Testing TBI with Shock Tube Technology
TBI, a form of brain injury caused by exposure to explosions and blast waves, has become a major subject of interest in recent years due to the increased use of improvised explosive devices (IEDs), mainly in the Afghanistan and been referred to as the “signature” wound of these wars.
Statistics on TBI diagnoses are astounding. The number of soldiers diagnosed with TBI is estimated at five times the number of amputees, and 70 percent of soldiers suffering from TBI were wearing a helmet, suggesting that current armor designs are lacking.
TBI is a lifelong, debilitating injury, causing symptoms including chronic migraines, nightmares, changes in personality, anxiety, and post-traumatic stress disorder. Many researchers, doctors, academic institutions, and government research facilities are currently working together in a multidisciplinary approach to solve this problem from multiple angles.
A team of Aerospace scientists has been using a shock tube, made from a surplus WWII submarine periscope tube, to research traumatic brain injuries (TBIs), such as those that soldiers might receive from a bomb blast.
“In an effort to diversify our shock tube research, we thought of different things that might be useful to hit with a shock wave. With our high speed imaging techniques for shock visualization, we thought we might be able to learn something about how a shock wave interacts with a human head, ” said Timothy Graves, a laboratory manager in the Propulsion Science Department.
The video above, which the researchers created using dynamic photoelasticity, shows the stresses in the material. Watch as the shock enters the skull through the eyes, and the brain pulls back.
“We got some very nice initial results, and we are currently working with several universities including MIT and the Center for Soldier Nanotechnologies to find funding and new research areas,” he said.
Shock tubes are normally used to study chemical reactions.
“Classically, shock tubes are a way to study high temperature and high pressure conditions such as those that exist in a rocket engine,” Graves said. “Primarily, our system has been used for understanding combustion chemistry under these conditions.”
Aerospace’s shock tube is six inches in diameter, 45 feet long, and consists of two sections — a high pressure region and a low pressure region. A barrier, or diaphragm, is placed between the two regions, and the first region is filled with high pressure gas.
The high pressure gas breaks the diaphragm, releasing a shock wave, which travels into the low-pressure region down the length of the shock tube. In a shock tunnel configuration, the shock wave then passes into a large tank that can be used to hold models or other diagnostics to study the shock wave.
“Our shock tube is actually unique in the world because of its ability to go to very high pressure (100 atmospheres),” Graves said. “Historically, this facility has been utilized in many different research areas including chemical laser development, atmospheric re-entry studies, alternative fuels research, and pure combustion chemistry. That research has led to numerous publications and scientific developments in each of those areas.”
For this particular TBI experiment, a model of the human skull is positioned near the exit of the shock tube in the dump tank, where it can receive the full force of the shock wave, head-on. The interaction of the shock wave with the skull structure can be visualized with a high speed camera, using techniques such as Schlieren imaging, which shows the density changes caused by the shock, and dynamic photoelasticity, which reveals where the stresses are in the model skull.
The experiment replicates the effect of shock on a person’s brain, which is the type of thing that might happen to someone positioned near an explosion. It is different from blunt force trauma, which is when something physically collides with the head. The shock passage is much faster, and its physical effects are much less understood.
“We are attempting to experimentally simulate, in a controlled way, the blast conditions believed to cause brain injuries in soldiers seeing combat,” said Andrea Hsu, a member of the technical staff in the Propulsion Science Department and lead Aerospace TBI researcher.
For these preliminary experiments, Hsu has been using an acrylic model skull found commercially through Amazon.com. Acrylic is somewhat similar to bone in its mechanical properties, and is also transparent, which helps visualize the experiment.
The models were solid, so the researchers carved out the shape of the brain and eyeholes, and filled the cavity with ballistic gelatin to represent the brain.
Using different experimental techniques, they were able to view the shock wave passing through the brain, and also to see the stresses in the bone-like skull material.
“It’s interesting to see it happen in real time because this could help doctors and biologists understand what is actually happening and what could be causing the brain damage,” Hsu said.
Using Schlieren imaging, the researchers were able to see how the shock wave interacts with the human head.
The team looked at different questions, such as which parts of the brain are most vulnerable, how the shock enters the brain, and where the shock is focused inside the brain.
So far the research has been preliminary. According to Hsu, there are many directions they could take in the future.
The team could choose to focus on the effects of the shock, which might be of interest to biologists and doctors — those who want to learn how to treat patients affected in this way.
If they take this route, they will probably need to obtain more realistic models of the brain, to more accurately understand what happens from a biological standpoint.
Alternatively, Aerospace could help armor developers learn how to better protect soldiers against shocks. The team’s initial results seem to indicate that the shock comes through the soft tissue, such as the eyes, so perhaps a face shield could be developed. Novel materials could also be utilized to absorb or deflect incoming shocks.
Using the versatility of the Aerospace shock tube, scientists could also set up experiments to simulate explosions at different distances and strengths, and from different directions (not just head on).
Regardless of the future research direction, the project illustrates an out-of-the-box idea to diversify and use company core competencies (such as shock wave interactions) to possibly contribute to new research areas.