INVESTIGATION ON BIOMECHANICS OF BLAST INDUCED TRAUMATIC BRAIN INJURY USING COMPUTATIONAL MODELS

Abstract

Blast induced traumatic brain injury (bTBI) is a substantial health concern in the era of asymmetric warfare. The requisite to understand the interaction of blast wave with the head-brain parenchyma is crucial for devising blast mitigation strategies, clinical interventions, therapeutics, and recreating injury in a laboratory. The goal of this work is three-fold: (a) to understand the evolution of the blast waves and examine how to recreate blast waves in the laboratory using shock tubes, (b) to comprehend blast wave interaction with the human head, and (c) to delineate the pathways through which blast wave reaches the brain causing injuries. Toward this end, we investigate the evolution of blast waves inside and outside of the compression-driven shock tubes using validated, finite element-based shock tube models. We assess the ability of easy-to-use pure Lagrangian and more sophisticated Coupling methods to simulate blast wave-head interaction from the accuracy and efficiency viewpoint. Further, we elucidate the biomechanical cascade of the brain under a primary blast using simplistic one-dimensional, detailed three-dimensional, and anatomically accurate, biofidelic full-body human models. These head models are extensively validated against available experiments. Our findings suggest that replicating free-field blast conditions using a shock tube involves tradeoffs that need to be weighed carefully and their effect on injury outcomes should be evaluated thoroughly during laboratory bTBI investigations. Our results reinforce that the Lagrangian method is a cost-effective, reasonably accurate method most suitable for quick and longer duration simulations; whereas, the Coupling method, though costlier, uniquely captures the geometry-driven-flow dynamics around the head. Further, through one-dimensional head models, we demonstrate that the wave propagation through head parenchyma plays an important role in blast wave transmission. The thickness, material properties of head layers, and rise time of an input pulse govern the temporal evolution of pressure in the brain. We found using anatomically accurate, full-body human models that the blast wave transmission, linear and rotational motion of the head are dominant pathways for the biomechanical loading of the brain. These loading paradigms generate distinct biomechanical fields within the brain. Blast transmission and linear motion of the head govern the volumetric response, whereas the rotational motion of the head governs the deviatoric response. We also observe that blast induced head rotation alone produces a diffuse injury pattern in white matter fiber tracts. In conclusion, these findings will assist the bTBI research community to judiciously conduct shock tube experiments, select the optimal blast wave-head interaction simulation methodology, and understand the mechanics of blast induced brain injury. These novel insights enhance the fundamental mechanistic understanding of blast TBI. Our work will augment laboratory, clinical investigations of bTBI, and help devise better blast mitigation strategies.