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Technical Briefs

Viscoelastic Properties of the P17 and Adult Rat Brain From Indentation in the Coronal Plane

[+] Author and Article Information
Benjamin S. Elkin

Department of Biomedical Engineering,
Columbia University,
New York, NY 10027;
MEA Forensic Engineers & Scientists,
Mississauga, ON L4Z 1S6, Canada
e-mail: ben.elkin@meaforensic.com

Barclay Morrison

Department of Biomedical Engineering,
Columbia University, New York, NY 10027
e-mail: bm2119@columbia.edu

1Corresponding author.

Contributed by the Bioengineering Division of ASME for publication in the Journal of Biomechanical Engineering. Manuscript received February 14, 2013; final manuscript received August 13, 2013; accepted manuscript posted September 12, 2013; published online October 1, 2013. Assoc. Editor: Guy M. Genin.

J Biomech Eng 135(11), 114507 (Oct 01, 2013) (5 pages) Paper No: BIO-13-1082; doi: 10.1115/1.4025386 History: Received February 14, 2013; Revised August 13, 2013; Accepted September 12, 2013

This technical brief serves as an update to our previous work characterizing the region-dependence of viscoelastic mechanical properties of the P17 and adult rat brain in the coronal plane (Elkin et al., 2011, “A Detailed Viscoelastic Characterization of the P17 and Adult Rat Brain,” J. Neurotrauma, 28, pp. 2235–2244.). Here, modifications to the microindentation device provided for the reliable measurement of load during the ramp portion of load relaxation microindentation tests. In addition, a correction factor for finite sample thickness was incorporated to more accurately assess the intrinsic mechanical properties of the tissue.The shear relaxation modulus was significantly dependent on the anatomic region and developmental age, with a general increase in stiffness with age and increased stiffness in the hippocampal and cortical regions compared with the white matter and cerebellar regions of the brain. The shear modulus ranged from ∼0.2 kPa to ∼2.6 kPa depending on region, age, and time scale. Best-fit Prony series parameters from least squares fitting to the indentation data from each region are reported, which describe the shear relaxation behavior for each anatomic region within each age group at both short (<10 ms) and long (∼20 s) time scales. These data will be useful for improving the biofidelity of finite element models of rat brain deformation at short time scales, such as models of traumatic brain injury.

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Figures

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Fig. 1

Example of experimental stress-relaxation load traces for three regions of the adult rat brain over the first 0.5 s (in gray) demonstrating the range of stiffness encountered along with calculated loads using the Prony series fits for each individual load curve (indicated in the legend). The inset shows the indenter displacement into the tissue as a function of time (equivalent to the indentation depth).

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Fig. 2

Average shear modulus at 10 ms (G10ms), 50 ms (G50ms), and 20 s (G20 s) after the start of indentation calculated from Prony series fits from each curve within each region of interest in the (a) P17 (n = 4–16 indentations per region), and (b) adult (n = 6–14 indentations per region) rat brain and the results of the post hoc tests on each region for (c) P17, and (d) adult rat (error bars represent standard error of the mean; *, p < 0.05; **, p < 0.01)

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Fig. 3

Prony series model fits for all regions of the (a) P17, and (b) adult rat brain. The inset shows the Kolmogorov–Smirnov comparisons of the Prony series fits for each region (*, p < 0.05).

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