Experimental model development using an animal brain phantom to study neural damage from traumatic brain injury

Abstract

This study aims to conduct shock tube experiments to determine neural damage from realistic non-impact blast loading using an in vitro animal test model (ellipsoid filled with simulated tissue). Traumatic Brain Injury (TBI) is caused by a sudden impact on the head that leads to the disruption of the brain's normal function. Specific to war-related traumatic brain injuries include those which are blast-induced. Microbubbles measured in microns can form in the Cerebral Spinal Fluid (CSF) inside the skull during the blast. The "formation and dramatic collapse" of these microbubbles, a process known as cavitation, could be responsible for neural tissue damage. As a pressure wave comes into contact with a head, a shock wave is transmitted through the skull, cerebrospinal fluid, and brain tissue and causes a negative difference in pressure observed at the opposite side of impact. An event that causes a quick difference in pressure within the CSF, and comes with a directional force, may result in gas bubbles forming opposite the site of impact along with the brain-skull interface and accusing damage to the surrounding tissues. Using a rabbit brain phantom model, this research measured the impact of different ranges of shock on brain tissue. Our simplified surrogate model of the head consisted of a transparent and shatterproof spherical dummy, and a simplified phantom model of the head consists of a transparent ellipsoid with dimensions of a rabbit skull. This study made a custom design 3D printed multi-directional shock device for the blast on the brain. The first test group conducted on a simplified surrogate filled with degassed water to simulate CSF and tissue altogether. A second test group included the rabbit phantom model that was filled with degassed water. In the third blast tests, the phantom contained Sylgard gel, surrounded by a layer of degassed water, to represent brain tissue and the CSF, respectively. Blast pressure in the shock-wave tests conducted at 10-20 pounds per square inch (psi; 69-138 kPa). Pressure in the modeled CSF was determined by a pressure sensors placed at 5, 10, 15 and 20 cm distances from the shock tube film. In all tests, the pressure difference at the countercoup before and after the blast was measured using an impact sensor. This study successfully found microbubbles from the first group of test. In addition, we found decreasing pressure, impact and strain on the model in relation to distance from the blast source. The results of this study will be used in our finite element model to predict the occurrence of acute subdural hematoma due to the blast inside along the interface between various brain tissue in future study.