A droplet-driven micro-surfboard with dual gradients for programmable motion

Self-propelled autonomous devices have great significance in energy, environment, and biomedical engineering, and thus vast achievements have been made in recent years. However, conventional propulsion often requires special chemicals or external energy, limiting their practical applications due to environmental pollution and energy waste. In this work, inspired by the character of a water strider on the water surface, a novel droplet-driven micro-surfboard (DDMS) is developed via femtosecond laser micro/nano fabrication, which can be driven in a green and controllable way. The DDMS is composed of a superhydrophobic sheet with superhydrophilic wedgy grooves. The droplet is put on superhydrophilic wedgy grooves to enter the water and form a jet, which further facilitates the directional motion of the DDMS. Also, a type of actuator with three superhydrophilic wedgy grooves is designed successively to achieve turn direction, which completes the programable motion by adding droplets to the three channels. Finally, an actuator with circular water storage area and a symmetrical vane-like rotating device with two superhydrophilic channels are developed, realizing long-distance and rotational motions. This work provides new insights into pollution-free autonomous devices and shows the great potential of droplet-driven autonomous devices in the fields of micromechanics and intelligent systems.