A radical new hi-tech football players can change colour is a player is at risk of a concussion.

As the NFL season kicks off, researchers say their technology could give an early warning of potential problems.

They say it could be developed for sportsmen and even soldiers.

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Philip Rivers of San Diego Chargers grimaces as he is caught between Jacksonville Jaguars defensive end Jason Babin, left, and defensive end Andre Branch (90): Researchers now say they are developing a colour changing helmet that could give an early warning of potential problems.

FOOTBALL HEAD INJURIES Deaths of former players and a lawsuit from others, books and documentaries about the league's reticence to come to grips with medical evidence, and now a Hollywood dramatizationhave all looked at the problem of concussion in football. Soldiers exposed to bomb blasts can have similar symptoms. The precise link between concussions and debilitating conditions like chronic traumatic encephalopathy is still being explored, but as the name suggests, repeated head injuries are a main culprit. Advertisement

Shu Yang, a professor in the School of Engineering and Applied Science, has led a team of researchers in developing a polymer-based material that changes colors depending on how hard it is hit.

The goal is to someday incorporate this material into protective headgear that could give an early warning sign of a concussion.

'If the force was large enough, and you could see that as easy as reading a litmus test, then you could immediately seek medical attention,' Yang says.

Yang Lab members Younghyun Cho, Su Yeon Lee, and Gaoxiang Wu contributed to the work, and the Penn team collaborated with Gang Feng's group at Villanova University and Jie Yin's group at Temple University.

'No one's been able to predict in clinical cases how much force it actually takes to cause a concussion,' the Cleveland Clinic's Richard Figler, former team physician for the Browns, told Bloomberg.

Players caught off guard by a soccer ball kicked from behind, for example, can sustain concussions from much smaller forces than someone braced for a tackle, whose neck muscles absorb some of the blow.

'The threshold is extremely wide,' Figler said.

Using holographic lithography -a laser-based method for patterning nanoscopic features into a three-dimensional material - Yang's team has previously made photonic crystals that feature carefully designed internal structures.

Like opals, these structures refract light into a particular color.

Concussive force can deform the crystals, changing the arrangement of those structures and, thus, the crystal's color.

In their new study, Yang and her colleagues developed an easier way of producing this effect that could hasten its adoption in consumer products like football helmets.

The key difference was using a polymer that could be coaxed into forming the same internal structures as found in their specialized photonic crystals.

First, the polymer was melted and poured into a mould consisting of silica beads.

After the polymer solidified and the beads were removed, the polymer crystals were able to act as 'inverse opals' and mimic these light-refracting features.

The researchers then applied varying amounts of force to the polymer crystal and recorded the colour change.

A strong hit caused it to change from red to green, while a stronger one changed it from red to purple.

'The strength of these forces are right in the range of a blast injury or a concussion-causing hard tackle,' Yang says.

The colour change in the polymer version of the crystal is permanent.