Engineers at the University of Washington, Seattle, claim to have fabricated the first 'biologically safe' contact lens inlaid with an electronic circuit and lights using microscale-manufacturing techniques.

They could be used to help the visually impaired or immerse video-gamers in a virtual world without restricting their range of motion. It could also project a vehicle's speed on to the windscreen or let people surf the web on a virtual display screen that only they could see.

'Looking through a completed lens you would see what the display is generating, superimposed on the world outside,' said Babak Parviz, a UW assistant professor of electrical engineering. 'This is a small step toward that goal, but I think it's extremely promising.'

The prototype device, tested on rabbits for up to 20 minutes with no ill effects, contains an electric circuit and red LEDs for a display. Building the lenses presented a dual challenge. Materials safe for use in the body, such as organic materials used in contact lenses, are delicate but manufacturing electrical circuits involves inorganic materials, high temperatures and toxic chemicals.

The researchers built the circuits from layers of metal a few nanometres thick, and constructed LEDs one third of a millimetre across. Electrical components were then placed on the flexible plastic substrate using a microfabrication technique called self-assembly.

The researchers hope to power the system using radio-frequency power and solar cells on the lens. Future improve-ments will add wireless communication to and from the lens.

The lenses were tested on rabbits for 20 minutes without ill effects