Dynamic Tensile Behavior of Fiber Bundles Freshly Isolated From Nerve Roots

Viscoelasticity of the nerve root may play a significant role in biomechanical stability of the spine. To date, however, relatively few studies have been conducted to characterize and elucidate this complex mechanical behavior. Thus, a series of tensile stress relaxation tests with a ramp-hold phase was performed using fiber bundles isolated from the nerve roots. In addition, the current study presents the application of a curve fitting technique, i.e., a stress relaxation response of the fiber bundles was theoretically predicted based on the measured data obtained at moderate to sub-traumatic loading conditions. To do that, a least squares optimization method was employed, and we revealed that this technique is applicable to reasonably predict even an instantaneous “elastic” response as well as subsequent slow stress decay of the neural fiber bundles. The resultant fitted coefficients also suggested that the viscoelastic tensile behavior of the nerve root is mainly dominated by the long-term time constants (100–1000 s) rather than the short-term time constants (0.1–1 s). Since a mathematical human body model is a powerful tool to investigate injury mechanisms involving high-contact sports and traffic accidents, our results will be useful in predicting potential spinal injuries and alleviating mechanical damage of the nerve roots, while preventing neck/low back pain due to such traumatic events.