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Research Papers

Mechanical Response of Brain Stem in Compression and the Differential Scanning Calorimetry and FTIR Analyses

[+] Author and Article Information
Wei Zhang, Run-run Zhang, Liang-liang Feng, Yang Li, Fan Wu

State Key Laboratory of Structural
Analysis for Industrial Equipment,
Department of Engineering Mechanics,
Dalian University of Technology,
Dalian 116024, China

Cheng-wei Wu

State Key Laboratory of Structural Analysis
for Industrial Equipment,
Department of Engineering Mechanics,
Dalian University of Technology,
Dalian 116024, China
e-mail: cwwu@dlut.edu.cn

1Corresponding author.

Contributed by the Applied Mechanics Division of ASME for publication in the JOURNAL OF APPLIED MECHANICS. Manuscript received April 7, 2016; final manuscript received June 12, 2016; published online July 1, 2016. Assoc. Editor: Junlan Wang.

J. Appl. Mech 83(9), 091005 (Jul 01, 2016) (6 pages) Paper No: JAM-16-1169; doi: 10.1115/1.4033890 History: Received April 07, 2016; Revised June 12, 2016

The stress–strain curves of brain stem in uniaxial compression demonstrate strain rate dependency and can be characterized with three regions: initial toe region, transitional region, and high strain region, suggesting strong viscoelastic behavior. To investigate the origin of this viscoelasticity at microscale, differential scanning calorimetry (DSC) and Fourier transform infrared (FTIR) spectra of brain stem tissue were recorded and analyzed. The emergence of endotherm thermal domains in DSC indicates that the conformation change of biomolecules can absorb and dissipate energy, explaining the viscous behavior of the brain stem. FTIR analyses indicate that the presence of polar functional groups such as amide, phosphate, and carboxyl groups in the biomolecules takes responsibility for the viscous performance of brain stem. Ogden, Fung, and Gent models were adopted to fit the experimental data, and Ogden model is the most apt one in capturing the stiffening of the brain stem with the increasing strain rate.

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Figures

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Fig. 2

Experimental rig for uniaxial compression test

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Fig. 5

FTIR of brain stem. The characteristic peaks indicate the presence of CO–NH2, COO, and PO2 groups.

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Fig. 1

Photo of a brain stem and the harvest location for brain stem specimen

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Fig. 3

Stress–strain curve at strain rate of 0.005/s (a), 0.05/s (b), and 0.15/s (c), insets: mean of six repetitions with error bar (±SD) and the definition of E1, E2, and E3. (d) The first derivative of mean of six repetitions presented in the insets of (a)–(c). The small drawing in each region illustrates the microstructural geometry of axonal fibers. Inset of (d) plots the calculated E1, E2, and E3 at different strain rates.

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Fig. 4

DSC curve of brain stem. Downward deflection represents endotherm process. Note that for clarification, the DSC curve ranging from 30 to 60 °C is not shown due to the lack of thermal domains.

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Fig. 6

Fitting of constitutive models to mean experimental compression data at various strain rates: 0.005/s (a), 0.05/s (b), and 0.15/s (c)

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