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A simple way to print circuits on a wide range of flexible substrates using an inkjet printer has eluded materials scientists. Until now.

One of the dreams of makers the world over is to be able to print electronic circuits on more or less any surface using a desktop printer. The great promise is the possibility of having RFID circuits printed on plastic or paper packaging, LED arrays on wallpaper and even transparent circuits on glass. Or simply to rapidly prototype circuits when designing new products.

There are no shortage of conducting inks that aim to do this but they all have drawbacks of various kinds. For example, many inks have low or difficult-to-control conductivity or need to be heated to temperatures of up to 400 degrees C after they have been printed thereby limiting the materials on which they can be printed. The result is that the ability to print circuits routinely on flexible materials such as paper or plastic has remained largely a dream.

Until now. Today, Jing Liu and pals at the Technical Institute of Physics and Chemistry in Beijing say they’ve worked out how to print electronic circuits on a wide range of materials using an inkjet printer filled with liquid metal.  And they’ve demonstrated the technique on paper, plastic, glass, rubber, cotton cloth and even an ordinary leaf.

The new technique is straightforward. The magic sauce is a liquid metal: an alloy of gallium and indium which is liquid at room temperature. They simply pump it through an inkjet printer to create a fine spray of liquid metal droplets that settle onto the substrate.

The droplets rapidly oxidise as the travel through the air and this oxide forms a surface layer on each drop that prevents further oxidisation. That’s handy because the liquid metal itself does not easily adhere to the substrates. But the metal oxides do and this is the reason, say Jing and co, that the circuits adhere so well to a wide range of surfaces.

They also say it’s relatively easy to create almsot any circuit pattern, either by moving the printer head over the substrate or by using a mask.  And they’ve demonstrated this by printing conducting circuits on cotton cloth, plastic, glass and paper as well as on a leaf.

That looks to be a useful development. The ability to print circuits in magazines or on t-shirts will surely attract much interest. And being able to test circuit designs by printing them out using a desktop printer will be invaluable to many makers.

Perhaps most exciting of all is that the technology behind all this is cheap and simple: there’s no reason why it couldn’t be pushed to market very rapidly. And that raises the prospect of being able to print prototype circuits in small businesses and even at home.

Could it be that liquid metal printers could bring about the same kind of revolution in home-built electronics that 3D printers triggered with material design? And might it be possible to combine them into a single machine that prints functional electronic devices?