Development of a Finite Element Model for Blast Brain Injury and the Effects of CSF Cavitation

Abstract

Blast-related traumatic brain injury is the most prevalent injury for combat personnel seen in the current conflicts in Iraq and Afghanistan, yet as a research community,we still do not fully understand the detailed etiology and pathology of this injury. Finite element (FE) modeling is well suited for studying the mechanical response of the head and brain to blast loading. This paper details the development of a FE head and brain model for blast simulation by examining both the dilatational and deviatoric response of the brain as potential injury mechanisms. The levels of blast exposure simulated ranged from 50 to 1000 kPa peak incident overpressure and 1–8 ms in positive-phase duration, and were comparable to real-world blast events. The frontal portion of the brain had the highest pressures corresponding to the location of initial impact, and peak pressure attenuated by 40–60% as the wave propagated from the frontal to the occipital lobe. Predicted brain pressures were primarily dependent on the peak overpressure of the impinging blast wave, and the highest predicted brain pressures were 30%less than the reflected pressure at the surface of blast impact. Predicted shear strain was highest at the interface between the brain and the CSF. Strain magnitude was largely dependent on the impulse of the blast, and primarily caused by the radial coupling between the brain and deforming skull.The largest predicted strains were generally less than 10%,and occurred after the shock wave passed through the head.For blasts with high impulses, CSF cavitation had a large role in increasing strain levels in the cerebral cortex and periventricular tissues by decoupling the brain from the skull. Relating the results of this study with recent experimental blast testing suggest that a rate-dependent strain-based tissue injury mechanism is the source primary blast TBI.

The Mechanics of Traumatic Brain Injury: A Review of What We Know and What We Need to Know for Reducing Its Societal Burden

“…Currently, publicly available models show an increasing sophistication in their anatomical detail and their correlation with available validation data. In the past five years, these same models were extended to study blast exposure [105,109,124,128,131,[134][135][136][138][139][140]143,144,157,[161][162][163][164]. In many cases, though, the absence of validation data remains a key concern and must be addressed with each model before the models can be meaningfully used to correlate blast exposure with specific injury risk.…”

“…Species include rodents [109,128,135,138,140,143,144,[161][162][163][164][165][166][167], pigs [168][169][170][171][172][173], and sheep [174][175][176]. These experimental models offered a measure that human physical models and human surrogate tests often could not provide-an estimate of the injuries that occurred throughout the brain as a result of the mechanical loading.…”

“…These models also provide to opportunity to design new features into experimental models of TBI-e.g., the shape of an impounder tip or the speed of impact in the well described cortical impact model of TBI can significant change the cortical lesion volume in this TBI model [177]. These models offer a direct translational path for studying blast exposure, and early results indicate that these models are transferrable when attention to details such as mesh size and material properties are made [22,164]. However, a systematic correlation of model results with the histopathology of injury is warranted to assess the efficacy of these models.…”

On the prospective contributions of the shock physics community to outstanding issues concerning blast-induced traumatic brain injury

“…Despite the focus on this simpler free-field loading scenario, few researchers justify their choice of free-field exposure conditions using estimated real operational scenarios, which is necessary to maintain relevance. One example of an appropriate justification is the use of a report on 18 incident cases from operation Iraqi Freedom [6] to guide the choice of loading conditions [7]. Panzer et al [7] used the ground detonation of standard 105 and 155 mm artillery rounds as classic IED scenarios and used the CONWEP software [8] to predict peak incident overpressure and positive phase duration for standoff distances varying between 1 and 5 m, leading to peak overpressures ranging from 50 to 1000 kPa and durations between 2 and 6 ms. Wood et al [9] further stated that a majority of IED threats are made from artillery rounds equivalent to 7.5 kg of TNT explosives or less.…”

Computational and In Vitro Studies of Blast-Induced Blood-Brain Barrier Disruption

“…This suggests that the injury mechanisms might occur at very small length scales, even at the scale of a single cell. Several hypothesis have been proposed: the disruption of BBB integrity [88,43,76]; cerebral vasospasm mechanotransduced by the blast wave [3]; impairment of axonal functionality [57,58]; shock wave excitation of phonons that decay into lower frequency oscillations [49] and the formation of cavitating bubbles [71,67,66,80,109,74,37], among others.…”