Blast-induced traumatic brain injury from improvised explosive devices (IEDs) is the "signature wound" of the current wars in Iraq and Afghanistan. With the damage to the brain often not immediately obvious and no objective information of relative blast exposure, soldiers may not receive appropriate medical care and are at risk of being returned to the battlefield too soon. To overcome this inadequacy, researchers have developed a color-changing patch that could be worn on soldiers’ helmets and uniforms to indicate the strength of exposure to blasts from explosives in the field.

The badges are comprised of nanoscale structures, in this case pores and columns, that mimic the reflective iridescence of a butterfly’s wing. The tiny shapes, which preferentially reflect certain wavelengths, are sculpted by lasers into a plastic sheet. Douglass H. Smith, MD, director of the Center for Brain Injury and Repair and professor of Neurosurgery at Penn, says that, similar to how an opera singer can shatter glass crystal, these color-changing crystals are designed to break apart when exposed to a blast shockwave, resulting in a substantial color change.

The researchers at the University of Pennsylvania School of Medicine and School of Engineering and Applied Sciences pioneered the microfabrication of three-dimensional photonic structures using holographic lithography. They then made the materials and characterized the structures before and after a blast to understand the color-change mechanism.

“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,” explained Shu Yang, PhD, associate professor of Materials Science and Engineering.

The material looks like layers of Swiss cheese with columns in between, explains Smith. Although the nanostructures are very stable in the presence of heat, cold or physical impact, they 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 only a few millimeters in diameter that could be sown onto a soldier’s uniform or attached to a soldier’s helmet.

In addition to its use as a blast sensor for brain injury, the team says the technology could also be used to test the blast protection of structures, vehicles and equipment for military and civilian use.

The UPenn team’s findings are described in the online issue of NeuroImage.