Acoustic fields and forces in drug delivery applications

Abstract

For ultrasound drug delivery applications, the ability to manipulate and move both the carriers and their payloads provides a way of increasing over efficacy. Both primary and secondary acoustic radiation forces have been used though the optimal acoustic forcing parameters and delivery system are subject to on-going investigations. The primary radiation or Bjerknes force occurs from inhomogeneous propagation of the acoustic field and has been used to direct targeted ultrasound contrast agents or particles in vessels towards endothelial cells or pathological targets at the vessel wall. Secondary Bjerknes forces arise from multiple scattering effects between neighboring particles. For corresponding attractive force regimes, greater particle congregation is possible. Overview of theoretical background and predictions of the acoustic radiation forces is given. The formulation of particle translation by primary radiation in the long wavelength limit is discussed with respect to unsteady drag. Pair wise interaction between particles moving in tandem is compared with formulations for along the lines of center. Nonstationary forcing with respect to amplitude modulation or frequency (chirp) alters the attraction and repulsion regimes compared to continuous forcing. Cellular transport for payloads may be enhanced using more optimally tuned pulse sequences.