Directly on the skin: aerosol-printing for electronic tattoos

October 04, 2019 // By Julien Happich
electronic tattoos
Using a purpose-built printer nozzle and water-based inks, electrical engineers at Duke University have demonstrated that electronically functional designs such as electrodes and transistors could be printed through an aerosol jet, without any post-processing.

This means the safe water-based inks could be applied on delicate surfaces such as human skin or fruits to design electronic tattoos or sensing tags without incurring any damage.

"When people hear the term 'printed electronics,' the expectation is that a person loads a substrate and the designs for an electronic circuit into a printer and, some reasonable time later, removes a fully functional electronic circuit," explains Aaron Franklin, the James L. and Elizabeth M. Vincent Associate Professor of Electrical and Computer Engineering at Duke.

"Over the years there have been a slew of research papers promising these kinds of 'fully printed electronics,' but the reality is that the process actually involves taking the sample out multiple times to bake it, wash it or spin-coat materials onto it," Franklin adds. "Ours is the first where the reality matches the public perception."

"For direct or additive printing to ever really be useful, you're going to need to be able to print the entirety of whatever you're printing in one step," argues Franklin. "Some of the more exotic applications include intimately connected electronic tattoos that could be used for biological tagging or unique detection mechanisms, rapid prototyping for on-the-fly custom electronics, and paper-based diagnostics that could be integrated readily into customized bandages."

Two electronically active leads directly printed along
the underside of Duke graduate student Nick Williams'
pinky successfully light up an LED when a voltage
is applied. Credit: Nick Williams, Duke University.

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.

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