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Battlefield Medic on a Chip

Sensors could one day diagnose and treat a soldier’s injuries.
November 4, 2008

The majority of deaths on the battlefield occur within half an hour after injury–often too quickly for a soldier to get to a medic, let alone a hospital. But a collaboration between researchers at the University of California, San Diego (UCSD), and Clarkson University, in New York, aims to change all that with a chip that could detect injuries and treat them almost instantly.

Smart sensor: Joseph Wang hopes to use flexible electrodes, like the one he’s holding here, to create a chip that diagnoses battlefield injuries.

At the center of the research is a sensor, still in development, that could be used to continuously monitor a soldier’s blood, sweat, or even tears for biomarkers. All of these fluids contain glucose, oxygen, lactase, and the hormone norepinephrine, which fluctuate depending on a person’s health and activity levels. Specific, collective changes in these markers can indicate the presence of an injury. And once the sensor picks that up, it could transmit the information elsewhere on the chip, or to another chip, and trigger release of an appropriate medication. That, at least, is the idea; the reality, however, could take a little while to develop.

The head of the project, Joseph Wang, is a nanoengineering professor at UCSD whose office is packed with electronic sensors of every shape but only two sizes: small and even smaller. Wang, who previously helped develop a noninvasive glucose monitor that samples sweat, is no stranger to continuous sensing. But rather than picking up just one signal, the new sensor will need to differentiate among multiple markers and interpret the results.

To do this, Wang is collaborating with Clarkson’s Evgeny Katz, who recently created a system that uses an enzyme-based logic gate to not only measure a combination of biomarkers but also use the results to make a limited diagnosis. Katz’s system is based on enzyme-driven reactions: in the presence of certain enzymatic products, one set of “gates” is unlocked and triggers a specific chain reaction; other products trigger a completely different set of gates. The end result is a logic chain that has the potential to identify certain medical conditions.

So far, Katz’s enzyme logic diagnostics work only in solution. But Wang and Katz envision a system that would use an electronic sensor, one containing enzymes, to detect the presence or absence of the four biomarkers mentioned above: glucose, oxygen, lactase, and norepinephrine. In different combinations, these biomarkers can indicate different injuries, such as brain trauma or shock. Depending on the injury, the electrodes would translate the enzymatic results into a code that activates signal-dependent membranes to release the appropriate medication. If a soldier were to go into hemorrhagic shock, for example, the electrode would detect rising levels of lactate, glucose, and norepinephrine. As the electrode enzymes’ product mixture begins to change, the reaction would trigger the logic gate unique to shock and, potentially, signal for the release of the appropriate medication. “We want to build a smart, intelligent sensor that can distinguish between different injuries, make the decision to treat, and, once it recognizes the injury, treat appropriately,” Wang says.

If this all sounds a bit theoretical, that’s because it is. Katz and Wang expect it will be four years before their newly funded project reaches completion. At this stage, Katz can’t even say for certain which injuries their system might be able to recognize, or exactly how it could treat them. Right now, he says, they’re simply designing a logic gate that can distinguish between different injures–what the biomarker combinations look like and the enzymatic code to interpret them. Next they’ll decide which bodily fluids would work best, and from there they can begin their electrode design.

Of the hundreds of sensors in Wang’s office, he points to a few he believes might be useful models. One, meant to be rolled up into a tight cylinder, is so minute that it could fit into a tear duct. Another, larger one could have a small subcutaneous sensor that sits just under the skin. “We want something that would be minimally invasive, or, more desirably, noninvasive, that could sample tears, saliva, or sweat,” he says.

The researchers have a big task ahead of them. “I think an important challenge is finding out of the things they can sense, how reliable [they] will be in a battlefield situation,” says Martin Bazant, a professor of mechanical engineering at Stanford University. “Will you be able to add value to the soldier without adding weight or risk of malfunction?”

Bazant is familiar with the difficulties of designing for soldiers in combat–he was one of the founding members of MIT’s Institute for Soldier Nanotechnologies–and he notes that development of the sensor itself would be a huge boon. “Having the ability to detect accurate levels of those chemicals in real time in the battlefield, reliably–that’s already interesting,” he says. “A medic could read it off, and use it to determine how critical a patient is, whether treatment is necessary, whether a patient should be moved to another location.” However, Bazant is skeptical about the use of a fully automated system for injury sensing and drug dosing in the absence of a medic.

If Wang and Katz are successful, their project will have applications not just during wartime but in everyday medicine. Doctors are always in need of sensors that provide a more accurate picture of what’s going on in a patient’s body. It could be adapted to detect cardiac markers–for example, to rapidly diagnose a heart attack or a stroke. “This can be useful whenever we have something urgent that needs quick action,” Wang says.

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