Shark Intestines Inspire 3D Printed Pipes

Sometimes, the answers to design questions are not hidden in plain sight, but rather, in shark intestines. Such was the case in a study conducted by researchers at the University of Washington. The team was on a mission to understand whether pipes designed like shark and ray intestines would promote asymmetric flow, meaning, the one-way flow of liquids. Their interest in the question was prompted by a 2021 publication that supposed “shark intestines may operate as Tesla valves,” and the University of Washington team wanted to test the claim. The National Science Foundation, the Washington Research Foundation, and the Fulbright Foundation funded this research.

Ido Levin, lead author of the study, explained his interest in the subject. “Flow asymmetry in a pipe with no moving flaps has tremendous technological potential, but the mechanism was puzzling,” he said. “It was not clear which parts of the shark’s intestinal structure contributed to the asymmetry and which served only to increase the surface area for nutrient uptake.”

These are eight of the research team’s pipes with various interior helices (photo credits: Ido Levin/University of Washington)

Many pipes, including human intestines, have liquid flow controlled by moving flaps. However, these flaps can fail and cause backflow. By contrast, shark and ray intestines contain helical structures that loop around a cylindrical hole, promoting flow down the digestive tract. The researchers at the University of Washington wanted to see if they could create pipes modeled after this structure and realized their designs did indeed promote the desired flow asymmetry. “The first measurement of flow asymmetry was a ‘Eureka’ moment,” Levin said. “Until that instant, we didn’t know if our idealized structures could reproduce the flow effects seen in sharks.”