Flow-Induced Deformations Amplify Flow Asymmetry in Shark-Inspired Helical Pipes

While human intestines are long hollow tubes, the intestines of sharks and rays contain interior helical structures surrounding a cylindrical channel. These structures may induce asymmetric flow, favoring anterior-to-posterior fluid passage through the digestive tract. Here, we design and 3D-print biomimetic models of shark intestines using both rigid and deformable materials. Using rigid models, we identify which physical parameters of the interior helices—pitch, channel radius, tilt angle, and number of turns—produce the largest flow asymmetries. These asymmetries exceed those of traditional Tesla valves, structures specifically designed to create flow asymmetry without moving parts. When printed in elastomeric materials that enable flow-structure coupling, flow asymmetry amplifies sevenfold compared to rigid structures. We confirm this enhancement arises from flow-induced deformation by printing a simulated deformed geometry from rigid material, which yields similar asymmetry enhancement. This ability to control flow direction through structural design has applications in biological tissues and engineered devices across many scales, from large industrial pipelines to microscale microfluidic systems. Our results demonstrate the significant advantages of incorporating deformability into fluidic device design.