Mechanical Characterization of Brain Tissue in High-Rate Extension

Abstract

Mechanical properties of brain tissue characterized in high-rate loading regime are indispensable for the analysis of traumatic brain injury (TBI). However, data on such properties are very limited. In this study, we measured transient response of brain tissue subjected to high-rate extension. A series of uniaxial extension tests at strain rates ranging from 0.9 to 25 s-1 and stress relaxation tests following a step-like displacement to different strain levels (15-50%) were conducted in cylindrical specimens obtained from fresh porcine brains. A strong rate sensitivity was found in the brain tissue, i.e., initial elastic modulus was 4.2 ± 1.6, 7.7 ± 4.0, and 18.6 ± 3.6 kPa (mean ± SD) for a strain rate of 0.9, 4.3, and 25 s-1, respectively. In addition, the relaxation function was successfully approximated to be strain-time separable, i.e., material response can be expressed as a product of time-dependent and strain-dependent components as:K(t) = G(t)σe(e), where G(t) is a reduced relaxation function, G(t) = 0.416e-t/0.0096+0.327e-t/0.0138+0.256e-t/1.508, and σe(e) is the peak stress following a step input of e. Results of the present study will improve biofidelity of computational models of a human head and provide useful information for the analysis of TBI under injurious environments with strain rates greater than 10 s-1.