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August 9, 2017

New study opens up novel ways to use sweat for biomedical measurements

Researchers at the University of Cincinnati have come up with a novel way to stimulate sweat glands on a small, isolated patch of skin, so test subjects can stay cool and comfortable and go about their daily routine without spending hours on a treadmill.

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UC professor Jason Heikenfeld and UC graduate Zachary Sonner developed a device the size of a Band-Aid that uses a chemical stimulant to produce sweat, even when the patient is relaxed and cool. The sensors also can predict how much patients sweat, an important factor in understanding the hormones or chemicals the biosensors measure. The study was published July 25 in the nanotechnology journal Lab on a Chip.

“The challenge is not only coming up with new technological breakthroughs like this, but also bringing all these technology solutions together in a reliable and manufacturable device,” Heikenfeld said. He has co-founded a biosensor company, Eccrine Systems, Inc., that is pursuing just that. The start-up was launched in 2013 with help from UC’s Technology Accelerator program.

Biomedical sensors set for explosive growth

Biomedical sensors are part of a medical-device industry valued at $88 billion in the United States, according to market-research firm IbisWorld. The industry will see explosive growth in the next five years with the advent of new technology and increasing competition. Eccrine Systems’ work is attracting international attention because of the profound way that it could change health diagnosis and monitoring, according to Heikenfeld.

Blood analysis is considered the gold standard for biometric analysis – to see if chemical concentrations are increasing or decreasing over time. But biometric testing with blood is invasive and often requires the use of a lab. It is far more difficult for doctors to perform continuous monitoring of blood over hours or days. Sweat provides a noninvasive alternative, with chemical markers that are more useful in monitoring health than saliva or tears. But because people don’t always sweat, it was ignored by researchers.

Sweat ignored for lack of availability

Heikenfeld, also director of UC’s Novel Devices Laboratory, has been studying the problem for seven years. Scientists say sweat provides much of the same useful information about patients as blood. The problem has always been getting the same consistent sample as is possible with a standard blood draw, he said. “We believe that the solutes you find in blood you will find in sweat,” he said. “We have postulated that for some time and, as of right now, have not seen anything to change our hypothesis.”

For the study, the researchers applied sensors and a gel containing carbachol, a chemical used in eyedrops, to their subject’s forearm for 2.5 minutes. They used three methods to obtain sensor data: the gel and sensors alone and in combination with memory foam padding (to provide better contact between the sensor and the skin) and iontophoresis, an electrical current at 0.2 milliamps that drives a tiny amount of carbachol into the upper layer of the skin and locally stimulates sweat glands but causes no physical sensation or discomfort.

Leap forward in sweat-sensing technology

Then they recorded data obtained from the subject’s sweat for 30 minutes using sensors that measured concentrations of sweat electrolytes. Carbachol was effective at inducing sweating under the sensor for as long as five hours. Heikenfeld said a subsequent study successful generated sensor results for several days using this process to stimulate sweat. “This work represents a significant leap forward in sweat-sensing technology,” the study concluded.

“Imagine being able to monitor cardiac patients after they have been released from the hospital, or preventing dehydration in athletes or even helping ensure that your body is getting the exact right concentrations of a prescription drug,” Heikenfeld states.

“The ultimate goal is convenience and reliability for biomedical applications,” adds alum Sonner, lead author of the paper. “The end goal is to take the idea from a benchtop test to a portable device — perhaps for people in high-stress jobs like airline pilots — and analyze them for stress. If you’re a pilot, you can’t do blood draws while you’re flying the plane. But a sensor could analyze sweat so we can begin to understand how their body responds to stressful situations.”

Many use cases

Possible uses include helping Olympic athletes to find out through cortisol level measurements if they train effectively or are pushed too hard. The U.S. Air Force Research Laboratory at Wright-Patterson Air Force Base, a UC research partner, is extremely interested in measuring cortisol in pilots facing mentally and physically stressful situations. Monitoring their health and performance over time using noninvasive sensors would be extremely helpful, Heikenfeld said.

Likewise, it could be useful for patients who might want to perform regular health monitoring at home after a surgery, Sonner said. “It’s particularly useful for follow-up visits where normally there is some type of blood testing that has to be done. They could wear a disposable patch for 20 minutes instead.

Find out more about the study on biomedical uses for sweat

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