  Mechanical characterization of brain tissue at high loading velocities is
crucial for modeling Traumatic Brain Injury (TBI). During severe impact
conditions, brain tissue experiences compression, tension and shear. Limited
experimental data is available for brain tissue in extension at dynamic strain
rates. In this research, a High Rate Tension Device (HRTD) was developed to
obtain dynamic properties of brain tissue in extension at strain rates of <
90/s. In vitro tensile tests were performed to obtain properties of brain
tissue at strain rates of 30, 60 and 90/s up to 30% strain. The brain tissue
showed a stiffer response with increasing strain rates, showing that
hyperelastic models are not adequate. Specifically, the tensile engineering
stress at 30% strain was 3.1 +/- 0.49 kPa, 4.3 +/- 0.86 kPa, 6.5 +/- 0.76 kPa
(mean +/- SD) at strain rates of 30, 60 and 90/s, respectively. Force
relaxation tests in tension were also conducted at different strain magnitudes
(10-60% strain) with the average rise time of 24 ms, which were used to derive
time dependent parameters. One-term Ogden, Fung and Gent models were used to
obtain material parameters from the experimental data. Numerical simulations
were performed using a one-term Ogden model to analyze hyperelastic behavior of
brain tissue up to 30% strain. The material parameters obtained in this study
will help to develop biofidelic human brain finite element models, which can
subsequently be used to predict brain injuries under impact conditions and as a
reconstruction and simulation tool for forensic investigations.
