Deformable microswimmer in an external force field

Abstract

External forces, such as gravity, influence swimming microorganisms. For flagellar microorganisms, such as Chlamydomonas, gravitactic swimming has been attributed to back-heaviness. Using a simple bead-spring microswimmer model, we show that back-heaviness is not necessary for the gravitactic swimming of flagellar microorganisms. The hydrodynamic interaction among beads results in the alignment of swimming direction with external force. By modulating flagellar beating patterns a microorganism can also change its swimming direction. This understanding can aid in the design of robotic swimmers.