Boffins 3D-print biomimetic shark skin
The energy-saving secrets of Jaws' denticles revealed
Scientists from Harvard University have used 3D printing to reveal just how sharks lower their energy consumption in a cruise thanks to miniature teeth-like "denticles" on their skin.
Sharks are coated with million of these "overlapping tooth-like scales", known to reduce drag, but until George Lauder, James Weaver and Li Wen set about creating artificial shark skin, the exact process was a mystery.
The team took a skin sample from a shortfin mako (Isurus oxyrinchus), scanned its surface and created a computer model of thousands of denticles. Creating their biomimetic shark swimsuit proved problematic, however. Lauder explains: "After considering a number of approaches, we decided that the only way to embed hard denticles in a flexible substrate was the 3D printer.
"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."
One year later, however, the team had managed to produce a convincing man-made shark skin, with "thousands of rigid synthetic shark denticles ... placed on flexible membranes in a controlled, linear-arrayed pattern".
Tests showed just how the denticles increased the shark's underwater efficiency. The boffins' abstract in the Journal of Experimental Biology explains: "This flexible 3D printed shark skin model was then tested in water using a robotic flapping device that allowed us to either hold the models in a stationary position or move them dynamically at their self-propelled swimming speed.
"Compared with a smooth control model without denticles, the 3D printed shark skin showed increased swimming speed with reduced energy consumption under certain motion programs. For example, at a heave frequency of 1.5 Hz and an amplitude of ±1 cm, swimming speed increased by 6.6 per cent and the energy cost-of-transport was reduced by 5.9 per cent.
"In addition, a leading-edge vortex with greater vorticity than the smooth control was generated by the 3D printed shark skin, which may explain the increased swimming speeds."
Lauder enthused: "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."
The scientists conclude: "The ability to fabricate synthetic biomimetic shark skin opens up a wide array of possible manipulations of surface roughness parameters, and the ability to examine the hydrodynamic consequences of diverse skin denticle shapes present in different shark species."
Naturally, printed shark skin also offers the possibility of Olympic swimmers clad in biomimetic denticle body suits, although Lauder admitted that won't be happening in the near future. "The manufacturing challenges are tremendous," he noted. ®