Researchers have created highly conductive and durable silver nanowire ink that can be used to print durable electronic circuits on paper.

The technology is being touted by the researchers at the University of Tennessee as a breakthrough in making inexpensive, flexible, disposable electronic sensors that can be used for a wide range of medical purposes, as well as an "electronic skin" that can act as touchpad sensors on robotics.

Robots with electronic skin could, for example, go to a patient's bedside and through touch, determine vital signs and other diagnostic data, or a patient could use the skin as a touch pad to alert medical staff or find information.

University of Tennessee A paper-printed circuit is dmonstrated.

The research, published in the journal ACS Applied Materials & Interfaces, highlights the low cost with which the foldable printed circuits can be made.

The system for printing circuit patterns with the silver ink takes only a few minutes, and the resulting electronics are then hardened with a pulsing light. The resulting nanowires have a diameter of 100 nanometers and a length of a few micrometers.

The paper-based circuits can be folded and unfolded up to 15 times, or rolled up 5,000 times without a failure in the device's operation.

Anming Hu, an assistant professor and lead researcher on the project, said the research found that nano wires are critical to developing a highly flexible device on paper substrates; that photonic sintering with flashing light is better for facile processing than thermal sintering; and that ink printing is a practical way to create sensors.

Previous printable devices on flexible substrates, Hu said, couldn't stand significant deformation, which resulted in the surface metallic electrodes peeling off the material.

"It is found that silver nanowires are highly adhesive with paper fibers," Hu said.

Printable circuits aren't unique. Georgia Tech, the University of Tokyo and Microsoft Research created them last year, and a company called Bare Conductive has also been selling a graphite ink that can be used to print circuits.

But, the University of Tennessee's technology is more flexible and durable than predecessors, Hu said.

The scientists have already used the printing process to create point-of-care diagnostic tests and portable DNA detectors that typically require more sophisticated and expensive manufacturing processes.

Hu said his team wanted to make a sensor that could be created on demand and respond to touch or to specific molecules, such as glucose.

"We are working [toward] printable biosensors and energy devices with paper-based or polymer-based substrates. We hope that we integrate micro-sized batteries into a sensor and form a standalone microsystem," Hu said.

The researchers are now working on a multi-nozzle printer that can lay down two or more nano inks, such as copper and silver.

"Another challenge is to further improve the printing resolution from tens of micrometers to micro and sub micrometer [sizes]," Hu said. "To address these two challenges will allow us to print 3D hybrid devices with different inks and a higher integration."