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Sandia Developing Specialized Computer Modeling and Simulation to Characterize Injury

Sandia National Laboratories is developing specialized computer modeling and simulation methods to better understand how blasts on a battlefield could lead to traumatic brain injury and injuries to vital organs, like the heart and lungs.

Researchers at Sandia have studied the mechanisms behind traumatic brain injury for about a decade. Their traumatic injury modeling and simulation project began with a head-and-neck representation, and now they’ve created a high-fidelity, digital model of a man from the waist up to study the minute mechanisms behind trauma.

“We’re also concerned about the possibility of injury to the life-support systems in the torso. Everything’s interconnected,” said Paul Taylor, who leads the project. “Clearly, we would love to have a representation of a full human, but certainly capturing all the regions where life-critical organs are located is a very good start.”

The information could help manufacturers develop better designs for helmets and body armor.

“Protection of the soldier, sailor or marine is essential, and well-aligned with our national security mission against challenging and new lethal threats,” said program manager Doug Dederman. “It is a privilege for our integrated military systems staff to team with the Department of Defense and medical communities to improve both diagnostic capabilities and mitigation of risk with improved protective equipment.”

Sandia’s most recent work grew from a Laboratory Directed Research and Development-funded project that wrapped up in late 2016. The team conducted both macroscale and microscale traumatic brain injury simulations, began working with doctors to correlate simulation predictions with clinical assessments of people with brain injury, and increased the size of their team.

They theorize that a phenomenon called fluid cavitation can lead to traumatic brain injury. They have developed macroscale simulations to test the hypothesis and extended their work into microscale studies to examine whether blast and short-pulse blunt impact, such as a projectile hitting body armor, could lead to fluid cavitation, forming bubbles whose collapse could damage sensitive brain and lung tissue, Taylor said.

Studying the mechanisms behind damage to brain, organs

“We’ve been able to demonstrate, at least theoretically, that the individual experiences fluid cavitation in the brain. We’ve subjected our head-neck model to blasts from the front, from the side, from the rear, and what we see are what looks like peppered regions in the brain, localized regions experiencing cavitation,” Taylor said, pointing to the occipital, temporal and brain stem areas on a slide from a simulation.

“Does cavitation occur and, if so, where might it be occurring?” said team member Candice Cooper, who developed the macroscale simulation. “Then we look at those areas on the microscale to see if cavitation is indeed occurring, how it might damage these tissues and lead to traumatic brain injury.”

The smallest area in the macroscale simulation is 1 cubic millimeter, which isn’t small enough to capture the physics of fluid cavitation very well, according to Taylor.

Enter Shivonne Haniff, who performs microscale modeling and simulation to complement Cooper’s macroscale work, simulating the formation and collapse of cavitation bubbles in the brain in scales less than 1 millimeter.

One of Haniff’s models represents axonal fiber bundle tracks within the brain’s white matter. Typically, white matter axons have myelin sheaths, a protective coating, similar to how insulation protects electric wiring. Myelin sheathing accelerates neurological pulses, allowing humans to process information very quickly. Diseases, such as multiple sclerosis, degrade myelin sheathing and drastically reduce pulse transmission.

The team hypothesizes that blast- and impact-induced cavitation and subsequent bubble collapse also could damage myelin sheathing.

Working out how to model damage mechanisms

Cooper also conducted modeling and simulations for a generic body armor configuration. The work was aimed at understanding the modeling problem rather than reaching conclusions applicable to specific armor. Her simulation studied pressures within the heart, lungs and other organs in different scenarios, such as a soldier standing about 10 feet from a roadside bomb blast.

“We looked at pressure, as well as the shearing stress that can lead to tissue tearing, and found that in this notional case, having padding behind the armor actually increased peak pressures in life-critical organs, the heart and the liver, which could lead to damage,” Cooper said. “It also led to an increase in shear stresses in all of the organs that we looked at.

“This is just an example of how we can use our modeling and simulation tools. If someone came to us with their armor design and said, ‘Would you take a look at this,’ we could vary the materials of the foam padding, the positioning of the foam padding, the size or geometry of the foam padding or of the armor plate itself,” she said. “We could look at variations on their design and let them know this change makes it better, that change makes it worse.”

The project has a long-term association with Dr. Corey Ford at the University of New Mexico Health Sciences Center and a more recent one with the Air Force San Antonio Military Medical Center. Cooper, Taylor, and team member Chad Hovey recently presented their research, which was funded through the Military Medical Center, at the International Mechanical Engineering Congress & Exposition. Haniff and Taylor gave a presentation at the same conference, outlining microscale cavitation studies—funded by the U.S. Office of Naval Research and conducted by Dr. Tim Bentley—and published a paper on the topic in a recent edition of Shock Waves. The fifth team member, Ryan Terpsma, has assisted in macroscale modeling of behind-helmet blunt trauma resulting from bullet impacts.

The team also works with experimental collaborators at Los Alamos National Laboratory, New Mexico Tech and its Energetic Materials Research and Training Center, and Michigan State University, some of whom perform blast tube experiments on a physical model. The project recently began working with Team Wendy, a company that manufactures military and civilian helmets.

To read the full Sandia press release, visit https://share-ng.sandia.gov/news/resources/news_releases/blast_impact/#.WmuB-ZM-dAY.

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