Vortex-Driven Rotation for Three-Dimensional Imaging Under Microscopy

The noninvasive rotary motion of bio-objects for three-dimensional (3-D) observation and posture adjustment has been a great challenge in microrobotics. This letter reports a harmless noncontact 360° rotation method with a controllable velocity, which applied the vortex induced by vibrating the micropipette in an open fluidic environment. The micropipette was driven by a piezo actuator, which was mounted on a copper pillar. By generating a resonance between the copper pillar and the piezo actuator fed with sine wave of a specific frequency, we controlled the micropipette to vibrate circularly. The vibration-induced vortex around the micropipette could trap micro objects close to it, and then drive the trapped objects to rotate with the uneven drag force acting on their surface. Experiments of 360° rotation of the microbeads were carried out to demonstrate this method and analyze the rotation velocity. An application in 3-D imaging under optical inverted microscopy was achieved. The spheroids assembled by single cells were rotated, which enabled us to observe the different aspects of the cell spheroids and reconstruct its 3-D view.