Schematic diagram of RUF-mediated co-localization of macrophages and drug-loaded microspheres in 3D.
Driven by the primary acoustic radiation force, all of the microparticles, including the cells and drug-loaded microspheres, can move to the pressure nodes and then aggregate such that the columns of clumps striate at half-wavelength intervals in the direction of the ultrasonic waves (A—C). Due to the effects of the secondary acoustic radiation force, these microparticle-composed clusters are then compressed and the slender bands are turned into short and thick as represented from C to E, whereby the cells and drug carriers are placed in close contact with one another. When the weight of enlarged agglomerates is higher than the acoustic radiation force imposed, the clumps fall down and the suspended configurations collapse (F). *t represents the time of RUF exposure.