The acoustic radiation force on a multi-layered polymer capsule placed in a fluid-filled tube

Acoustic manipulation has a series of application in biomedicine, colloidal assembly, and chemistry. A three-layered polymer capsule is generally used structure in manipulation system because it has better protection to the core filled drug or compounds and possesses higher flexibility. In this paper, a theoretical model of acoustic radiation force acting on a three-layered drug capsule in a vessel is established. The acoustic radiation force on a capsule, which comprises of a drug core, a poly(lactide-co-glycolide) mid shell and a chitosan outer shell in the cylindrical tube filled with ideal fluid, is calculated using acoustic wave theory. The influences of the tube, the surrounding fluid and the geometric size of chitosan, poly(lactide-co-glycolide) shell and drug core on acoustic radiation force are investigated. The numerical simulations based on finite element method are introduced to compute the acoustic radiation force and compared with the analytical results. Moreover, the comparison among the capsule in impedance tube, in rigid tube and in unbounded space is obtained simulating specific environment. Simulation results show that the influences of the rigid tube on the acoustic radiation force of the capsule can be ignored when the capsule is much smaller than the radius of the tube. With the increase of the capsule radius, the acoustic radiation force of the capsule changes demonstrably with the frequency and the tube radius because of the influence of the reflective wave resulted from the inner surface of the tube. The properties of the surrounding fluid affect the position of the resonant peaks. Outer radius and mid layer radius have more effects on the acoustic radiation force, but the drug core radius almost exerts no effect on it. The study illustrates that the capsule can be manipulated by acoustic wave with the suitable selection for the outer or mid shell radii, and the selection of drug core radius is of more freedom in this process.