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Christian Franck discusses traumatic brain injuries in an interview
June 7, 2024

Ask an expert: Franck breaks down blast and bump injuries to the brain

Written By: Alex Holloway


Christian Franck is the Bjorn Borgen Professor of mechanical engineering. He studies traumatic brain injuries and leads the multi-institutional, interdisciplinary PANTHER research initiative. PANTHER’s work focuses on understanding, detecting and preventing traumatic brain injuries, and researchers work closely with the U.S. Department of Defense, among other partners.

In Franck’s research, he applies mechanical engineering principles to understand how impact forces interact with brain tissue to cause traumatic brain injuries. As military service members’ exposure to blasts has gained increasing media attention, Franck has shared his expertise on the topic, including for a New York Times investigation into the long-term effects that repeated blast exposures can have on soldiers.

In this interview, Franck discusses how blasts damage brain tissue, describes efforts to monitor and protect military service members, and explains the delay that can happen between a traumatic brain injury and when symptoms occur.

Q: From attacks on U.S. military bases in the Middle East to media reports highlighting concern about blast exposure in military training, blast injuries have had a lot of focus recently. What about blasts makes them so potentially harmful?

A: There are two facets to that. The first is that there is of course a significant amount of energy released by a blast that then enters the brain tissue. And unfortunately, in many cases, when that happens, it causes injury or trauma.

The second aspect is that it’s an invisible injury. So if you look at things like firing artillery, I think for years the thinking in the military and even among us scientists was that this ought to be safe. But recent scientific evidence, as we continue to study this, and even anecdotal evidence and self-reporting, has shown that it may not be—and now in many cases, people are starting to feel that it’s not safe, period.

And people need to understand it’s not just the really large-caliber weapons like artillery. It’s also powerful rifles—as long as your head is close to where these powerful blast waves are being created.

Q: Is there an appreciable difference in the type of damage a blast causes compared to the damage athletes might experience?

A: Our current understanding is that the injury type, or pathology, you see in these repeated blast exposures is quite different from what athletes experience. The delineating factor between the two is just how fast this damage is being introduced to the brain tissue.

In a blast, you have an explosion, and the resulting shockwave typically moves at or faster than the local speed of sound. That is so, so quick. We’re talking on the order of microseconds—100 to 1,000 times faster than in a head-to-head collision on a football field or an accident such as falling out of a chair.

Those pressure waves come in and pass through the brain. Because our brains are almost spherical, these waves will reflect and bounce back and forth inside our skulls. It’s sort of like how you might use a satellite dish to focus radio waves to get a radio or television signal; as these waves bounce around, you can get a similar focusing effect inside the skull.

What’s potentially very detrimental about that is during this bouncing, you can get areas of negative pressure. It’s in those areas of negative pressure that we suspect cavitation happens, and when cavitations happen, it can put a lot of stress on the brain tissue. You can imagine cavitation as this bubble that expands, contracts and collapses very, very rapidly. But as it stretches out, it pushes the tissue around it. When it collapses, it pulls on the tissue around it. All of that tissue matter around it is made of our brain cells.

But, as we understand it right now, it’s the repetitive nature that can be so dangerous. This is something that we’re still researching, but it seems that one exposure to a blast, depending on the intensity, probably does very little to you in terms of long-term neuro-cognitive damage.

On the other hand, we know that the sorts of concussions that an athlete might be exposed to playing football, which happen much slower, can be debilitating after just one or two or three exposures.

Q: Is there a push within the military to monitor or reduce the risk from blast exposures? How does PANTHER support that work?

There are congressional inquiries and legislation, and other ongoing efforts within the Department of Defense. I think those are good starting points, but we need a lot more of that. Part of the struggle that policymakers and military personnel have now is figuring out what they’re monitoring for. There are a lot of questions on the parameters.

I think that’s really where we [PANTHER] come in, and I think we can help guide that. Our work helps to inform on how to more effectively monitor exposure and track alterations in the brain. So we’re helping to lay the foundation—rooted in hard science, physics and biology—to understand what we’re looking at, how we understand the forces interacting with the human brain, and how best to monitor and mitigate it. We look at the brain cellularly, biologically, mechanically — in all these different ways to understand how these forces change it.

We are now collaborating with other researchers in the Department of Defense that study the neurocognitive effects of the brain of the discharges of different types of weapons used in training by service members. We are essentially forensic examiners trying to recreate exactly how the pressure and blast waves given off by these weapons interact with the brain and whether there might be any concern for injury based on our foundational biophysics knowledge of the brain. We’re looking through and evaluating a range of weapons that have historically been deemed safe, and I think in many of those cases we’re seeing that they’re not as safe as we thought. I think this is something that, from an engineering perspective, we have the tools to look into and resolve. Ultimately, the hope is that we can dig into this and come back with new safety guidelines and precautionary measures to fully safeguard our people.

Q: What’s one message you want the public to know about traumatic brain injuries?

A: Often, when it comes to brain injuries, the debilitating effects that follow may not become apparent for some time. If you look at case studies of a lot of NFL athletes who have suffered from chronic traumatic encephalopathy, or CTE, almost every single one of them played football for some years and many of them seemed perfectly fine when they retired. And maybe for some years after that, they seem fine. Then all of a sudden, everything goes downhill and they start showing all the hallmark signs of debilitating traumatic brain injuries and CTE.

The problem is, once you get to that point, there’s no coming back. When we analyze those brains, we can see that this is a progressive disease that starts early. While it’s progressing, you may think it’s fine because you don’t feel it, but that’s the wrong message.

If there’s anything I want people to understand about traumatic brain injuries, it’s that they’re not always the type of injury we can relate to from other parts of our daily lives—like when we get a cut or a bruise or break a bone and can see or feel it immediately.

So often I see kids riding bikes without helmets and they think: “If I fall and I can get back up, I’m fine. It’s been a year since then and I’m fine.” What about 10 years down the line?

Q: What are some advances that excite you about the future of TBI treatment or prevention?

A: As we come to better understand the brain, I think we’re moving closer to being able to predict when someone’s brain will become injured, which opens up huge opportunities for prevention, mitigation and treatment. While the brain remains one of the most complex and challenging biological frontiers, programs like PANTHER have allowed us to bring many experts with diverse backgrounds together and accelerate our work forward. We are getting close to, for the first time, actually resolving with molecular resolution and hard numbers when and how the brain actually becomes injured.

We’re also making advances to develop better and safer helmet technologies. Here in the College of Engineering, Ramathasan Thevamaran has developed these incredible, innovative new materials that we’ve been working with companies to try to get incorporated into their consumer production lines for anything from sports to hardhat helmets.

There’s a lot to be excited about, not only because we’re coming to understand the injury biology so much better but because we’re going to hopefully be able to put new products into people’s hands to keep their brains much, much safer than we currently can.

Featured image caption: Christian Franck discusses traumatic brain injuries in an interview. Franck researches TBIs and leads the multi-institutional, interdisciplinary PANTHER research initiative. Photo by Joel Hallberg.