3D-printed spines for programmable liquid topographies and micromanipulation.

Manipulating floating objects, whether solid or liquid, from microscopic to mesoscopic sizes, is crucial in various microfluidics and microfabrication applications. While capillary menisci naturally self-assemble and transport floating particles, their shapes and sizes are limited by the properties of the fluid and the objects involved. We herein harness the superposition of capillary menisci to curve liquid interfaces controllably. By using 3D-printed spines piercing the interface, we can finely adjust height gradients across the liquid surface to create specific liquid topographies. Thus, our method becomes a powerful tool for manipulating floating objects into programmable paths. Combining experimental demonstrations, numerical simulations, and theoretical modeling, we study the liquid elevation created by specific spine dispositions and the three-dimensional manipulation of submillimetric particles. Multiple examples showcase the method's potential applications, including sorting and capturing particles, which could pave the way for cleaning fluid interfaces.