Butterfly wings and rice leaves could inspire high-tech surfaces

Researchers including an Indian origin scientist have taken a new look at butterfly wings and rice leaves surface, to improve a variety of products.

For example, the researchers were able to clean up to 85 percent of dust off a coated plastic surface that mimicked the texture of a butterfly wing, compared to only 70 percent off a flat surface.

The Ohio State University engineers explained that the textures enhance fluid flow and prevent surfaces from getting dirty – characteristics that could be mimicked in high-tech surfaces for aircraft and watercraft, pipelines, and medical equipment.

“Nature has evolved many surfaces that are self-cleaning or reduce drag,” Bharat Bhushan, Ohio Eminent Scholar and Howard D. Winbigler Professor of mechanical engineering at Ohio State, said

“Reduced drag is desirable for industry, whether you’re trying to move a few drops of blood through a nano-channel or millions of gallons of crude oil through a pipeline.

“And self-cleaning surfaces would be useful for medical equipment – catheters, or anything that might harbor bacteria,” they said.

Bhushan and doctoral student Gregory Bixler used an electron microscope and an optical profiler to study wings of the Giant Blue Morpho butterfly (Morpho didius) and leaves of the rice plant Oriza sativa.

They cast plastic replicas of both microscopic textures, and compared their ability to repel dirt and water to replicas of fish scales, shark skin, and plain flat surfaces.

Common to Central and South America, the Blue Morpho is an iconic butterfly, which has the ability to cast off dirt and water with a flutter of its wings.

For a butterfly out in nature, staying clean is a critical issue, Bhushan explained.

“Their wings are so delicate that getting dirt or moisture on them makes it hard to fly,” Bhushan said.

“Plus, males and females recognize each other by the color and patterns on their wings, and every species is unique.

“So they have to keep their wings bright and visible in order to reproduce,” he said

The electron microscope revealed that the Blue Morpho’s wings aren’t as smooth as they look to the naked eye. Instead, the surface texture resembles a clapboard roof with rows of overlapping shingles radiating out from the butterfly’s body, suggesting that water and dirt roll off the wings “like water off a roof,” Bhushan said.

“Reduced drag is desirable for industry, whether you’re trying to move a few drops of blood through a nano-channel or millions of gallons of crude oil through a pipeline.

The rice leaves provided a more surreal landscape under the microscope, with rows of micrometer- (millionths of a meter) sized grooves, each covered with even smaller, nanometer- (billionths of a meter) sized bumps – all angled to direct raindrops to the stem and down to the base of the plant.

The leaf also had a slippery waxy coating, which keeps the water droplets flowing along.

As to the Blue Morpho’s beautiful wings, their ability to keep the butterfly clean and dry suggests that the clapboard roof texture might suit medical equipment, where it could prevent the growth of bacteria.

This research was published in a recent issue of the journal Soft Matter.