Acoustofluidic Properties of Polystyrene Microparticles

Acoustophoresis has become a powerful tool to separatemicroparticlesand cells, based on their material and biophysical properties, andis gaining popularity in clinical and biomedical research. One majorapplication of acoustophoresis is to measure the compressibility ofcells and small organisms, which is related to their contents. Thecell compressibility can be extracted from the acoustic mobility,which is the main output of acoustic migration experiments, if thematerial properties and sizes of reference particles, the size ofthe cells, and the surrounding medium are known. Accurate methodsto measure and calibrate the acoustic energy density in acoustophoresissystems are therefore critical. In this Perspective, polystyrene microparticleshave become the most commonly used reference particles in acoustophoresis,due to their similar biophysical properties to cells. We utilizeda two-step focusing method to measure the relative acoustic mobilityof polystyrene beads of various sizes and colors and present a quantitativeanalysis of the variation in acousto-mechanical properties of polystyrenemicroparticles, showing a large spread in their material properties.A variation of more than 25% between different particle types wasfound. Thus, care is required when relying on polystyrene particlesas a reference when characterizing acoustofluidics systems or acousto-mechanicalproperties of cells.

Automated summary

Acoustophoresis has become a popular tool in clinical and biomedical research for separating microparticles and cells based on their properties. One important application is measuring cell compressibility, which can be extracted from acoustic migration experiments. However, accurate measurement and calibration of acoustic energy density is crucial for reliable results. Polystyrene microparticles are commonly used as reference particles, but our study shows significant variation in their material properties, suggesting caution when using them as references.