Acoustic Manipulation of Bio-Particles at High Frequencies: An Analytical and Simulation Approach.

Manipulation of micro and nano particles in microfluidic devices with high resolution is a challenge especially in bioengineering applications where bio-particles (BPs) are separated or patterned. While acoustic forces have been used to control the position of BPs, its theoretical aspects need further investigation particularly for high-resolution manipulation where the wavelength and particle size are comparable. In this study, we used a finite element method (FEM) to amend analytical calculations of acoustic radiation force (ARF) arising from an imposed standing ultrasound field. First, an acoustic solid interaction (ASI) approach was implemented to calculate the ARF exerted on BPs and resultant deformation induced to them. The results were then used to derive a revised expression for the ARF beyond the small particle assumption. The expression was further assessed in numerical simulations of one- and multi-directional standing acoustic waves (SAWs). Furthermore, a particle tracing scheme was used to investigate the effect of actual ARF on separation and patterning applications under experimentally-relevant conditions. The results demonstrated a significant mismatch between the actual force and previous analytical predictions especially for high frequencies of manipulation. This deviation found to be not only because of the shifted ARF values but also due to the variation in force maps in multidirectional wave propagation. Findings of this work can tackle the simulation limitations for spatiotemporal control of BPs using a high resolution acoustic actuation.