External chemical gradient leads to efficient swimming of chiral swimmers

Abstract: External gradients can strongly influence the collective behavior of microswimmers. In this paper, we study the behavior of two hydrodynamically interacting self-propelled chiral swimmers, in the low-Reynolds number regime, under the influence of an external linear chemical gradient. We use the generalized squirmer model called the chiral squirmer, a spherically shaped body with an asymmetric surface slip velocity, to represent the swimmer. We find that the external gradient favors the attraction between the swimmers and, in some situations, leads to a bounded state in which the swimmers move in a highly synchronous manner. Further, due to this cooperative motion, swimmers efficiently reach the chemical target compared to the individual swimmers. This study may help to understand the collective behavior of chiral swimmers and to design synthetic microswimmers for targeted drug delivery.