Region specific viscoelastic properties of the adult rat brain under indentation following traumatic brain injury

Traumatic Brain Injury (TBI) is a serious health epidemic that places high societal and economic burdens on victims and their caregivers. Further, the associated neuropathological consequences that result from TBI are often complex and cause secondary injuries that are focal, diffuse and time dependent. Current computational models can predict loading and deformation associated with TBI; however, accurate knowledge of region specific material properties from both healthy and mechanically damaged brain is needed. In this study, the mechanical properties of both uninjured and traumatically injured brain tissue are presented. Adult male Sprague-Dawley rats were injured through a controlled cortical impact protocol. Ramp and hold indentation tests were performed at five locations on the surface of tissue samples excised from whole brain specimens. Force displacement data were analyzed using quasi-linear viscoelastic theory. An analysis revealed the tissue to be viscoelastic and spatially nonlinear with mechanical properties that depend on both region and level of injury. After normalizing the data, the nonlinear components of the instantaneous elastic force and shear modulus were found to be significantly lower, 26%, in the region containing the contusion cavity on severely injured samples compared to uninjured tissue at the same region in controls.