Ohio State University mechanical engineering professor Bharat Bhushan looks to nature for solutions to society’s common problems.

One such problem is finding water in arid environments. Prof. Bhushan, Ph.D. student Dev Gurera and OSU engineering researchers looked to a trio of desert denizens — a cactus, desert grasses and a beetle — to see how these organisms gather water from nighttime dew and direct the moisture where they need it to go.

The researchers carried out two tests. In the first, they studied the mechanisms each organism uses to Barrel cactus, Namibia. Source: Pius Mahimbi / CC BY-SA 2.0collect water. To compare their relative effectiveness, the team used a 3D printer to reproduce the physical collectors, placed the collectors in an enclosed humid atmosphere and calculated the amount of water each collected.

The first test results demonstrated that each organism’s collection method has its advantages.

• Conical shapes, like a cactus spine, gather more water than cylindrical shapes due to the Laplace pressure gradient. Since cactus spines are a type of modified leaf, their role in water collection makes sense.
• Grooved surfaces, like those on grasses, move water faster.
• Hydrophilic surfaces gathered more water than non-hydrophilic surfaces. The beetle’s back is a combination of hydrophilic and non-hydrophilic surfaces that facilitates water movement toward the beetle’s mouth.

For the second test, the researchers created a structure combining multiple cones, the most efficient water-collecting structure. They discovered that placing the cones close together increased the amount of water collected because water droplets coalesced between the cones. The hydrophilic spots on the beetle’s back demonstrated that collector material, in this case, the cones, also matters.

The Ohio State research, published December 24, 2018, in Philosophical Transactions of the Royal Society, is one of several recent projects figuring out how to pull water from ambient air.

Lawrence Berkeley Lab and King Abdulazziz City for Science (Saudi Arabia) constructed a prototype system incorporating metal-organic framework (MOF) technology. An aluminum-based MOF captured 400 ml of water with a kilogram of MOF.

The University of Texas at Dallas harvests water using a slippery rough surface that works better than state-of-the-art liquid repellent surfaces. The pitcher plant inspired this surface. A scaled-up version can harvest 120 liters of water per square meter per day.

Harvard’s Wyss Institute for Biologically Inspired Engineering and John A. Paulson School of Engineering and Applied Sciences also studied cacti, desert beetles and pitcher plants to design an optimized hydrophilic surface. The Harvard team looked specifically at ways to control droplet size, speed of formation and flow direction. Their results were published in Nature in February 2018.