WIN Seminar - Professor Leslie Yeo "Acoustofluidics: Manipulating Fluids at the Microscale and Nanoscale for Biomedical Applications"

Though uncommon in most microfluidic systems due to the dominance of viscous and capillary stresses, it is possible to induce inertial transport at microscale and nanoscale dimensions using ultrasound. In particular, microfluidic actuation and manipulation is particularly efficient when driven using surface acoustic waves (SAWs), which are nanometer order amplitude electroelastic waves that can be generated on a piezoelectric substrate. Due to the confinement of the high frequency acoustic energy to a thin localized region along the substrate surface and its subsequent leakage into the body of liquid with which the substrate comes into contact, SAWs are an extremely efficient mechanism for driving ultrafast microfluidics. We demonstrate that it is possible to generate a variety of efficient microfluidic flows using the SAW. For example, the SAWs can be exploited to pump liquids in microchannels or to translate free droplets typically one or two orders of magnitude faster than conventional electroosmotic or electrowetting technology. In addition, it is possible to drive strong microcentrifugation for micromixing and bioparticle concentration or separation. In the latter, rich and complex colloidal pattern formation dynamics have also been observed. At large input powers, the SAW is a powerful means for the generation of jets and atomized aerosol droplets through rapid destabilization of the parent drop interface. In the former, slender liquid jets that persist up to centimeters in length can be generated without requiring nozzles or orifices. In the latter, a monodispersed distribution of 1–10 micron diameter aerosol droplets is obtained, which can be exploited for drug delivery and encapsulation, nanoparticle synthesis, and template-free polymer array patterning.