Optimal hyperplastic coe cients of the micromechanical constituents of the human brain stem were investigated. An evolutionary optimization algorithm was combined with a Finite Element (FE) model of a Representative Volume Element (RVE) to nd the optimal material properties of axon and Extra Cellular Matrix (ECM). The tension and compression test results of a previously published experiment were used for optimizing the material coe cients, and the shear experiment was used for the validation of the resulting constitutive model. The optimization algorithm was used to search for optimal shear moduli and ber sti ness of axon and ECM by tting the average stress in the axonal direction with the results of the experiment. The resulting constitutive model was validated against the shear stress results of the same experiment, showing strong agreement. The instantaneous shear moduli and ber sti ness of both axon and ECM increased at higher strain rates, while the axon-to-ECM shear modulus ratio decreased from the value of 10 at a strain rate of 0.5/s to the value of 5 at a strain rate of 30/s. The proposed characterization procedure and the resulting coe cients may be applied to future multi-scale FE studies of the human brain.
Traumatic brain injury (TBI) has long been known as one of the most anonymous reasons for death around the world. A presentation of a model of what happens in the process has been under study for many years; and yet it remains a question due to physiological, geometrical and computational complications. Although the facilities for soft tissue modeling have improved and the precise CT-imaging of human head has revealed novel details of brain, skull and the interface (the meninges), a comprehensive FEM model of TBI is still being studied. This study aims to present an optimized model of human head including the brain, skull, and the meninges after a comprehensive study of the previous models. The model is then used to investigate the effects of various sudden velocity-acceleration impulses on the strain field of the brain by using FE method. Next, the results are summed up and compared with an existing criterion on damage threshold in the brain during trauma. To reach this aim, a full geometrical model of a 30-year-old patient’s head has been generated from CT-scan and MR data. The model has been exposed to 20 angular velocity-acceleration pulses. Subsequently, the changes in the strain field have been compared with the results obtained in the previous studies yielding acceptable accordance with a major previous criterion. The results also show that certain criteria can be generated on the threshold of damage in the brain.
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