Advances in wearables and bioelectronics call for integration of different classes of materials. Metals and organics possess two very dissimilar surface energies, thus, do not readily adhere to each other – a challenge exacerbated by roughness. Mesoscale mechanical bonds (interdigitation), however, transcend the necessities of surface energy matching or interfacial secondary bonding for adhesion. Interdigitation exploits surface texture and, in granular matter, particle packing and jamming. 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 metallic 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, enhanced particle packing, hence conformal deposition, 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.

Heat-free printing of conductive metallic traces on soft matter

ACS Fall 2021

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