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Harvesting body heat using thermoelectricity provides a promising path to realizing self-powered, wearable electronics that can achieve continuous, long-term, uninterrupted health monitoring. This paper reports a flexible thermoelectric generator (TEG) that provides efficient conversion of body heat to electrical energy. The device relies on a low thermal conductivity aerogel–silicone composite that secures and thermally isolates the individual semiconductor elements that are connected in series using stretchable eutectic gallium-indium (EGaIn) liquid metal interconnects. The composite consists of aerogel particulates mixed into polydimethylsiloxane (PDMS) providing as much as 50% reduction in the thermal conductivity of the silicone elastomer. Worn on the wrist, the flexible TEGs present output power density figures approaching 35 μWcm⁻²at an air velocity of 1.2 ms⁻¹, equivalent to walking speed. The results suggest that these flexible TEGs can serve as the main energy source for low-power wearable electronics.

This review discusses methods, challenges, and opportunities for direct‐write and 3D printing of low melting point, gallium‐based liquid metal alloys at room temperature. Alloys of gallium exhibit high conductivity and high stretchability making them well suited for use in soft circuitry for stretchable electronics and soft robotics. In addition, the liquid nature of the metal enables entirely new ways to pattern metals at room temperature; herein, the focus is placed on additive printing via nozzle‐based methods. Room temperature printing of liquid metals enables rapid fabrication of complex geometries (with dimensions as small as 10 µm) on a wide range of materials, such as polymers. These processes can be used to make metallic conductors for devices with self‐healing capabilities, soft/stretchable electrodes, and sensors.