Temporary tattoos feature light-emitting technology

Scientists at University College London (UCL) and the Italian Institute of Technology (IIT) have created a temporary tattoo with light-emitting technology used in TV and smartphone screens, paving the way for a new type of ‘smart tattoo’ with a range of potential uses. Their work has been published in the journal Advanced Electronic Materials.

The technology, which uses organic light-emitting diodes (OLEDs), is applied in the same way as water transfer tattoos. That is, the OLEDs are fabricated onto temporary tattoo paper and transferred to a new surface by being pressed onto it and dabbed with water. Among the advantages of OLEDs are that they can be used on flexible, bendy surfaces, and that they can be made from liquid solvents. This means they are printable.

The OLED device the researchers developed is 2.3 µm thick in total — about a third of the length of a single red blood cell. It consists of an electroluminescent polymer (a polymer that emits light when an electric field is applied) in between electrodes. The light-emitting polymer is 76 nm thick and was created using a technique called spin coating, where the polymer is applied to a substrate which is spun at high speed, producing an extremely thin and even layer. An insulating layer is placed in between the electrodes and the commercial tattoo paper.

“At the Italian Institute of Technology we have previously pioneered electrodes that we have tattooed onto people’s skin that can be used to perform diagnostic tests such as electrocardiograms,” noted ITT researcher Dr Virgilio Mattoli, senior author on the paper. “The advantage of this technology is that it is low cost, easy to apply and use, and washes off easily with soap and water.”

Once they had built the technology, the team applied the tattooable OLEDs, which emitted green light, onto a pane of glass, a plastic bottle, an orange and paper packaging. The researchers say it could be combined with other tattoo electronics to, for instance, emit light when we need to get out of the sun to avoid sunburn. OLEDs could also be tattooed on packaging or fruit to signal when a product has passed its expiry date, or used for fashion.

“The tattooable OLEDs that we have demonstrated for the first time can be made at scale and very cheaply,” said UCL’s Professor Franco Cacialli, senior author on the paper. “They can be combined with other forms of tattoo electronics for a very wide range of possible uses. These could be for fashion — for instance, providing glowing tattoos and light-emitting fingernails. In sports, they could be combined with a sweat sensor to signal dehydration.

“In health care they could emit light when there is a change in a patient’s condition — or, if the tattoo was turned the other way into the skin, they could potentially be combined with light-sensitive therapies to target cancer cells, for instance.

“Our proof-of-concept study is the first step. 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.”

Images credit: Barsotti, Italian Institute of Technology.

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