Bioinspired Liquid Diode Valve Enables Programmable Control of Liquid Flow in Open‐Channel Microfluidics

Abstract Open‐channel microfluidics relies on capillary force to drive spontaneous liquid flow, holding the potential to construct devices for applications in biochemical analysis and point‐of‐care diagnostics. Operation in an open‐channel microfluidic device requires microfluidic valves to control fluids. However, current capillary valves are difficult to program for liquid flow, which hinders the construction of complex open‐channel microfluidic systems. Here, bioinspired liquid diode valves (LDVs) are presented to enable the programming of diverse liquid flows in open‐channel microfluidics. The LDV leverages the asymmetric capillary effect to achieve liquid flowing in one direction and pinning in the opposite direction, which can be further dynamically regulated when LDVs are made from magnetic materials. It is demonstrated that the flowing and pinning can be precisely tuned with wettability, edge angle, orientation, and deflection of the LDV. Through proper positioning and sequential opening of LDV arrays in microfluidic channels, spatiotemporal control over liquid flow can be achieved. The utility is demonstrated by performing controllable chemical reactions and point‐of‐care testing of unknown chemicals by on‐demand opening of LDVs and constructing reconfigurable liquid circuits using LDVs as electric components. The tunability, integrability, and flexibility of the LDVs will advance the construction of scalable and programmable open‐channel microfluidic systems.