AUTHOR=Codutti Agnese , Bachmann Felix , Faivre Damien , Klumpp Stefan 

TITLE=Bead-Based Hydrodynamic Simulations of Rigid Magnetic Micropropellers

JOURNAL=Frontiers in Robotics and AI

VOLUME=Volume 5 - 2018

YEAR=2018

URL=https://www.frontiersin.org/journals/robotics-and-ai/articles/10.3389/frobt.2018.00109

DOI=10.3389/frobt.2018.00109

ISSN=2296-9144

ABSTRACT=The field of synthetic microswimmers, micro-robots moving in aqueous environments, has
evolved significantly in the last years. Micro-robots actuated and steered by external magnetic
fields are of particular interest because of the biocompatibility of this energy source and the
possibility of remote control, features suited for biomedical applications. While initial work has
mostly focused on helical shapes, the design space under consideration has widened considerably
with recent works, opening up new possibilities for optimization of propellers to meet specific
requirements. Understanding the relation between shape on the one hand and targeted actuation
and steerability on the other hand requires an understanding of their propulsion behavior. Here we
propose hydrodynamic simulations for the characterization of rigid micropropellers of any shape,
actuated by rotating external magnetic fields. We approximate the shape of micropropellers by
an ensemble of rigidly connected spheres, for which the mobility matrices can be calculated via
the method of reflections. We characterize the influence of model parameters such as bead size,
distance between beads and magnetic properties on the swimming behavior of helical propellers
to identify optimal simulation parameters. We then apply the simulation to randomly shaped
propeller, specifically to a recently characterized propeller shape and study their frequency-
dependent swimming behaviors. The simulations show that the orientation of the magnetic
moment with respect to the propeller’s internal coordinate system has a strong impact on the
propulsion behavior and has to be known with a precision of ≤ 5 ◦ to predict the propeller’s
velocity-frequency curve. This result emphasizes the importance of the magnetic properties of
the micropropellers for the design of desired functionalities for potential biomedical applications,
and in particular the importance of their orientation within the propeller’s structure.