Magnetically maneuverable micromixer using acoustically excited bubbles

Abstract This paper proposes a new type of magnetically actuated micromixer that rotates using acoustically excited bubbles to enhance the mixing performance for not only micro total analysis systems ( μ TAS) but also targeted drug delivery technologies. The micromixer is capable of being transported to a desired location at various microstructures using magnetic actuation. It can also increase mixing efficiency in viscous environments through minimally invasive process based on acoustically excited bubbles. The micromixer consists of four microtubes containing bubbles and a magnetic liquid metal that can be controlled by magnetic force. High-speed images are used to measure the maximum flow velocity of the microstreaming induced by an acoustically excited bubble in the microtubes of varying lengths and under different acoustic frequencies. When the bubbles of the micromixer are excited acoustically, the micromixer is rotated with microstreaming from the bubbles, and the rotating speed increases as acoustic frequencies approach the bubble’s natural frequency. To investigate the mixing performance, the micromixer mixes a safranin solution in an aqueous medium or a mixture of water and glycerin. The mixing index is then calculated using an image analysis program. The micromixer achieves complete mixing within 40 s, whereas natural diffusion without the micromixer takes considerably longer. The transportation of the micromixer through magnetic actuation is demonstrated and quantified by means of a neodymium magnet placed under a microchannel. As a proof of concept, we experimentally demonstrate the mobility of the proposed micromixer through magnetic actuation and its drug-mixing functionality, which is driven by acoustically excited bubbles in a Y-shaped microchannel.