Characterization and Modeling of Biomimetic Untethered Robots Swimming in Viscous Fluids Inside Circular Channels

Miniaturized robots with bioinspired propulsion mechanisms, such as rotating helical flagella, are promising tools for minimally invasive surgery, diagnosis, targeted therapy, drug delivery, and removing material from the human body. Understanding the locomotion of swimmers inside fluid-filled channels is essential for the design and control of miniaturized robots inside arteries and conduits of living organisms. In this paper, we describe scaled-up experiments and modeling of untethered robots with a rotating helical tail and swimming inside a tube filled with a viscous fluid. Experiments mimic low Reynolds number swimming of miniaturized robots inside conduits filled with 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 geometric parameters are manufactured and used to obtain swimming speeds and body rotation rates of robots inside the cylindrical channel. Three-dimensional incompressible flow around the robot inside the channel is governed by Stokes equations, which are solved numerically with a computational fluid dynamics (CFD) model. Predicted velocities of robots are compared with the experimental results for the validation of the CFD model, which is used to analyze effects of the helical radius, pitch, and the radial position of the robot on the swimming speed, forces acting on the robot, and efficiency.