The word "print" does not mean what it used to. For centuries, it referred to the act of transferring ink on to surfaces to create books and textiles.
In more recent years, 3D technology has shown it can print anything from toys to body parts to entire buildings. Now, thanks to new advances in ink, materials and printer technology, scientists are discovering ways of printing fully functional electronic devices.
As part of a recent experiment by Purdue University in the US, engineers created something astonishing and slightly spooky: a working keypad and controller, printed directly on to a sheet of paper. They were able to use that piece of paper to type letters on to a screen and swipe a finger across a printed volume control. This demonstration of so-called papertronics is an astonishing party trick (paper iPad, anyone?) but it's also part of an exciting new wave of flexible computing, both literally and figuratively.
What ink is being used to make this kind of magic happen? Evidently it’s not found in your standard cart. Chemicals, nano particles and organic molecules can be combined in various ways to create all kinds of possibilities. Electroluminescent ink can enable displays on objects of all shapes and sizes. Solar cells, lighting elements, sensors and detectors can be printed – and not only on to standard electronic substrates such as film, but on to a whole range of materials. Better still, it can be done in small quantities on demand, or potentially scaled up to mass production.
“There is a lot of work and progress towards printing electronics in a high-throughput, roll-to-roll manufacturing style, very similar to newspaper printing,” says Aaron Franklin, a professor of electrical and computer engineering at Duke University in the US. “And then there is a more inkjet-style printing to a given surface, which is much more customisable.”
Franklin says this could revolutionise the process of prototyping. In time, the idea of printed electronics could end up working exactly as you might expect: load material into a printer, upload a circuit pattern, push a "print" button, and watch a fully functional electronic device emerge.
“We have seen how 3D printing of physical structures has taken over the world in educational and manufacturing systems,” he says. “If we could do the same with a multifunctional printer for electronics, in classrooms and makerspaces, that could create a lot of really exciting opportunities.”
Those opportunities are only just starting to be explored. Ramses Martinez, the professor overseeing the experiment with papertronics at Purdue, outlined how it could be used to create smart food packaging, or to add fingerprint sensors to parcels to allow people to identify themselves as the recipient.
But it is not only paper that can be transformed by these new processes. Until recently, the printing of electronics has had to be combined with other non-printing processes, such as oven-baking or chemical baths. Franklin's work is striving to print circuitry to any material, including sensitive surfaces, with no such post-processing needed. Perhaps his most notable achievement has been to print directly on to human skin. Take a finger, print it with two small, metallic-looking conductive traces. Add a light at one end, and a voltage at the other. When the circuit completes, a light glows – the human body and electronics, working as one.
"This could facilitate biomedical monitoring capabilities, and I think it has some very realistic possibilities in the coming three to five years," he says. "Some of the custom electronic devices that are currently integrated into wearables could have tremendous capabilities if they were printed directly on to the skin."
One of the extraordinary aspects of the Purdue papertronics experiment is that the device is self-powered, as it generates electricity from contact with the finger of the person operating it. Studies done at Binghamton University in New York have gone even further, with pieces of office paper being transformed into batteries by using bacteria – all for the cost of a few cents. But this does not only present a cost advantage – these self-powered devices are made of biodegradable material. This innovation may help to solve one of the most pressing problems faced by the tech industry: the massive amount of toxic e-waste generated by obsolete gadgets.
“Papertronics can be particularly useful in remote areas with limited resources because they are powered by bacteria that can inhabit even the most extreme of conditions,” says Professor Seokheun Choi, who oversaw the work at Binghamton. “They don’t need a well-established power grid, either. In addition, new batteries can be created from recycled paper and they are fairly straightforward to make.”
This new work, particularly with printed nanomaterials, brings new kinds of functionality – way beyond a simple paper controller – that we cannot yet imagine, Franklin says.
"If we are willing to really drill down into harnessing this technology, we could also do incredible things."