What if your skin could monitor your heart rate, body temperature, and blood sugar levels? Well, not your skin, exactly – more like an electronic skin on top of your skin. Called e-skin, this new wearable device was developed by Caltech's Wei Gao, who is an assistant professor in the Andrew and Peggy Cherng Department of Medical Engineering. The characteristic that makes this particular e-skin stand out is that, unlike other wearable devices, it is powered entirely by you and your sweat.
That’s right, sweat! Which means no need for a pesky battery that needs to be constantly recharged. Instead, it runs on biofuel cells powered by your body's own waste products. The authors of the study explain:
Existing electronic skin (e-skin) sensing platforms are equipped to monitor physical parameters using power from batteries or near-field communication. For e-skins to be applied in the next generation of robotics and medical devices, they must operate wirelessly and be self-powered. However, despite recent efforts to harvest energy from the human body, self-powered e-skin with the ability to perform biosensing with Bluetooth communication is limited because of the lack of a continuous energy source and limited power efficiency. Here, we report a flexible and fully perspiration-powered integrated electronic skin (PPES) for multiplexed metabolic sensing in situ.
"One of the major challenges with these kinds of wearable devices is on the power side," adds Gao. "Many people are using batteries, but that's not very sustainable. Some people have tried using solar cells or harvesting the power of human motion, but we wanted to know, 'Can we get sufficient energy from sweat to power the wearables?' and the answer is yes."
The engineers behind this project took advantage of the chemical properties of sweat to make e-skin pump. The e-skin’s fuel cells absorb sweat’s high levels of lactate, combining it with oxygen from the atmosphere to produce water and pyruvate. Through this process, the biofuel cells generate enough electricity to power sensors and a Bluetooth device. The energy generated from the biofuels monitored key metabolic analytes such as urea, NH4+, glucose, and pH, as well as skin temperature and muscle contraction during prolonged physical activities.
The Bluetooth feature is novel in such a device. "While near-field communication is a common approach for many battery-free e-skin systems, it could be only used for power transfer and data readout over a very short distance," Gao says. "Bluetooth communication consumes higher power but is a more attractive approach with extended connectivity for practical medical and robotic applications."
The paper describing the e-skin, titled, "Biofuel-powered soft electronic skin for multiplexed and wireless sensing," was published in Science Robotics. Gao says the hope is to develop the e-skin as a human-machine interface to collect molecular information in order to design and optimize next-generation prosthetics.