Friday, September 12, 2008


Sharks may conjure up notions of great and fearsome predators, but one day, people may think of sharks equally as great teachers. Boat manufacturers to swimsuit designers today are scrutinizing sharks for design ideas. Pre-dating the dinosaurs, the design solutions generated over their 400-million-year evolutionary odyssey and embodied in their contemporary form give us plenty of reason to think sharks may hold design lessons for us. Over this enormous time period, shark evolution has successfully addressed a number of design challenges that turn out to relate directly to technological challenges currently facing humanity in our own quest to become a sustainable species.

Beauty Is Skin Deep (But Sometimes That’s Enough)
Shark skin is a multifunctional marvel. Seawater and the countless potential ecto-parasites within it (barnacle larvae, algae, bacteria, etc.) are a constant flow hazard for sharks, for whom moving efficiently through water is an imperative. Most shark species move through water with high-efficiency in order to catch fast-moving prey, obtain sufficient oxygen through largely passive gills, and maintain buoyancy. Through its ingenious design, their skin turns out to be an essential aid in this behavior by reducing friction drag and auto-cleaning ecto-parasites from their surface. Boat manufacturers have recently taken an interest in how sharks achieve their unimpeded movement through water both because friction drag and the attachment of organisms on a ship’s hull are major sources of energy inefficiency.

For decades, modern designers and engineers concerned with movement efficiency focused on the coarse shape and smoothness of an object. Howard Hughes’ H-1 Racer, for example, an aircraft which broke numerous speed records in the 1930s, sported revolutionary design features such as retractable landing gear and flush rivets. More recently, armed with greater tools for observation (such as scanning electron microscopes) and manufacturing, designers and engineers are developing an appreciation for the impact of finer-scale surface interaction dynamics. For example, while a shark’s coarse shape is famously hydrodynamic, shark skin is anything but smooth. The very small individual scales of shark skin, called dermal denticles (“little skin teeth”), are ribbed with longitudinal grooves which result in water moving more efficiently over their surface than it would were shark scales completely featureless. Over smooth surfaces, fast-moving water begins to break up into turbulent vortices, or eddies, in part because the water flowing at the surface of an object moves slower than water flowing further away from the object. This difference in water speed causes the faster water to get “tripped up” by the adjacent layer of slower water flowing around an object, just as upstream swirls form along riverbanks. The grooves in a shark’s scales simultaneously reduce eddy formation in a surprising number of ways: (1) the grooves reinforce the direction of flow by channeling it, (2) they speed up the slower water at the shark’s surface (as the same volume of water going through a narrower channel increases in speed), reducing the difference in speed of this surface flow and the water just beyond the shark’s surface, (3) conversely, they pull faster water towards the shark’s surface so that it mixes with the slower water, reducing this speed differential, and finally, (4) they divide up the sheet of water flowing over the shark’s surface so that any turbulence created results in smaller, rather than larger, vortices.

At the same time, three factors appear to help prevent marine organisms from being able to adhere to (“foul”) shark skin: (1) the accelerated water flow at a shark’s surface reduces the contact time of fouling organisms, (2) the roughened nano-texture of shark skin reduces the available surface area for adhering organisms, and (3) the dermal scales themselves perpetually realign or flex in response to changes in internal and external pressure as the shark moves through water, creating a “moving target” for fouling organisms.

Why It Matters
New surface coatings for boats which emulate shark skin texture and fine-scale movement have been shown to reduce fouling by 67% over conventional surfaces, and at 4-5 knots be completely self-cleaning. Due to their clean surfaces, boat hulls treated with these new shark-inspired surfaces are subsequently much more energy efficient. In addition, such boats do not require the toxic, biocidal chemicals used previously to clean their hulls of adhering organisms. Finally, the transportation of invasive aquatic species from one geographical location to another is greatly reduced. The applications for synthetic shark skin surfaces extend beyond boats, however, and range widely, from better-performing medical implants to faster swimsuits. The swimsuit company Speedo, for example, has incorporated shark-inspired textures into their swimsuits. The 3% improvement in swimming speed due to the original “shark-skin” suit likely contributed to the fact that 80% of the swimming medals won in the 2000 Olympics were won by athletes wearing Speedo’s Fastskin suits; swimmers wearing the suit also broke 13 of 15 world records. Speedo has made further modifications to their Fastskin suit based on continued research of shark skin and increased the swimming speed of its wearers further, generating further anticipation over the suit’s performance in the upcoming 2008 Olympics.

Beyond their skin, sharks are inspiring other technological innovations as well. A company called BioPower Systems, for example, has developed a device akin to a shark’s tail which converts wave energy to electrical energy, which is both more likely to withstand extreme weather conditions and less likely to injure marine species than blade-style wave-energy generators. Active research into sharks also includes understanding whether sharks have special mechanisms of immunity to reduce the incidence of cancer, and whether a gel-like substance they produce may be capable of converting thermal differences into electricity.

Shark Conservation

There are over 450 different species of sharks of incredible variety. However, the health of the world’s shark populations are of great concern. Tens of millions of sharks are killed by people each year due to intentional hunting and by-catch, and the number is increasing. In response, global shark populations are estimated to have plummeted by over 70% in the last two decades, pushing dozens of species towards extinction and triggering fundamental ecological changes in our oceans. Twenty percent of the world’s shark species are now classified as threatened with extinction, with new species being added to the threatened list with each new assessment.

Sharks have much to teach us and we have much to thank them for. Help us protect life’s genius through the Innovation for Conservation program.

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