Artificial gills (human)

Artificial gills are devices to let a human take in oxygen from surrounding water. This technology neither exists nor is in the early stages of development.

Methods

Several potential methods exist for the development of artificial gills. One proposed method is the use of liquid breathing with a membrane oxygenator to solve the problem of carbon dioxide retention, the major limiting factor in liquid breathing. It is thought that a system such as this would allow for diving without risk of decompression sickness.

They are generally thought to be unwieldy and bulky, because of the massive amount of water that would have to be processed to extract enough oxygen to supply an active diver, as an alternative to a scuba set.

An average diver with a fully closed-circuit rebreather needs 1 liter (roughly 1 quart) of oxygen per minute. As a result, at least 192 litres (51 US gal) of sea water per minute would have to be passed through the system, and this system would not work in anoxic water.

These calculations are based on the dissolved oxygen content of water. Other methods involve electrolysing water to produce gaseous hydrogen and gaseous oxygen. A diver needs, on average, about 1 mole of oxygen gas per hour. Water contains 88% oxygen by weight, and as two molecules of water are necessary to produce one molecule of diatomic oxygen gas, about 36 grams of water are needed to produce 32 grams of oxygen or one mole of oxygen gas. Assuming 1.0 grams/ml as the density of water, 36 ml (about 2.5 tablespoons) of water needs to be converted to oxygen per hour, assuming 100% efficiency. The reason for this large difference is the specific volume of a gas vs. a liquid. Natural gills work because nearly all animals with gills are thermoconformers, so they need much less oxygen than a thermoregulator of the same size.

Another potential source of oxygen generation is plastron respiration. A foam with hydrophobic surfaces immersed in water becomes superhydrophobic, which provides a water-air interface across which oxygen can diffuse into the foam. In nature, this method is used by some aquatic insects (such as water boatman, Notonecta) and spiders (such as Dolomedes triton) to breathe underwater without a gill. This method was experimentally proven by professor Ed Cussler on his dog.

Like-A-Fish

Like-A-Fish Technologies, an Israeli business founded by Alan Bodner in 2001, is currently testing an artificial gills prototype. Like-A-Fish's technology uses a centrifuge causing lower pressure at the center, where dissolved air comes out of the water.

As with any artificial gill using dissolved oxygen, air from a huge volume of seawater would have to be extracted to provide enough for breathing, requiring large amounts of power for pumping. Therefore, a key issue remaining is battery life. Currently, a 1-kg battery would only last for one hour, whereas a regular scuba tank can last longer (depending on depth). Regular scuba gear is also far simpler, and thus safer, with less to go wrong.

Like-A-Fish currently holds patents in Europe for its system.

See also

• Henry's law

External links

• (subscription required) History of attempts to develop artificial gills and the principles and problems involved.

• www.likeafish.biz Official website
• 'Like A Fish' Underwater Breathing System: Artificial Gills for U.S. Navy SEALs?
• Specific publication reference dates from an unusual source