Ultrasound-Enabled Spatial Multi-Droplet Manipulation on Slippery Surfaces.

Controllable droplet manipulation plays a crucial role in microfluidics, biomedicine, and energy harvesting. Despite significant advances, synchronously controlling multiple droplets on a monolayer surface or spatially dislocated surfaces remains challenging. Here, a droplet ultrasonic bowl (DUB) is developed to enable the multi-droplet manipulation on a spatial slippery liquid-infused surface. By leveraging multiple twin-trap ultrasonic fields and dynamically modulating their quantity and positions, the DUB achieves programmable manipulation of single and multiple droplets on a monolayer surface such as single droplet precise movement, synchronous position exchange of two droplets, and simultaneous transport of three droplets. Furthermore, the spatial reach of the twin trap allows for the synchronized manipulation of multiple droplets on double-layer surfaces as well as steady control of pendant droplets. These capabilities demonstrate the applications in intelligent droplet circuits, spatial chemical reactions, and obstacle avoidance, offering a promising strategy for contactless droplet manipulation.