A tissue level tolerance criterion for living brain developed with an in vitro model of traumatic mechanical loading

Traumatic brain injury (TBI) is caused by brain deformations resulting in the pathophysiological activation of cellular cascades which produce delayed cell damage and death. Understanding the consequences of mechanical injuries on living brain tissue continues to be a significant challenge. We have developed a reproducible tissue culture model of TBI which employs organotypic brain slice cultures to study the relationship between mechanical stimuli and the resultant biological response of living brain tissue. The device allows for the independent control of tissue strain (up to 100%) and strain rate (up to 150 s-1) so that tolerance criteria at the tissue level can be developed for the interpretation of computational simulations. The application of texture correlation image analysis algorithms to high speed video of the dynamic deformation allows for the direct calculation of substrate strain and strain rate which was found to be equi-biaxial and independent of radial position. Precisely controlled, mechanical injuries were applied to organotypic hippocampal slice cultures, and resultant cell death was quantified. Cell death was found to be dependent on both strain magnitude and rate and required several days to develop. An immunohistological examination of injured cultures with antibodies to amyloid precursor protein revealed the presence of traumatic axonal injury, suggesting that the model closely replicates in vivo TBI but with advantages gained in vitro. We anticipate that a combined in vitro approach with optical strain mapping will provide a more detailed understanding of the dependence of brain cell injury and death on strain and strain rate.