Stability of Helical Microswimmers Under Confinement

Artificial microswimmers are prospective agents for various microfluidic and medical applications. Many swimming scenarios involve confinement such as arteries or microchannels. Confinement affects swimming trajectories and velocities both for artificial and natural swimmers. Typically, helical swimmers which are rotated by an external torque follow helical trajectories in the pusher-mode while they follow the centerline of the channel in the puller-mode depending on the geometry of the swimmer and the channel. In order to study the effects of geometric parameters on the trajectories of swimmers inside channels, kinematics of the swimmer is coupled with a CFD model, which is used to obtain linear and angular velocities of the time-varying system subject to magnetic torques and contact forces. The force dipole created by the rotating swimmer contributes to pusher-mode instability.  The level of instability is measured by the non-dimensional radius of the helical trajectories. The effects of geometric and physical parameters on stability are reported to improve the understanding on stability of the swimmers under confinement which is expected to be crucial for controlled navigation.