top of page

Volumetric Measurement Of The Acoustically Induced Fluid Flow In A Micro Chamber With A Two-Dimensional Standing Surface Acoustic Wave Field

Sebastian Sachs (1), Zhichao Deng (1), Hagen Schmidt (2), Jörg König (1), Christian Cierpka (1)

1. Technische Universität Ilmenau, Ilmenau, Germany
2. Leibniz Institute for Solid State and Materials Research, Dresden, Germany


The non-invasive, contactless and label-free trapping and patterning of individual cells with acoustic tweezers is a key technology to reliably analyze single cells and cell-cell interactions in biological applications. By using two-dimensional standing surface acoustic waves (2DsSAW), the precise manipulation of the cells in a micro chamber is primarily governed by the acoustic radiation force, which acts directly on the cells due to scattering effects of the acoustic waves. However, a fluid flow of three-dimensional nature is concurrently induced acoustically, which additionally influences the cell pattern by Stokes' drag. In this study, we shed light on the complex acoustically induced fluid flow forming in an acoustic tweezer by 3D3C velocity measurements using the astigmatism particle tracking velocimetry (APTV). Vortex structures above the antinodes of the 2DsSAW field were revealed. The fluid flow converge and diverge in the vicinity of the chamber bottom and ceiling, respectively. Hence, the fluid flow influences the stable trapping locations of cells or particles in different ways depending on their height position, which might explain the recently reported formation of various particle patterns at different height levels. Moreover, the experimental findings are used to validate a three-dimensional numerical model. The numerical model provides deep insights into the underlying acoustic fields responsible for the formation of the fluid flow and acoustic radiation force. By combining the experimental and numerical results, a profound understanding of the physical mechanisms for cell or particle trapping and patterning is established.

bottom of page