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.

Electricity harvest from ubiquitous water has been endeavored, using nanogenerators based on carbon nanomaterials, to acquire renewable and clean energy and cope with fossil depletion and pollution as well. Meanwhile, though many biological organisms can harness water for bioelectricity, it is still challenging to produce biological nanogenerators based on biological nanomaterials with billions of tons of annual production in nature. Herein biological nanofibrils, including cellulose, chitin, silk fibroin, and amyloid, are produced either by liquid-exfoliation of biomasses or by supramolecular assembly of bio-macromolecules. With the intrinsic hydrophilicity and charged states, they can capture moisture from air and form hydrated nanochannels, in analogue to ionic channels of cytomembranes. When exposing their aerogels to moist air flow, there is a balance of water absorption and evaporation, thus producing a streaming potential and an open-circuit voltage across the aerogel. With flexibility, sustainability, biocompatibility, and biodegradability, these biological nanogenerators can harvest electricity from moist air flow in nature (e.g., wind, respiration and perspiration) and in industry, and serve for environmentally-friendly, low-cost, high-efficiency, wearable, and miniaturized power devices.