Color-changing polymer to indicate severity of hits to the head

A polymer-based material developed at the University of Pennsylvania could help in the diagnosis of traumatic brain injury(Credit: ACS)

A head trauma can be difficult to diagnose and destroy a life years after the event. Being able to tell immediately if the force someone has suffered is sufficient to result in a traumatic brain injury can make all the difference in limiting the damage. A team from the University of Pennsylvania has developed a material that could one day be incorporated into headgear to instantly gauge the severity of blows and provide a clearly visible indication of injury.

The long-term complications of head trauma have become better known of late, with recent research and media reports drawing attention to soldiers and professional athletes suffering memory loss, dementia and headaches as a result of past head trauma. Where it gets tricky is determining when a person has taken a strong enough blow to the head to warrant immediate concern, with the injuries often invisible at the time of impact.

The Pennsylvania team's answer is a polymer-based material that changes colors following a blow depending on the level of force. The idea is to provide an immediate indication of head trauma, so evaluation and treatment can be sought in a timely manner and activities that can result in further damage can be avoided.

The first version of the material was made using a technique called holographic lithography (HL). This uses two or more lasers to create interference patterns that are set in a film or other substance using photolithographic processing.

This process resulted in photonic crystals, which feature optical nanostructures that give them a particular color. Applying a force to the crystal changes the structure and in turn the color, providing a visual indicator as to the level of impact.

Unfortunately, HL turned out to be too expensive a process to make the photonic crystals commercially feasible, so the team turned to self-assembly and polymer-based materials. These resulted in a material that was cheaper to produce over a larger area.

Instead of building up the material's structure holographically, the team created a mold using silica particles of various sizes which were made to self-assemble into the desired pattern. A heated polymer was then introduced into the mold and allowed to set, before the silica mold was removed. The finished material picked up the pattern of the mold to form inverted polymer crystals.

According to the team, the early results have been promising with the polymer crystal changing color consistently based on the force applied. They said that a 30 mN force, which is about that of a sedan hitting a wall at 80 mph (129 km/h), turned the material from red to green. A 90 mN force, which is equivalent to a truck hitting the same wall at the same speed, turned it purple.

"This force is right in the range of a blast injury or a concussion," says Shu Yang, who led the research.

The team is now looking to improve on this approach by developing materials that indicate the speed at which a force is applied, which can influence the extent of damage of a particular trauma on the brain. Being lightweight and not requiring a power source, such materials would offer advantages over other battery-powered devices designed to measure head impacts.

The team's results were presented at the 250th National Meeting & Exposition of the American Chemical Society (ACS).

The video below discusses the new material.

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