Metallic gels for conductive 3D and 4D printing

This paper reports printable metallic gels (pendular suspensions) consisting of an aqueous suspension of copper particles connected by bridges of liquid eutectic gallium indium alloy (EGaIn). Pendular suspensions rely on capillary forces to form networks between solid particles with a composition-dependent rheology, but prior studies have focused on insulating suspensions. Here, the rheology of a conductive solid-liquid-liquid suspension is tuned for 3D printing by varying the composition and the pH; the latter promotes metallic wetting. The dry printed parts have metallic electrical con-ductivity (1:053105 S/m) without requiring a sintering step. Drying at elevated temperatures can accelerate the removal of water while creating stress that drives shape change (i.e., 4D printing). As a demonstration, we print a conductive spider that lifts and assembles its own body from an initially flat shape. Such conductive inks are promising for printing metallic structures under ambient conditions.

Automated summary

This paper presents printable metallic gels made of an aqueous suspension of copper particles connected by bridges of liquid eutectic gallium indium alloy. The rheology of the conductive solid-liquid-liquid suspension is tuned for 3D printing by adjusting the composition and pH. The printed parts exhibit metallic electrical conductivity without the need for sintering, and drying at elevated temperatures enables shape change for 4D printing. A conductive spider is successfully printed, demonstrating the potential for printing metallic structures under ambient conditions.