Region‐ and loading‐specific finite viscoelasticity of human brain tissue

Abstract

AbstractComputational simulations are a powerful tool to understand the mechanical behavior of our brain in health and disease, with the ultimate goal to prevent pathological conditions. Accurate numerical predictions, however, require the development of appropriate constitutive models and, equally important, the careful calibration of the corresponding constitutive parameters. This has been exceptionally challenging due to the ultrasoft and heterogeneous nature of brain tissue, resulting in a distinctly nonlinear, rate‐dependent, compression‐tension asymmetric, and region‐dependent behavior. Previous constitutive models have been deduced from a single loading mode, but fail to predict the behavior under various loading conditions. Here, we developed a large strain, nonlinear, viscoelastic constitutive model for brain tissue on the basis of cyclic and relaxation experiments under multiple loading modes, simple shear, compression, and tension. We carefully calibrated individual parameter sets for four different regions of the human brain, the cortex, the basal ganglia, the corona radiata, and the corpus callosum. The model captures effects such as nonlinearity and compression‐tension asymmetry, but also time‐dependent effects with substantial pre‐conditionning during the first loading cycle, only minor conditioning effects during subsequent cycles, and successive softening when the applied strain is stepwise increased. With close consideration of the underlying microstructure, we evaluate the physical meaning of viscoelastic material parameters with rate‐dependent regional trends. Our results help to improve the accuracy of human brain simulations during development and disease or to predict outcomes of neurosurgical procedures.