Cactus-Inspired Conical Spines with Oriented Microbarbs for Efficient Fog Harvesting

In nature, cacti use conical spines with oriented microbarbs and hydrophilic trichomes as an effective fog harvesting system. However, the fabrication dilemma of complex cactus-inspired conical spines with oriented microbarbs limits their applications. Here, a magnetorheological drawing lithography (MRDL) method is developed to additively manufacture 3D cactus-inspired conical spines with/without oriented microbarbs on a superhydrophilic porous substrate for efficient fog harvesting. Cactus-inspired conical spines with/without microbarbs exhibit spontaneous and continuous deposition, coalescence, transport, and absorption of fog water. The strategy of the cactus-inspired conical spine with backward barbs on a superhydrophilic porous substrate can significantly speed up unidirectional transport of water drops and achieve a higher fog-harvesting efficiency. These properties are mainly attributed to the cooperation effect of the Laplace pressure gradient generated from the conical shape of the spine and microbarbs, the capillary pressure arising from the concave meniscus between the spine and backward barbs, and the wettability of a superhydrophilic porous substrate. This robust strategy has tremendous potential for application in high-efficient fog harvesting, liquid manipulation, and microfluidics.