The intrinsic laminarity of microfluidic devices impedes the mixing of multiple fluids over short temporal or spatial scales. Despite the existence of several mixers capable of stirring and stretching the flows to promote mixing, most approaches sacrifice temporal or spatial control, portability, or flexibility in terms of operating flow rates. Here, we report a novel method for rapid micromixing based on the generation of cavitation bubbles. By using a portable battery-powered electric circuit, we induce a localized electric spark between two tip electrodes perpendicular to the flow channel that results in several cavitation events. As a result, a vigorous stirring mechanism is induced. We investigate the spatiotemporal dynamics of the spark-generated cavitation bubbles and quantify the created flow disturbance. We demonstrate rapid (in the millisecond timescale) and efficient micromixing (up to 98%) within a length scale of only 200 µm and over a flow rate ranging from 5 to 40 µL/min.
Active mixer Cavitation bubbles Rapid mixing Pocket microfluidics Portable sensors
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The authors thank IIT and Compagnia di San Paolo SIME 2015-0682 for financial support. Microscopy data and images for this study were acquired at NIC@IIT (Nikon Imaging Center) at Istituto Italiano di Tecnologia, Genova, Italy.
Supplementary material 1 video depicting the mixing process for flow velocity 2.7 mm/s and spark repetition rate 96 Hz (AVI 3237 kb)
Supplementary material 2 schematic of the electric circuit used as spark generator (Fig. S1), PIV analysis (Fig. S2), and fluorescence versus dye concentration (Fig. S3) (PDF 594 kb)
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