As a kid, temporary tattoos might have been just a way to show your love of Bugs Bunny, but soon we could be wearing them as gaudy touchpads or to measure the levels of glucose or alcohol in our blood. A team of researchers from Waseda University in Japan has developed a simple new method to manufacture these electronic tattoos, printing the conductive "wiring" with a basic inkjet printer and joining components without the need for solder.

The team's electronic tattoos are made of ultra-thin sheets of a flexible elastomeric film measuring just 750 nanometers thick. To form the wiring, conductive silver lines were inkjet-printed onto one of these nanosheets, in the same way that circuits have been printed onto film, fabric or paper in the past. Components like chip resistors and LEDs can then be placed along the wires where needed, before a second layer of the film is placed over the top, sandwiching the circuitry in between.

Made to be self-adhesive, the two layers of the new film not only stick to each other, but also to the skin they're placed onto, without the need for any tapes, glues, chemical bonding or, in the case of the electronic components, soldering. Aided by the lack of solder, the film can stretch over the skin easily without breaking the circuits, and the researchers report their nanosheets are 50 times more flexible than similar materials.

Since the circuitry can be printed on a home inkjet printer, and the whole process can be done at room temperature without the need for a sterile "clean room," the devices are easy and cheap to produce. The researchers tested their system on a patch of artificial skin, and it was able to function for a few days at a time – although it might not last that long when it's worn by a person going about their regular day.

The potential applications for electronic tattoo technology is pretty wide, and already we've seen them put to work monitoring muscle movements, tracking vital signs during exercise, harvesting sweat for energy or acting as a 5G wireless hotspot. Making those kinds of devices easier to manufacture is the goal, and the next step for the researchers.

The study was published in the Journal of Materials Chemistry C.