High frequency modelling of porcine brain tissue

摘要

The objective of this study is to contribute to the improvement of FE head models used to predict the mechanical response of brain during head impact. The topic of that research is the mechanical characterization of high frequency behaviour of porcine brain tissue from own experimental results obtained in small deformation, oscillatory shear experiments. These results are the first experimental data corresponding to a large frequency range associated with non-penetrating ballistic and accidental impacts or inertial loadings. Cylindrical samples of white matter of adult pigs (diameter: 10 mm, thickness: 150 - 250 μm) are harvested, conserved in physiological solution at 6℃ and tested within the day post-mortem. The complex shear modulus of the samples are measured in a custom-designed oscillatory shear testing device at shear strain amplitudes of 0.002% from 0.251 to 10 000 Hz, at 37℃ and 100% humidity. In this range, the elastic (G′) and viscous (G″) component of the complex shear modulus increased with the frequency from 0.455 kPa to 133.9 kPa and 0.133 kPa to 63.7 kPa respectively. Results show two successive intersections between the two moduli which indicate that the viscous behaviour is predominant between 250 and 3700 Hz. Moreover, a constitutive description capable of capturing the material behaviour observed in the material experiments is developed. The model chosen is a linear multi-mode Maxwell model which allows to fit both storage and loss modulus at low and high frequency. It is important to note that up to now only the elastic part is taken into account in viscoelastic modelling of brain tissue in FE head models which has the effect of overestimating the elastic moduli and underestimating the viscosities of rheological model. Our work is expected to enhance the biofidelity of computational models and provide a better understanding for the mechanisms of traumatic brain injury.