Propulsion Mechanism of Flexible Microbead Swimmers in the Low Reynolds Number Regime

Abstract

A propulsion mechanism for a flexible microswimmer constructed from superparamagnetic microbeads with different diameters and subjected to an oscillating field was studied experimentally and theoretically herein. Various types of artificial swimmers with different bending patterns were fabricated to determine the flexibility and an effective waveform for a planar beating flagellum. Waveform evolutions for various swimmer configurations were studied to determine the flexible mechanism of the swimmers. A one-armed microswimmer can propel itself only if the friction of its wavelike body is anisotropic. A swimmer with a larger head and a stronger magnetic dipole moment with a flexible tail allows the bending wave to propagate from the head toward the tail to generate forward thrust. The oscillating head and tail do not simultaneously generate positive thrust all the time within a period of oscillation. To increase the propulsion for a bending swimmer, this study proposes a novel configuration for a microbead swimmer that ensures better swimming efficiency. The ratio of the oscillation amplitude of the head to the length of the swimmer (from 0.26 to 0.28) produces a faster swimmer. On the other hand, the swimmer is propelled more effectively if the ratio of the oscillation amplitude of the tail to the length of the swimmer is from 0.29 to 0.33. This study determined the optimal configuration for a flexible microbead swimmer that generates the greatest propulsion in a low Reynolds number environment.

Propulsion efficiency of achiral microswimmers in viscoelastic polymer fluids

“…These swimmers of varying bead diameters achieve nonreciprocal motion because of structural deformation within its cyclic motion 21 . However, the assembled structure of these flexible swimmers are found to be unstable and achieve low propulsion efficiencies 22 . It has been shown that for non‐flexible swimmers, while the shape of an object is essential, the orientation of its transverse magnetic dipole governs swimming 23 .…”

“…21 However, the assembled structure of these flexible swimmers are found to be unstable and achieve low propulsion efficiencies. 22 It has been shown that for non-flexible swimmers, while the shape of an object is essential, the orientation of its transverse magnetic dipole governs swimming. 23 Recently magnetic microspheres that form rigid assemblies-termed achiral microrobots 24 have been shown to propel themselves when subject to an external magnetic torque.…”