A Helmet Patch to Measure Blasts

Since the start of the war in Iraq, soldiers have returned home at an alarming rate with a highly complex battlefield injury: traumatic brain injury (TBI). The injury, which is frequently caused by the blast from an improvised explosive device (IED) or rocket-propelled grenade, can be difficult to detect and diagnose. The difficulty is made worse because the number and severity of the blasts to which a soldier has been exposed are often unknown.

In an effort to understand brain injuries, the U.S. Defense Advanced Research Project Agency (DARPA) has awarded a $5 million, three-year contract to the Palo Alto Research Center (PARC) to develop a strip of plastic that can be “taped” onto a soldier’s helmet to measure his or her exposure to explosions. The tape, which will cost less than a dollar per strip, is a flexible plastic substrate that will contain printed electronics, analog memory, and sensors. It will record seven days’ worth of information, which will then be transferred to a soldier’s medical record. The disposable tape will be replaced.

IEDs emit shock waves–waves of air pressure–that travel at around a thousand feet per second, or close to the speed of sound. Such an explosion can cause severe brain damage, which often goes undiagnosed until weeks after a soldier’s return home. “TBI is going to be the signature injury of the war, but to understand it, we need the data,” says Kevin “Kit” Parker, an assistant professor of biomedical engineering at Harvard University and a U.S. Army Reserve captain who served in southern Afghanistan from 2002 to 2003.

Last year, the U.S. Army awarded a million-dollar contract to Simbex, of Lebanon, NH, to build sensor-studded helmets, but the technology is cost prohibitive and has not made it to the battlefield.

The sensor tape being developed by PARC will be fabricated using its ink-jet printing technology, a patterning technique developed for large-area electronics, such as flexible, flat-panel displays, RFID tags, solar cells, and electronic paper. To print the components–electronics, memory, and sensors–on the tape, the ink-jet printer will deposit solution-processed materials, including organic semiconductors, polymer dielectrics, and metal nanoparticles, on a plastic substrate.

The tape will have an area no greater than a standard four-by-four-inch medical pad, with a minimum of a one-inch bend radius, making it small and lightweight. The suite of sensors on the tape will include accelerometers; pressure, acoustic, and light sensors; and a thermometer. “One reason for measuring all these [parameters] is that no one is certain which one, or which combination, will best act as a proxy for the harmful brain injury that results from accumulated blast exposure,” says Jennifer Ricklin, DARPA program manager for the Sensor Tape Program.

One “alarming issue” is that “soldiers are sustaining repeated exposures [to blast events] when they may not be recovered from the first one,” says Robert Cantu, a neurosurgeon at Emerson Hospital, and a professor of neurosurgery at Boston University School of Medicine. “This can lead to second impact syndrome, which is fraught with a 50 percent mortality rate, or permanent post concussion syndrome, which is basically persistent concussion symptoms.” (“Concussion” is the medical term for mild traumatic brain injury, and symptoms can include headaches, sleep problems, depression, and memory and concentration difficulty.)

Data from the sensor tape will be extracted and stored with the soldier’s medical records using a device (not yet built) that makes it easy for a soldier’s full blast history to be displayed and analyzed. “Cumulated blast exposure should be recorded such that if these exceed a prescribed level, the patient could be flagged for appropriate follow-up evaluation,” says Ricklin. She expects to have 25 prototypes to test the components by spring 2009, and 1,000 prototypes for field testing by 2010.

The DARPA program, which is in its initial stages, is focused on the interaction between IEDs and the neurological system, to determine what is most likely to cause neurological injury. “The sensor tape is an important and badly needed technology to get at that data,” says Parker.