Bioinspired Cilia Array Surfaces for Programmable Unidirectional Liquid Transport across Surface Tension Regimes

Unidirectional liquid transport is critical for diverse applications, e.g., atmospheric water harvesting, integrated microfluidics, and high-efficiency heat transfer. However, existing strategies are mostly limited to narrow surface-tension ranges. Here, we designed bioinspired asymmetric cilia arrays (BACAs) mimicking the 45° inclined cilia of Alchemilla mollis, achieving unidirectional liquid transport over an ultrabroad surface-tension range of 22.2-72.8 mN m^-1. Systematic studies show that transport modes depend on surface tension, solid surface energy, and cilia spacing. For 0.6 mm-spaced BACAs (∼16.4 mJ m^-2), ethanol/water mixtures exhibit reverse transport above 32.1 mN m^-1, forward transport below 28.0 mN m^-1, and bidirectional flow in between. These phenomena arise from the dynamic equilibrium between gravity and capillarity. We further established a theoretical predictive framework based on the bidirectional transport contact angle to quantify transport modes, which contributed to achieve programmable liquid routing and precise spatiotemporal control over liquid transport.