Even with scuba gear, you can only stay underwater for as long as the meagre air supply on your back allows. Yet the ocean contains oxygen, so why can't we swim around like fish, extracting the gas from the water as we need it?
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In 2002, a diver spent half an hour submerged in a swimming pool doing just this, breathing oxygen extracted from the water by an artificial gill. The device was built by Fuji Systems of Tokyo, Japan, using high-tech silicon membranes. These are permeable to gases but not liquids, so oxygen can diffuse into the breathing air from the water, while carbon dioxide diffuses out-just like the gills of a fish.
But you won't see divers using artificial gills any time soon, because simple diffusion gills produce dangerously low levels of oxygen, Israeli inventor Alan Bodner has tried to get around this problem with a gadget that exploits "the champagne effect": gases dissolved in water bubble out when the pressure falls. Bodner has shown his method can produce a breathable gas. Problem solved?
Unfortunately not. We need a lot of oxygen and there just isn't that much dissolved in a litre of seawater. So no matter how efficient the extraction method is, you would have to pump a huge volume of water through It to get enough. And while you do not need to carry air, you do need batteries and the means to make air, which means much more to go wrong.
Artificial gills may have a rosier future for other applications, however. Underwater robots powered by fuel cells could use gills to obtain oxygen. They are also likely to be used to get rid of excess carbon dioxide from submarines and underwater habitats, perhaps boosting the oxygen supply at the same time.
Source Citation:Le Page, Michael. "8 Breathe underwater.(Fuji Systems)(Brief article)." New Scientist 201.2692 (Jan 24, 2009): 48(1). Academic OneFile. Gale. BROWARD COUNTY LIBRARY. 4 May 2009
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