Printing Swarks of the skin

The shark is a unique swimmer, fast and silent, and it achieved such results largely due to the unique structure of the skin. The skin of the sharks is covered with tiny scales (skin cloves), which are dentin plates with a relief surface. Each record ends with a protruding enamel spike, inside it, like a real tooth, has blood vessels and nerve endings. In different species and even different representatives of the same species, the form of scales varies. On the fins and torso of the shark, dentures are also of different shapes. In recent years, scientists are actively interested in how rough scales affects water resistance. This problem has been dealt with by Harvard University specialists led by Professor George Lauder. Scientists analyzed the stationary models of scales, as well as the hydrodynamic properties of pieces of real skin. These experiments have shown that roughness improves the hydrodynamic properties of the surface, but, alas, the researchers could not change the structure of scales and, therefore, study in detail the influence of different parameters on the speed of swimming. So, in experiments with natural shark skin, they used polished shreds with worn scales as control. However, the researchers did not achieve “smooth” control, the processed surface still remained. Therefore, they decided to make artificial skin, consisting of hard cloves attached to a flexible membrane, and test it in different hydrodynamic conditions. In this case, the shape and structure of scales can be changed, and use a clean membrane for comparison.

Researchers studied a fragment of the skin of a herring shark, it is also a shark of maco Isurus oxyrinchus, caught near Boston, and with the help of computed tomography received detailed three -dimensional images of its skin cloves. Then thousands of artificial hard cloves were printed on a BD printer. The real scales of the sharks are so small that the printer cannot recreate them with due accuracy. Researchers had to make a model increased 12.4 times. But even with such an increase, the artificial scales turned out to be tiny - only 1.5 mm in length.

Artificial solid scales are firmly “nucked” in a flexible membrane in size 177 by 77 mm. As a control, scientists used a smooth membrane, and so that it did not differ in mass from the prototype, make it a little thicker. Artificial skin or smooth membrane was glued on two sides on a sheet of flexible plastic. Samples were placed in a tank of water and tested at different flow speeds. Researchers used a device that allows you to bend a sample with various amplitude and speed, simulating the movements of skin shark during swimming.

In many experiments, the skin covered with scales has advantages over smooth. If the sample is motionless, it has less static resistance. When it fluctuates, it facilitates the shark swimming. For example, at a rate of oscillations of 1.5 Hz and amplitude, one centimeter speed should increase by 6.6% with a reduction in energy expenses by 5.9%. The hydrodynamic characteristics of the skin, apparently, depend not only on the geometry of scales, but also on their mutual location, which changes during movement. The oscillation rate of the sample affects its curvature, and therefore, the mutual arrangement of the teeth, the dynamics of the flow of water at the surface and on the speed of swimming.

George Lauder and his employees praise 3D printing, which allows you to very quickly make a fairly large and complex structure of the sample, which combines materials with different mechanical properties. None of the other method allows you to reproduce the structure of skin sharks with such accuracy. The only restriction of the method is that the 3D printer cannot print very small details, so the researchers had to be satisfied with the enlarged model. However, non -compliance with the size did not interfere with the experiment. In addition, different types of sharks are scales of different sizes, and some of them can be recreated in full size.

Now that the researchers have developed a 3D printing technology with artificial shark skin, they can change the size, morphology and mutual arrangement of cloves, which opens up new opportunities for studying the hydrodynamic properties of various rough surfaces. Such studies will help to understand why sharks have different scales on different parts of the body. And, of course, the work will have applied value.

On the basis of the article: LI Wen, JC Weaver and GV Lauder “Biomimes Shark Skin: Design, Fabrication and Hydrodynamo Function”, The Journal of Experimental Biology, 2014, 217, 1656-16666666666666666666666666666666666666666666666666666666666666666666666666666666666666666666U DOI: 10.1242/jeb.097097