Heat-free technology can print metal on flowers

Researchers from Iowa State University have developed heat-free technology that they claim can print conductive, metallic lines and traces on just about anything — from flowers to gelatin. Their work has been described in the journal Advanced Functional Materials.

Undercooled metal technology, developed by Martin Thuo and his research group, features liquid metal trapped below its melting point in polished, oxide shells, creating particles about 10 millionths of a metre across. When the shells are broken — with mechanical pressure or chemical dissolving — the metal inside flows and solidifies, either creating a heat-free weld or printing conductive, metallic lines and traces on everything from a concrete wall to a leaf.

This could have all kinds of applications — from sensors to measure the structural integrity of a building or the growth of crops, to paper-based remote controls that read changes in electrical currents when the paper is curved. Engineers also tested the technology by making electrical contacts for solar cells and by screen printing conductive lines on gelatin — a model for soft biological tissues, including the brain.

Printed electronic traces on gelatin.

An assistant professor of materials science and engineering at Iowa State, Thuo said he launched the project three years ago as a teaching exercise — and once students learned to use a few metal-processing tools, they started solving some of the technical challenges of flexible, metal electronics.

“The students discovered ways of dealing with metal and that blossomed into a million ideas,” Thuo said. “And now we can’t stop.”

Since then the researchers have learned how to effectively bond metal traces to everything from water-repelling rose petals to watery gelatin. Based on what they now know, Thuo said it would be easy for them to print metallic traces on ice cubes or biological tissue.

“This work reports heat-free, ambient fabrication of metallic conductive interconnects and traces on all types of substrates,” the researchers wrote. They said their experiments “highlight the versatility of this approach, allowing a multitude of conductive products to be fabricated without damaging the base material”.

Thuo also serves as an associate of the US Department of Energy’s Ames Laboratory and a co-founder of the Ames start-up SAFI-Tech, which is now commercialising the liquid-metal particles.

Images courtesy of Martin Thuo.

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