This illustration shows the self-wrinkling biofilm repelling barnacles.Phanindhar Shivapooja and Qiming Wang
A new coating for ships keeps clean by literally shaking off barnacle buildup. The coating moves, at a molecular level, whenever it's stimulated with stretching, pressure or electricity. A ship owner looking to give her hull a clean could then just activate the coating with electricity — no elbow grease needed.
"We have developed a material that wrinkles, or changes its surface, in response to a stimulus," Xuanhe Zhao, an engineer at Duke University who led the development of the coating, said in a statement. "This deformation can effectively detach biofilms and other organisms that have accumulated on the surface."
Barnacles and other marine hangers-on clog underwater sensors and reduce how efficiently ships move through the water. Even bacteria can be a problem, because they create persistent colonies called biofilms that encourage the growth of larger organisms, such as seaweed and shellfish.
Ship owners now can buy several antibacterial paints for ship hulls, but researchers are always looking for a better solution. Zhao and his colleagues at Duke came up with a next-generation coating they say could be produced using chemicals that are commonly used in self-cleaning hull paints today.
The Duke engineers have tested the new coating with bacteria and barnacles grown in seawater in their lab. After 10 minutes of activation, the coating shook off 95 percent of a four-day-old biofilm of Cobetia marina, the researchers found. In a separate experiment, they found that a self-wrinkling surface removes attached adult barnacles if it wrinkles forcefully enough. At lower levels of movement, the surface reduces the force needed to clean off barnacles.
The researchers say they were inspired by microscopic, hairlike structures called cilia that many living things have to keep themselves clean. Cilia wave around on their own, to keep bacteria and other organisms from attaching to a surface.
People have cilia, as engineer Gabriel López explained. "Cilia can move foreign particles from the lungs and respiratory tract," he said. "These types of structures are used by mollusks and corals to keep their surfaces clean. To date, however, it is been difficult to reproduce the cilia, but controlling the surface of a material could achieve the same result."
Zhao, López and their colleagues published a paper about their work Jan. 6 in the journal Advanced Materials.
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