Shear Stress Response and Bond-Breaking Under Moderate Frequency Sinusoidal Translational Shear Deformation of Heterogeneous Rat Cerebrum

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Blast waves, which include sinusoidal shear waves, may cause mild traumatic brain injury (mTBI) in brain tissue. The experiments model repeated insults separated by a period of rest via application of translational sinusoidal shear waves to hydrated, heterogeneous rat cerebrum at six deformation frequencies between 25 Hz and 125 Hz and displacement amplitudes of 10% or 25%. Each deformation frequency produces transient and apparent steady shear stress states that frequency analysis describes by harmonic wavelet and Fourier frequency components. Sinusoidal shear deformation waves induce bond and synapse breaking at as little as 10% displacement amplitude. Even in vitro, some bonds reform during rest. An increase in deformation frequency increases drag force between the ECF and solid matter, probably due to increased fluid acceleration and inertia. Imaging and histology do not clearly detect mild damage due to bond breaking that underlies mTBI, which the analysis of the shear stress response captures.