3D-printable oil-in-liquid metal foam emulsion

Gallium-based low-melting-point liquid metals offer a unique combination of flexibility, conductivity, and thermal transport, making them attractive for soft electronic and thermal systems. However, their extremely low viscosity, high surface tension, and rapid oxidation pose substantial challenges for 3D patterning. While rheological modifications can enable 3D printing, they often compromise conductivity, require complex post-processing, or introduce toxicity. Here, we introduce an oil-in-liquid metal foam emulsion ink that enhances extrudability while largely preserving the intrinsic properties of the base metal. The ink maintains low electrical resistivity ($7.25\pm 0.07\times {10}^{-7}\mathrm{\Omega }·\mathrm{m}$$7.25\pm 0.07\times {10}^{-7}\mathrm{\Omega }·\mathrm{m}$ at $20°$$20°$C) and high thermal conductivity ($14.86\pm 0.43\mathrm{W}/\mathrm{m}·\mathrm{K}$$14.86\pm 0.43\mathrm{W}/\mathrm{m}·\mathrm{K}$ at $20°$$20°$C) and remains liquid down to $-30°$$-30°$C due to supercooling. We demonstrate direct ink writing of complex 3D geometries with resolutions down to $0.5\text{mm}$$0.5\text{mm}$ and characterize the ink’s thermal and electrical performance. This formulation offers a practical route for processing liquid metals in three dimensions, enabling new opportunities in flexible electronics, thermal interfaces, and soft sensing systems.