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Design Innovation

Adaptation of a Planar Microbiaxial Optomechanical Device for the Tubular Biaxial Microstructural and Macroscopic Characterization of Small Vascular Tissues

[+] Author and Article Information
Joseph T. Keyes, Darren G. Haskett

Graduate Interdisciplinary Program in Biomedical Engineering,  The University of Arizona, Tucson, AZ 85721

Urs Utzinger

Graduate Interdisciplinary Program in Biomedical Engineering, BIO5 Institute for Biocollaborative Research, Department of Biomedical Engineering,  The University of Arizona, Tucson, AZ 85721

Mohamad Azhar

BIO5 Institute for Biocollaborative Research, Department of Cell Biology and Anatomy,  The University of Arizona, Tucson, AZ 85721

Jonathan P. Vande Geest1

Graduate Interdisciplinary Program in Biomedical Engineering, The Department of Aerospace and Mechanical Engineering, BIO5 Institute for Biocollaborative Research, Department of Biomedical Engineering,  The University of Arizona, Tucson, AZ 85721jpv1@email.arizona.edu

1

Corresponding author.

J Biomech Eng 133(7), 075001 (Jul 29, 2011) (8 pages) doi:10.1115/1.4004495 History: Received March 01, 2011; Revised May 24, 2011; Posted June 30, 2011; Published July 29, 2011; Online July 29, 2011

Murine models of disease are a powerful tool for researchers to gain insight into disease formation, progression, and therapies. The biomechanical indicators of diseased tissue provide a unique insight into some of these murine models, since the biomechanical properties in scenarios such as aneurysm and Marfan syndrome can dictate tissue failure and mortality. Understanding the properties of the tissue on the macroscopic scale has been shown to be important, as one can then understand the tissue’s ability to withstand the high stresses seen in the cardiac pulsatile cycle. Alterations in the biomechanical response can foreshadow prospective mechanical failure of the tissue. These alterations are often seen on the microstructural level, and obtaining detailed information on such changes can offer a better understanding of the phenomena seen on the macroscopic level. Unfortunately, mouse models present problems due to the size and delicate features in the mechanical testing of such tissues. In addition, some smaller arteries in large-animal studies (e.g., coronary and cerebral arteries) can present the same issues, and are sometimes unsuitable for planar biaxial testing. The purpose of this paper is to present a robust method for the investigation of the mechanical properties of small arteries and the classification of the microstructural orientation and degree of fiber alignment. This occurs through the cost-efficient modification of a planar biaxial tester that works in conjunction with a two-photon nonlinear microscope. This system provides a means to further investigate how microstructure and mechanical properties are modified in diseased transgenic animals where the tissue is in small tube form. Several other hard-to-test tubular specimens such as cerebral aneurysm arteries and atherosclerotic coronary arteries can also be tested using the described modular device.

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Copyright © 2011 by American Society of Mechanical Engineers
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References

Figures

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Figure 1

Solid model renderings of the MOD in the planar (right) and tubular (left) configurations. (a) the sample, (b) inlet tube, (c) outlet flow screw. Note the preserved components in both configurations.

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Figure 2

Cross section schematic of the tubular fixture pieces that fits into the testing device. (a) outlet flow screw, (b) specimen, (c) custom capillary tubes, (d) attachment pieces to pushrods in bath. Thick arrow shows the flow direction from the pump.

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Figure 3

Screenshot from the testing program. Scale is 0.5 mm. Black markers are cyanoacrylate/ceramic markers with marker tracking boxes. The diameter is recorded in the elongated rectangle shown.

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Figure 4

Excised heart from mouse after cleaning of extraneous tissue

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Figure 5

(a) Vessel prior to mounting (ruler is in centimeters with millimeter submarkings). (b) Vessel mounted and placed in testing bath.

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Figure 6

Testing procedure for macroscopic and microscopic testing

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Figure 7

Representative multiphoton images of the mouse aorta in the unpressurized (a and b) and pressurized (c and d) states. (a) and (c) show the vessel near the outside of the thickness, (b) and (d) show the vessel towards the intima. Red is SHG signal (collagen), green is autofluorescence (elastin). Scale bar is 100 μ m.

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Figure 8

Representative stress versus strain plots for tubular mechanical test of a wild-type mouse aorta. Axial stress is represented on the left, while circumferential stress is represented on the right. Blue data points represent the acquired data and the surfaces represent a Fung fit.

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Figure 9

Representative histogram plot of collagen (a) and elastin (b) fiber angle percent occurrences for unpressurized (red) and pressurized (pink) states. The full width at half maximum is shown on the plots and increased from the unpressurized (0 ± 5 mmHg) to pressurized (100 ± 5 mmHg) states. (c) Representative percent collagen and elastin through the wall thickness as measured with thresholding.

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Figure 10

Representative mode of the orientation histograms through the thickness of the aortic wall. (a) shows how collagen orientation changes and (b) shows how elastin orientation changes.

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