Researchers have found a new method to ensure liquids flow in just one direction, eliminating the need for flaps which are commonly used in engines and our circulatory systems to prevent fluid backflow. The innovative solution involves a flexible pipe designed with a helical interior structure, inspired by the anatomy of shark intestines, resulting in a prototype that has potential uses in both engineering and medical fields.
Flaps serve crucial functions. In systems like pumping hearts and engines, they facilitate the unidirectional flow of fluids. Without them, it’s difficult to maintain the correct path for liquids.
A team of researchers from the University of Washington has developed a method to direct liquid flow solely in one direction without relying on flaps. According to a paper published on September 24 in the Proceedings of the National Academy of Sciences, the research highlights a flexible pipe with a helical structure akin to shark intestines that effectively manages fluid flow direction without the need for mechanical components.
Human intestines function as hollow tubes, whereas the intestines of sharks and rays are notable for their spiral design that wraps around a central opening. In research published in 2021, another team suggested that this distinctive design facilitates unidirectional fluid movement—known as flow asymmetry—through the digestive systems of sharks and rays, without the use of flaps or similar devices to stop backflow. This concept piqued the interest of UW postdoctoral researcher Ido Levin, the primary author of the current study.
“The idea of achieving flow asymmetry in a pipe without active flaps offers vast technological possibilities, but the underlying mechanism was unclear,” notes Levin. “We needed to identify which parts of the shark’s intestinal architecture affected the flow asymmetry and which merely expanded the surface area for nutrient absorption.”
To address these inquiries, Levin led a research team that included co-authors Sarah Keller and Alshakim Nelson, both professors of chemistry at UW, along with fellow postdoc Naroa Sadaba. They created a series of “biomimetic pipes,” which all featured internal helices resembling those found in shark intestines. They varied the design parameters of these prototypes, including the helix’s pitch angle and the number of turns. Their initial models were made from rigid materials, and some displayed a significant preference for unidirectional flow.
“The first observation of flow asymmetry felt like a ‘Eureka’ moment,” Levin recounted. “At that point, we were uncertain whether our conceptual structures could replicate the flow phenomena observed in sharks.”
By further refining the design parameters and producing additional models, the researchers were able to enhance the flow asymmetry to the point where it matched or even surpassed the designs of the renowned inventor Nikola Tesla. More than a century ago, Tesla patented a one-way fluid flow device—known as the Tesla valve—that operates without moving parts.
“It’s not every day you can claim you’ve outdone Tesla!” exclaimed Levin.
However, shark intestines—just like human intestines—are not rigid structures. The research team hypothesized that “deformable structures,” constructed from more flexible materials, could yield even better results as Tesla valves. They then produced a second series of prototypes from the softest commercially available and 3D-printable polymer. These flexible designs, which more closely resemble shark intestines due to their pliability and internal helices, exhibited performance that was at least seven times superior to any previously tested Tesla valves.
“Chemists are already keen on creating polymers that are soft, strong, and 3D-printable,” stated Nelson, who specializes in developing innovative polymer types. “The prospects of using these polymers to manage fluid flow in diverse fields, from engineering to healthcare, significantly motivates this work.”
“Real intestines are roughly 100 times softer than our soft material, so there is still substantial opportunity for improvements,” said Sadaba.
Keller attributes the success of the project to the interdisciplinary collaboration across biology, chemistry, and physics, as well as to the unique structures found in sharks themselves.
“Biomimicry serves as a powerful avenue for discovering new design possibilities,” noted Keller. “We might not have arrived at these structures on our own.”
This research was supported by the National Science Foundation, the Washington Research Foundation, and the Fulbright Foundation.
