Liquid Metal Microgels for Three-Dimensional Printing of Smart Electronic Clothes

Gallium-based liquid metals (LMs), with the combination of liquid fluidity and metallic conductivity, are considered ideal conductive components for flexible electronics. However, huge surface tension and poor wettability seriously hinder the patterning of LMs and their wider applications. Herein, a recyclable liquid-metal-microgel (LMM) ink composed of LM droplets encapsulated into alginate microgel shells is proposed. During the mechanical stirring process, the released Ga3+ can cross-link with sodium alginate to form microgels covering the surface of LM droplets, which exhibits shear-thinning performance due to the formation and rupture of hydrogen bonds under different stress conditions, making the LMM ink possess excellent printability and superior adhesion to various substrates. Although patterns printed with the LMM ink are not initially conductive, they can be activated to recover conductivity by microstrain (<5%), pressing, and freezing. Additionally, the activated LMM circuit exhibits superior Joule heating behaviors and electrical performance in further investigation, including excellent conductivity, significant resistance response to strain with small hysteresis, great durability to nonplanar forces, and so forth. Furthermore, smart electronic clothes were fabricated and investigated by directly printing functional circuits on commercial clothes with the LMM ink, which integrate multiple functions, including tactile sensing, motion monitoring, human–computer interaction, and thermal management.