Since the first Improvised Explosive Device (IED) targeting U.S. troops exploded in Afghanistan in 2003, American service members have suffered no fewer than 330,000 brain injuries in combat, according to military statistics.
Explosions are obviously the most common cause of brain injuries for troops. But scientists don’t understand exactly how a blast damages the brain. And this limits their ability to prevent, diagnose, and treat the injury.
Desperate for a breakthrough, one Navy researcher looked to some seemingly unlikely inspirations: propellers, submarines, and shrimp—and a phenomenon known as “cavitation,” which occurs when a shock wave compresses gas into tiny bubbles that then burst.
Dr. Timothy Bentley, a program manager at the Office of Naval Research in Arlington, Virginia, told The Daily Beast he believes explosions could cause bubbles to form inside troops’ brains. The formation and subsequent popping of the bubbles could damage brain cells and, over time, contribute to a host of conditions. Post-traumatic stress. Loss of hearing and eyesight. Even Alzheimer’s.
“It’s such a powerful force,” Bentley said of cavitation.
The Navy is painfully familiar with cavitation because it’s one of the major causes of the gradual breakdown of ships’ propellers. As it spins, a propeller causes cavitation in the surrounding water that can, in turn, eat away at the propeller’s metal. The sound of the tiny bubbles bursting can also give away the location of, say, a submarine attempting to sneak up on enemy vessels.
But Bentley, a marine biologist, said he’s also familiar with cavitation for another reason. It’s the mechanism by which a crustacean called a snapping shrimp—a “beautiful” animal, according to Bentley—attacks the snails and clams that it eats. The shrimp clicks its claws, compressing the gas in the surrounding water into bubbles. When the bubbles pop, the force of the collapse is strong enough to shatter a nearby clamshell and can even generate a quick flash of light.
It was several years ago when Bentley first imagined the same tiny but proportionally powerful explosive force tearing through the soft tissue of a human brain. Cavitation seems to explain the gradual, systemic breakdown that afflicts many troops who’ve been exposed to bomb blasts: depression and post-traumatic stress followed by cognitive and sensory deterioration and, in some cases, early-onset Alzheimer’s.
Bentley went looking for a scientist to explore his cavitation theory and found Dr. Michael Cho, chairman of the Department of Bioengineering at the University of Texas at Arlington. Cho was already pursuing the line of inquiry Bentley had in mind. Bentley helped direct Navy funding to Cho’s research.
It’s difficult work. For one, there’s no imaging technology that can reliably detect cavitation in a living brain. Scientists have tested out the cavitation theory mathematically and on fake “phantom” brains made out of jello—and those tests indicate Bentley and Cho are on to something, Cho told The Daily Beast.
Many neurologists conduct their experiments on live or dead animals. But Cho said his team doesn’t do animal tests. Instead, it relies on “biomimetic” material—manmade fake brain tissue that’s thin enough to fit on a microscope. Cho and his people expose the biomimetics to controlled explosions in a sort of blast chamber. “Thunder and lightning” is how Cho described the tests.
If Cho can prove the cavitation theory, there are practical steps the military can take to protect troops, Bentley said. “These blast forces are now striking the head and penetrating into the head and that can occur even with the helmets we have,” he explained. “It may be helpful to have face shields that deflect forces around the head. We might be better able to understand how to make helmets.”
Bentley said that proving cavitation’s role in brain injuries could also lead to different military tactics as well as to treatments for traumas that have already occurred.
Of course, Cho’s research could prove that cavitation doesn’t play a big role in brain injuries. But with hundreds of thousands of troops already suffering from brain trauma and more service members joining those ranks every day, the military is understandably desperate to pursue all leads.
“It’s worth taking a chance,” Bentley said.