Collecting Water Cactus-style

The bunny ears cactus, Opuntia microdasys, keeps itself hydrated by gathering moisture from the air using spines and hairlike trichomes on its stem. Researchers led by Lei Jiang of China’s Beijing National Laboratory for Molecular Sciences wondered whether smaller structures might also play a role in the water-harvesting phenomenon. When they took a closer look, they found that within the clusters of spines on the cactus stem, there are also tiny cones, roughly 100 μm tall, that contribute to the cactus’s ability to collect water (Adv. Funct. Mater. 2014, DOI: 10.1002/adfm.201402229). Jiang’s team then made mimics of these arrays of cones out of polydimethylsiloxane and studied how various arrangements influenced the structures’ water-harvesting abilities. Arrays with a hexagonal arrangement proved to be the most efficient because air flowed through these staggered cones rapidly, quickly moving water droplets along each cone. “This investigation opens up new avenues to collect water efficiently and may also provide clues to research about dust filtering and smog removal, which is attracting increasing attention worldwide,” the researchers note.