Geometry-Gradient Magnetocontrollable Lubricant-Infused Microwall Array for Passive/Active Hybrid Bidirectional Droplet Transport

Manipulation of droplets has increasingly garnered globalattention,owing to its multifarious potential applications, including microfluidicsand medical diagnostic tests. To control the droplet motion, geometry-gradient-basedpassive transport has emerged as a well-established strategy, whichinduces a Laplace pressure difference based on the droplet radiusdifferences in confined state and transport droplets with no consumptionof external energy, whereas this transportation method has inevitablyshown some critical limitations: unidirectionality, uncontrollability,short moving distance, and low velocity. Herein, a magnetocontrollablelubricant-infused microwall array (MLIMA) is designed as a key solutionto this issue. In the absence of a magnetic field, droplets can spontaneouslytravel from the tip toward the root of the structure as a result ofthe geometry-gradient-induced Laplace pressure difference. When thesubject of an external magnetic field, the microwalls bend and overlapsequentially, ultimately resulting in the formation of a continuousslippery meniscus surface. The formed meniscus surface can exert sufficientpropulsive force to surmount the Laplace pressure difference of thedroplet, thereby effectuating active transport. Through the continuousmovement of the microwalls, droplets can be actively transported againstthe Laplace pressure difference from the root to the tip side of theMLIMA or continue to actively move to the root after finishing thepassive self-transport. This work demonstrates passive/active hybridbidirectional droplet transport capabilities, validates its feasibilityin the accurate control of droplet manipulation, and exhibits greatpotential in chemical microreactions, bioassays, and the medical field.

Automated summary

By designing a magnetocontrollable lubricant-infused microwall array (MLIMA), this work solves critical limitations in droplet transportation and demonstrates passive/active bidirectional droplet transport capabilities. It shows great potential in chemical microreactions, bioassays, and the medical field.