Chest-worn patch tracks both biochemical and electrical signals, sending the info to a smartphone.

Nancy Crotti

Engineers at the University of California, San Diego have developed the first flexible, wearable device capable of monitoring both biochemical and electric signals in the human body.

The Chem-Phys patch records electrocardiogram (EKG) signals and tracks levels of lactate, a biochemical that is a marker of physical effort, in real time, according to a statement from the university. It could be the closest thing yet to the mythical tricorder of Star Trek fame.

The device can be worn on the chest and communicates wirelessly with a smartphone, smart watch, or laptop. It could have a wide range of applications, from athletes monitoring their workouts to physicians monitoring patients with heart disease.

The patch includes a flexible suite of sensors and a small electronic board. The nanoengineering and electrical engineering researchers describe their work in the May 23 issue of Nature Communications.

The researchers' biggest challenge was making sure that signals from the two sensors didn't interfere with each other. They used screen printing to manufacture the patch on a thin, flexible polyester sheet that can be applied directly to the skin. An electrode to sense lactate was printed in the center of the patch, with two EKG electrodes bracketing it to the left and the right. Engineers went through several iterations of the patch to find the best distance between electrodes to avoid interference while gathering the best quality signal. They found that a distance of 4 cm (roughly 1.5 in.) between the EKG electrodes worked best.

Researchers also had to make sure the EKG sensors were isolated from the lactate sensor. The latter works by applying a small voltage and measuring electric current across its electrodes. This current can pass through sweat, which is slightly conductive, and can potentially disrupt EKG measurements. So they added a printed layer of soft, water-repelling silicone to the patch to keep the sweat away from the EKG electrodes.

The sensors were then connected to a small custom printed circuit board equipped with a microcontroller and a Bluetooth Low Energy chip, which wirelessly transmitted the data gathered by the patch to a smartphone or a computer.

The patch was tested on three male subjects, who wore the device near the base of their sternum while doing 15 to 30 minutes of intense activity on a stationary bike. Two of the subjects also wore a commercial wristband heart rate monitor. The data collected by EKG electrodes on the patch closely matched the data collected by the commercial wristband, according to the university. The data collected by the lactate biosensor closely followed data collected during increasing intensity workouts in other studies.

Plenty of wearables measure steps, heart rate, or both.  However, hardly any measure chemical signals such as lactate, according to electrical engineering professor Patrick Mercier.

"One of the overarching goals of our research is to build a wearable tricorder-like device that can measure simultaneously a whole suite of chemical, physical and electrophysiological signals continuously throughout the day," Mercier said in the statement. "This research represents an important first step to show this may be possible."

The device has implications for athletes as well as for cardiac patients. Mercier and nanoengineering professor Joseph Wang have been fielding inquiries from Olympic athletes about the technologies that the university's Center for Wearable Sensors produces. Wang's team worked on the patch's sensors and chemistry, while Mercier's team worked on the electronics and data transmission.

Next steps include improving the way the patch and the board are connected and adding sensors for other chemical markers, such as magnesium and potassium, as well as other vital signs. 

Nancy Crotti is a contributor to Qmed.

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