Researchers studying how beetles trap air to keep from drowning suggest that artificial gills could similarly help people breathe underwater.
Scientists in England investigated super-water-repellent surfaces which possess tiny structures that rise like trees in a forest, upon which water droplets rest.
The structures trap air between the surface they jut up from and the water on top of them.
Insects and spiders usually drown when submerged. However, aquatic insects, such as the great diving beetle Dytiscus marginalis, possess rigid hairs on their abdomen that repel water so much that they create a silvery film of air that does not collapse.
The silk nests of some ground-dwelling spiders and the eggshells of a number of insects also develop these sheaths of air.
The air layers essentially behave as gills, allowing oxygen dissolved in the surrounding water to flow in and carbon dioxide in the air to diffuse out.
Glen McHale, a physicist at Nottingham Trent University in England, and his colleagues investigated whether synthetic materials could mimic this natural effect.
They created a hollow cylinder made of super-water-repellent porous foam, inside which they sealed a device that consumed oxygen.
When submerged in aerated water, sensors within the cylinder showed that oxygen had made its way inside.
The most likely use for this effect, McHale and his team say, would be to supply oxygen for fuel cells, enabling miniaturized machines to work underwater without the need for stored or external oxygen supplies.
They also note that a surface area of roughly 970 square feet could provide enough oxygen for a single person to breathe continuously.
"The actual surface area required would depend on the gases in the water, water movement and the level of oxygen required," McHale told LiveScience.
Such a large surface could be folded or corrugated to some extent for greater portability.
However, that would just deplete nearby water of usable oxygen more efficiently, researcher Neil Shirtcliffe explained.
"As with fish and sharks, unless water is pumped past or the 'gill' is moving, there is little advantage to structuring the surface," he said.
More research needed
How long a machine or person could stay underwater "is indefinite, provided the water does not become deoxygenated," McHale said.
But, he added, "if other gases, such as methane, were in elevated levels in the water, such as in stagnant pools, these gases would be transferred into the breathing air as efficiently as oxygen and could potentially cause serious problems."
McHale also cautioned that his team did not measure carbon dioxide levels within the test cylinder, "and it is a buildup of carbon dioxide that would kill people before lack of oxygen."
Still, "the rate of removal of carbon dioxide is expected to be high, as the gas is very soluble in water."
McHale and his colleagues reported their findings Sept. 4 in the journal Applied Physics Letters.
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