Wearable Patch Monitors Physical Activity

The patch was screen printed onto a thin, flexible polyester sheet. An electrode to sense lactate was printed in the center of the patch, with two isolated EKG electrodes bracketing it to the left and the right.

The lactate sensor works by applying a small voltage and measuring electric current across its electrodes; since this current can pass through sweat, which is slightly conductive, it can potentially disrupt EKG measurements. The researchers therefore added a printed layer of soft water-repelling silicone rubber to the patch, and configured it to keep the sweat away from the EKG electrodes, but not the lactate sensor.

The researchers also went through several iterations of the patch to find the best distance between electrodes in order to avoid interference, and found that a distance of four centimeters between the EKG electrodes was optimal. The sensors were then connected to a small custom printed circuit board equipped with a microcontroller and a Bluetooth Low Energy chip, which wirelessly transmits the data gathered by the patch to a smartphone, smart watch, or laptop computer.

The patch was tested on three male subjects, who wore the device on their chest while doing 15-30 minutes of intense activity. The data collected by the EKG electrodes closely matched that collected by a commercial wristband heart rate monitor. The researchers now intend to adding sensors for other chemical markers, such as magnesium and potassium, as well as other vital signs. The study describing the Chem-Phys patch was published in the May 23, 2016, issue of Nature Communications.

“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,” said senior author professor of electrical engineering Patrick Mercier, of the UCSD. “This research represents an important first step to show this may be possible.”

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University of California, San Diego