Experimental study of active control of microbubbles in blood flow by forming their aggregations

We have experimented a method to control behavior of microbubbles in flow using an artificial blood vessel with multiple transducers to emit ultrasonic plane wave. Microbubbules are propelled in flow owing to a primary Bjerknes force, which is a physical phenomenon where an acoustic wave pushes an obstacle along its direction of propagation. Also they form aggregation when they are put into an ultrasound field because of secondary Bjerknes force, which acts as attractive or repulsive factor among neighboring microbubbles. Thus we consider that forming bubble aggregations is effective to be propelled before entering into an ultrasound field to receive greater primary Bjerknes force. We have investigated the phenomenon of bubble aggregations and observed behavior of aggregations with and without red blood cells in artificial blood vessels under various conditions of ultrasound exposure. As the results, when microbubble aggregations were formed, the efficiency was improved more than the condition without forming aggregation. The existence of red blood cells near microbubbles contributed to the increase in the size of aggregations propelled against the vessel wall.