Asymmetric fibers for efficient fog harvesting

Access to sustainable, clean, and safe freshwater remains a global challenge. Harvesting atmospheric fog droplets with mesh collectors enables an environmental-friendly supply of good-quality freshwater. However, the functional outcomes of existing fibers used in collectors are not satisfactory, because of the inadequacies of conventional fiber design in engineering the surface microstructures and properties. By selectively combining functionalities and advantages of natural structures, we design fibers with synergistic asymmetry in their shape, surface roughness, and surface chemistry to simultaneously enhance fog deposition and water drainage. We draw inspiration from the rugged shape of Gunnera leaf to enhance fog deposition, the hierarchical surface roughness of Cotula leaf to lubricate the pathway for rapid water drainage, and the heterogeneous wettability of the Namib Desert beetle to promote the directional water transport in bridging fog deposition and water drainage. These fibers achieve a fog-harvesting rate of up to 8.2 × 10⁻³ g cm⁻² s⁻¹, a 7-time enhancement, and thus represent a step-change in addressing the grand challenge of global water shortage.