The capture of flowing microbubbles with an ultrasonic tap using acoustic radiation force.

The accumulation of 1–10 μm phospholipid-shelled microbubbles was demonstrated by creating an “ultrasonic tap” using acoustic travelling waves. Microbubbles were flowed through a 200 μm cellulose tube at rates ranging between 14–50 ml/h, in order to approximate the velocities and wall shear rates found throughout the human circulatory system. The generated acoustic radiation force directly opposing the flow direction was sufficient to hold microbubbles in a fluid flow up to 28 cm/s. Clusters of microbubbles subject to wall shear rates of up to 9000 s−1 were retained near a pressure null for several seconds.