A novel drug delivery method by using a 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 on the microrobot as a grasping tool. First, for the three-dimensional (3D) propulsion of the microrobot in arbitrary shaped blood vessels, an electromagnetic system consisting of the horizontal and vertical pairs of Helmholtz and Maxwell electric coils is designed and manufactured along with the verification of the magnetic flux density generated from the designed system with theory. Using the developed electromagnetic system, the propulsion of a spherical microrobot (800 μm dia.) made of a cylindrical magnet covered with clay is successfully demonstrated in x-y and x-z plains along with a T-shaped glass channel. Second, an acoustically oscillating bubble induced microstreaming is separately investigated by using a high speed camera integrated with a zoom lens and laser as a light source. When a bubble is acoustically excited by a piezoactuator around its natural frequency, it oscillates and simultaneously generates microstreaming and radiation forces, which can be used to manipulate (pull and push) neighboring objects. Finally, as the concept proof, the manipulation of a fish egg (800 μm dia.) in a microfabricated channel with tandem rectangular hills is experimentally achieved by the microrobot incorporated with an acoustically oscillating bubble.