Caltech wants to take this a step deeper to learn more about humans from their skin, as such Wei Gai has developed an electronic skin that is to be applied directly on top of real skin. According to the paper published in Science Robotics this e-skin is made from soft flexible rubber and is embedded with sensors to monitor information such as heart rate, body temperature, blood sugar levels, as well as metabolic byproducts that are indicators of health and the nerve signals that control muscles. Once more, the e-skin can do all this without the need of assistance from a battery for power, this device is able to run solely on biofuel cells that are powered by one of the body’s own waste products.
“One of the major challenges with these kinds of wearable devices is on the power side,” says 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.”
Human sweat contains high levels of lactate which is a chemical compound that is generated as a byproduct of normal metabolic processes, especially during exercise by the muscles. The e-skin has built in fuel cells that absorb lactate and combine it with oxygen to generate water and pyruvate; as they operate the cells generate enough electricity to power sensors as well as a Bluetooth device that is similar to one that would connect to a mobile device and this allows the e-skin to transmit readings from its sensors wirelessly.
“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 e-skin will have a variety of sensors embedded in them eventually, so it can be used for multiple purposes. The biofuel cells are made from carbon nanotubes that are impregnated with a platinum and cobalt catalyst with a composite mesh that holds an enzyme which breaks down lactate to help it last a long time with high power intensity and minimal degradation; meaning the cells can generate continuous stable power output over multiple days in human sweat.
“We want this system to be a platform,” he says. “In addition to being a wearable biosensor, this can be a human–machine interface. The vital signs and molecular information collected using this platform could be used to design and optimize next-generation prosthetics.“
