Liquid Shuttle Mediated by Microwick for Open-Air Microfluidics

Microfluidics has experienced rapid progress in additive manufacturing and microfluidic soft robots. The design of microfluidics is already moving into a more intelligent, integrated, and detachable direction. However, the pipeline resistance needs more external energy input to achieve high flow speed. Guided transport of liquid in the open-air-space microfluidics will be an effective solution. Inspired by the water shuttle on the pitcher plant tendril, herein, an open-air microfluidic transport device is designed that consists of a superhydrophilic microwick with multi-microgrooves by stereolithography. The liquid film confined in microgrooves can promote rapid fluid shuttle on the wet surface to enhance transport rate and inhibit the Rayleigh-Plateau instability from forming larger dripping drops. The dripping volume and threshold Capillary number are optimized for effective liquid transport and drainage. State-of-the-art microwick liquid shuttle technologies can guide liquid continuously in a prescribed direction or into multiple directions with 98% transport efficiency (the ratio of liquid collection volume and liquid injection volume) for water and 97% for ethanol in the closed-open-closed space. The proposed mechanism has the potential to streamline microfluidic applications—and, therefore, accelerate relevant liquid delivery development and ultimately their applications in microfluidic chip and additive manufacturing. © 2023 Wiley-VCH GmbH.