Abstract
ABSTRACT
Enzyme‐driven micromotors provide a promising platform for mimicking biological chemotaxis and for developing responsive materials. We recently developed a method to make cell‐sized asymmetric urease‐functionalized poly(lactic‐co‐glycolic acid) (PLGA) microcapsules that are highly motile in the presence of urea. Here, we investigate the chemotactic behavior of these microcapsules in urea gradients in a chemotaxis chamber. We demonstrate that urease‐functionalized microcapsules exhibit negative chemotaxis, migrating down urea gradients over a wide range of gradient magnitudes. The chemotactic flux increases with increasing urea gradients but saturates at high gradients, whereas increasing the average substrate concentration in a fixed gradient suppresses directional migration. We find that the direction of migration is independent of the orientation of the asymmetric particles. Buffered environments suppress chemotaxis, supporting a mechanism of motion that involves local pH changes or ionic self‐diffusiophoresis. A transport model of substrate consumption demonstrates that chemotactic behavior correlates with the relative concentration difference across the particle, whereas particle speed scales with the absolute concentration/corresponding osmotic pressure difference. These results establish negative chemotaxis as a robust feature of urease‐functionalized polymeric microcapsules and provide mechanistic insight into how enzymatic activity, substrate gradients, and ionic environments govern directional motion.