Acoustofluidic micromixers: From rational design to lab-on-a-chip applications

Microfluidics that permits to manipulate fluids at the micrometer or submicrometer scale offers fundamentally new opportunities in chemical and biomedical engineering. The past decade has witnessed considerable progress in the development of microfluidic systems for use in micro-/nanomaterials synthesis, biosensing, separation, catalysis, tissue engineering, and so on. Among many microfluidic mixers to enable those functions, the fusion of acoustics and microfluidics (termed acoustofluidics) represents an emerging promising platform. Acoustofluidics can manipulate fluids spatiotemporally by using the interaction of sound waves with solids, liquids, and/or gasses in a confined space for active and intensive mixing. This review accesses the utility of acoustofluidic technology in chemical and biomedical engineering for both academic research and industrial applications. We summarize the established categories of acoustic micromixers (sharp-edge, bubble, surface acoustic wave, resonant acoustic mixing, etc.), discuss the underlying principles, highlight the current achievements for diverse lab-on-a-chip application fields (chemical synthesis, biosensing, protein engineering, separation, cell lysis, etc.), and finally set out the practical challenges facing acoustofluidics to inspire future research in this field.