Our sweat contains a bunch of useful information about our bodies, but diving in to retrieve it hasn't always been so straightforward. Eyeing a future where wearables not only track our heart rate and activity, but things like hydration and muscle fatigue as well, Berkeley engineers have developed a flexible sensor that can measure biochemicals in perspiration in real-time to build a more complete picture of our well-being.
"Human sweat contains physiologically rich information, thus making it an attractive body fluid for non-invasive wearable sensors," says Ali Javey, a professor of electrical engineering at UC Berkeley and leader of the research team. "However, sweat is complex and it is necessary to measure multiple targets to extract meaningful information about your state of health. In this regard, we have developed a fully integrated system that simultaneously and selectively measures multiple sweat analytes, and wirelessly transmits the processed data to a smartphone. Our work presents a technology platform for sweat-based health monitors."
Javey and his team set out to develop a device that tracks key chemicals in real-time and can be worn comfortably while the subject moves around during exercise. They approached this by fitting an array of sensors onto a flexible circuit board to measure metabolites glucose and lactate, and electrolytes sodium and potassium, along with skin temperature.
Attached to the sensor array is a wireless printed circuit board with a microprocessor and chips for analyzing and transmitting the data. By gauging the concentrations of these different biochemicals, while also allowing for the effect of skin temperature on the readings, the system is able to uncover information about the subject's physical state. Examining sodium and potassium, for example, can offer an insight into hydration levels, while lactate can give an indication as to muscle fatigue.
The team fitted its new sweat sensor into wristbands and headbands and tested it out on dozens of volunteers across various exercises such as jogging and cycling on stationary bikes. The concentrations of each of the chemicals were synched to a purpose-built smartphone app, giving the researchers a new way of tracking a subject's physiological well-being.
"Having a wearable sweat sensor is really incredible because the metabolites and electrolytes measured by the Javey device are vitally important for the health and well-being of an individual," says UC Berkeley professor of integrative biology George Brooks, a co-author on the study. "When studying the effects of exercise on human physiology, we typically take blood samples. With this non-invasive technology, someday it may be possible to know what's going on physiologically without needle sticks or attaching little, disposable cups on you."
The UC Berkeley team aren't alone in this pursuit of more comfortable and accessible ways to gather biological data. Scientists at the University of Cincinnati are working on a similar device, having unveiled an early prototype in 2014 that'scapable of measuring sodium and chloride in sweat. Meanwhile, Mexican students are developing a sweat-analyzing in-vehicle sensor system that detects when the driver is drunk and prevents them from starting up the engine.
While all this is certainly promising, don't expect Fitbit to be releasing a sweat-tracking bracelet any time soon. The approach does hold some obvious advantages over blood sampling, namely the immediacy of the results, but it is not nearly as reliable as this established method of assessing health, something Javey describes as the gold standard. The content of sweat is more variable and can be influenced by skin microbes, so further testing would need to be carried out to establish just how trustworthy this data is.
While all this is certainly promising, don't expect Fitbit to be releasing a sweat-tracking bracelet any time soon. The approach does hold some obvious advantages over blood sampling, namely the immediacy of the results, but it is not nearly as reliable as this established method of assessing health, something Javey describes as the gold standard. The content of sweat is more variable and can be influenced by skin microbes, so further testing would need to be carried out to establish just how trustworthy this data is.
With that said, the researchers have high hopes for the technology, imagining that it can one day be improved to measure an even wider range of biochemicals, allowing for applications beyond simply monitoring performance during exercise.
"While Professor Javey's wearable, non-invasive technology works well on sweating athletes, there are likely to be many other applications of the technology for measuring vital metabolite and electrolyte levels of healthy persons in daily life," says Brooks. "It can also be adapted to monitor other body fluids for those suffering from illness and injury."
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