Fast, Strong Capillary Liquid Metal Muscles

Harnessing liquid surface tension to perform mechanical work is widespread in nature and underpins many bioinspired technologies. However, fully exploiting liquid surface energy requires rapid, reversible, and wide‐range tuning of surface tension—capabilities lacking in conventional liquids such as water and oil. Gallium‐based liquid metals overcome this limitation by combining exceptionally high surface tension (≈600 mN m −1 at room temperature) with the unique ability to reversibly tune it to near zero via electrochemical control. Despite this, translating such tunability into actuators that simultaneously achieve high force, fast response, and large stroke has remained a major challenge. Here, capillary liquid metal muscles (CLMMs) are introduced as a new class of actuators that confine liquid metal within microchannels to maximize surface energy. This design enables a step change in performance: CLMMs deliver high force output (capable of lifting 1 kg), ultrafast response (<25 ms), and low‐voltage operation (<10 V), while providing precise and programmable control of both force and position. Notably, CLMMs achieve the highest pressure‐per‐volt performance for electro‐driven liquid actuators, exceeding previous systems by up to sevenfold. These results reveal a new mechanism for converting interfacial energy into useful mechanical work, providing a foundation for scalable soft actuators and adaptive systems.