Encountering obstacles: microrollers interacting in complex and structured environments.

Micro swimmers in a fluid can either self-propel or be driven by external forces. The interactions between micro swimmers and their surroundings lead to a wide range of phenomena: self-assembly, phase separation, hydrodynamic trapping, etc. They can also sense the microstructure of the fluid or the boundary geometries, which changes their motion. In our experiments, I explore how magnetically driven microrollers maneuver in a structured environment. When the rollers are spun by an external magnetic field, they pump fluid around themselves, driving them to move in the desired direction. This also generates strong and long-range flows. I will demonstrate how such flows interact with a complex fluid and generate new structure, and how the fluid structure influences the roller motion. I will also discuss how the boundary geometries interact with microrollers through the flow and manipulate the microroller motion.