Electronic ink printed on posters and clothes

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Press ‘print’ for a light-emitting T-shirt ELECTRONIC displays that can be printed onto virtually any surface, including paper and fabric, are now a step closer, thanks to the creation of a light-emitting ink. A team at Dai Nippon Printing in Tokyo, Japan, has used a conventional screen-printing technique to deposit a thin layer of the ink, a luminescent gel, onto a surface. The gel consists of a ruthenium compound that emits a bright light when a voltage is applied to it, along with an electrolyte and silica nanoparticles. The electrolyte is a liquid salt, an ionic liquid which does not easily evaporate. It also prevents the ink from degrading, allowing displays to be printed onto surfaces without

the need for a protective coating. The ink will not washing off in water, making it suitable for use with textiles. Meanwhile, the silica nanoparticles blend with the lightemitting liquid to form a gel, allowing

“The ink holds a compound of ruthenium that emits a bright light when a voltage is applied across it” it to be printed onto different surfaces in discrete blobs, to form pixels. So far, the ink is only able to emit reddish hues when activated, although the researchers are working on other metal compounds that emit green and blue light, to eventually

give them the whole spectrum. The screen-printing technique allows only rough pixels to be generated, and so the images produced currently are fuzzy. The team is developing techniques to deposit the gel onto surfaces using an ink-jet printer, which would allow them to create smaller pixels and hence higher resolution. Ink-jet printing is also much cheaper than the lithographic techniques used to build digital displays. The company hopes to market the technology within five years and reckons it could be used to make light-emitting posters, clothing, flexible displays and new lighting applications. Michael Fitzpatrick ■

Glowing plaster to zap skin cancer THE humble sticking plaster is getting a high-tech upgrade. As well as simply patching up small cuts and grazes, plasters embedded with light-emitting diodes could be used to treat skin cancer in combination with light-sensitive drugs. Polymertronics, based in Banbury, UK, is developing the plasters, which are impregnated with a ser ies of organic light-emitting diodes (OLEDs). The light plasters are designed for use in photodynamic therapy, in which light-sensitive drugs are applied to the skin as a cream. When you shine red light on the area it activates the drugs, which destroy the tumour as they soak though the skin. At the moment, expensive lamps and lasers supply the red light for photodynamic therapy, and so the treatment can only be performed in hospitals. The light plasters could allow people with skin cancer to treat themselves at home, says Stephen Clemmet, CEO of Polymertronics. “We’re looking at developing a faster, cheaper, easier way to treat skin cancer.” OLEDs emit light when a voltage

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negotiate obstacles and one to demonstrate navigation in an open space. Minguez says the volunteers learned to use the wheelchair confidently in about 45 minutes. “The purpose of this work was to demonstrate the usability of the wheelchair,” he says. “All the subjects successfully solved all the navigation tasks and learned how to deal with the device in a similar way,” he says. It’s not the first wheelchair to be controlled by brain waves, but it is the only design to incorporate mind-control in a system capable of real-time navigation, route planning and collision avoidance, says Palaniappan Ramaswamy from the University of Essex in Colchester, UK. The prototype chair can so far only process two thought commands per minute. However, since the wheelchair navigates itself from point A to point B automatically, the command rate is less important than for systems where the user has to instruct the wheelchair at every step along the route. Automatic navigation also reduces the mental burden on the user, says Minguez. So far, volunteers have only been in the chair for a maximum of 2 hours. Ramaswamy points out that if people want to use the chair for longer, as they would in real life, you would need to find a new way to attach the electrodes to the scalp. The wet gel used now begins to dry up after a couple of hours, reducing the system’s performance. Minguez says he is aware of this problem, and other research teams are already working on alternative ways to attach the electrodes. The Zaragoza team is trying to increase the command response rate of their chair without reducing its accuracy. They also plan to give users more control by allowing them to issue commands to the wheelchair once it is moving towards its destination, allowing them to change course while on the go. ■

is applied to them. The company has developed a way to print square clusters of battery-powered red OLEDs, each 4 millimetres square, onto a strip of flexible plastic. The pattern of OLEDs exactly matches the shape of the patient’s tumour. The plaster is then placed over the tumour, allowing the red light to be targeted directly at the cancerous tissue. The company has shown that its OLEDs are able to destroy a range

of cancer cells in the laboratory, and will soon begin human trials of the light-emitting plasters. It presented the devices at a meeting on polymer electronics in London on 21 April, and hopes to launch them commercially within two years. Another UK company, Lumicure, a spin-off from the University of St Andrews, is working on a similar OLED-plaster, also for treating skin cancer. Jon Evans ■

2 May 2009 | NewScientist | 19