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Understanding and manipulating microbubble streaming flows : size-sensitive sorting and mixing
Ultrasound-induced oscillation of microbubbles gives rise to intense, steady streaming flows. We show that the flow patterns can be flexibly and interactively shaped by the superposition of a transport flow and adjustment of driving amplitude and/or frequency. In this way, sensitive selection, focusing, and sorting of microparticles by size is possible in microfluidic setups without the need for moving boundaries or external forces on the particles [1]. The method separates particles for which both the absolute size and the size differential are only a few micrometers, in a setup whose smallest geometric scale is about 100 microns. Understanding the changes of flow pattern with ultrasound frequency allows for further manipulation of flow through frequency modulation ; here, we observe dramatically improved micromixing when adopting a modulation protocol that makes full use of flow portrait variability [2]. Devices based on these novel concepts are easy to fabricate and can be directly tailored to a variety of transported objects, including cells and vesicles.
[1] C. Wang, S. V. Jalikop, and S. Hilgenfeldt, Appl. Phys. Lett. 99, 034101 (2011).
[2] C. Wang, B. V. Rallabandi, and S. Hilgenfeldt, Phys. Fluids, submitted (2012).