May 15, 2014

Scientists from Harvard University have created artificial shark skin using 3D scanning and 3D printing, and they discovered that the remarkable structure can increase shark swimming speeds by 6.6%.

It's only when you get up close to a shark that you could see the sleek-looking skin is peppered with millions of microscopic overlapping tooth-like scales, called 'denticles'. The denticles disrupt the smooth flow of water over the animal's surface, reducing the drag that holds them back.

But scientists didn't know exactly how this happens. 'You can't modify real shark skin', explains George Lauder from Harvard University, USA. So Lauder and his colleagues Li Wen and James Weaver decided to try to create artificial shark skin instead.

After finding a mako shark in a local fish market, Lauder took a high-resolution scan of its surface. Next, he and Wen zoomed in on one denticle to build a detailed model of the structure, just 0.15mm long, and then create a 3D model of shark skin made of thousands of denticles.

a 3D model of a single denticle / via BBC

The next step is to construct the skin. 'After considering a number of approaches, we decided that the only way to embed hard denticles in a flexible substrate was the 3D printer', recalls Lauder, but this proved to be easier said than done.

'We had to figure out how to print them with multiple materials… The denticles are embedded into the membrane and overlap, which posed a key challenge for 3D printing,' recalls Lauder.

However, after a year of testing different materials, printing protocols and enlarging the denticles and their spacing, Weaver finally produced a convincing sample with the denticles secured in a flexible support. Because the limitation of 3D printer, the artificial denticles are about 10 times larger than the real ones seen on the skin of a mako shark.

'Seeing the [scanning electron micrograph] SEM of the curved membrane with the denticles was a great moment for us', smiles Lauder, who admits that the image of the SEM in the research paper is one of his favourite research images of recent years.

The 3D printed artificial shark skin included tough "denticles" embedded in a flexible membrane /via BBC

But how well would the artificial skin function in practice?

The team stuck the 3D printed artificial shark skin onto a flexible foil that could be held stationary in flowing water or flapped to move like a swimming fish, and studied it in a water tank.

they were impressed to see that the foil with the artificial skin reduced the drag by 8.7% at the lowest flow speeds, although at the highest flow speed the shark skin produced 15% more drag than the smooth membrane. However, when the team began flapping the foil like a fish, the shark skin improved swimming speed by 6.6%, using 5.9 percent less energy.

'This is the first time that anyone has measured the energetic cost of shark skin and the reduction in swimming cost relative to a smooth surface', says Lauder.

The next step is to test how changing the arrangement of the denticles will affect performance. However, Lauder doesn't think that we'll be wearing swimming costumes made from artificial shark skin soon: 'The manufacturing challenges are tremendous', he said.

The artificial skin has impressed Oliver Crimmen, a fish expert at the Natural History Museum who has previously advised Speedo on swim suit design.

"I used to think, how on earth would you mimic that complex structure accurately?" he told BBC. "3D printing is it - what a marvellous application for it."


Posted in 3D Printing Applications

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Noddy wrote at 9/26/2014 4:24:10 PM:

What 3D print process was to produce the sample skin? 2-Photon Lithography?

HUbert wrote at 5/17/2014 11:46:39 PM:

could be interesting to measure the impact of 3D printed shark skin in aerodynamic environment.

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