BLOG: Brain injury helps engineers design better protective gear
by Matthew B. Panzer, PhD
At the University of Virginia Center for Applied Biomechanics, we are focused on studying how injuries occur during impact events so we can develop technologies needed to mitigate injury in sports, automotive crashes and the military.
We operate under the Ben Franklin axiom that, “an ounce of prevention is worth a pound of cure,” and we apply this premise regarding the brain: Preventing a traumatic brain injury (TBI) is better than treating one. But effective prevention demands that we understand what happens to the brain during an impact that causes TBI — and that isn’t so simple to figure out.
No visible damage with mild TBIs
After a moderate to severe TBI, internal bleeding may be visible on a CT scan. However, with most mild TBIs (like concussions), there is no visible structural damage. That doesn’t mean structural change isn’t happening — it’s just occurring at a microscopic level that we can’t detect with standard diagnostic imaging. Instead, we have to rely on a combination of animal studies, human donor studies and computer modeling to evaluate how rapid head motions might affect neural tissue, the meninges (or membranes that protect the brain) and the skull, and the deformations of these tissues in turn might affect the neurological response to injury.
One of the things we have learned is that rapid rotation of the head induces considerably more brain strain than linear motions. Rapid head rotation induces deformations in the brain that can cause microscopic stretching and shearing of neurons, which can then trigger a whole cascade of neurological and biochemical processes. These processes evolve over time, from the initial seconds after impact to months or even years later.
What happens to the brain when hit
You might imagine that when someone gets hit in the head, the brain crashes into the skull and then ricochets back to the other side, bouncing around in the skull causing damage. But that is a myth — there is simply not enough room in the skull for the brain to do this. Rather, the outer portions of the brain move quickly with the skull within a few milliseconds of the impact, while the inner portions are relatively stationary. This subtle motion differential is what induces neuron strains. The inner parts of the brain will “catch up” with the motion of the outer parts, sometimes even overshooting the outer motion. This back-and-forth motion of brain tissues makes the brain appear to jiggle.
You can think of the jiggling motion of the brain like the response you would see if you shake a bowl of gelatin, only gelatin vibrates quite a bit more than brain tissue, which will dampen out quickly. So perhaps the brain as a flan is a better analogy.
It’s also important to realize that internally the brain is still moving after the motions of the head have stopped (like if you shake a flan and then suddenly stop, the flan will continue to jiggle). That may be important in evaluating real-world head impacts such as a football tackle, where a player may be hit in the head in rapid succession by another player’s helmet, then a shoulder and then the ground. Does an impact to the head when the brain is still moving from the previous impact exacerbate the severity of the subsequent hit? There is still much to learn.
Every patient is unique
We do know that every concussion and every concussion patient is unique. As biomechanical brain injury research advances, we hope to gain a better understanding of how injuries affect specific regions of the brain to better model the relationships between injury types and symptomology. From a mechanical engineering and prevention standpoint, it would be valuable to identify how much the biomechanics of the brain — rather than genetics or prior health history, for example — influences how long it takes to recover or why one person has sleep issues and memory problems after a concussion while another person has vision or balance issues.
All this information can help us design better helmets, better airbags and more effective military gear. That way, even when there is a head impact, mitigation technologies can do a better job of preventing impact-related neurological and biochemical damage.
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Matthew B. Panzer, PhD, is associate professor of mechanical and aerospace engineering, associate professor of biomedical engineering and deputy director of the Center for Applied Biomechanics at the University of Virginia in Charlottesville. He also serves as a member of the UVA Brain Injury and Sports Concussion Center. Panzer's research covers computational and experimental methods to study high-rate nonlinear mechanics in the fields of tissue mechanics, impact biomechanics, vehicle crashworthiness, military blast and ballistics, and sports injury. He has served as the principal investigator for more than 30 programs funded by various federal and industrial sponsors.
Disclosure: Panzer reports no relevant financial disclosures.
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