The skin is the biggest organ of human, and it is responsible for many important tasks, including physical protection, perspiration, and perception. American scientists have recently researched and developed a wearable device of “electronic skin” that is not only equipped with sensors and wireless communication, but is also capable of detecting body temperature, blood sugar, and heart rhythm. This tiny device also eliminates the concern on battery time, as it is powered by sweat.

Battery capacity and dimension are the two major factors in the development of wearable devices as long battery life and suitable dimension will both impact the level of sales, for which the problem might have been solved by Caltech, where the research team uses the biological fuel cell in the electronic skin to convert the lactic acid within human sweat into the source of power.

At first glance the electronic skin appears to be merely a rubber patch on the skin, what is hidden inside is actually a biological fuel cell that is made of carbon nanotubes, where enzyme is decomposed through platinum, cobalt catalyst, and lactate, and lactic acid within the human sweat is converted into electricity, then finally combines with oxygen to produce water and pyruvic acid, which is the same process as general metabolism.

However, the research did not indicate the degree of power generation, and only expressed that the device generates a few MW for every square meter, though the research team also added that the electronic skin can provide sufficient electricity for the sensors to monitor heart rates, body temperature, and blood sugar, for which the data can be transmitted through Bluetooth at the same time.

Wei Gao, assistant professor of the Caltech Bioengineering Department, expressed that the primary transmission technology used for electronic skins in the past was near-field communication (NFC), which is capable of data transmission only within a proximity of a few centimeters. As for Bluetooth, despite its need for stronger power, it has a more extensive connection with actual medical and robot application, which makes a product even more appealing.

Researchers also pointed out that the electronic skin can operate for days with the help of human sweat. Looking ahead to the future, the research team believes that this type of electronic skin not only functions as a wearable biological sensor, but also serves as a component in the field of human-machine interface, which further optimizes and designs the next generation of prosthetics through the collection of various vital signs and molecular signals.

Electronic skin is indeed a method to infuse “feeling” to prosthetics. In March 2017, the Bendable Electronics and Sensing Technologies (BEST) team at University of Glasgow developed a solar electronic skin using graphene, which imitates the touch response of human skin through its internal sensors, then in 2018 the team created a flexible 3D foam layer using graphene and silver, and developed a super capacitance that can be used on wearable devices, which allows future wearable health detection systems to charge through sunlight.

 (Cover photo source: Caltech)