Self-Propelled Janus Microdimer Swimmers under a Rotating Magnetic Field

Abstract

Recent strides in micro- and nanofabrication technology have enabled researchers to design and develop new micro- and nanorobots for biomedicine and environmental monitoring. Due to its non-invasive remote actuation and convenient navigation abilities, magnetic propulsion has been widely used in micro- and nanoscale robotic systems. In this article, a highly efficient Janus microdimer swimmer propelled by a rotating uniform magnetic field was investigated experimentally and numerically. The velocity of the Janus microdimer swimmer can be modulated by adjusting the magnetic field frequency with a maximum speed of 133 μm·s^-1 (≈13.3 body length s^-1) at the frequency of 32 Hz. Fast and accurate navigation of these Janus microdimer swimmers in complex environments and near obstacles was also demonstrated. This efficient propulsion behavior of the new Janus microdimer swimmer holds considerable promise for diverse future practical applications ranging from nanoscale manipulation and assembly to nanomedicine.

Keywords: Janus microdimer; propulsion mechanism; rotating magnetic field.

Figure 1

Design and fabrication of Janus microdimer swimmers. (A) schematic of rotating magnetic field generation system; (B) fabrication of Janus microdimers; (C) optical microscopy image of microdimers after magnetization; (D) representative microdimers of different sizes.

Figure 2

Propulsion of microdimer swimmer under a rotating uniform magnetic field. (A) propulsion mechanism of microdimer in a rotating magnetic field; (B) time-lapse optical microscopy images depicting the motion of a microdimer within ~1 s.

Figure 3

Simulation of microdimer swimmer under a rotating magnetic field and near-wall flow field. (A) side and top views of the simulation models. Janus microspheres are represented by the blue and white balls, and the wall surface is depicted in cyan; (B) the applied rotating magnetic field with frequency of 5 Hz and strength of 5 mT; (C) the sequence profile of near-wall flow field surrounding the microdimer swimmer.

Figure 4

Performance of microdimer swimmers under different experimental parameters. The velocity of (A) single microspheres and (B) microdimers varied with the drive frequency; (C) tracking lines illustrating the traveled distances of different microdimers over a 1 s period in a rotating uniform magnetic field with frequencies from 10 to 40 Hz; (D) simulation results of microdimers velocity varied with the drive frequency; (E) velocity of microdimers at different magnetic field strength with a driving frequency of 1 Hz.

Figure 5

Controllable and flexible motility performance of microdimer swimmers. (A) change of the direction of movement of the microdimer swimmer caused by changing the magnetic field; (B) controllable curve motion of microdimer swimmer; (C) ‘star’ trajectory of microdimer swimmer; (D) how a microdimer swimmer detoured around an obstacle.