Colour changing crystals indicate potential brain injury from bomb
9 Dec 2010
Photonic crystals that change colour on exposure to the blast
from an explosion could be used to indicate the potential brain damage
to people nearby.
Investigators at the University of Pennsylvania School of
Medicine and School of Engineering and Applied Sciences have developed a colour-changing patch that could be worn on soldiers' helmets and
uniforms. Future studies aim to calibrate the colour 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. The
findings are described in the ahead-of-print online issue of NeuroImage.
“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”, says senior author Douglas H.
Smith, MD, director of the Center for Brain Injury and Repair and
professor of Neurosurgery at Penn. “Similar to how an opera singer
can shatter glass crystal, we chose colour-changing crystals that
could be designed to break apart when exposed to a blast shockwave,
causing a substantial colour 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 being
returned 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,” notes Cullen. 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 says.
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 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 colourful display,” she explains. Her lab made the
materials and characterized the structures before and after the
blast to understand the colour-change mechanism.
"It looks like layers of Swiss cheese with columns in between,"
explains Smith. 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 colour. The material is designed so that the
extent of the colour change corresponds with blast intensity.
The blast-sensitive material is added as a thin film on small
round badges 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.