Mechanically Induced Diffuse Axonal Injury: Brain Injury Due to Periodic and Indicial Traumatic Events

Diffuse axonal injury (DAI) is the predominant mechanism of traumatic brain injury (TBI) after sudden periodic and impulsive events. It is common in all TBI, regardless of severity, and is characterized by a shear action induced on axons by surrounding tissue. DAI leads to progressive changes that may ultimately lead to the loss of connections between nerve cells. The slow progression of events in DAI (that continues long after injury) further complicates the effects of transportation-related injuries, but also creates a window of opportunity for therapeutic intervention. A common denominator between these two contradicting factors is the need for a small animal model that will not only allow multiple repetitions of deceleration induced injuries cost effectively, but also enable the drug efficacy trials combat DAI. Use of small animals is customary in most fields of biomechanics, but in the case of mechanically induced injury, reduction in brain mass implies scaling of kinetic parameters for similarity in inertia forces and strain levels to be maintained. Parameters that have to be “scaled-up or down” for a successful comparison are then ones affecting the order of magnitude of the rotational motion causing brain tissue to sustain shear strains, namely, acceleration and impulse duration. This scaling was implemented in the design of testing platforms used to test more than 250 rodents. DAI was observed on several animals tested. A test platform was designed and built for periodic and indicial (sudden, single-stroke) events. Constraining adaptors were fabricated to constrain and isolate motion around various axis of motion. Furthermore, motion of the head was isolated from motion of the rest of the body.