Synthetic running and tumbling: an autonomous navigation strategy for catalytic nanoswimmers

Equipping miniaturised catalytic swimming devices with the ability to autonomously navigate in response to solution borne stimuli is an attractive route to enabling drug delivery and other transport applications. Here we use simulations of swarms of swimming devices made from pH responsive size changing hydrogels, to investigate their statistical response to pH variations. We find that the velocity modulation associated with size change, a recently discovered fundamental feature for the catalytic swimmer propulsion mechanism, produces a significant rapid statistical accumulation in high pH regions. This is augmented by size change induced modulation of the Brownian rotational rate, which unexpectedly also causes an accumulation in high pH regions, due to a caging effect imposed by the pH gradient. These simulations consequently show the feasibility of using size changing materials to navigate swimming devices autonomously in response to a stimulus within a constant fuel concentration environment.