An electronic tattoo for part time cyborgs

For some researchers, the Internet of Things only seems complete when humans are also networked with it as a kind of smart element. Human Computer Interaction (HCI), as described by Peter Samulat in "Industry 4.0 or the Industrial Internet of Things," has long been concerned with the interaction between users and (mobile) end devices. In the past, however, so-called wearables were mainly responsible for monitoring and information. Now, however, computer scientists at Saar University and the U.S. company Google want to open a new chapter with electronic tattoos.

They are to serve as a touch-sensitive input surface for mobile devices. For this purpose, they are to be attached to prominent parts of the body. With this idea, computer scientists from Saar University and the US company Google want to make everyday life easier. Mobile devices could be intuitively controlled by touching, squeezing or pulling alone. The advantage over conventional controls is that the user's own body parts are usually so familiar that the individual controls can even be operated with eyes closed. In addition, they enable a completely new type of interaction and also provide natural operating instructions.

Precisely placing electronics on the skin

Initial tests by the Saarbrücken computer scientists were successful. Together with researchers from the U.S. Carnegie Mellon University, they had developed "iSkin", touch-sensitive stickers, for the skin from flexible silicone and conductive electrosensors. When applied to the forearm and connected to the smartphone, the sticker could be pressed to answer a call or adjust the volume. According to the researchers, this method "was only suitable for certain parts of the body, however, because it required a relatively flat surface. In addition, the stickers were comparatively large".

Martin Weigel, a doctoral student with Jürgen Steimle, professor of human-computer interaction at Saarland University, didn't let that stop him, however. "We want to go to parts of the body where no interaction was possible before. But placing electronics precisely on the skin and then in such a way that it adapts to bone structures like the knuckles or microstructures like wrinkles is very complicated."

A part-time cyborg in 60 minutes

However, it was also clear to the researchers: it would be worth it for the users. "If you have to press the first knuckle of your left hand, you intuitively know where it is. The same goes for the inside of your index finger," Weigel continues. Together with Alex Olwal from Google, Weigel, his colleague Aditya Shekhar Nittala and Professor Jürgen Steimle tinkered with the right combination of conductive ink and printing process to print the conductive tracks and electrodes as compactly and thinly as possible on the temporary tattoo paper.

After quite a few tests, the breakthrough finally came. A conductive plastic called Pedot:Pss was the solution. With it, the researchers were able to print the tattoo even thinner than a hair, ensuring that it would both fit over the knuckles and capture wrinkles. At the same time, it should also be flexible enough to withstand compression and stretching. The researchers call the electronic tattoos SkinMarks. They are transferred to the skin with water and come off after a few days. In the lab, the scientists need only 30 to 60 minutes to print such a tattoo. "It can be done even faster. We are convinced that in the future everyone will be able to make their own e-tattoo in less than a minute on a standard printer," explains Steimle.