A novel procedure for micromechanical characterization of white matter constituents at various strain rates

Abstract

Optimal hyperplastic coeficients 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 coeficients, 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 coeficients may be applied to future multi-scale FE studies of the human brain.