An in vitro traumatic injury model to examine the response of neurons to a hydrodynamically-induced deformation

A novel in vitro system was developed to examine the effects of traumatic mechanical loading on individual cells. The cell shearing injury device (CSID) is a parallel disk viscometer that applies fluid shear stress with variable onset rate. The CSID was used in conjunction with microscopy and biochemical techniques to obtain a quantitative expression of the deformation and functional response of neurons to injury. Analytical and numerical approximations of the shear stress at the bottom disk were compared to determine the contribution of secondary flows. A significant portion of the shear stress was directed in the r-direction during start-up, and therefore the full Navier-Stokes equation was necessary to accurately describe the transient shear stress. When shear stress was applied at a high rate (800 dyne cm-2 sec-1) to cultured neurons, a range of cell membrane strains (0.01 to 0.53) was obtained, suggesting inhomogeneity in cellular response. Functionally, cytosolic calcium and extracellular lactate dehydrogenase levels increased in response to high strain rate (> 1 sec-1) loading, compared with quasistatic (< 1 sec-1) loading. In addition, a subpopulation of the culture subjected to rapid deformation subsequently died. These strain rates are relevant to those shown to occur in traumatic injury, and, as such, the CSID is an appropriate model for studying the biomechanics and pathophysiology of neuronal injury.