Micro-object manipulation in a microfabricated channel using an electromagnetically driven microrobot with an acoustically oscillating bubble

• We developed a new type of electromagnetic system for the three-dimensional (3D) actuation of a microrobot.
• We investigated micro-object manipulation using an acoustically oscillating bubble.
• Micro-object manipulation in a microfabricated channel is achieved by the electromagnetically driven microrobot incorporated with an acoustically oscillating bubble.

This paper presents an untethered microrobot swimming in human blood vessels through electromagnetic actuation to manipulate bio/micro-objects using an acoustically oscillating bubble attached to the microrobot as a grasping tool. First, for the three-dimensional (3D) actuation of the microrobot in arbitrarily shaped blood vessels, an electromagnetic system consisting of horizontal and vertical pairs of Helmholtz and Maxwell electric coils is designed and manufactured, and the magnetic flux density generated from the designed system is verified with theory. Using the developed electromagnetic system, the actuation of a spherical microrobot (800 μm dia.) made of a cylindrical neodymium magnet covered with clay is successfully demonstrated in X–Y and X–Z planes along with a T-shaped glass channel. Second, micro-object manipulation using an acoustically oscillating bubble is separately investigated. When a bubble is acoustically excited by a piezoactuator around its natural frequency, it oscillates and simultaneously generates microstreaming and secondary radiation force, which can be used to capture a neighboring object. The capturing distance of an acoustically oscillating bubble (550 μm dia.) and its oscillation amplitude in different frequencies and voltages are measured by using a fish egg (1 mm dia.) and high-speed camera, respectively. The capturing distance is proportional to the bubble oscillation amplitude. The maximum capturing distance and bubble oscillation amplitude (ɛ = Δ/D) at its natural frequency (11 kHz) and 250 Vrms are approximately 2.3 mm and 0.13, respectively. Finally, as a proof of concept, the manipulation of a fish egg (800 μm dia.) in a microfabricated channel with tandem rectangular hills is experimentally achieved by the electromagnetically driven microrobot incorporated with an acoustically oscillating bubble.