In a first paper titled "Silver nanowire inks for direct-write electronic tattoo applications" appearing in the Nanoscale journal, Franklin's lab describes a novel ink containing silver nanowires that can be printed onto any substrate at low temperatures with an aerosol printer. It yields a thin film that maintains its conductivity without any further processing. Once printed, the ink dries within two minutes and retains its high electrical performance even after enduring a 50 percent bending strain more than a thousand times.
A second paper published in the ACS Nano journal, "Flexible, Print-in-place 1D-2D Thin-film Transistors Using Aerosol Jet Printing" focuses on expanding the aerosol printing technique with other inks, including dispersed carbon nanotubes and hexagonal boron nitride flakes. Through precise ink formulations, the researchers were able to print 1D–2D thin-film transistors consisting of 1D CNT channels, a 2D hexagonal boron nitride (h-BN) gate dielectric and traces of silver nanowires as the conductive electrodes, all deposited using the same printer.
"Nobody thought the aerosolized ink, especially for boron nitride, would deliver the properties needed to make functional electronics without being baked for at least an hour and a half," boasted Franklin, "but not only did we get it to work, we showed that baking it for two hours after printing doesn't improve its performance. It was as good as it could get just using our fully print-in-place process."
Franklin doesn't see his printing method replacing large-scale manufacturing processes for wearable electronics. But he does see a potential value for applications such as rapid prototyping or situations where one size doesn't fit all.
"Think about creating bespoke bandages that contain electronics like biosensors, where a nurse could just walk over to a work station and punch in what features were needed for a specific patient," said Franklin. "This is the type of print-on-demand capability that could help drive that."