“Breathability is something desirable for an on-skin sensor since it allows both sweat and air to move freely into and out of skin, which prevents irritation and inflammation,” explains team member and lead author of the study Akihito Miyamoto of the University of Tokyo and the Japan Science and Technology Agency. “In collaboration with dermatologists, we were able to show that our on-skin patch did not cause any skin problems for 20 subjects over a one-week period.”

The researchers, led by Takao Someya, made their new sensors from a mesh structure containing biocompatible polyvinyl alcohol (PVA) nanofibres, 300–500 nm in diameter, electrospun into a sheet. These sheets are covered with a 70–100 nm layer of gold evaporated onto their surface. To laminate the sensors onto skin, Someya and colleagues used water to dissolve the PVA. “The result is a gold nanomesh that adheres well to skin,” says Miyamoto.

“This nanomesh is high permeable to gases and allows skin to breath naturally,” he tells nanotechweb.org. “It does not block sweat glands and is stretchable so does not cause discomfort if fixed onto the skin for a long period of time.”

Skin patch tests

Skin patch tests by the researchers revealed that the new sensors caused significantly less inflammation than conventional devices based on plastic and elastomer films, which, although conform well to skin, have a lower gas permeability. The mesh conductors can also be attached to irregular skin surfaces, such a finger tips and continue working even when the skin is stretched or folded thousands of times. Importantly, they can be connected to a wireless system that can be used to record tests like electromyograms (EMGs) with a quality that is as high as that obtained using standard gel electrodes.

“One major application for these devices is the long-term monitoring of patient vital signals under normal, everyday conditions (which means even at home),” says Miyamoto. “Another potential area is the continuous, precise monitoring of athletes’ physiological signals (temperature, for example) without impeding their performance.” The sensors are described in Nature Nanotechnology doi:10.1038/nnano.2017.125.

John Rogers of the Center for Bio-Integrated Electronics at Northwestern University in Illinois, who was not involved in this work, suggests that it might be interesting to explore similar concepts involving different materials, such as semiconductors and dielectrics, with the goal of establishing a complete portfolio of nanomesh materials for active skin-integrated electronics. “Here, one could envision interfaces not only with the surface of the skin, but perhaps internal organs as well,” he writes in a related Nature Nanotechnology News & Views article.

Someya and colleagues say that they are now busy increasing the operational time of their sensor so that it can be employed in long-term health monitoring applications. “After this, we plan on expanding the types of bio-signals we can detect,” reveals Miyamoto.