Effective mixing strategies with microbubble streaming flows

Homogeneous mixing of chemical/biological samples and reagents is one of the essential preparation steps for lab-on-a-chip systems. As effective Stokes flows driven by fast time scale oscillatory flows, microbubble streaming flows are a tool uniquely positioned between passive and active mixing approaches. Guided by thorough theoretical understanding of the flows and of micromixing itself, we investigate various designs of microbubble mixers, employing two key strategies: (a) introducing controlled unsteadiness in the acoustic driving pattern, e.g. by duty-cycling and driving frequency modulation, and (b) optimizing the arrangement of multiple bubbles, such as the number, position, and orientation of the microbubbles, particularly to generate 3D chaotic flow patterns. Both of these approaches significantly improve mixing over that of previous steady 2D bubble micro-mixers, and the strategies can be combined for greater effect.