We have previously reported our attempts for active control of microbubble aggregations, by making use of Bjerknes force, which acts to propel microbubbles and to adjust the size of aggregations. However, because we have used simple shape of artificial blood vessels, the behavior of aggregations in a capillary, e.g., probability to obstruct in bloodstream, possibility of embolization, has not been predicted. Thus we measured the sticked area of produced aggregation on a wall of artificial blood vessel before evaluating the volume flown to downstream. First we prepared the straight path model of artificial blood vessel with the diameter of 2 mm to produce aggregation by emitting ultrasound against flow, which conditions were with 5 MHz and 300-500 kPa-pp. The size of aggregation increased according to the sound pressure, whereas there would be an optimal flow velocity and suspension density to obtain maximum trapped performance. The flat rate of aggregation showed that sound pressure works to compress the shape of aggregation rather than the effect of flow velocity. Then we derived the conditions to obtain a desired volume of aggregation to apply to the multi-bifurcation model of artificial blood vessel, which has repeatedly divided paths until the middle of the model from the inflow path of 2 mm to the minimum diameter of 0.5 mm, to confirm the behavior of an aggregation. Using the flow velocity of 20 mm/s, maximum sound pressure of 300 kPa, and suspension density of 0.08 μl/ml, the volume of aggregation was expected to be 0.6 mm3, which is greater than the section area of the narrow path in the bifurcation model. The result showed that the aggregation, in 50 s after the injection of the suspension, flaked off the vessel wall, flew to downstream, and was caught at a bifurcation. Finally we clearly confirmed that the aggregation blocked a path, where colored water could not penetrate to downstream.
