Sharp-edge acoustic microfluidics: Principles, structures, and applications

Abstract The development of microfluidic devices for lab-on-a-chip applications has largely been limited by a lack of flexible control and intensive mixing. The fusion of acoustics and microfluidics, termed acoustofluidics, has been demonstrated to be a promising tool for precisely manipulating micro-/nanoscale fluids and objects. When introducing sharp-edges inside the microchannel of acoustofluidic devices, the sound waves can drive highly controllable streaming flows via oscillating these microsolid structures. Considering its precise fluid control, simple device design, greatly reduced reaction duration, contactless operation, and good biocompatibility, sharp-edge acoustofluidics has demonstrated superior on-chip mixing and pumping performance for many application fields. Herein, we provide a comprehensive overview of the research and development of sharp-edge acoustofluidics. In particular, we discuss the design principles and underlying physics of sharp-edges, summarize the existing different types of sharp-edge microreactors (including sidewall wedge, sidewall rod, off-sidewall sharp-edges, and inlet conjunction needle), and highlight established applications of sharp-edge acoustofluidic technology in materials synthesis, bioliquefaction, enzyme bioassay, biomanipulation, and cell lysis. Finally, we point out the current challenges and future directions for inspiring further research in this field. The scope of this work is not only to provide an in-depth understanding of the state-of-the-art sharp-edge acoustofluidics, but also to inspire research efforts on the development of advanced on-chip platforms to satisfy the demanding needs of both academic and industrial communities.