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3D printing reveals the power of shark skinBy Jonathan WebbScience reporter, BBC NewsThe printed replica included tough denticles embedded in a smooth, flexible membraneContinue reading the main storyScientists have used a 3D-printed model of shark skin to show how tooth-like scales help the predators to cruise efficiently.Viewed up close, a sharks skin bristles with tiny teeth or denticles which aid swimming.Engineers have tried to mimic the roughness of shark skin when designing swim suits and even racing cars.But the denticles have never been so well reproduced before, says a reportin the Journal of Experimental Biology.Perhaps counter-intuitively, creating turbulence near the edge of a moving object can reduce drag. In this way, the denticles act like the dimples on a golf ball. Now, researchers have also seen them alter specific currents that help propel the shark through water.George Lauder and his colleagues took a detailed scan of a tiny square of skin from a mako shark, and built a 3D model of a single denticle just 0.15mm long.The challenge was then to manufacture a synthetic skin, with thousands of these denticles embedded in a smooth, flexible membrane.It took us about a year, said Prof Lauder, of Harvard University.First the team made a detailed 3D model of a single denticle3D printing builds up new objects layer-by-layer, following a computer-generated design. To print the shark skin, the scientists had to use two different materials for the hard, tooth-like structures and for the flexible base - much like the different coloured inks used to print a picture.The particular shape of the denticles also posed difficulties: Because theyre overhung, the 3D printers have to print a supporting material, which you then have to remove, Prof Lauder told the BBC. It took a while to work out all the tricks.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 said. 3D printing is it - what a marvellous application for it.Because the resolution of even the latest 3D printers is limited, the artificial denticles are about 10 times larger than the real ones seen on the skin of a mako shark.Nonetheless, when the team stuck the new artificial skin onto a small, flexible paddle and studied it in a water tank, they were able to see the benefit sharks glean from their unusual scales.A paddle with the new, toothy skin delivered a boost of up to 6.6% in swimming speed, compared to one coated with the smooth membrane alone. The artificial denticles also allowed the paddle to travel the same simulated distance while using 5.9% less energy.Thats a huge effect, when factored over the entire lifetime of an animal that is constantly swimming, said Prof Lauder.Sharks specialised skin appears to help most when they are cruising, rather than accelerating to catch preyMr Crimmen agrees. If you think about it, sharks, which dont have a swim bladder. are on the go most of their lives. Swimmings hard work, especially if youre of any size.Interestingly, the advantages were most obvious at relatively slow speeds, when the shark is cruising rather than pouncing. Its during the steady, long-distance migrations that youd really begin to see the benefits, Prof Lauder explained.Using a specialised technique to photograph the flow of water, the team also found that the leading edge vortex, a small whirlpool of low pressure generated by the paddles movement, was stronger with the denticles than without.Prof Lauder believes this change in water flow could be crucial. It can help suck the fish forward, he said. One of the things that our flow visualisation has suggested is that the structure of the skin may actually increase the thrust - the engine of propulsion - rather than just reducing the drag.When attached to a paddle and studied in a water tank, the artificial skin strengthened the leading edge vortex created by a swimming motion. Video courtesy of L. Wen, J. Weaver, G. LauderResearchers have studied the fluid dynamics of moulds and real samples of shark skin before. Prof Lauder is especially pleased with this new, 3D-printed model because it moves and bends, just like sharks. You have a rigid scale structure embedded into a flexible membrane, that can then swim.Dont expect to be pulling on a denticle-laden swim suit any time soon, however. Transferring this type of design to a textile might take decades, Prof Lauder said. But if you could do it, you would see a dramatic effect on swimming performance!The idea of copying design elements from biological systems is known as biomimetics.3D printing technology has made such mimicry a lot easier and, importantly, it allows the designs to be tweaked. For example, Prof Lauder and his team have already begun to play with the spacing, arrangement and shape of the denticles. I want to know what causes this effect, he said.Aside from that curiosity, Prof Lauder enjoys learning from nature. It pays us to understand how the natural world works, he told BBC News. Millions of years of evolution give us solutions to problems that we may not have thought of.3D打印解密鲨鱼皮的作用BBC新闻乔纳森韦伯报导被打印出的仿制品上有一层坚韧的“齿”，它们嵌入光滑的，柔韧的细胞膜表面。Figure 1被打印出的仿制品上有一层坚韧的“齿”，它们嵌入光滑的，柔韧的表面。科学家应用3D打印出的鲨鱼皮模型来研究齿形鳞片是如何帮助捕食者更有效的巡游。近处观察发现，鲨鱼皮上有很多直立的牙或小齿，这些有助于它在水中游动。于是，工程们在设计游泳衣甚至赛车时试图模拟鲨鱼皮的粗糙度。但是小齿在过去从未被仿制的这么好，一位试验生物学日报的记者如是说或许这是反直觉的，在移动物体边缘制造涡流会减少阻力。在此种情况下，小齿的作用相当于高尔夫球上的坑凹。现在，科研人员认为他们改变了流体的流动从而帮助推动鲨鱼在水中移动。乔治兰黛和他的同事对灰鲭鲨皮进行了一次小范围详细地扫描，并且建立了只有0.15mm长的单齿3D模型。接下来的挑战是制造人造皮，就是把成千上万个小齿嵌入到一个柔韧的、光滑的膜上。“这个过程耗时一年，”哈佛大学兰黛教授如是说。Figure 2制作出的详细的单齿3D模型3D打印技术是根据计算机设计要求，一层一层堆积的来制造新产品。为了打印出鲨鱼皮，科学家们必须使用两种不同的材料，一种用来制造硬的、齿形的结构，一种用来制造柔韧的基体，就好像是在打印一幅图像时应用不同颜色的墨水。小齿的特定形状也为研究制造了困难。“因为它们是悬挂式的，3D打印机必须打印出一种支撑结构，而起到支撑作用的这部分材料在稍后的进一步加工时需要被移除，”兰黛博士对BBC这样说。“寻求这些问题的解决办法花了我们一些时间。”奥利弗克里曼，国家历史博物馆的一名渔业专家对这种人造皮很感兴趣，他曾经建议速比涛在泳装上采用此种设计。“我过去总是在想，在地球上何种技术可以精确地仿制这么一个复杂的结构？”他说“3D打印技术可以，它的应用是多么惊人啊。”因为即便是最新的3D打印技术，其分辨率也是有限的，人造小齿大约是实际灰鲭鲨表皮上小齿的十倍大小。尽管如此，当团队把人造皮贴到一个小的、柔韧的船桨表面上并在水箱中进行实验时，他们便发现了鲨鱼从这种不寻常的鳞片中得到的益处。拥有齿形表皮的船桨与普通船桨相比会使船在水中的移动速度得到6.6%的提升。人造小齿也会使船在移动相同的模拟距离时使用节省5.9%的能量。“对于一个一生都在水中不停游动的海洋动物来说，这影响非常巨大，”兰黛博士说。Figure 3研究显示，鲨鱼特殊的皮主要是帮助它去巡游，而不是帮它在捕食中加速克里曼先生同意这