Publications

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We conducted computational macroscale simulations predicting blast-induced intracranial fluid cavitation possibly leading to brain injury. To further understanding of this problem, we developed microscale models investigating the effects of blast-induced cavitation bubble collapse within white matter axonal fiber bundles of the brain. We model fiber tracks of myelinated axons whose diameters are statistically representative of white matter. Nodes of Ranvier are modeled as unmyelinated sections of axon. Extracellular matrix envelops the axon fiber bundle, and gray matter is placed adjacent to the bundle. Cavitation bubbles are initially placed assuming an intracranial wave has already produced them. Pressure pulses, of varied strengths, are applied to the upper boundary of the gray matter and propagate through the model, inducing bubble collapse. Simulations, conducted using the shock wave physics code CTH, predict an increase in pressure and von Mises stress in axons downstream of the bubbles after collapse. This appears to be the result of hydrodynamic jetting produced during bubble collapse. Interestingly, results predict axon cores suffer significantly lower shear stresses from proximal bubble collapse than does their myelin sheathing. Simulations also predict damage to myelin sheathing, which, if true, degrades axonal electrical transmissibility and general health of the white matter structures in the brain.

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A microscale model of the brain was developed in order to understand the details of intracranial fluid cavitation and the damage mechanisms associated with cavitation bubble collapse due to blast-induced traumatic brain injury (TBI). Our macroscale model predicted cavitation in regions of high concentration of cerebrospinal fluid (CSF) and blood. The results from this macroscale simulation directed the development of the microscale model of the superior sagittal sinus (SSS) region. The microscale model includes layers of scalp, skull, dura, superior sagittal sinus, falx, arachnoid, subarachnoid spacing, pia, and gray matter. We conducted numerical simulations to understand the effects of a blast load applied to the scalp with the pressure wave propagating through the layers and eventually causing the cavitation bubbles to collapse. Collapse of these bubbles creates spikes in pressure and von Mises stress downstream from the bubble locations. We investigate the influence of cavitation bubble size, compressive wave amplitude, and internal bubble pressure. The results indicate that these factors may contribute to a greater downstream pressure and von Mises stress which could lead to significant tissue damage.

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