Experimental Study on Non-Exit Ballistic Induced Traumatic Brain Injury

Ballistic-induced traumatic brain injury remains the most severe type of injury with the highest rate of fatality. Yet, its injury biomechanics remains the least understood. Ballistic injury biomechanics studies have been mostly focused on the trunk and extremities using large gelatin blocks with unconstrained boundaries [1, 2]. Results from these investigations are not directly applicable to brain injuries studies because the human head is smaller and the soft brain is enclosed in a relatively rigid cranium. Thali et al. developed a “skin-skull-brain” model to reproduce gunshot wounds to the head for forensic purposes [3]. These studies focused on wound morphology to the skull rather than brain injury. Watkins et al. used human dry skulls filled with gelatin and investigated temporary cavities and pressure change [4]. However, the frame rate of the cine X-ray was too slow to describe the cavity dynamics, and pressures were only quantified at the center of skull. In addition, the ordnance gelatin used in these studies is not the most suitable simulant to model brain material because of differences in dynamic moduli [5]. Sylgard gel (Dow Corning Co., Midland, MI) demonstrates similar behavior as the brain and has been used as a brain surrogate to determine brain deformations under blunt impact loading [6, 7]. Zhang et al. used the simulant for ballistic brain injury and investigated the correlation between temporary cavity pulsation and pressure change [8, 9]. However, the skulls used in these models were not as rigid as the human cranium. The presence of a stronger cranial bone may significantly decrease the projectile velocity and change the kinematics of cavity and pressure distribution in the cranium. In addition, projectiles perforated through the models in these studies. Patients with through-and-through perforating gunshot wounds to the head have a greater fatality rate than patients with non-exit penetrating wounds [10]. Therefore, it is more clinically relevant to investigate non-exit ballistic traumatic brain injuries. Consequently, the current study is designed to investigate the brain injury biomechanics from non-exit penetrating projectile using an appropriately sized and shaped physical head model.