Active control of microbubbles in a capillary flow by producing multiple acoustic radiation forces

We have ever reported our attempt to control the direction of microcbubbles in the flow of an artificial blood vessel by acoustic radiation force. However, the shape of the blood vessel was Y-form therefore too simple to be considered in vivo. Furthermore, the acoustic radiation force affected wide focal area because plane ultrasound was used. To set multiple transducers accurately, we need to position them using a very special configuration. Thus, we have improved our experiment by using a complex artificial blood vessel model and constructed an experimental system with multiple transducer fixtures including xyz-stage to set their respective focal points. In addition, we introduced focused waves of ultrasound for fine bubble control. Thus we prepared artificial blood vessels according to a capillary model, which were made of poly (vinyl alcohol) (PVA) by grayscale lithography method, with a minimum diameter of 0.5 mm. Then, we prepared two transducers to orient bubbles toward one desired path out of four originating from consecutive two bifurcations. Two acoustic fields were targeted at the consecutive bifurcations. We evaluated brightness of the four paths past the two bifurcations, which is decreased with bubbles existence. As a result, observed brightness of the desired path was significantly decreased compared with those of other paths. Difference between observed brightnesses increased with the number of ultrasound sources, which affect the amount of acoustic radiation force received by bubbles. From these results, microbubbles could be oriented to one desired path of multistep capillary. For further analysis, we are aiming at active control of bubbles in vivo.