2018 Volume 32 Issue 1 Pages 108-115
Microbubbles (MB) are widely used as contrast agents in ultrasound diagnostic imaging because of its surpassing responsiveness to several MHz band. Recently, many researchers are trying to apply MB and ultrasound to drug delivery system (DDS) using MB as drug carrier or gene transfer. For clinical application of MB-DDS, it is crucial to manipulate microbubbles contactlessly, capture in a desired place, and destruct them near the target. In this research, we developed a promising method to capture and manipulate Sonazoid using a concave transducer which radiates focused ultrasound. We used concave transducers, witch calibers were 40 mm and focal distances were 40 mm. The center of the transducers was made a 20-mm diameter hole in to allow observation light to pass through. We found that MB in focused ultrasound field can manipulate moving ultrasound focus mechanically, it is mainly the effect of primary Bjerknes force. The accuracy of the two-dimensional manipulation was 10 μm order. The manipulation force by primary Bjerknes force was 6 pN in 5.46 MHz, 4 kPa ultrasound conditions. The accuracy of the manipulation is sufficiently better compared to the focal width radiated by the concave transducer. When estimating trapping force near a bubble cluster formed at the focal region, secondary Bjerknes force is mainly acting on MBs in 10 μm order distance.
