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What if the helmet your child wears while playing football had the ability to diagnose head trauma at the time of impact? A rough tackle can inflict brain damage that destroys lives, yet these injuries are often invisible until later. To detect head trauma immediately, a team of researchers developed a polymer-based material that changes color depending on how hard it is hit. The goal is to someday incorporate this material into protective headgear, on the battlefield as well as the gridiron, providing an immediate indication of injury.

Clare Goldsberry

August 18, 2015

2 Min Read
Color-changing polymer in helmets could signal severity of head injuries

West Point football

Image courtesy West Point/Flickr.

The American Chemical Society (ACS) announced on Aug. 17 that this potentially life-saving technology is close to being realized thanks to scientists at the University of Pennsylvania, led by Shu Yang, PhD. They are researching the use of holographic lithography (HL) to create photonic crystals with carefully designed structures to give them a particular color, just like opals. Deforming the crystals with an applied force changes their internal structures and, thus, the crystal's color. The material does not require power to detect forces and is lightweight, which offers an attractive way for medical personnel to identify a damaging force on site without the use of expensive tools. However, making these crystals is an expensive process that isn't suitable for mass production, Yang explains.

Obviously mass production of a material of this type is important given the scope of the problem of head trauma and brain injury in a number of settings. So the team next turned to self-assembly and polymer-based materials that are cheaper to produce over a larger area than the earlier HL method. Younghyun Cho, PhD, a postdoctoral fellow in Yang's lab, described the team's development, which could offer a path to commercialization.

The first step was to mold the polymer into a structure that worked just like the specialized photonic crystals. To make the mold, the researchers mixed up silica particles of various sizes and allowed them to self-assemble into crystals with the desired pattern. They heated the polymer, which infiltrated the mold, allowed it to solidify and then removed the silica mold, leaving behind the inversed polymer crystals.

The researchers then applied varying amounts of force to the polymer crystal and recorded the color change. The results were encouraging. "We were able to change the color consistently with certain forces," Yang said.

For example, applying a 30 mN* force—approximately the force of a sedan moving at 80 miles per hour crashing into a brick wall—caused the crystal to change from red to green. A force of 90 mN—the equivalent of a speeding truck hitting that same wall—turned the polymer purple, Cho added.

"This force is right in the range of a blast injury of concussion," Yang said.

In future studies, Yang plans to develop materials that can indicate how quickly a force is applied, which affects how damaging a particular trauma is on the brain.

Yang acknowledged funding from the Berkman Opportunity Fund, as well as her collaborators Gang Feng, PhD, of Villanova University, and Jie Yin, PhD, of Temple University.

* Newton force is named for Isaac Newton's Second Law of Motion. 1 Newton is the force needed to accelerate 1 kilogram of mass at the rate of 1 meter per second squared.

About the Author(s)

Clare Goldsberry

Until she retired in September 2021, Clare Goldsberry reported on the plastics industry for more than 30 years. In addition to the 10,000+ articles she has written, by her own estimation, she is the author of several books, including The Business of Injection Molding: How to succeed as a custom molder and Purchasing Injection Molds: A buyers guide. Goldsberry is a member of the Plastics Pioneers Association. She reflected on her long career in "Time to Say Good-Bye."

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