Self-propelled liquid metal motors steered by a magnetic or electrical field for drug delivery.

Self-propelled motors have inspired enormous potential in accomplishing various tasks when navigating in an aqueous environment due to their virtues of requiring no external energy source and autonomous locomotion. However, without reliable controllability, their potential value would be heavily reduced. Here, we demonstrate an innovative millimeter-scale self-propelled motor steered by an external magnetic or electric field, which successfully enables the motor to avoid out-of-control motion behavior encountered previously. A nickel cap is electroplated on a liquid metal droplet. The on-board fuel aluminum foil not only triggers the autonomous movement, but also enhances the adhesion between the nickel cap and the droplet. The current motor, composed of a nickel cap, aluminum and liquid metal, is capable of running with a velocity of 3 cm s-1 for hours without the use of an external energy source. In addition, the integration of the nickel cap renders a magnetic field exploitable to easily alter the performance of the motor remotely. Furthermore, an external electrical field offers a feasible way to accelerate the motor directionally in a reliable manner. More importantly, as a conceptual experiment, when loaded with soft alginate-based biomaterial containing aluminium nanoparticles as drugs, such a motor is still able to be self-propelled, exhibiting steerable motion for drug delivery. The remarkable features of the liquid metal motor, such as softness, controllable self-propelled movement and drug-delivery application, represent a critical step toward functional intelligent soft robots or machines.