A Quantitative Study of the Secondary Acoustic Radiation Force on Biological Cells during Acoustophoresis

Davood Saeidi,Mohsen Saghafian,Shaghayegh Haghjooy Javanmard,Martin Wiklund

doi:10.3390/mi11020152

Abstract

We investigate cell-particle secondary acoustic radiation forces in a plain ultrasonic standing wave field inside a microfluidic channel. The effect of secondary acoustic radiation forces on biological cells is measured in a location between a pressure node and a pressure anti-node and the result is compared with theory by considering both compressibility and density dependent effects. The secondary acoustic force between motile red blood cells (RBCs) and MCF-7 cells and fixed 20 µm silica beads is investigated in a half-wavelength wide microchannel actuated at 2 MHz ultrasonic frequency. Our study shows that the secondary acoustic force between cells in acoustofluidic devices could play an important role for cell separation, sorting, and trapping purposes. Our results also demonstrate the possibility to isolate individual cells at trapping positions provided by silica beads immobilized and adhered to the microchannel bottom. We conclude that during certain experimental conditions, the secondary acoustic force acting on biological cells can dominate over the primary acoustic radiation force, which could open up for new microscale acoustofluidic methods.

Highlights

Particle and cell manipulation by utilizing the acoustic radiation force has been extensively investigated [1,2,3,4,5,6,7]
We have investigated the secondary acoustic radiation force acting between biological cells, including red blood cells (RBCs) and MCF-7 cells, and silica particles in an ultrasonic standing wave
In the acoustic field, cells in close proximity of silica particles can cause cell pathway deflection in the transversal direction relative to the wave propagation direction

Summary

Introduction

Particle and cell manipulation by utilizing the acoustic radiation force has been extensively investigated [1,2,3,4,5,6,7]. The secondary acoustic force typically becomes important when there are two or more bubbles or particles in close proximity to each other [15] and causes attractive or repulsive forces This phenomenon has been widely studied theoretically and experimentally on bubble pairs by, for example, Bjerknes [16], Crum [17], and Doinikov [18], there are fewer studies focusing on the interaction between solid particles in acoustophoresis. Their study was limited to the case when two solid particles are already located within the pressure nodal line and without any primary acoustic force At this condition the secondary acoustic force is the only acting force on the particle

Methods

Results

Conclusion