Influence of saline solution absorption and compressive rate on the material properties of brain tissue

Traumatic brain injuries (TBI) affect millions of people each year and can result in long-term difficulties in thinking or focusing. Due to the number of people affected by these injuries, significant research has been dedicated to determining the mechanical properties of the brain using postmortem tissue from animals harvested within 24 h. The postmortem brain tissue is often stored in a solution until a rheological experiment is ready to begin. However, the effect of storage duration on the mechanical behavior of brain tissue is not understood. In this paper, postmortem porcine brains were placed in normal saline solution (0.9% NaCl) and refrigerated between 30 min and 6.5 h to allow the brain to absorb the solution. Afterwards, samples from both soaked and freshly extracted brains were subjected to unconfined compression tests at compressive rates of 5, 50, and 500 mm/min. The fractional Zener viscoelastic model was applied to obtain the brain's mechanical properties. While the results did not show a significant relationship between absorption and the long-term stiffness (E_∞), both the relaxation time (τ₀) and fractional order (α) were statistically influenced by both the length of time in the solution and compressive rate. Further, the instantaneous stiffness (E₀) was statistically influenced by the length of time in solution, though not the compressive rate.