Regional Differences in Mechanical Properties of the Porcine Central Nervous System

Computational modeling is a potentially powerful tool to provide information about the mechanisms of traumatic brain injury. In order to ensure that the estimates calculated by these computer models provide the most useful information, it is essential that these models contain accurate central nervous system (CNS) tissue properties. Previous material property measurements lack strict control over crucial experimental parameters that may influence material properties and tail to examine any regional variation in the measured response.

To address these issues, we measured the material response of two regions of the CNS, the brainstem and the cerebrum. Specifically, adult porcine tissue was subjected to high loading rate mechanical deformation using a custom designed oscillatory shear device. Complex shear moduli were calculated over a range of frequencies (20-200 Hz) at two engineering strain amplitudes (2.5%, and 5.0%). For 2.5% strain, the magnitude of the storage modulus was significantly greater (∼20%) for the brainstem than the cerebrum, while the loss modulus showed no regional dependence. As a result, the complex modulus, G*, showed no statistical difference between regions for 2.5% strain. For 5.0% strain, both components of the complex modulus of the brainstem were greater than those of the cerebrum (∼80%). At this strain, the regional difference in G* was statistically evident. The modulus calculations at the higher strain magnitude should be incorporated into current anatomically detailed finite element models These region-specific differences provide essential information for enhancing our understanding of traumatic brain injury mechanisms.