A variety of sensors (depicted as colored components in close-up at right), when incorporated into a flexible wristband, can monitor substances in sweat and wirelessly provide information about the metabolic processes taking place inside the body.

A variety of sensors (depicted as colored components in close-up at right), when incorporated into a flexible wristband, can monitor substances in sweat and wirelessly provide information about the metabolic processes taking place inside the body.

Der-Hsien Lien and Hiroki Ota

New wristband measures sweat to monitor health risks

Most fitness trackers—even the most sophisticated ones on the market—can’t do much more than count your steps or measure your heart rate. But researchers have developed a device that can do much more: Built into a headband or wristband, it can monitor chemicals in the body’s sweat that may be used to non-invasively assess medical conditions, discern drug abuse, or help coaches and trainers optimize the performance of elite athletes, scientists say.

Wearable electronics might be all the rage among the health-conscious, but the functions of these devices—many of them worn on the wrist like a watch—are often limited to calculating calorie burn on the basis of heart rate or distance traveled. But there’s a wealth of information to be garnered from something that every active person does: sweat. Human sweat is full of substances that betray what’s going on inside, says Ali Javey, an electrical engineer at the University of California, Berkeley.

Javey and his colleagues developed a prototype band that can tap into sweat’s bounty of information. The device has two main parts. One portion, made of flexible plastic, contains custom-built sensors that measure the concentrations of sodium and potassium ions (key electrolytes that make sweat salty) as well as glucose and lactate, which provide insights into the processes happening in a person’s cells. At high levels in cells, lactate—the negatively charged ion from lactic acid, which accumulates when cells lack sufficient oxygen—can disrupt a person’s pH balance. A temperature sensor helps calibrate the information gleaned by the other sensors, Javey says. The other portion of the device is a flexible circuit board that includes 11 off-the-shelf computer chips, which together interpret the information coming from the sensors and transmit it wirelessly to a nearby laptop or cell phone.

The device creatively dodges two problems that have plagued previous attempts to tap into sweat: flexibility and computing power. In the past, engineers using silicon-based computer chips found that the inflexible components often don’t maintain contact with a person’s skin, Javey says. Other teams using pliable, plastic-based electronic devices found that those typically didn’t have the computing power required to measure more than one substance or include more than simple functions.

No one else has measured multiple things simultaneously, says Jason Heikenfeld, an electrical engineer at the University of Cincinnati in Ohio, who was not involved in the project. “Every time you can measure something else, you get smarter.”

The device functioned as predicted in lab tests on volunteers riding stationary bikes, the researchers report online today in Nature. Besides being portable and noninvasive (no needles required!), the prototype monitors chemicals in real time, eliminating the time and effort usually needed to collect samples and transport them for analysis to a lab with large, expensive equipment.

“The ability to monitor sweat continuously offers new capabilities,” says John Rogers, a materials scientist at the University of Illinois at Urbana-Champaign. Besides basic studies of human physiology, including how people respond to exercise or other stress, the device could find use in a variety of clinical situations. Doctors could monitor everything from depression to drug use, customizing sensors to measure the breakdown products of drugs (either legal or illegal ones) and various biomarkers.

Or, Javey says, the device could be used over a period of time to monitor how quickly or slowly individual patients respond to a drug during treatment, thus enabling a doctor to tailor its dosage. The device could also be used to alert athletes and patients to a variety of medical conditions, including fatigue, dehydration, and overheating.

For now, the circuit-board portion of the team’s prototype is large. But the 11 computer chips that the researchers used could be consolidated on a single custom-designed chip, thus making future versions of the device smaller and available for use on babies and children as well as adults. Plus, next-generation versions could feature the ability to disconnect the sensors and dispose of them but keep and reuse the electronics.

To commercialize the team’s device as a medical product would require lengthy clinical testing and assessments by the FDA—a process that could easily take years, says Javey. But versions to be used solely as a fitness monitor wouldn’t require such testing and evaluation.

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