Strain Rate Effects on the Tensile Behavior of Fiber Bundles Isolated from Nerve Root

Abstract

Fresh porcine spinal cords (N = 5) were obtained at a local abattoir, and intact nerve roots were excised at cervical, thoracic, and lumbar levels using a surgical scalpel and fine forceps with a special caution. In total, 77 fiber bundles with a dimension of 30 mm in length and 0.5 mm in diameter were isolated from the excised nerve roots. By conducting a series of uniaxial stretching tests at three different velocities, 0.1, 1, and 10 mm/s, we revealed that mechanical properties of fiber bundles were relatively insensitive to strain rates under such a sub-impulsive loading condition. On average, elastic moduli, linear portion of stress–strain curve, resulted in 3.8, 3.3, and 4.5 MPa for 0.1, 1, and 10 mm/s, respectively. In addition, strain at failure was almost constant, ~0.15, irrespective of a 100-fold increase in the applied loading rate, while at the same time axial strains were distributed non-homogeneously along fiber direction. We also found that spinal level effect may exist in the spinal nerve roots, suggesting that we should pay more close attention even to an anatomical site where excised samples are obtained.