For better health and fitness, sweat out that data
Someday soon, perhaps within a year, you’ll be able to slap a soft, stretchy patch on to your arm that tells you if you’re dehydrated. Or that your electrolytes are dangerously out of balance. Or even that you have diabetes.
Fitness trackers such as Fitbit and Apple Watch already track step counts, heart rate and sleep rhythms. But they tend to be rigid and bulky, and mostly gather mechanical metrics, rather than assess a person’s underlying biology.
A new generation of devices instead aim to analyze sweat for many chemicals at once, producing a real-time snapshot of the wearer’s health or fitness. These devices also fit intimately against the skin, and are comfortable for anyone, from premature babies to the elderly. One version is already being advertised by Gatorade.
The latest advance in this technology, described last month in the journal Science Advances, provides real-time information on the wearer’s pH, sweat rate, and levels of chloride, glucose and lactate — high levels of which could signal cystic fibrosis, diabetes or a lack of oxygen.
“It fits into a broader trend that you’re seeing in medicine, which is personalized, tailored approaches to treatment and delivery of care,” said John Rogers, a biomedical engineer at Northwestern University in Illinois and the key architect of the device.
Technology like this has been anticipated for years, but the field has accelerated rapidly. Some similar devices in development are soft. Some use electric sensors to read chemicals. Others rely on colori-metrics, in which the intensity of the colour in the readout matches the concentration of the chemical being monitored. The new device delivers all of that in a battery-free and wireless form.
“This looks like the first version in which they integrated all of it in one device,” said Martin Kaltenbrunner, an engineering professor at Joannes Kepler University Linz, in Austria, who was not involved in the research. “The level of technology that is in this paper is very, very advanced.”
The new device has minuscule holes at its base into which sweat naturally flows. From there, a complex network of valves and microchannels, each roughly the width of a human hair, route the sweat into tiny reservoirs. Each reservoir contains a sensor that reacts with a chemical in the sweat, such as glucose or lactate.
“That’s basically it,” Rogers said. “There’s nothing that penetrates the skin, and there’s no power supply that’s driving flow.”
To be marketed at large scale, any sweat-based sensor would need to be manufactured at a low cost. Many teams are focused on this goal because of the potential of the devices to transform health care, Kaltenbrunner said. “If I have to go to the clinic once a day to have my data collected, I wouldn’t really do it,” Kaltenbrunner said. “But it just means wearing a patch and being able to self-monitor myself, then eventually this barrier will be reduced.”
Rogers’s team has begun testing the technology as a way to screen for cystic fibrosis, a rare genetic condition. Doctors already look at chloride concentrations in sweat to identify children with the condition, but they typically use a rigid, uncomfortable device that straps tightly onto the child’s arm for a onetime measurement.
“Really what is needed is big data for human health,” said Ali Javey, a member of the team that proposed the earlier sensor and a professor of electrical engineering and computer science at the University of California, Berkeley. The device invented by Rogers “is really important,” Javey said, because it is “comfortable to wear, has different sensing modalities and is robust.”
Rogers’s team has been testing their device with children who have cystic fibrosis at Lurie Children’s Hospital of Chicago. It is in the late stages of a clinical trial, and plans to apply for approval from the Food and Drug Administration.
A much bigger market for sensors lies in the approximately 30 million people with diabetes in North America track their glucose levels. The most advanced diabetes sensor, approved by the FDA in 2017, is a soft skin patch coupled to a small reader, and relies on tiny needles that pierce the skin to monitor blood glucose. The ideal device would not involve needles or draw blood. To use sweat instead, however, scientists first need to learn more about it — how sweat rates vary among individuals, how different biochemicals make their way into sweat, and how well those levels reflect blood glucose.