Changes in mechanical properties within brain tissues after losses in cell viability have not been well investigated. Lack of oxygen and nutrient transport can induce hypoxic neuronal injury and increase cell membrane permeability, and cell membranes and matrix components can lose their structural and mechanical integrity. These physical changes may have an effect on mechanical properties of brain tissue [1]. In this study, the viscoelastic behavior of two anatomical regions (cerebral cortex and hippocampus) in acute rat brain tissue slices were measured as a function of cell viability using indentation combined with optical coherence tomography (OCT). Neuronal viability in brain tissue slices was determined by measuring Fluoro-Jade C (FJC) staining to assay neuronal death or degeneration as a function of incubation time. OCT-measured deformation depths were compared with finite element (FE) simulations to estimate the relaxation of shear modulus. Measured equilibrium shear modulus (μ∞) after 8 hrs incubation was lower than μ∞ measured after 2 hrs incubation in the cerebral cortex (μ∞, 2hrs = 225 Pa, μ∞, 8hrs = 62 Pa) and hippocampus regions (μ∞, 2hrs = 170 Pa, μ∞, 8hrs = 33 Pa). Instantaneous shear modulus (μ0) after 8 hrs incubation was also an order of magnitude lower than μ0 after 2 hrs incubation in cortex (μ0, 2hrs = 1600 Pa, μ0, 8hrs = 100 Pa) and hippocampus regions (μ0, 2hrs = 370 Pa, μ0, 8hrs = 70 Pa). The results of this study provide a timeline for measuring mechanical properties of brain tissues ex vivo and provide better understanding of changes in brain modulus after injury or cell death.
Optically based-indentation technique for acute rat brain tissue slices and thin biomaterials
