For a kid growing up in the ’90s, few things were better than running around in light-up sneakers that emitted a rhythmic glow with every footfall, while brandishing arms covered in temporary tattoos of favorite superheroes and cartoon characters. Fortunately, or unfortunately, vestiges of the ’90s are seeing a comeback: pastel windbreakers, Midwest emo, the fashion of the Seattle grunge scene, and … the temporary tattoo. As with any trend’s return, it’s a bit different the second time around. Enter the OLED temporary tattoo. Created through a collaboration between the University College London (UCL) and the Italian Institute of Technology (IIT), these glowing tattoos are applied in the same way as the water-transfer tattoos of yesteryear. The OLEDs are fabricated on tattoo paper and transferred to the skin or another surface by applying pressure to the back of the paper using a moist cloth. “The advantage of this technology is that it is low cost, easy to apply and use, and washes off easily with soap and water,” said Virgilio Mattoli, a researcher at IIT. An artistic rendering of a temporary tattoo featuring OLED technology. Courtesy of Pixabay/PublicDomainPictures. The OLED device isn’t bulky, partly because batteries are not included. Applied to the skin, it is only 2.3 μm thick, or about a third of the length of a red blood cell. The tattoo consists of an electroluminescent polymer sandwiched between electrodes, with an insulating layer between the electrodes and the paper. “Our proof-of-concept study is the first step,” said Franco Cacialli of UCL’s Department of Physics and Astronomy. “Future challenges will include encapsulating the OLEDs as much as possible to stop them from degrading quickly through contact with air, as well as integrating the device with a battery or supercapacitor.” OLED tattoo devices engineered by researchers at the Italian Institute of Technology. Courtesy of J. Barsotti/Italian Institute of Technology. The applications of the technology go beyond flourishing light-up fingernails or sporting an illuminated Bat-Signal on your arm. When combined with other tattoo electronics, the technology could emit light when an athlete is dehydrated, for example, or when a person has been exposed to too much sun. Or, it could potentially be combined with light-sensitive therapies to target cancer cells, for instance. The tattoos may also find use in packaging applications, where they could indicate that a perishable product has expired. And, of course the technology could be used to create an awesome Darth Vader tattoo, complete with glowing red lightsaber.