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Research Papers

The Influence of Test Conditions on Characterization of the Mechanical Properties of Brain Tissue

[+] Author and Article Information
M. Hrapko, G. W. Peters, J. S. Wismans

Materials Technology Institute, Eindhoven University of Technology, P.O. Box 513, 5600 MB Eindhoven, The Netherlands

J. A. van Dommelen1

Materials Technology Institute, Eindhoven University of Technology, P.O. Box 513, 5600 MB Eindhoven, The Netherlandsj.a.w.v.dommelen@tue.nl

1

Corresponding author.

J Biomech Eng 130(3), 031003 (Apr 22, 2008) (10 pages) doi:10.1115/1.2907746 History: Received March 14, 2007; Revised September 07, 2007; Published April 22, 2008

To understand brain injuries better, the mechanical properties of brain tissue have been studied for 50years; however, no universally accepted data set exists. The variation in material properties reported may be caused by differences in testing methods and protocols used. An overview of studies on the mechanical properties of brain tissue is given, focusing on testing methods. Moreover, the influence of important test conditions, such as temperature, anisotropy, and precompression was experimentally determined for shear deformation. The results measured at room temperature show a stiffer response than those measured at body temperature. By applying the time-temperature superposition, a horizontal shift factor aT=8.511 was found, which is in agreement with the values found in literature. Anisotropy of samples from the corona radiata was investigated by measuring the shear resistance for different directions in the sagittal, the coronal, and the transverse plane. The results measured in the coronal and the transverse plane were 1.3 and 1.25 times stiffer than the results obtained from the sagittal plane. The variation caused by anisotropy within the same plane of individual samples was found to range from 25% to 54%. The effect of precompression on shear results was investigated and was found to stiffen the sample response. Combinations of these and other factors (postmortem time, donor age, donor type, etc.) lead to large differences among different studies, depending on the different test conditions.

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Copyright © 2008 by American Society of Mechanical Engineers
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Figures

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Figure 3

Dynamic modulus G* and phase angle δ for DFS tests at 23°C and 37°C

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Figure 4

(a) Measured DFS data for one sample before applying TTS (gray lines) and master curve after applying TTS (black lines); (b) Measured SR data of 20% strain for one sample before applying TTS (gray lines) and master curve after applying TTS (black lines)

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Figure 5

Polar plots of (a) G′ (solid lines) and G″ (dashed lines) from DFS tests, (b) stress at 4.5% strain (gray line), 8% strain (solid line), and stress after 10s of relaxation (dashed line) during a SR test.

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Figure 6

Mean shear properties for each anatomical plane with bars representing the variation caused by anisotropy: (a) DFS test, ((b) and (c)) SR test

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Figure 7

DFS results as a function of (a) height of the gap between plates, (b) normal force. SR results as a function of (c) height of the gap between plates, (d) normal force.

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Figure 8

(a) Summary of shear SR experiment results reported in literature. (b) Summary of constant strain rate experiment results reported in literature, for shear (black) and uniaxial (gray) deformations.

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Figure 1

Summary of the linear viscoelastic properties of brain tissue reported in literature. Notice that Fallenstein (48), McElhaney (43), and Wang and Wineman (49) have reported data for one frequency only.

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Figure 2

Eccentric test configuration. Samples are placed on an eccentric rotating disk, which can rotate to change the orientation ϕ in order to study anisotropy. Shear strain is applied to the sample by an angular displacement θ of the bottom plate. The upper wall is designed to carry a moist chamber whereas the lower wall provides the attachment to original setup.

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