Swimming Kinematics of Achiral Microswimmers in Viscous Media

As opposed to more common flexible and chiral structures which can swim in bulk fluid, geometrically simpler achiral structures have often relied on nearby solid boundaries to break the symmetry of cyclic swimming strokes. However, achiral microswimmers with at least two planes of geometric symmetry have been found capable of propulsion in the absence of confining walls. Here, microswimmers consisting of three and four concatenated magnetic microparticles, forming arc structures with two planes of symmetry, are fabricated through self-assembly. As achiral microswimmers are envisioned for biological applications where the microenvironment is made up of mostly non-Newtonian fluids, using a uniform rotational magnetic field, we investigated their swimming kinematics, specifically velocity, precession angle, and their ability to change direction in a series of dilute methylcellulose solutions which mimic biofluids. Non-linear relationships are observed between methylcellulose concentration and propulsion characteristics. The observed swimming behaviors may enable the development of future achiral microswimmer designs and control strategies for propulsion in complex media.