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Tour De Force: Sweat Patch Takes A Licking, Keeps On Sticking

Serious physical training is all about making the body tougher and figuring out the weak points. When GE Research engineers sent the first generation of their adhesive sweat patch to a U.S. Air Force Academy boot camp simulation in March 2018, cadets were encouraged to go hard on the Band-Aid-like wearable device designed to wirelessly detect specific levels of electrolytes in their sweat. “We told them to break it, to understand its vulnerabilities during use,” says GE materials scientist Azar Alizadeh.

And they did. After several hours in the field with the Air Force, the patches were falling off the cadets’ forearms while they were performing special ops training. The hours on sweaty, hardworking bodies provided the engineers with invaluable feedback to build an improved version of the patch. “We went back to the drawing board,” she says. “We redid the design to make the patch more compact and include more capabilities, like new sensing modalities, better data handling and ergonomics.”

The team developing the patch includes GE scientists as well as outside partners from the Air Force Research Laboratory, NextFlex, the State University of New York at Binghamton, New York state’s Empire State Development and the Nano-Bio Manufacturing Consortium. They’ve added a mobile app to monitor multiple sensor channels simultaneously. They’ve also improved the wireless connection to ensure the patch’s signal stays connected to the app, even when it is more than 30 feet away. And if the connection is lost, the patch will continue to record data onboard.

The new version of the palm-size patch, which users now attach to their backs (the most comfortable and optimized location for this application), also contains two key components from the original device that passed the boot camp with flying colors, albeit now more finely tuned: microfluidics technology and sensors.

The GE team tapped microfluidics know-how originally developed for jet engines to manipulate cooling air flowing through the engine and channel it to optimize efficiency and performance. The updated sweat patch uses tiny pathways to channel perspiration across three sensors: the first two seeking to detect levels of electrolytes such as sodium or potassium in the sweat and the third measuring sweat volume. That’s an upgrade from the original device, whose sole sensor measured only a single electrolyte. “We added sweat volume because the amount of sweat lost correlates with other information like core body temperature,” Alizadeh says.

Top and above images: The new version of the palm-size patch, which users now attach to their backs (the most comfortable and optimized location for this application), also contains two key components from the original device that passed the boot camp with flying colors, albeit now more finely tuned: microfluidics technology and sensors. Image credits: GE Research.

The sensors turn the data into an electrical signal and transmit it wirelessly to a mobile app for monitoring. Dehydration, which occurs when you have electrolyte imbalances from losing too much water from the body, can lead to nausea, lethargy and fluid retention, conditions that could be dangerous for fighter pilots as well as first responders and elite athletes. By monitoring the real-time measurements, for example, fire chiefs can better decide when to swap in another firefighter and prevent injury.

Now that the Air Force has broken in the sweat patch, Alizadeh and her team are testing it with recreational athletes at the University of Connecticut. “The Air Force was an opportunity to see how the patch fared in a harsh physical environment, but not a controlled one,” Alizadeh says. “We’re now looking at the patch from a clinical merit standpoint to better understand its performance against a global standard.”

At the university, researchers monitor male and female volunteers as they exercise in a hot, humid environment for body mass loss, the saltiness of their urine and its pH, and body temperature, among other things. “The University of Connecticut has a world-leading research institute for heat-related injuries which allows us to push the limits of athletes in adverse conditions,” says Materials Science and Engineering Professor Mark D. Poliks of SUNY Binghamton, one of the outside partners. “There, the researchers will get the physiological data and fully analyze opportunities for what the patch offers.”

Alizadeh says this patch is just part of an array of wearable devices under development at GE that aim to measure physiological markers like core body temperature, blood oxygenation, respiration rate and blood pressure as well as biochemical markers like lactate, inflammatory and metabolic markers. These patches will use different technology than the sweat patch and may be helpful for physicians remotely monitoring patients. The early prototypes for these patches will begin testing later this fall, Alizadeh says, while the sweat patch should be ready for more field trials by early 2020.

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