Multi-axial non-contact in situ micromanipulation by steady streaming around two oscillating cylinders on holonomic miniature robots

Abstract

In the field of micromanipulation, an in situ three-axial rotation of a microscale object remains difficult to realize, with rotational resolution and repeatability remaining low. In this paper, we describe the fundamental principle, properties, and experimental results of multi-axial non-contact in situ micromanipulation of an egg cell driven by steady streaming generated around an oscillating cylinder. A continuously oscillating cylinder generates the steady streaming that draws an egg cell toward the cylinder. If it is trapped by an eddy near the tip of the cylinder, it continuously rotates around the vertical axis at a fixed point. If it is trapped by a swirl flow generated around the side of the cylinder, it rotates around the horizontal axis. We define Reynolds number, Re, as arcω/ν, where a is half of the oscillation’s amplitude, rc is the cylinder’s radius, ω is the oscillation’s angular frequency, and ν is the kinematic viscosity. We demonstrate that the conditions of the vertical and horizontal rotations are determined by two dimensionless numbers: Re and a/rc. In our experiments, we obtained rotational resolutions of 0.05° and 0.11° and maximal angular velocities of 34.8°/s and 188°/s for the vertical and horizontal rotations, respectively. We also developed unique micromanipulation methods using two oscillating pipettes attached to holonomic miniature robots. We successfully manipulated five degrees of freedom (DoF) of the cell (three posture angles and two translational displacements along the X and Y axes) with the steady streaming. The proposed method enables a multi-axial, non-contact, in situ, and compact micromanipulation independent of the electrical, optical, magnetic, shape, and stiffness properties of the objects; moreover, it can be applied in microfluidics, biomedical, and heterogeneous microassembly applications.