Micro elastofluidic liquid diode for programmable unidirectional flow control.

Abstract

Controllable liquid transport is essential for fluid regulation in wearable biosensing platforms. Particularly, unidirectional flow offers a passive, geometry-dependent strategy to direct liquid movement without external actuation. However, most previous studies have focused solely on achieving unidirectional flow, with limited exploration of real-time tunability or reconfigurability. Here, we present a tuneable open-channel microfluidic platform featuring a chevron-ratchet geometry that enables passive and reversible liquid diode behaviour. Flow directionality and velocity are dynamically modulated through surface wettability tuning and mechanical stretching. A theoretical force model was first established to describe asymmetrical spreading, governed by Laplace pressure gradients and geometric curvature. Numerical simulations based on energy-minimization principles further elucidated wetting behaviour on structured surfaces. Concurrently, experimental validation confirmed three distinct flow regimes-pinned, unidirectional, and bidirectional-controlled by plasma-induced wettability modulation and applied mechanical strain. Stretching the channels along orthogonal axes led to programmable switching of flow states and geometry-sensitive pinning thresholds. We further integrated a hydrogel film as a sweat-acquisition interface and demonstrated sustained unidirectional transport under physiologically relevant inflow. This proof-of-concept validation complements the fundamental findings and highlights the translational potential of our open-channel platform as a simple, tuneable, and pumpless approach for wearable diagnostics, adaptive liquid routing, and flexible microfluidic circuitry.