Characterization and modeling of biomimetic untethered robots swimming in viscous fluids inside circular channels

Miniaturized robots with bio-inspired propulsion mechanisms, such as rotating helical flagella, are promising tools for minimally invasive surgery, diagnosis, targeted therapy, drug delivery and removing material from human body. Understanding the swimming behavior of swimmers inside fluid-filled channels is essential for design and control of miniaturized robots inside arteries and conduits of living organisms. In this work, we present scaled-up experiments and modeling of untethered robots with rotating helical tails placed inside tubes filled with viscous fluids to mimic swimming of miniaturized robots in aqueous solutions. A capsule that contains the battery and a small dc motor is used for the body of the robots. Helical tails with different wavelengths and wave amplitudes are used in experiments to compare swimming speeds and body rotation rates of robots in a cylindrical channel with the diameter of 36 mm. Three-dimensional governing partial differential equations of the fluid flow, Stokes equations, are solved with computational fluid dynamics (CFD) to predict velocities of robots, which are compared with experiments for validation, and to analyze effects of helical radius, pitch and the radial position of the robot on its swimming speed, forces acting on the robot and efficiency.