Brain injuries are common in soldiers following explosions on the battlefield. In many cases, though, symptoms of concussion may not be noticed because they’re not acute enough and medics could be triaging only those who are clearly wounded. Clinical researchers and engineers at University of Pennsylvania have developed a small patch that can be attached to clothing or helmets that will change color following a strong enough shock, so it could be used as an indicator for proper and expedient care.
The badges are comprised 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.
Yang’s [Shu Yang, PhD, associate professor of Materials Science and Engineering] group pioneered this microfabrication of three-dimensional photonic structures using holographic lithography. “We came up 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 explains. 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," explains Smith [Douglas H. Smith, MD, director of the Center for Brain Injury and Repair and professor of Neurosurgery at Penn]. Although very stable in the presence of heat, cold or physical impact, the nanostructures are selectively altered by blast exposure. The shockwave causes the columns to collapse and the pores to grow larger, thereby changing the material’s reflective properties and outward color. The material is designed so that the extent of the color change corresponds with blast intensity.
The blast-sensitive material is added as a thin film on small round badges the size of fill-in-the-blank circles on a multiple-choice test that could be sewn onto a soldier’s uniform.
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.
Full story from UPenn: Color-Changing “Blast Badge” Detects Exposure to Explosive Shock Waves…