Amphibio artificial gills for a flooded future
If global warming causes catastrophic flooding that inundates most of the world's coastal urban areas by the end of the century, how will we cope? Biomimicry designer and material scientist Jun Kamei at the Royal College of Art's answer is Amphibio – a sort of lightweight 3D-printed vest made out of a polymer that acts as both an artificial gill and a breathing reservoir that will allow people to hang out in the submerged megacities.
Designed in collaboration with the RCA-IIS Tokyo Design Lab, Amphibio is Kamei's solution to a projected future in 2100 when global warming has melted the ice caps and rising oceans have affected 30 percent of the world's population. The intuitive reaction to such a disaster might be to move inland, but Kamei believes that a better idea would be to adopt a semi-aquatic lifestyle using something like the Amphibio artificial gill.
Still in the concept stage, Amphibio is a biomimetic artificial gill that's based on diving spiders and insects that have a superhydrophobic skin surface that allows them to gather a bubble of air around their bodies. These bubbles act like gills that let in oxygen dissolved in the surrounding water and release carbon dioxide.
Amphibio uses the same principle with a special and unspecified porous hydrophobic material that is suitable for 3D printing to create a sort of scalloped vest made of a series of air bladders that feed into a mask that covers the nose and mouth. Kamei describes Amphibio as being the intermediate point between free diving and scuba diving that allows divers to stay underwater longer using lighter equipment.
So far, Kamei has conducted lab tests with a test bladder filled with carbon dioxide and suspended in a tank to demonstrate its ability to absorb oxygen. He does admit that the design still has a long way to go, citing the fact that the surface area is too small and needs to be at least 32 m² (344 ft²) to gather enough oxygen for a person.
Though Kamei does acknowledge the engineering side of Amphibio, the technology is a very long way from being feasible, much less practical. The idea of an artificial gill has been mainstream since underwater pioneer Captain Jacques Cousteau declared in 1962 that the future of sea exploration was the creation of "menfish" who will breathe water. The problem is that there is a very large gap between the idea and the reality.
Since the first experiments were made using semipermeable plastic membranes to extract oxygen from water, the hurdles in making the idea practical quickly mounted up. At first, the technology looked like a winner as researchers put hamsters in membrane boxes submerged in fish tanks, but making something that does what a fish gill does is a lot harder.
If you look at a list of sea life, you'll notice that none of the sea mammals have gills. There are a number of reasons for this, but one of the biggest is that mammals have very high metabolisms that require a lot of oxygen to support. If you take a liter (34 oz) of air, it will hold 200 ml (6.76 oz) of oxygen. But if you have water, that comes out to only 5 to 10 ml (0.17 to 0.34 oz) of oxygen per liter. That's fine for cold-blooded fish, but an artificial gill worn by a person must process 10 to 20 times more water by volume than air, or 100 liters (26.5 gal) per minute at 100 percent efficiency to keep the diver alive.
That means a number of things are required. For one thing, it means a very large surface area comparable to the 50 to 75 m² (540 to 810 ft²) of the human lungs and it also means a lot of water flow. That's why early artificial gill designs featured heavily corrugated membranes stuffed into large backpacks with batteries, top-up air tanks, and massive impellers to push water through the device.
This isn't where the problems end. If oxygen and carbon dioxide can pass through an artificial gill material, so can neutral gases. While the gill can pick up oxygen from water, it can't get nitrogen, so the nitrogen in the diver's lungs, which makes up 78 percent, will quickly seep out and the hoses will collapse and the breathing mask will flood with water. This would be even worse with Amphibio because the layer of air trapped by the hydrophobic surface would be reduced and soon disappear as the nitrogen is diffused into the surrounding water.
The same applies to pressure. Artificial gills work best in very shallow water. If the diver goes down more than a few feet, water pressure will, again, collapse the hoses and the bladders and the face mask will flood. Scuba doesn't have this problem because it's designed to automatically compensate using a regulator, which provides air at ambient pressure for a given depth.
None of this invalidates the idea behind Amphibio, but it does need a lot more work on a very basic level to make it practical. If it ever does reach the market, it might be nice to go diving in some flooded cathedral. Though we'd recommend a mask, flippers, weight belt, and flippers instead of a diaphanous gown for the occasion.
The video below shows the tank test of an Amphibio bladder.
Source: Jun Kamei