Two-dimensional manipulation of microbubbles using primary Bjerknes force

In this paper, two-dimensional (2D) microbubble manipulation is demonstrated using the primary Bjerknes force resulting from an ultrasound pressure gradient. This technique is expected to be useful in a variety of medical applications such as drug delivery systems, gene transfer mechanisms, and so on. Should this technique become established, it could allow microbubbles to be applied selectively to target cells and allow the positional relation between cells and microbubbles to be investigated quantitatively. However, in previous works, the acoustic manipulation of microbubbles has not been applied to precise spatial control in more than one dimension. Accordingly, as proposed microbubble manipulation tools, we prepared two devices, one utilizing four flat transducers and another using a six-channel (6-ch) ring transducer, both of which could create 2D acoustic pressure fields. Using these devices, it was found to be possible to trap and manipulate microbubbles as desired.