Hydrodynamic interactions between enzyme-powered microswimmers for pH-sensitive locomotion in gastric mucus

Artificial microswimmers have been widely studied for applications in drug delivery, medical imaging, and microsurgery. This study investigates the hydrodynamic interactions between enzyme-coated microswimmers in various arrangements to improve drug delivery in the gastric environment. Coating the microswimmers with urease facilitates movement by liquefying gel-like gastric mucus, as the structure of gastric mucus turns into a Newtonian fluid with an increase in pH. Furthermore, utilizing a second substance acting contrarily to urease improved swimming performance by maintaining the pressure difference between the two sides of the swimmers. Taylor's swimming sheet was used to model the two-dimensional rectangular swimmers in COMSOL Multiphysics. Brinkman and Newtonian models were used for the gel and liquefied mucus, respectively. Hydrodynamic interactions were investigated for two or more microswimmers initially located near each other with horizontal, vertical, or diagonal spacing. A velocity increase was observed for two swimmers in the horizontal arrangement compared with a single swimmer under the same conditions. However, the swimming velocities of the two swimmers in the vertical arrangement decreased. The diagonal case illustrated the features of the previous arrangements. Moreover, synchronization of the swimmers was the most important phenomenon in the diagonal case. Simulations were extended to groups of more than two swimmers. The horizontal arrangement again led to a significant increase in velocity. Furthermore, the zigzag arrangement was proposed to retain the features of both horizontal and diagonal cases. These arrangements can be used to design drug delivery cycles with swimming speeds lower or higher than a single swimmer.