New e-skin can better withstand sweat thanks to Japanese paper-cutting technique

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The quest to track health information without drawing blood has inspired wearables like Fitbit and Apple Watch, but it's also pushing engineers to develop thin sensors that adhere to the skin like a bandage. Some of these devices can struggle to stay sticky, especially when faced with profuse sweating, but a group of engineers recently developed a new type of electronic skin, or e-skin, that can track vital signs and other information even during intense exercise.

Today's most popular wearables are great for everyday consumers' casual use. But they are thick and rigid, and, therefore, they cannot conform to the curvature of the skin. This has led to less accurate measurement of the vitals, said Hanwool Yeon, a materials engineer at MIT and one of the lead authors of the paper published in the journal Science Advances in June. With its thinness and clinginess, e-skin can close that gap and improve the quality of the measurements of heart rate, body temperature and more.

But even the high-tech e-skins have a downside: Many of them aren't sweat proof. A person wearing the e-skin might be able to get away with light sweating, as the sweat would vaporize quickly, but the readings from the sensors would start to become imprecise if the person starts sweating profusely. Even worse, the e-skin might detach from the skin or cause irritation.

To allow the sweat to pass through, Yeon and his co-workers turned to one of the oldest tricks in the book: kirigami, a Japanese paper-cutting technique. First, the team punched holes on the e-skin to match the size of sweat pores and the distance between them. Then, inspired by kirigami, the team cut away even more material between two holes in an alternating pattern. The resulting pattern looks like a crisscross of dumbbells, which, when tested, could tolerate bending and stretching more than the conventional e-skin with simple holes.

The team then assessed if the new e-skin could indeed withstand profuse sweating. When a test subject with the e-skins, new and conventional, attached to his forehead ate spicy food, the conventional e-skin started accumulating sweat underneath the surface while the new one showed no change. And when tested for a two-week period, which included exercises at the gym, the new e-skin stayed adhered the entire time. It also measured the hydration level and the temperature change more precisely than the conventional one, and the human skin showed no sign of irritation.

The paper made good progress toward solving one of the primary issues with e-skins, said Ravinder Dahiya, an electronics engineer at the University of Glasgow in Scotland, who was not involved in the study. He wondered, though, how the e-skin with a long life span would be used.

He said most e-skins are developed with medical applications in mind rather than everyday consumer use, and it's unlikely that patients would wear the e-skin for a few weeks straight. To that, Yeon said Amorepacific, a South Korean cosmetics conglomerate that funded his research, intends to use this technology to test the effectiveness of their skin care products.

Yeon said it took many tries to perfect the design -- perhaps a bit more than it should have because he and his team were relatively new to the field. "But because we were not a traditional e-skin laboratory," Yeon said, "we were able to look at the field with a fresh set of eyes, coming up with fresh ideas."

Inside Science Editor's Note: The interview with Hanwool Yeon was conducted in Korean, and the quote was translated into English by the author.

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