Characterizing dynamic behaviors of three-particle paramagnetic microswimmer near a solid surface
Wang et al. Robot. Biomim.
Characterizing dynamic behaviors of three-particle paramagnetic microswimmer near a solid surface
Qianqian Wang 0
Lidong Yang 0
Jiangfan Yu 0
Li Zhang 0 1
0 Department of Mechanical and Automation Engineering, The Chinese University of Hong Kong , Shatin, Hong Kong SAR , China
1 Chow Yuk Ho Technology Centre for Innovative Medicine, The Chinese University of Hong Kong
Particle-based magnetically actuated microswimmers have the potential to act as microrobotic tools for biomedical applications. In this paper, we report the dynamic behaviors of a three-particle paramagnetic microswimmer. Actuated by a rotating magnetic field with different frequencies, the microswimmer exhibits simple rotation and propulsion. When the input frequency is below 8 Hz, it exhibits simple rotation on the substrate, whereas it shows propulsion with varied poses when subjected to a frequency between 8 and 15 Hz. Furthermore, a solid surface that enhances swimming velocity was observed as the microswimmer is actuated near a solid surface. Our simulation results testify that the surface-enhanced swimming near a solid surface is because of the induced pressure difference in the surrounding fluid of the microagent.
Swimming microrobot; Magnetic actuation; Boundary effect; Low Reynolds number; Dynamic behavior
Introduction
Microswimmers remotely actuated by magnetic fields
have been considered as promising microrobotic tools
because of their great potential in biomedical
applications [
1
], such as targeted therapy [
2
], drug delivery [
3,
4
] and minimally invasive surgery [5]. Various designs of
microswimmers combined with diverse magnetic
actuation strategies have been proposed [
6–10
]. Among them,
inspired by E. coil bacterial, helical microswimmer has
drawn attention of many researchers. For propulsion
of helical microswimmers, rotating magnetic fields are
widely used for the generation of corkscrew motion at
low Reynolds number. It was reported that, actuated by
a rotating magnetic field, the “artificial bacterial flagella”
(ABF) perform versatile swimming behaviors and can
act as effective tools for cargo transport and
micromanipulation tasks [
11–15
]. These ABF were fabricated using
self-scrolling technique [
11
], 3-D direct laser writing [
14
],
glancing angle deposition technique [
16, 17
], DNA-based
flagellar bundles [18], and so on. The dynamics of such
helical swimmers have been studied systematically
below, near and higher than the step-out frequency. For
instance, to perform corkscrew motion with continuous
rotation, usually a magnetic helical swimmer should be
actuated with an input frequency that is below its
stepout frequency, whereas the actuation with a frequency
that is higher than the step-out frequency will lead to a
so-called “jerky motion” [
19, 20
], i.e., the combination of
a rotation with stops and backward motions [21], which
results in a decrease in its translational velocity [
12, 22–
24
]. Interestingly, Ghosh et al. [24] reported that a helical
microswimmer could exhibit bistable behaviors under an
external field near the step-out frequency, showing
random switch between two configurations, i.e., propulsion
or tumbling motion.
Unlike the propulsion of tiny structures with
chirality in low Reynolds number regime, it has been
demonstrated recently that randomly shaped microswimmers
can also be actuated effectively using a rotating magnetic
field [
25, 26
]. These microswimmers are obtained using
iron oxide nanoparticle aggregations with varied shapes
based on hydrothermal carbonization. Alternatively,
Cheang et al. [27] reported that achiral three-particle
microswimmers exhibit controlled swimming motion
under a rotating magnetic field. These microswimmers
consist of three polystyrene microparticles embedded
with paramagnetic or ferromagnetic nanoparticles, and
varied swimming behaviors are triggered because of their
different magnetic properties, despite the geometrical
similarity.
It is notable that recent studies of three-particle
microswimmers focus on swimming behaviors in fluid with
negligible boundary effects [
27–29
]; however, their
swimming behaviors near a solid surface can be
significantly affected due to the boundary effect. Previously, the
boundary effects were reported on both natural
swimming organisms and artificial swimmers. The influence
of solid boundaries has been observed and analyzed for
E. coil bacteria [
30, 31
], and spermatozoa self-organized
into dynamic vortices resembling quantized rotating
waves on a planar surface [32]. A solid surface affects
swimming direction of ABF, resulting in drifting
behaviors [
14
], and wobbling motion of the ABF enhances the
sidewise drift due to wall effects [
33
]. Simulation results
indicate that microswimmer exhibits enhanced mobility
when swimming between inclined rigid boundaries [
34
],
and a surface can deform the induced streamlines of a
rotating microagent [
35
].
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