When it comes to naturally repelling things, the humble cicada seems to have a few tricks up its sleeve. Already its studded wings have shown a remarkable ability to repel bacteria, something that could prove useful in keeping eye implants and other medical devices germ-free. Now scientists have zeroed in on the insect's ability to repel water, which could provide inspiration for anti-icing and self-cleaning materials further down the track.
The repelling abilities of the cicada can be attributed to the bed of tiny blunted spikes that coat its wings. These nanoscale nipples are spaced far enough apart and are just the right size, that when a bacterium lands on top of them, its elastic outer membrane sags down in between until it eventually pops and the microorganism dies.
This effect could one day be replicated in a material used to coat things like door knobs or handrails in hospitals, where keeping the environment germ-free is vital. And last year a team of researchers harnessed this effect to produce a germ-repelling synthetic polymer that could form the basis for resilient new types of eye implants.
The insect's ability to repel water comes courtesy of this same characteristic. A team from the University of Illinois studied cicada wings using high-speed microscopic photography to investigate how they repel water.
"The property that allows a surface to repel water is called hydrophobicity and it causes water to bead up and roll away," said engineering professor Nenad Miljkovic, who co-led the study. "Superhydrophobicity is simply an extreme form of this property and cicada wings that have this feature have a rough nanotexture that creates open spaces around water droplets, allowing surface tension to force the droplets to jump off of the wings."
What's interesting about the research is the samples that the scientists chose to study. Previously, these cicada-wing studies had focused on species that live in the wetlands. Instead, the researchers took four species from a range of environments, including forests and prairie lands.
"We expected to find that the specimens from drier habitats would lack superhydrophobicity," said Catherine Dana, study co-author. "We were surprised to find the opposite, and that habitat is not a good predictor of this extreme water-repelling ability of the cicada wings."
The team says this new knowledge could prove useful in the development of artificial surfaces with de-icing, anti-fogging and self-cleaning abilities. These types of materials could then find their way into roads, sidewalks, power lines and airplane wings.
"Our work with cicadas is letting us explore a field called bioinspiration," said Miljkovic. "We are learning as much as we can from the natural design of cicada wings to engineer artificial objects that are useful to humans."
The research was published in the journal Applied Materials & Interfaces, while the video below shows the cicada's hydrophobicity in action.
Source: University of Illinois