Liquid Metal Droplets Wrapped with Polysaccharide Microgel as Biocompatible Aqueous Ink for Flexible Conductive Devices

Nanometerization of liquid metal in organic systems can facilitate deposition of liquid metals onto substrates and then recover its conductivity through sintering. Although having broader potential applications, producing stable aqueous inks of liquid metals keeps challenging because of rapid oxidation of liquid metal when exposing to water and oxygen. Here, a biocompatible aqueous ink is produced by encapsulating alloy nanodroplets of gallium and indium (EGaIn) into microgels of marine polysaccharides. During sonicating bulk EGaIn in aqueous alginate solution, alginate not only facilitates the downsizing process via coordination of their carboxyl groups with Ga ions but also forms microgel shells around EGaIn droplets. Due to the deceasing oxygen-permeability of microgel shells, aqueous ink of EGaIn nanodroplets can maintain colloidal and chemical stability for a period of >7 d. Crosslinked alginate-gel with tunable thickness can retard the generation and release of toxic cations, thereby affording high biocompatibility. The soft alginate shells also enable to recover electric conductivity of EGaIn layers by mechanical sintering for applications in microcircuits, electric-thermal actuators, and wearable sensors, offering huge potential for electronic tattoos, artificial limbs, electric skins, etc.