Magnetic Propulsion and Manipulation of Achiral Swimmers in Polymer Fluids

Micro and nano scale swimmers, wirelessly controlled using magnetic fields, are envisioned to play a vital role in the future of targeted therapeutics. Thus far, design of these small scale devices has been guided by the Scallop theorem which states that, at low Reynold’s number, swimmers must exhibit non-time-symmetric motion. Common examples of artificial micro swimmer strategies include rotating rigid chiral helices, mimicking flagellated bacteria, and undulating flexible tails, reminiscent of spermatozoa locomotion. In addition to these methods of generating thrust, achiral objects that have no flexibility have been demonstrated to swim by meeting a minimum set of geometric requirements. These relatively simple swimmers can consist of linked particles or simple shapes that can be easily massively produced for potential application in biofluid environments. Here we characterize the swimming of mulit-bead achiral swimmers in different polymer fluids, demonstrating the effect of polymer chain length on swimming characteristics. We show the effect of bulk viscosity on the velocity profiles, step out frequency, and precession angle of the achiral swimmers. Our results show the ability to achieve controlled active propulsion of achiral swimmers in physiologically relevant viscosity ranges, providing evidence that these simple devices have potential for future in-vivo sensing and therapeutic applications.