Research Papers

Dynamic Tensile Behavior of Fiber Bundles Isolated From Spinal Neve Roots: Effects of Anatomical Site and Loading Rate on Mechanical Strength

[+] Author and Article Information
Atsutaka Tamura

Department of Mechanical
and Aerospace Engineering,
Tottori University,
4-101 Koyama-minami,
Tottori 680-8552, Japan
e-mail: a-tamura@mech.tottori-u.ac.jp

Mizuki Sakaya

Department of Mechanical
and Aerospace Engineering,
Tottori University,
4-101 Koyama-minami,
Tottori 680-8552, Japan
e-mail: mizuki.sakaya@gmail.com

1Corresponding author.

Manuscript received November 30, 2017; final manuscript received February 28, 2018; published online March 26, 2018. Assoc. Editor: Assimina Pelegri.

ASME J of Medical Diagnostics 1(3), 031001 (Mar 26, 2018) (6 pages) Paper No: JESMDT-17-2053; doi: 10.1115/1.4039560 History: Received November 30, 2017; Revised February 28, 2018

We found a significant difference (P < 0.05) between the linear portion of the elastic modulus (∼20 MPa) and tensile strength (∼2 MPa) at the 0.2 mm/s (low: 0.01 s−1), 2 mm/s (medium: 0.11 s−1), and 20 mm/s (high: 1.11 s−1) loading rates by performing a series of uniaxial stretching tests. However, the mechanical properties of the neural fiber bundles were resultantly of the same magnitude, indicating that their mechanical responses were relatively insensitive to a given strain rate regardless of a 100-fold increase in the applied stretching velocities. We also confirmed that a “spinal level effect” exists in the nerve roots, i.e., a fiber bundle isolated from the lumbar spinal level is weaker in mechanical strength compared to that from the cervical and thoracic spinal levels (P < 0.05), suggesting that closer attention should be paid to an anatomical site from which test samples are excised.

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Grahic Jump Location
Fig. 1

Schematic view of a custom-made uniaxial tensile tester

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Fig. 2

Magnified region of interest subjected to dynamic uniaxial stretching

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Fig. 3

Test protocol consisting of a set of preconditioning cycles, 60 s rest, and a final stretch up to material failure. Applied stretching rates 0.2, 2, and 20 mm/s corresponded to strain rates 0.01, 0.11, and 1.11 s−1, respectively.

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Fig. 4

Typical mechanical response of a fiber bundle isolated from the spinal nerve root subjected to uniaxial stretch. Each stress–strain curve was divided into two distinct regions, i.e., toe and linear regions.

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Fig. 5

Comparison of the representative mechanical parameters of a fiber bundle varying by distinctive spinal levels; C: cervical nerve root; T1: thoracic nerve root (upper region); T2: thoracic nerve root (middle region); T3: thoracic nerve root (lower region); and L: lumbar spinal nerve root. Asterisks indicate a statistical significance, i.e., **P < 0.01 and *P < 0.05 (N,number of subjects: N = 22).

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Fig. 6

Representative samples of histological cross sections harvested from porcine nerve roots (objective 10×; scale bar = 100 μm)



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