Lawrence Berkeley National Laboratory

Metals and organics possess two very dissimilar surface energies, hence, do not naturally adhere to each other. This incompatibility is exacerbated by surface roughness yet advances in wearables and bioelectronics call for their integration. Mesoscale mechanical bonds, however, transcend the necessities of surface energy matching while taking advantage of surface texture. Herein, transient carrier fluids, particle size polydispersity, and capillary-driven autonomous size-sorting are exploited to conformally jam undercooled liquid metal particles on textured soft substrate. The well packed undercooled metal particles are then chemically activated to induce phase change, leading to a solid electrically conductive metal trace. Static and dynamic deposition of the particles is amenable to this surface-templated printing of conductive traces. This process allows for printing across surfaces with varying surface features like on the brain, on paper (asymmetric porosity), or across smooth and rough brain sections. By tuning particle size and slurry concentration, good particle packing is demonstrated on a multi-scale rough surface like a rose flower. This printing method is therefore compatible with delicate (low modulus), heat sensitive, and textured substrates hence compatible with biological tissues and organic substrates.