Micro-capsule trapping and destruction in an acoustic standing wave

Abstract

Micro‐capsule trapping and destruction in an acoustic standing wave is examined. In an ultrasonic drug delivery system, micro‐capsules are expected to release the drugs inside at the moment of their destruction. In this report, optical observation of capsule destruction using a high‐speed video camera is carried out. As the driving sound pressure of the standing wave is increased, the capsule can be trapped at the anti‐node. The sound pressure threshold for capsule trapping depends on the radii of micro‐capsules and is lowest under the resonance condition, i.e., the larger capsule can be trapped easily at the anti‐node; however, the larger‐than‐resonance capsule cannot be trapped at the anti‐node. Micro‐capsule destruction is also examined in continuous and the pulsed waves. At the moment of destruction, the micro‐capsule has a non‐spherical shape and the internal gas jets out of the capsule instantly. As the driving pulse duration is increased, the capsule destruction becomes violent. The sound pressure threshold for capsule destruction has its lowest value at resonance. Capsule destruction by pulsed waves depends mostly on the amplitude of the sound pressure rather than the pulse duration.