Validation of tracking performance of cell–bubble aggregation versus variation of acoustic field

We are now developing an in vivo cell delivery system, which is realized by producing aggregates in which bubbles attach onto the surface of cells with acoustic radiation force. We confirmed the controllability of the aggregation of cells with bubbles compared with those without bubbles. However, because of the destruction of bubbles under continuous ultrasound exposure, there is a compatibility problem between controllability and duration of aggregation. Therefore, we introduced the use of a standing wave of an acoustic field to trap the aggregates in the nodes, in which the aggregates are not directly exposed to a high-pressure sound, and manupilation by varying the acoustic field. We prepared the travelling and oscillation motions of the ultrasound standing wave and investigated the mobility of aggregates that were trapped in the nodes of the standing wave to be translated two-dimensionally. Regarding travelling motion, we found that the node velocities of 10 and 20 µm/s showed better performance than that of 40 µm/s. Regarding oscillation motion, we succeeded in the continuous oscillation of aggregates for 36 s. Also, we found the problem of immobile cells, which was considered to be due to the destruction of bubbles.