Butterfly ‘Blast Badge’ a Brain Bodyguard

Thursday, December 2, 2010 @ 08:12 AM gHale

A butterfly could be a lifesaver for soldiers in war, or even down the road, workers in an explosive environment.
Mimicking the reflective iridescence of a butterfly’s wing, researchers developed a color-changing patch soldiers could wear on their helmets and uniforms to indicate the strength of exposure to blasts from explosives in the field, said investigators at the University of Pennsylvania School of Medicine and School of Engineering and Applied Sciences. Future studies aim to calibrate the color change to the intensity of exposure to provide an immediate read on the potential harm to the brain and the subsequent need for medical intervention.
“We wanted to create a ‘blast badge’ that would be lightweight, durable, power-free, and perhaps most important, could be easily interpreted, even on the battlefield”, said Douglas H. Smith, MD, director of the Center for Brain Injury and Repair and professor of Neurosurgery at Penn and senior author of a paper on the subject. “Similar to how an opera singer can shatter glass crystal, we chose color-changing crystals that could be designed to break apart when exposed to a blast shockwave, causing a substantial color change.”
Blast-induced traumatic brain injury is the “signature wound” of the current wars in Iraq and Afghanistan. However, with no objective information of relative blast exposure, soldiers with brain injury may not receive appropriate medical care and are at risk of returning to the battlefield too soon.
“Diagnosis of mild traumatic brain injury [TBI] is challenging under most circumstances, as subtle or slowly progressive damage to brain tissue occurs in a manner undetectable by conventional imaging techniques,” said D. Kacy Cullen, PhD, assistant professor of Neurosurgery at Penn. There is also a debate as to whether mild TBI is confused with post-traumatic stress syndrome. “This emphasizes the need for an objective measure of blast exposure to ensure solders receive proper care,” he said.
The badges consist of nanoscale structures, in this case pores and columns, whose make-up preferentially reflects certain wavelengths. Lasers sculpt these tiny shapes into a plastic sheet.
Shu Yang, PhD, associate professor of Materials Science and Engineering at Penn and her group pioneered this microfabrication of three-dimensional photonic structures using holographic lithography. “We came up with the idea of using three-dimensional photonic crystals as a blast injury dosimeter because of their unique structure-dependent mechanical response and colorful display,” she said. Her lab made the materials and characterized the structures before and after the blast to understand the color-change mechanism.
“It looks like layers of Swiss cheese with columns in between,” Smith said. Although very stable in the presence of heat, cold or physical impact, blast exposure can alter the nanostructures. The shockwave causes the columns to collapse and the pores to grow larger, thereby changing the material’s reflective properties and outward color. The design of the material is such that the extent of the color change corresponds with blast intensity.
In addition to use as a blast sensor for brain injury, other applications include testing blast protection of structures, vehicles and equipment for military and civilian use.