Undercooled metal technology was developed that features liquid metal (in this case, Field's metal, an alloy of bismuth, indium, and tin) trapped below its melting point in polished, oxide shells, creating particles about 10-millionths of a meter across. When the shells are broken — with mechanical pressure or chemical dissolving — the metal inside flows and solidifies, creating a heat-free weld or, in this case, printing conductive, metallic lines and traces on all kinds of materials, from a concrete wall to a leaf.
The technology could have applications including sensors to measure the structural integrity of a building or the growth of crops. The technology was tested in 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.
The researchers effectively bonded metal traces to everything from water-repelling rose petals to watery gelatin. Metallic traces could be printed on ice cubes or biological tissue.