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Sensor Patch Tracks Chemical, Physical Vital Signs

Chem-Phys patch

Chem-Phys patch demonstrated by co-author Amay Bandodkar (University of California, San Diego)

24 May 2016. Engineers at University of California in San Diego developed a patch device worn on the skin with sensors that measure chemical indicators as well as physical vital signs. The UC-San Diego team that designed the device published its findings in yesterday’s issue of the journal Nature Communications.

The researchers led by nanoengineering professor Joseph Wang and electrical engineering professor Patrick Mercier are looking for ways of incorporating real-time measurement of chemical biomarkers in the body with physical vital indicators already captured in wearable health tracking devices. Wang is director of UC-San Diego’s Center for Wearable Sensors that collaborates with industry partners and already spun-off a company to commercialize headsets with sensors capturing brain and cardiovascular activity.

Current technology, say the authors, does a good job at capturing physical vital signs, including blood pressure, heart and respiration rates, and brain activity, in real time and with compact, wearable devices. Missing from these devices, however, are sensors that also measure changes in body chemistry, such as electrolytes and metabolites in sweat that offer a trove of health indicators, such as dehydration before muscles start cramping or medications in the blood. Most of these chemical indicators require taking separate samples and analyzing them in the lab.

To met this need, Wang, Mercier, and colleagues designed the Chem-Phys patch that attaches to the skin, and measures both physical and chemical biomarkers. The device needed to be fabricated on flexible materials that can be applied to the skin and worn comfortably. Yet the multiple sensors also must be separated on the patch so their signals to not interfere with each other. Plus the device must be self-contained, and still be small enough to be unobtrusive to wearers. The authors report many trial-and-error attempts to find the optimal size and configuration for their patch.

The prototype device developed for the study has an electrocardiogram sensor measuring electrical activity in the heart, and a sensor measuring lactate levels in sweat, an indicator of energy metabolism when exercising. The sensors are screen-printed, with controller and wireless transmission circuits, on layers of thin polymer, and a layer of silicon rubber keeping the electrocardiogram sensor dry. The upper chest near the base of the sternum was the location selected for wearing the device, which would capture heart activity as well as generate perspiration, but also be relatively immobile during physical activity.

In a proof-of-concept study, the UC-San Diego team tested the Chem-Phys prototype with 3 volunteers who wore the device for 15 to 30 minutes of exercise, at times intense, on a stationary bike. Results show electrocardiogram measures on the Chem-Phys patch were similar to readings on commercial wristband monitors worn by two of the participants. Likewise, lactate measures on the patch were comparable to readings taken in similar exercise sessions using a specialized lactate measuring device.

The authors say the tests show the feasibility of a wearable device capturing both physical measures and chemical biomarkers, with the next steps aimed at adding more functions to the patch. A university statement says Wang and Mercier are already receiving inquiries from Olympic athletes.

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