By Matthew Stock

A skin-worn sensor that turns the human body into a touch sensitive surface for controlling mobile devices has been developed by scientists in Germany. iSkin is made from biocompatible silicone rubber with pressure-sensitive sensors that are stuck to the skin of the users, allowing them to use their own body to control mobile devices.

Developed by scientists at the Max Planck Institute for Informatics and Saarland University, the experimental system has been produced in different shapes and sizes to suit various locations on the body, such as the finger, forearm and even behind the ear-lobe. The sensor is capable of detecting touch input pressure even when being stretched or bent. With the current prototypes; wearers can answer incoming calls, play music and adjust volume. A roll-up keyboard for use with a smart watch has also been designed.

iSkin's thin, soft and flexible design presents new possibilities for mobile interaction that have not been possible with existing hardware, according to co-developer Martin Weigel.

"Current electronics are mostly using rigid components which are very uncomfortable to wear on the body and are limiting the locations to, for example, the wrist or on the head to be worn. But our sensor is a flexible and stretchable sensor, so it can cover many locations. For example, even the backside of the ear or the forearm. So, we have a much larger input space than current electronics allow for," he said.

The prototype is based on advances in so-called 'electronic skin' that allow robots to better sense their environment, as well as more human-like prostheses that can sense contact, pressure and temperature. iSkin's makers saw this as an ideal platform for on-body interaction for mobile computing.

"(The) technology is initially coming from robotics where it's used to give robots kind of a feeling similar to the human body, to human skin. However, we are the first to look into how we can use it on the body to control mobile devices; so as a kind of second-skin which nicely conforms to your body," said Weigel.

The base material is polydimethylsiloxane (PDMS), an easy-to-process silicone-based organic polymer. Conductive carbon black powder is added to the liquid silicone before it is spread flat by a thin-film applicator. After creating the tattoo-like designs on a computer, a laser-cutter traces out the design which makes up the sensor. This is then sandwiched between two clear sheets of silicone.

"The sensor is made out of bio-compatible silicone and carbon-doped silicone. So there are carbon particles inside the silicone which make it conductive so we can use it for electronics," explained Weigel.

The stickers are attached to the body using a medical-grade adhesive that can be easily peeled off after use without hurting the skin.

The current prototypes are wired to a computer, although the technology could evolve to use integrated microchips. Weigel also hopes that it could one day be possible to incorporate an energy-harvesting system that would power iSkin via the wear's body.

While they have no immediate plans to develop this iSkin prototype further, the team hope it will inspire future research on electronic skin for human-computer interaction.