# Dynamics of groups of magnetically driven artificial microswimmers

## TL;DR

This paper investigates the collective dynamics of magnetically driven artificial microswimmers, revealing how they move and interact under magnetic fields, which is crucial for future biomedical applications involving controlled microscale motion.

## Contribution

It provides a detailed analysis of the fluid and group dynamics of microswimmers driven by magnetic fields using simulations, highlighting their coherent motion and fluid flow characteristics.

## Key findings

- Swimmers move in circular trajectories around a common center.
- The fluid velocity field resembles a rotlet, a point-torque flow.
- Groups of swimmers tend to move coherently, especially with uniform magnetization.

## Abstract

Magnetically driven artificial microswimmers have the potential to revolutionize many biomedical technologies, such as minimally-invasive microsurgery, micro-particle manipulation, and localized drug delivery. However, many of these applications will require the controlled dynamics of teams of these micro-robots with minimal feedback. In this work, we study the motion and fluid dynamics produced by groups of artificial microswimmers driven by a torque induced through a uniform, rotating magnetic field. Through Stokesian dynamics simulations, we show that the swimmer motion produces a rotational velocity field in the plane orthogonal to the direction of the magnetic field's rotation, which causes two interacting swimmers to move in circular trajectories in this plane around a common center. The resulting over all motion is on a helical trajectory for the swimmers. We compare the highly rotational velocity field of the fluid to the velocity field generated by a rotlet, the point-torque singularity of Stokes flows, showing that this is a reasonable approximation on the time average. Finally, we study the motion of larger groups of swimmers and show that these groups tend to move coherently, especially when swimmer magnetizations are uniform. This coherence is achieved because the group center remains almost constant in the plane orthogonal to the net motion of the swimmers. The results in the paper will prove useful for controlling the ensemble dynamics of small collections of magnetic swimmers.