Researchers from the University of Washington have discovered a new way to help liquid flow in only one direction — but without flaps. In a paper published in the Proceedings of the National Academy of Sciences, the researchers report that a flexible pipe — with an interior helical structure inspired by shark intestines — can keep fluid flowing in one direction without the flaps that engines and anatomy rely upon.
Shark intestines, unlike human intestines, feature a network of spirals surrounding an interior passageway. In a 2021 publication, a different team proposed that this unique structure promoted a one-way flow of fluids, also known as flow asymmetry, through the digestive tracts of sharks and rays without flaps or other aids to prevent backup. That claim caught the attention of UW postdoctoral researcher Ido Levin, the lead author of the new paper.
“Flow asymmetry in a pipe with no moving flaps has tremendous technological potential, but the mechanism was puzzling,” Mr Levin said. “It was unclear which parts of the shark’s intestinal structure contributed to the asymmetry and which served only to increase the surface area for nutrient uptake.”
To answer these questions, the research team 3D-printed a series of ‘biomimetic pipes,’ all with interior helices inspired by the layout of shark intestines. They varied the geometrical parameters among these prototype pipes, such as the pitch angle of the helix or the number of turns. The first pipes were printed from rigid materials, and the team found that some showed a strong preference for unidirectional flow.
“The first measurement of flow asymmetry was a ‘Eureka’ moment,” Mr Levin said. “Until that instant, we didn’t know if our idealised structures could reproduce the flow effects seen in sharks.”
By further tuning the geometrical parameters and printing new designs, the researchers increased the flow asymmetry until it rivalled and even exceeded the designs of famed inventor Nikola Tesla.
“You don’t get to beat Tesla every day!” Mr Levin said.
But shark intestines — like human intestines — aren’t rigid. The team suspected that so-called ‘deformable structures,’ made from more flexible materials, might perform even better as Tesla valves. They 3D-printed a second series of prototypes made from the softest printable and commercially available polymer. These flexible pipe designs, which are better mimics for shark intestines through their ‘deformability’ and interior helices, performed at least seven times better than all previously measured Tesla valves.
Alshakim Nelson, an expert in developing new polymers, said, “Chemists were already motivated to develop polymers that are simultaneously soft, strong and printable. The potential use of these polymers to control flow in applications ranging from engineering to medicine strengthens that motivation.
Naroa Sadaba, a postdoctoral researcher on the team, said, “Actual intestines are still about 100 times softer than our soft material, so there is plenty of room for improvement.
Image: PRILL Mediendesign/stock.adobe.com
