Bioinspired enzyme-powered microswimmer for pH-sensitive locomotion in the gastric mucus

Helicobacter pylori penetrates the gastric mucus by producing ammonia with urease, which locally raises the pH and turns the nearby gel into a solution. Here, we mimic this strategy by proposing an enzyme-powered microswimmer in the gastric mucus in one- and two-enzyme configurations. The surface-immobilized urease is considered the primary enzyme, which turns the gel into a viscous solution, while in some cases, a secondary enzyme is also coated and transforms the solution into the gel. The viscous solution and the gel are modeled as a Newtonian fluid and a Brinkman medium, respectively. A “binary” or “zero-one” coating pattern is established in which the “one” regions are coated with urease while the “zero” regions are coated with the second enzyme or are not coated. A parameter formulates the coating by specifying which part of the microswimmer’s half is coated with the first enzyme. Owing to this pattern, a winglet of the viscous solution is created for each half of the microswimmer. The diffusion of urease combines these two winglets to create a fluid pocket around the microswimmer, similar to H. pylori, but the second enzyme inhibits the development of this fluid pocket. The creation of the winglets and the pressure difference between the two sides propel the microswimmer in the mucus. The two-enzyme configuration better maintains the pressure difference by isolating the two winglets and reducing the symmetry. We obtain optimal coating parameters for each configuration to simultaneously create solution regions and maintain the pressure difference around the microswimmer.