Omnidirectional printing of elastic conductors for 3D-structured stretchable electronics

Abstract Printing solid-state elastic conductors into self-supporting three-dimensional (3D) geometries promises the design diversity of soft electronics, enabling complex, multifunctional, and tailored human–machine interfaces. However, the difficulties in manipulating their rheological characteristics have only allowed for layerwise deposition. Here, we report omnidirectional printing of elastic conductors enabled by emulsifying elastomer composites with immiscible, nonvolatile solvents. The strategy simultaneously achieves superior viscoelastic properties that provide the structural integrity of printed features, and pseudoplastic and lubrication behaviours that allow great printing stability. Freestanding, filamentary, and out-of-plane 3D geometries of intrinsically stretchable conductors are directly written, achieving a minimum feature size 150%. Particularly, the evaporation of the continuous phase in the emulsion results in microstructured, surface-localized conductive networks, significantly improving their electrical conductivity. To illustrate the feasibility of our approach, we demonstrate skin-mountable electronics that visualize temperature on a matrix-type stretchable display based on omnidirectionally printed elastic interconnects.