EFFECTS OF ANATOMICAL SITE AND LOADING RATE ON TENSILE BEHAVIOR OF FIBER BUNDLES ISOLATED FROM NERVE ROOTS

The present study has investigated the characteristics of the tensile behavior of fiber bundles isolated from the spinal nerve roots. By conducting a series of uniaxial stretching tests at three different velocities, 0.2, 2, and 20 mm/s, we found a significant difference (P < 0.05) in failure strain (similar to 0.15), linear portion of elastic modulus (similar to 20 MPa), and tensile strength (similar to 2 MPa) between low (0.2 mm/s) and high (20 mm/s) loading rates. However, it was revealed that mechanical properties of fiber bundles were resultantly on the order of the same magnitude, indicating that their mechanical responses were relatively insensitive to a strain rate irrespective of a 100-fold increase in the applied stretching velocities. It was also confirmed that the "spinal level effect" does exist in the nerve roots, i.e., a fiber bundle isolated from the thoracic spinal level is the strongest in mechanical strength compared to that of the cervical and lumbar spinal levels (P < 0.01), which suggests we should pay more close attention to an anatomical site where excised samples are obtained. The mechanical data obtained here will be useful to improve a mathematical human body model and to assess the potential injury in crash simulations relevant to whiplash associated disorder.