3D Printed Stretchable Electronics

Integrating room temperature liquid metals (LMs) into 3D stretchable devices remains a manufacturing challenge due to its intrinsically low viscosity and high surface tension. This work presents a 3D printable strain-induced electrically conductive LM emulsion for the programmable assembly of soft conductive composites. This LM emulsion exhibits shear yielding and shear thinning rheology that is compatible with direct ink writing (DIW). Examples of complex self-supported 3D printed structures with spanning features are presented to demonstrate its 3D printability. Stretchable LM composites are fabricated by integrating this emulsion into a multi-material printing process with a 3D printable elastomer. The as-printed composites exhibit a low electrical conductivity but can be transformed into conductive composites by a single axial strain at low stresses (< 0.3 MPa). Electromechanical characterization showed that the electrical conductivity increases with activation strain, with a maximum conductivity of 8.61𝑥10^5 𝑆𝑚^(−1). The electrical conductivity of these composites reaches a steady state for each strain after one cycle, remaining stable (< 6% standard deviation (SD)) over 1,000 cycles. All samples exhibit strain sensitivities that are lower than a bulk conductor. The composites showed low hysteresis at high strains, and high hysteresis at low strains. The utility of these composites is shown by employing them as wiring into a stretchable array of LEDs.