Research Papers

Dynamic, Regional Mechanical Properties of the Porcine Brain: Indentation in the Coronal Plane

[+] Author and Article Information
Benjamin S. Elkin, Ashok Ilankova, Barclay Morrison

Department of Biomedical Engineering,  Columbia University, New York 10027, NY

J Biomech Eng 133(7), 071009 (Jul 29, 2011) (7 pages) doi:10.1115/1.4004494 History: Received February 28, 2011; Revised June 12, 2011; Posted June 30, 2011; Published July 29, 2011; Online July 29, 2011

Stress relaxation tests using a custom designed microindentation device were performed on ten anatomic regions of fresh porcine brain (postmortem time <3 h). Using linear viscoelastic theory, a Prony series representation was used to describe the shear relaxation modulus for each anatomic region tested. Prony series parameters fit to load data from indentations performed to ∼10% strain differed significantly by anatomic region. The gray and white matter of the cerebellum along with corpus callosum and brainstem were the softest regions measured. The cortex and hippocampal CA1/CA3 were found to be the stiffest. To examine the large strain behavior of the tissue, multistep indentations were performed in the corona radiata to strains of 10%, 20%, and 30%. Reduced relaxation functions were not significantly different for each step, suggesting that quasi-linear viscoelastic theory may be appropriate for representing the nonlinear behavior of this anatomic region of porcine brain tissue. These data, for the first time, describe the dynamic and short time scale behavior of multiple anatomic regions of the porcine brain which will be useful for understanding porcine brain injury biomechanics at a finer spatial resolution than previously possible.

Copyright © 2011 by American Society of Mechanical Engineers
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Figure 1

Coronal schematic of the porcine brain sliced through (a) the cortex and thalamus and (b) the cerebellum and brainstem. All anatomic regions tested in this study are labeled.

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Figure 2

(a) Measured indentation profile for a single indentation. (b) Average load for a soft region (cerebellum gray matter; CbmG) and a stiff region (cortex) with the theoretical load calculated from the hereditary integral of the indenter displacement and the fit relaxation function.

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Figure 3

(a) G10 ms , (b) G50 ms , and (c) G (note change in scale) from Prony series fits for each region for 10% indentation strain (CA1 = hippocampal CA1, CA3 = hippocampal CA3, DG = dentate gyrus, Ctx = cortex, Th = thalamus, CR = corona radiata, CC = corpus callosum, BS = brainstem, CbmG = cerebellum gray matter, CbmW = cerebellum white matter). (d) Results from post hoc tests for G. (*, p < 0.0011; mean ±95% confidence interval.)

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Figure 4

(a) Relaxation modulus plotted using Prony series parameters for each region from Table 1 (inset = 0 to 0.1 s). (b) KS statistic showing significant differences in time-dependent shear relaxation shown in (a), Bonferoni-corrected for multiple comparisons between each region (*, p < 0.0011).

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Figure 5

(a) Average load for all three step indentations in corona radiata with Prony series fits performed at each indentation. (b) Prony series fit parameters for each step analyzed individually. (c) Equilibrium (G) and short-term (G10 ms ) modulus from fit parameters for each indentation (mean ±95% confidence interval; G50 ms not shown also increases with indentation strain). (d) Reduced relaxation function normalized to G10 ms for each step indentation. (n = 14 indentations in tissue from eight animals.)

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Figure 6

(a) Storage and (b) loss modulus represented as mean (solid line) and 95% confidence interval (dotted line) of microindenter data converted to the frequency domain using Eqs. 3,4 for the cortex, corona radiata, and cerebellum gray matter



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