The range of potential skin patch applications in health monitoring is astounding. We’ve covered various skin patch technology developments for several years. In 2014, Alfred Poor wrote about collaboration at Northwestern University and the University of Illinois developing a skin patch to monitor blood flow. In 2016, I wrote about work by researchers at the University of Illinois and Hanyang University in Seoul who created a stretchable, battery-free skin patch with biometric sensor payloads that got power via near field communication (NFC). The multitude of academic and private sector groups developing wearable patch technology makes it pretty clear this wearable category will be a key healthcare platform.

Researchers at Caltech recently announced an electronic skin patch powered by sweat. The patch is made from soft flexible rubber. The Caltech scientists designed the e-skin to carry embedded biometric sensors that monitor health indicators such as heart rate, body temperature, and levels of blood sugar and other metabolic byproducts. The sweat-powered patch can also track nerve signals for functions such as muscle control.

According to Caltech assistant professor Wei Gao, human sweat contains high levels of lactate. Fuel cells in the e-skin absorb and combine the lactate with oxygen from the atmosphere to generate water and pyruvate. This chemical process produces sufficient electrical energy to power the biosensors and a low-energy Bluetooth transmitter that sends off the sensor data. Bluetooth uses more power than near-field communications (NFC), but operates over longer distances. The Caltech biofuel cells can generate continuous power for several days. The fuel cells are made from carbon nanotubes impregnated with a platinum /cobalt catalyst and a composite that holds an enzyme that breaks down the sweat lactate.

The next steps at Caltech include developing a variety of sensors to embed in the e-skin. Gao refers to the e-skin as a platform that can also serve as a human-machine interface to collect data for multiple future applications such as controlling next-generation powered prosthetics. The Caltech researchers published a paper in Science Robotics that describes the e-skin technology.