Electronic tattoo monitors vital functions

Scientists working with John Rogers at the University of Illinois in Urbana have developed an electronic foil that adheres like an adhesive tattoo and stretches on the skin without affecting its wearer. The device - filled with almost any components - could be used for medical diagnostics, but also as a human-machine interface.

The team designed a circuit of tiny, serpentine wires as well as membranes. In this design, Rogers and his colleagues applied sensors, light-emitting diodes, transistors, capacitors, wireless antennas and solar cells for power supply, among other things, to an ultra-thin, soft and gas-permeable rubber layer. The specially shaped electronics could now be bent, twisted and stretched without losing functionality.

In total, the electronic "skin" weighs barely 0.1 grams and is less than 40 micrometers thick, making it thinner than a human hair. To ensure that the filigree construct keeps its shape, the researchers first reinforce it with a similarly thin film made of water-soluble polymer. In this way, the circuits can be applied to the human skin with water like a temporary tattoo. After that, the electronic patch sticks to the skin solely through intermolecular forces of attraction (Van der Waals forces).

According to Rogers' team, the electronic tattoo would be particularly suitable for biomedical applications, such as monitoring heart, muscle or brain activity. Unlike conventional electrodes, it does not require conductive gel, glue or bulky accessories such as cables and batteries. That makes treatment much more comfortable for patients, he said. In the first tests, the electronic foil adhered to the arm, neck, forehead, cheek and chin for up to 24 hours under ideal conditions - without irritating the skin. The results also matched those of conventional electrodes that simultaneously recorded data on the same body sites.

Moreover, when the researchers attached the ultra-thin sensors to a subject's neck, they found that the signals elicited by moving muscles were sufficient to distinguish simple words. With a hit rate of more than 90 percent, even a computer game could be controlled in this way, report the scientists around Rogers, demonstrating the potential for a human-computer interface. Beyond that, however, many other applications are conceivable with their technology.