3D and 4D Printing Metals at Room Temperature using Metallic Gels

Researchers at NC State University have created a way to print solid metals at room temperature using metallic gels that can be used for 4D printing.  

Four-dimensional (4D) printing refers to 3D printed structures that change shape with respect to time in response to an external stimulus. To date, 4D printing techniques have focused primarily on electrically insulating materials, such as polymers. Adding conductive fillers to polymer could increase the functionality of the printed parts, but the high loadings necessary to achieve conductivity represent a trade-off with printability.

Herein, we connect copper (Cu) particles with soft eutectic gallium indium alloy (EGaIn) bridges to form a conductive 4D printing ink (Cu-GaIn) with gel-like properties that are well-suited for printing.  The inks are similar to wet sand.  Wet sand consists of solid particles (sand) connected by "bridges" of water surrounded by air.  Here, the sand is replaced with copper, the water 'bridges' replaced by liquid metal, and the air replaced by water.  

The final printed parts have a total metal content as high as 97.5 wt% and the remainder methylcellulose, a rheological modifier. The printed parts have an extremely high electrical conductivity (1.05×105 S/m) without requiring a sintering step. Cu-GaIn addresses the contradiction between conductivity and printability, and should open up new opportunities for electronic, thermal, and composite devices.

For more information:

Xing et al., "Metallic Gels for Conductive 3D and 4D Printing", Matter 6, 1–15
https://doi.org/10.1016/j.matt.2023.0...

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