The Influence of Strain Rate Dependency on the Structure–Property Relations of Porcine Brain

Abstract

This study examines the internal microstructure evolution of porcine brain during mechanical deformation. Strain rate dependency of porcine brain was investigated under quasi-static compression for strain rates of 0.00625, 0.025, and 0.10 s(-1). Confocal microscopy was employed at 15, 30, and 40% strain to quantify microstructural changes, and image analysis was implemented to calculate the area fraction of neurons and glial cells. The nonlinear stress-strain behavior exhibited a viscoelastic response from the strain rate sensitivity observed, and image analysis revealed that the mean area fraction of neurons and glial cells increased according to the applied strain level and strain rate. The area fraction for the undamaged state was 7.85 ± 0.07%, but at 40% strain the values were 11.55 ± 0.35%, 13.30 ± 0.28%, and 19.50 ± 0.14% for respective strain rates of 0.00625, 0.025, and 0.10 s(-1). The increased area fractions were a function of the applied strain rate and were attributed to the compaction of neural constituents and the stiffening tissue response. The microstructural variations in the tissue were linked to mechanical properties at progressive levels of compression in order to generate structure-property relationships useful for refining current FE material models.

Fitted hyperelastic parameters for Human brain tissue from reported tension, compression, and shear tests

“…However, in this initial effort, the force in tension showed strain softening, which was not consistent with the experimental response documented by Jin et al (2013), which shows stiffening for strains higher than around 0.2. These results suggest that the mechanical response of the brain cannot be adequately simulated with one term in the hyperelastic energy functions, similar to that found by a few others who used two or more terms for fitting experimental data (Begonia et al, 2010, Franceschini et al, 2006. However, even with two terms, the response of the Ogden model under tension was almost linear for white matter and corona radiata tissue.…”

Mechanical Characterization of Immature Porcine Brainstem in Tension at Dynamic Strain Rates

“…Similar to the material behavior of adult brain specimens found in some previous reports [ 13 , 32 – 36 ], the immature brainstem tissue showed a significant rate dependence in dynamic tensile tests in the present study. With an increase of the strain rate in the tensile tests, the immature porcine brainstem tissue became stiffer.…”

Age-dependence of intracranial viscoelastic properties in living rats

“…Second, for reasons related to the size of the head and brain we could not perform mechanical testing in all ages under identical conditions. The slightly different loading rates and absolute strain could influence the measured values (Begonia et al, 2010). However, our observation that the changes in elastic and viscous parameters occurred at different age intervals indicates that the data are not an artifact of slightly different test parameters.…”