Liquid metal (LM) alloys such as eutectic gallium indium (EGaIn) and gallium-indium-tin (Galinstan) have been used in the fabrication of soft and stretchable electronics during the past several years. The liquid-phase and high electrical conductivity of these materials make them one of the best candidates for fabrication of deformable electronics and multifunctional material systems. While liquid metals are mhighly reliable for fabrication of simple circuits and stretchable microfluidic devices, their application for producing complex circuits faces fabrication challenges due to their high surface tension and surface oxidization. In this study, we propose a scalable, cost-effective, and versatile technique to print complex circuits using silver nanoparticles and transform them into stretchable electronics by incorporating eutectic gallium indium alloys to the circuit. As a result, the deposited liquid metal considerably increases the electrical conductivity and stretchability of the fabricated electronics. The reliability and performance of these stretchable conductors are demonstrated by studying their electromechanical behavior and integrating them into skin-like electronics, termed electronic tattoos.

Step by step fabrication process of temporary electronic tattoos for populating the printed circuit with microchips: (a) soldering microchips by applying EGaIn droplets, (b) applying HCl vapor to remove the oxide layer, (c) coating the entire circuit with diluted PDMS to encapsulate the circuit (scale bar = 2.5 mm).

Conductive AgNP-Ga-In traces for flexible electronic tattoos: (a) populated AgNP-Ga-In circuit is transferred to forearm (b) integrated blue LED is light up to ensure that traces remain functional during the process and applied deformations on skin.