Micromanipulation using cavitational microstreaming generated by acoustically oscillating twin bubbles

Abstract

This paper describes a novel non-invasive micromanipulation technique that employs the cavitational microstreaming generated by acoustically oscillating twin bubbles. First, a single acoustically oscillating bubble was attached to the tip of a rod that was combined with a three-dimensional traverse system, and a fish egg (diameter: 1mm) was then manipulated in an aqueous medium. Although the microstreaming generated by the single oscillating bubble was sufficiently strong to push and move the fish egg, the manipulation direction was uncontrollable. Hence, to improve the manipulation controllability, identical twin bubbles with the same size and resonant frequency were employed. The identical gas bubbles were generated on a microfabricated chip comprising sharp tip-shaped electrodes by employing an electrochemical method, electrolysis, and controlling the applied voltage and time. Subsequently, the bubbles were sequentially transferred to the tips of a U-shaped rod coated with a hydrophobic layer to improve the surface adhesion. The force generated from the acoustically oscillating bubbles and its direction were analyzed under various acoustic excitation conditions by using high-speed images. Our results showed that the generated force was proportional to the bubble oscillation amplitude, whereas the direction of the force depended on the distance between a bubble and object. A steel ball (500μm diameter) was used for investigating the force direction. When a bubble (600μm diameter) was acoustically excited, the steel ball was pulled toward the oscillating bubble when the distance between the bubble and ball was short (<3mm), whereas the steel ball was pushed away from the oscillating bubble when the distance was long (>3mm). Finally, a fish egg (diameter: 1mm) and glass beads (diameter: 100μm) were experimentally manipulated using acoustically oscillating twin bubbles.