Biomimetic liquid metal ink sac

Mimicking the intriguing ink-jetting escape strategy of cephalopods such as cuttlefish in robotics has remained rare. Here, we report a liquid metal ink sac (LMIS) and demonstrate its bio-inspired capability to mimic the macroscopic defensive functions of natural animals. The principle is based on discovering the instantaneous and powerful electrochemical ink-jetting phenomena among liquid metal (Galinstan). Through applying a specific polarization voltage, the liquid metal vigorously jets ink in aqueous solutions spanning the full pH range, from acidic to alkaline and even in artificial seawater. This forms a biomimetic “ink” that effectively blocks light to serve as a primary visual screen, while also offering a supplementary electromagnetic interference (EMI) shielding capability. Notably, the composition and morphology of the ink-jetting products vary significantly with the applied polarization voltage and solution environment. The system exhibits remarkable efficiency and cyclability. A mere 0.1 mL of liquid metal can generate a total ink suspension volume of approximately 600 mL over 40 cycles, equivalent to 6000 times the initial liquid metal volume. As practical illustrations, we integrated the LMIS into a biomimetic cuttlefish robot, demonstrating two operational modes: pulsed jetting that mimics natural behavior and a continuous jetting mode that surpasses it. Furthermore, the robot could sustain continuous ink-jetting for over an hour as needed. This principle equips underwater robots with an advanced defense capability and significantly expands the robotic uses of liquid metals. Based on the electrochemical findings on liquid metals, a biomimetic liquid metal ink sac is proposed and demonstrated with robotic uses. Assisted by DC voltage, liquid metal could generate “artificial inks” containing nanoparticles, providing a light-blocking effect. Underwater robots thus equipped would gain cuttlefish-like ink-jetting capability for defense and escape.