Everything that we feel comes to us through our skin. All tactile sensations — be it pain, pleasure, pressure, excitement, heat, or cold — are experienced via nerve endings present in our skin. How our body reacts to these sensations are visible in different forms, such as through sweating, goosebumps, and blushing.
However, a researcher at Caltech wanted to use these indicators in a productive way. Our skin can also tell the outside world a great deal about us, including our health.
To this end, Wei Gao, an assistant professor in the Andrew and Peggy Cheng department of Medical Engineering developed an electric skin that is applied on top of natural skin directly.
Also known as the “e-skin,” it’s constituted by flexible, soft rubber, and embedded sensors that monitor vital health indicators, such as body temperature, blood sugar level, heart rate, metabolic byproducts, and nerve signals. It does so without the need for a battery, as it runs solely on biofuel cells powered by one of the body’s own waste products.
Human sweat contains high levels of chemical lactate, a normal metabolic byproduct. It is generated in higher quantities by muscles during exercise. The biofuel cells present in the e-skin absorb that lactate and fuse it with atmospheric oxygen to produce pyruvate and water.
While working, these cells generate sufficient electricity to power sensors and an attached Bluetooth device.
The e-skin performs all of these functions without any battery as it is powered by biofuel cells running on our body’s waste products.
“One of the major challenges with these kinds of wearable devices is on the power side,” said 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 wanted to know if we can get sufficient energy from sweat to power the wearables and the answer is yes.”
The readings from the e-skin are transmitted wirelessly from its sensors to other devices.
“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,” explains Gao. “Bluetooth communication consumes higher power but is a more attractive approach with extended connectivity for practical medical and robotic applications.”
These biofuel cells were created from carbon nanotubes impregnated with a composite mesh holding an enzyme that breaks down lactate and a platinum/cobalt catalyst. They are capable of generating long-lasting, stable power output for many days using human sweat.
Gao is now working on the development of various sensors that can be embedded in the e-skin to increase its areas of application.