Honed to hunting perfection by millions of years of evolution, there's a lot we can learn from sharks. More than just "Stay out of the water", "Keep the hell away from Amity Island" and how to play the cello. Their skin is a nanostructured surface perfected for their role as nature's flesh-seeking missile, and while human swimmers and boats aren't generally blood-motivated murderizers they can benefit from the same coating.
Synthetic shark skin might sound like the ultimate in faux-fashion disasters, but work at the University of Florida by materials engineer Tony Brennan and colleagues has allowed us to coat boats and even Olympic swimmers in this material. It turns out that shark skin is not smooth, but consists of thousands of "dermal denticles" and yes, that means "denticle" as in "dentistry and teeth". Not content with going through up to thirty thousand actual teeth in its lifetime, sharks are actually coated in adapted versions of the things - meaning it maintains its speed advantage literally by the skin of its teeth.
These scales have small-scale structure, a series of grooved channels which move slightly as the scales turn and flex with the shark's motion. It turns out that the smoothest possible surface won't increase your speed in the water - the layer of fluid right next to the smooth surface will be slowed down by friction, and as that water drags against the faster water further away turbulent vortices are created, every one of them slowing the submerged object down. The mini-ridges in the shark scales channel the water into faster flow, as well as mixing the slower and faster faster flows in a less turbulent manner. This involves hydrodynamics which takes a degree and some high-level simulation software to calculate, but a few million generations of sharks seem to worked out the hard way.
These coatings have been used in Speedo Fastskin swimsuits and boat hulls. You might associate Speedo with not wearing very much at all, but the FastSkin suit actually does cover a lot of flesh, and has conferred significant advantages on those who do so - wearers won 80% of all medals and broke 13 (of 15!) world records in the 2000 . Speedo have upgraded their shark-simulating skin, so expect to see even better performances (but hopefully no feeding frenzies) in Beijing this year.
Posted by Luke McKinney.
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