Characterization of three-dimensional steering for helical swimmers

Helical microswimmers capable of propulsion at low Reynolds numbers have been proposed for many applications. However, closed-loop controlled helical swimmers are still challenging because of the limits of optical tracking, and a lack of control parameters lying on the swimming characteristics of both linear propulsion and steering. Although the linear propulsion characteristics of helical swimmers were extensively studied, the steering characteristics have not yet been clearly shown. Helical microswimmers are efficient in propulsion, whereas their high surface-to-volume ratio limits the steering performances. In this paper, we characterized both the direction and inclination steering using a real-time visual tracking of orientation. The direction steering efficiency could be increased in terms of response time with a higher inclination angle both in floating conditions and on a sticky substrate. We thus developed a 3D steering strategy by combining direction and inclination steering to improve the steering performance. We further expect that the characterization of steering performance can contribute to defining the control parameters for future closed-loop control.