Characterizing brain mechanics during a two-phase response to dynamic overpressure loading

Over the last decade, blast-induced Traumatic Brain Injury (bTBI) research on both animal and computational models has largely focused on investigating injury mechanisms due to overpressure. However, more recent efforts have demonstrated that primary blast loading results in a two-phased response: a short (~1 ms) kinetic event followed by a much longer duration (~300 ms) kinematic response. The characterization of this two-phase response suggests that multiple injury mechanisms in the brain, including early phase stress and later phase strain, should be considered when studying bTBI. Experimental characterization of these responses provides data needed for validating computational models and elucidates each response’s potential mechanistic contribution to injury outcomes. The objective of this effort was to characterize both the intracranial pressure response and relative brain displacement due to dynamic overpressure loading conditions that may correlate to bTBIs. A series of shock tube tests were performed on the head-neck complex of a post mortem human surrogate (PMHS) to simulate exposure to blast loading. The overpressure dose applied to the specimen was measured using a sensor affixed to the anterior skull while the pressure transmitted through the skull was collected at four locations within the cranial cavity. Four columns of radiopaque displacement markers were implanted into the brain and tracked using a customdeveloped high-speed cineradiography system to provide local brain tissue displacement. The resulting intracranial pressure and brain displacement data collected confirmed the presence of a two-phase response. The pressures were found to initiate and subside within 10 ms of the incident pressure imparted to the PMHS. Peak pressure transmission into the skull was less than 20% of the incident pressure applied to the specimen. This loading resulted in global head motion and subsequent brain motion. The brain motion occurred over a 300 ms duration and excursions ranged from 1.9 13.4 mm. These data are being used to describe the mechanics of brain response during overpressure loading and to validate the predicted response from a detailed head-neck finite element model. Further experimental studies will be performed to capture the effect of head-neck orientation and secondary blunt impact.