Researchers have developed a metallic gel that is highly electrically conductive and can be used to print three-dimensional (3D) solid objects at room temperature. The paper, "Metallic Gels for Conductive 3D and 4D Printing," has been published in the journal Matter.

Summary: water + copper particles + room-temperature liquid metal (consisting of indium and gallium) = highly conductive gel with interesting properties.

Drying it slowly to evaporate the water allows simply getting conductive traces. Drying it fast allows printing objects that transform their shape when heated.

Commentary from me: indium and gallium are expensive metals. This is promising stuff, but not promising enough to go replicating at once. For most use cases, cables, soldering and PCBs are still the better option.