Magnetically Controlled Mechanical Cutting of Water

Precisely controlling the cutting of water using mechanical forces remains challenging due to water's inherent surface tension and rapid self-healing properties. Inspired by the effortless movement of water striders, a strategy is developed involving magnetic manipulation of a hydrophobic sphere across hydrophobic particle-encapsulated water (HPEW). Stable mechanical cutting of water is first demonstrated by coating its surface with hydrophobic particles (silica nanoparticles, paraffin, and polytetrafluoroethylene (PTFE)) and maintaining the water thickness below 1 mm. Through systematic theoretical and numerical analyses, it is clarified how water thickness and particle distribution influence cutting performance and accuracy. Moreover, a magnetically controlled approach is established for precise cutting, creating versatile open millifluidic chips suitable for diverse applications such as biochemical assays, chemical synthesis, and 3D cell culture. The approach thus offers a robust platform with wide-ranging implications in materials science, chemistry, physics, biomedical engineering, and microfluidics.