An aquatic microrobot for microscale flow manipulation

Abstract

Microrobots have been developed and extensively employed for performing the variety tasks with various applications. However, the intricate fabrication and actuation processes employed for microrobots further restrict their multitudinous applicability as well as the controllability in high accuracy. As an alternative, in this work an aquatic microrobot was developed using a distinctive concept of the building block technique where the microrobot was built based on the block to block design. An in-house electromagnetic system as well as the control algorithm were developed to achieve the precise real-time dynamics of the microrobot for extensive applications. In addition, pivotal control parameters of the microrobot including the actuating waveforms together with the operational parameters were verified and discussed in conjunction with the magnetic intensity simulation. A mixing task was performed with high efficiency based on the trajectory planning and rotation control of the microrobot to demonstrate its capability in flow manipulation which can be advantageous for microreactor applications down the load. Aside from it, a dissolution test was further conducted to provide an on-demand flow agitation function of the microrobot for the next level of lab chip applications. The presented work with detail dynamic analysis is envisaged to provide a new look of microrobot control and functions from the engineering perspective with profoundly potential applications.

Figure 1

Fabrication of the aquatic microrobot and electromagnetic actuation system. (a) The fabrication process of the microrobot. (b) Geometry of the microrobot, top-left is the isometric view of microrobot design; top-right is the top front view of microrobot design; the bottom-right is the top view of the microrobot under microscope imaging. (length: 1000 µm, width: 300 µm, Height: 300 µm). (c) Setup of the in-house eight-coil electromagnet platform for the microrobot control.

Figure 2

Performance of the microrobot under different control parameters. (a) Typical illustration of all the three waveforms, moving trajectories in x and y-direction of microrobot controlled by triangle (black curve), sawtooth (red curve), and sinusoidal (green curve) waveforms with 9 Hz of frequency respectively along with the microphotographs of the microrobot. (b) Moving trajectories in x-direction and (c) y-direction of the microrobot controlled by sinusoidal waveform with 3, 6, 9, 12, and 15 Hz of frequency. Error bars represent one standard deviation in either direction from three repeated trials.

Figure 3

Effects of the magnetic actuation on the mixing efficiency in the absence of microrobot (mode I), under static rotation (mode II), and rotation with translation (mode III). In the top-left, Microphotographs (time-lapse snapshots) captured during moving speed edge to edge moving speed for mixing enhancement at t = 0 s and t = 40 s. In the bottom-left, Schematic illustration of the microrobot’s motion (edge-to-edge rotation with translation motion) in water under a rotating magnetic field for various time period (t = 10, 20, 30, and 40 s). Error bars represent one standard deviation in either direction from three repeated trials. Scale bar is 1 mm.

Figure 4

Performance of the microrobot in dissolution of NaCl crystal. (a) Shrinkage percentage of NaCl crystal dissolved in an open tank in the absence of microrobot (mode I), under static rotation (mode II), and rotation with translation mode (mode III). Microphotographs (time-lapse snapshots) captured during rotation with translation mode at t = 0 s and t = 200 s. (b) Shrinkage percentage of NaCl crystal dissolved in the closed channel in the absence of microrobot, and with microrobot. Microphotographs (time-lapse snapshots) captured during the second mode (with microrobot) at t = 0 s and t = 150 s. Error bars represent one standard deviation in either direction from three repeated trials. Scale bar is 1 mm.