The development of this metallic gel began with a solution of micrometer-sized copper particles suspended in water. Scientists first added a small amount of gallium-indium alloy (EGaIn) and hydrochloric acid to the solution. The hydrochloric acid adjusted the pH of the water to 1.0, removing oxides from the EGaIn and temporarily turning it into a liquid metal. Then, the copper particle solution and the liquid EGaIn mixture were stirred, allowing EGaIn particles to adhere to the stronger copper particles, forming a metallic gel "network" of copper particles connected by EGaIn bridges in the aqueous solution. Methylcellulose was added to expand the mixture.

A new study published in Matter magazine reveals that a research team, including researchers from North Carolina State University, has developed a metal gel that can be used to 3D print solid objects at room temperature. This highly conductive gel opens the door for 3D printing various heat-sensitive electronic components and devices.

The development of this metal gel began with a solution of micron-sized copper particles suspended in water. The scientists added a small amount of gallium-indium alloy (EGaIn) and hydrochloric acid to the solution. The hydrochloric acid adjusted the pH of the water to 1.0, removing oxides from the EGaIn and temporarily turning it into a liquid metal. Then, the copper particle solution and the liquid EGaIn mixture were stirred, allowing EGaIn particles to adhere to the more robust copper particles, forming a "network" of copper particle metal gel connected by EGaIn bridges in the aqueous solution. Methylcellulose was added to expand the mixture.

The resulting gel can be extruded from the nozzle of a standard 3D printer at room temperature, building objects layer by layer. When the finished product dries at the same temperature, the water and hydrochloric acid evaporate. The result is a rigid, highly conductive three-dimensional object with a metal content as high as 97.5%.

According to the researchers, the arrangement of particles in the gel affects how the material dries. For example, when printing a cylindrical object, the sides will shrink more than the top and bottom as it dries; if the object dries at room temperature, this process is slower and does not affect the structural changes; however, if it is heated, such as under an 80℃ heat lamp for rapid drying, it may cause structural deformation.

“Because these deformations are predictable, it means that by controlling the pattern of the printed object and the heat applied during drying, the shape of the printed object can be altered,” said Michael Dickey, a professor of chemical and biomolecular engineering at North Carolina State University. “3D printing is revolutionizing manufacturing, and this metal gel will open the door to the creation of a wide range of electronic components and devices.”