1

Configuration of collagen distribution in 2D sketch. α is the angle of the collagen fibers away from θ direction.

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Figure 2

Stress-strain curves from uniaxial test of both layers at the abdominal, thoracic, and cervical region

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Figure 3

Circumferential and axial strength of the muscle and mucosal layer at the abdominal, thoracic and cervical regions. * indicates that the samples are significantly stronger axially than circumferentially (p<0.05).

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Figure 4

Circumferential and axial ultimate stretch ratio of the muscle and mucosal layer at the abdominal, thoracic, and cervical regions. * indicates that the samples are significantly more extensible circumferentially than axially, except for the cervical region of mucosal layer, where it is more extensible axially than circumferentially (p<0.05).

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Figure 5

Comparisons of strength and ultimate stretch ratio between the muscle and mucosal layer in the circumferential and axial directions at the abdominal, thoracic, and cervical regions. * indicates the significance level of p<0.05 and ** denotes p<0.05.

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Figure 6

Comparisons of strength and ultimate stretch ratio among the abdominal, thoracic, and cervical regions in the circumferential and axial directions of the muscle and mucosal layer. * indicates that the difference is significant with respect to the abdominal region and # denotes the significance with respect to the thoracic region (p<0.05).

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Figure 7

Cauchy (true) stresses vs stretch ratios with symbols denoting the experimental data and solid line denoting the modeling curves. The dash line represents the stress contributed by the collagen.

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Figure 8

The circumferential (left panels) and axial (right panels) residuals for the six muscular specimens at the abdominal region. The specimens with similar patterns of residuals were grouped together for clearer visual inspection.

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Figure 9

Plots of bootstrapped values of the four material parameters for the six muscular specimens (left-hand set of data) and the six mucosal specimens (right-hand set of data) at the abdominal region

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Figure 10

Plots of the three material parameters for the muscle (left-hand set of data) and mucosal (right-hand set of data) layer

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