Controlled Noncontact Manipulation of Nonmagnetic Untethered Microbeads Orbiting Two-Tailed Soft Microrobot

摘要

A rotating two-tailed soft microrobot induces a frequency dependent flow-field in lowReynolds number fluids. We use this flow-field to achieve noncontact manipulation of nonmagnetic microbeads with average diameter of 30 mu m in 2-D space. Our noncontact manipulation strategy capitalizes on exerting a rotational magnetic torque on the magnetic dipole of the microrobot. The induced flow-field enablesmicrobeads in the surrounding fluid to orbit the microrobot along a sprocketlike trajectory due to a periodic and asymmetric flow-field caused by the two tails. Ahydrodynamic model of the two-tailed microrobot and the orbiting microbeads is developed based on themethod of regularized Stokeslets for computing Stokes flows. The relations between the angular velocity of the orbiting microbeads and the rotation frequency of the microrobot, their proximity (p), and tail length ratio of the microrobots are studied theoretically and experimentally. Our simulations and experimental results showthat the angular velocity of the orbiting microbeads decreases nearly as vertical bar p vertical bar(-2) with the distance to the microrobot and its tail length ratio. We also demonstrate closed-loop control of the microbeads toward target positions along sprocketlike trajectories with an average position error of 23.1 +/- 9.1 mu m (n = 10), and show the ability to swim away without affecting the positioning accuracy after manipulation.