Beetles Are Inspiration For New Antibacterial Coatings

Thu, 21 Jan 2010

Scientists at M.I.T. looking to add new chemical functionalities to spray coatings have turned to the beetle for inspiration. Some beetles that live in very arid climates get their drinking water by trapping water droplets from fog. The droplets collect on a bumpy surface on their backs and once they become big enough, the water drops slide down a smooth surface into their mouths. These dueling surfaces are being mimicked by scientists in order to create antibacterial coatings.

When you think of a beetle, you think creepy, crawly critters. Now add one more adjective to the list: Clever -- clever because despite living in the desert, the beetle is able to gather drinking water.

"The beetle is able to gather, out of this very light fog, enough water to survive -- to take a drink every morning and survive to live another day," Robert Cohen, a chemical engineer at MIT in Cambridge, tells DBIS.

The Namib Desert beetle has dueling surfaces on its back. The smooth parts repel water, while the top bumpy parts collect water.

MIT materials scientist Michael Rubner says that pattern motif creates this incredible ability to gather and harvest small drops of water from the fog. As fog rolls in, the bumps on its back trap water. As the droplets get bigger, the water then rolls down into the beetle's mouth.

Scientists are trying to mimic this idea by dipping glass into solutions of charged polymers, imitating the porous and smooth coating of the beetle. The material is then coated with a Teflon-like substance, making it water-repellent.

Their next step is to add an antibacterial agent into the coating that may be used on common hospital, kitchen and bathroom surfaces to stop germs from spreading. If all goes well, the beetle could possibly stop germs in their tracks.

"What we're very interested now is the possibility of adding more chemical functionality to what the beetle has taught us," Rubner says.

There is also promise of creating larger-scale pieces of water-repellent material that could be used to collect water in arid climates. The scientists say the key is creating dueling surfaces in areas where water is present, but hard to collect.

BACKGROUND: Inspired by the Namib Desert beetle that lives in one of the driest regions of the world, researchers at the Massachusetts Institute of Technology, in Cambridge, have developed a new material that can capture and control tiny amounts of water, just like the beetle does. Applications include its use for self-contaminating surfaces that could channel and collect harmful substances, such as germs, that could then be easily killed or deactivated. It could also be used for lab-on-a-chip diagnostics of DNA screening.

ABOUT DESERT BEETLES: The desert beetle has a built-in water collection system that allows it to survive where there is no water to be found, even when the humidity in the air is close to zero. This is important since normal condensation can't take place in the Namib Desert because the fog is too light. When fog blows across the surface of the beetle's back, water droplets begin to gather on top of the bumps on the insect's back These bumps attract water. They are also surrounded by waxy, water-repellent channels that pins the water drops on the beetle's back. Over time, the droplets get bigger, until they are large enough to roll down into the insect's mouth.

ABOUT THE MATERIAL: The new material developed by the MIT scientists can capture and control tiny amounts of water because its structure mimics that of the desert beetle. There are two surfaces, one water-repellant and another water attracting, that act together to separate and channel water drops. The researchers found they could control the surface texture of their material by repeatedly dipping glass or plastic substrates into charged polymer solutions. With every dip, another layer coats the surface, gradually making the material more porous so it easily attracts water. Adding silica nanoparticles -- particles only a few millions of a millimeter wide -- creates even more bumps to trap the collected water droplets. The final touch is a Teflon-like coating that makes the material super-water-repellent. And the scientists can create any pattern they want by adding more layers of charged polymers or nanoparticles in specific areas.