Untethered microrobot actuated by an electromagnetic field with an acoustically oscillating bubble for bio/micro-object manipulation

This paper presents a novel non-invasive micromanipulation technique where a microrobot swimming in a three-dimensional space through electromagnetic actuation manipulates micro-objects using an acoustically oscillating bubble attached on the microrobot as a grasping tool in an aqueous environment. The concept of the micromanipulation method is experimentally proved along with studying both electromagnetic and acoustic actuation. Two dimensional manipulation of a magnetic piece is achieved through electromagnetic actuation using two pairs of electric coils installed in the surrounding of a water chamber. Micro-object manipulation is separately tested with glass beads (80 μm diameter) using an air bubble in an aqueous medium. When a bubble is acoustically excited by a piezoactuator around its resonant frequency, a radiation force generated from it pulls and grasps neighboring glass beads. The grasping force is indirectly measured by exposing the glass beads grasped by an oscillating bubble to a stream flow generated by an auto-syringe pump in a mini-channel. By measuring the maximum speed of the flow when the grasped glass beads are detached from the oscillating bubble and washed downstream, the grasping force is calculated as 50 nN based on the Stokes drag approximation. Finally, manipulation of a fish egg (800 μm diameter) is achieved with the integration of both electromagnetic actuation and acoustic excitation using a millimeter sized square magnetic piece where a bubble is attached on the bottom surface. This micromanipulation technique can be applied to emerging applications such as micro devices assembly and single-cell manipulation.