Investigating the Head Impact Force-Induced Evolution of Hyperphosphorylated Tau Proteins in Brain Tissue Through Mechanical Mesoscale Finite Element Simulation

For human heads that experienced repetitive subconcussive impacts, abnormal accumulation of hyperphosphorylated tau (p-tau) proteins was found in the postmortem brain tissue. To numerically understand the cause–effect relationship between the external force and the microscopic volume change of the p-tau protein, we created a mesoscale finite element model of the multilayer brain tissue containing microscopic voids representing the p-tau proteins. The model was applied under the loading boundary conditions obtained from a larger length scale simulation. A formerly developed internal state variable elastoplasticity model was implemented to describe the constitutive behaviors of gray and white matters, while the cerebrospinal fluid was assumed to be purely elastic. The effects of the initial sizes and distances of p-tau proteins located at four different brain regions (frontal, parietal, temporal and occipital lobes) on their volumetric evolutions were studied. It is concluded that both the initial sizes and distances of the proteins have more or less (depending on the specific brain region) influential effects on the growth or contraction rate of the p-tau protein. The p-tau proteins located within the brain tissue at the frontal and occipital lobes are more heavily affected by the frontal impact load compared with those at the parietal and temporal lobes. In summary, the modeling approach presented in this paper provides a strategy for mechanically studying the evolution of p-tau proteins in the brain tissue and gives insight into understanding the correlation between macroscopic force and microstructure change of the brain tissue.