Microscale acoustic streaming for biomedical and bioanalytical applications

Over the past few decades, acoustofluidics, one of the branches of microfluidics, has rapidly developed as a multidisciplinary cutting edge research topic, covering many biomedical and bioanalytical applications. Acoustofluidics usually utilizes acoustic pressure and acoustic streaming effects to manipulate liquids and bioparticles. Acoustic manipulation using acoustic radiation force has been widely studied; however, with the recent development of new piezoelectric devices that enable faster acoustic streaming, particle manipulations using drag force induced by acoustic streaming have attracted more attention. Despite many review articles on acoustic radiation force-based acoustophoresis, acoustic streaming is less frequently covered. Here, we review the recent development of microscale acoustic streaming, especially high-frequency transducer-induced high-speed streaming, confinement and programed streaming, and acoustic streaming tweezers, which combine the acoustic radiation force and drag force to tackle the size limitations of conventional acoustic manipulations. A brief review of acoustic streaming theory and its generation is summarized. Recent progress in applying acoustic streaming for fluidic handling and bioparticle manipulations is reviewed. Representative applications of micro acoustic streaming are provided, and the key issues in these applications are analyzed. Finally, the future prospects of micro acoustic streaming in bioanalytical and biomedical applications are discussed.