Human blood is key to artificial gills

Press, 7 September 1984, Page 16

Human blood is key to artificial gills

From “The Economist,” London

Human blood is set to revolutionise underwater exploration. Using haemoglobin, the blood protein that carries oxygen, two American scientists have come up with an artificial gill for extracting oxygen from sea water and so allowing combustion engines to work under water. At present, deep-sea submersibles lug around oxygen cylinders and rely on short-lived batteries, yet oxygen is dissolved in the water all around them. If they could extract it, they could stay under indefinitely and use fossil fuels instead of electricity as a source of power: petrol can provide 300 times as much energy as a battery of the same weight.

The people inside the submersibles — or, for that matter, divers — could do without oxygen tanks. Substances that are good at getting oxygen out of water do so by reacting with it to form an oxide; they therefore do not give it up again without a struggle.

Nature has solved this problem with ingenious molecules like haemoglobin. At the heart of haemoglobin is an iron atom, with a high affinity for oxygen, but around it is a protein overcoat. Buried deep inside the protein, the iron atom is transformed into a tease: the oxygen can look but it cannot quite touch. It is only loosely held..

Doctors Joseph and Celia Bonaventura, co-directors of Duke University’s marine biomedical centre in North Carolina, have worked out how to use natural haemoglobin (from blood banks) in an artificial structure. It consists of a sponge of polyurethane or silica in which the haemoglobin molecules are immobilised. When in contact with sea water, the “hemosponge” collects oxygen just as a fish’s gill does. There are then two possible ways to remove oxygen from the structure; it is not yet clear which will work best. In the first, the sponge is placed in a vacuum, which mimics the lowering of the oxygen concentration that occurs when blood reaches, say, a muscle. In the second, ah electric charge is passed through the haemoglobin, stripping an extra electron from the iron atom and so destroying its affinity for oxygen.

The Bonaventuras’ technology is already patented. By the end of the year, they expect to have a prototype hemosponge that will enable an engine to breathe under water. By the end of 1985, they hope to do the same for a man. A cylinder, 10 feet long by three feet in diameter could supply 150 men working on the seabed with oxygen. a diver’s gill could be the size of an aqualung.

First, though, there are teething troubles to overcome. The Bonaventuras are trying to whittle the haemoglobin down to just the bit that matters, the iron-containing part called haem, without upsetting its properties. They are also experimenting with alternatives to the sponge structure, such as hollow fibres. Seawater could then be washed over the exterior of the fibre and oxygen drawn from its interior. The idea has stirred commercial interest. Aquanautics corporation of San Francisco bought the rights to the hemosponge for ?1 million and put $300,000 and some of its own scientists into the venture. Dr Max Perutz of Britain’s Medical Research Council in Cambridge, who shared a Nobel Prize for determining the structure of haemoglobin and myoglobin, has joined the board of Aquanautics. The company has also formed a joint venture with Duke University to exploit the wider applications of the technology. For instance, Dr Joseph Bonaventura believes that the hemosponge could provide cheaper oxygen for industrial use than conventional cylinders. Or a similar device, in which the sponge is impregnated with the enzyme carbonic anhydrase, could be used to scrub carbon dioxide from exhaled air in a breathing apparatus. Copyright, “The Economist.”