Tube size-dependent hydrodynamics and low-field magnetic immobilization of microrollers in channel flow

Magnetic microrollers demonstrated significant potential to navigate within blood vessels for biomedical applications. While the mechanisms of microroller movement in blood flow have been investigated, the influence of the fluid flow on their rotational behavior remains unexplored. This study establishes a dynamic model to analyze the motion of a magnetic microroller rolling along the wall of a confined tube. From a qualitative analysis perspective, the model reveals trends in how tube diameter and fluid flow affect the microrollers' rotational and translational motion. We conducted actual experiments, and the results demonstrated trends similar to those observed in the simulations. In addition, we analyze the motion of the microroller from the perspective of torque. Based on this understanding, a method was proposed to remotely immobilize microrollers in flow using a uniform static magnetic field, achieving immobilization at flow speeds up to 70 mm/s in a 4-mm-diameter tube with only a 4 mT field. This research enhances the understanding of the hydrodynamic behavior of magnetic microrollers within tubes, providing a bio-analogous perspective on microrollers in blood vessels of varying sizes and flow rates to optimize their magnetic control for practical use.