Acousto-viscoelasticity for microfluidic manipulation of fluids and particles

Acoustofluidics enables contactless manipulation of fluids and suspended particles using sound waves in microchannels, with applications ranging from chemical processing to biomedical technologies. However, most acoustofluidic systems are designed for simple Newtonian fluids, while many biologically relevant fluids and polymer solutions exhibit viscoelastic behavior. The elastic nature of these fluids can significantly change how acoustic energy is transferred and how the fluid flows, thereby affecting the forces acting on suspended particles and their motion. This study investigates how fluid viscoelasticity influences acoustic waves, fluid flow, and particle transport in microchannels using theoretical, numerical, and experimental approaches. The results show that viscoelasticity can modify the acoustic response of the fluid and significantly change the forces driving particle motion. It further demonstrate that the elastic properties of the fluid can be used to control acoustic streaming, allowing the flow to be enhanced, suppressed, or even reversed by tuning the fluid properties. The combined effects of acoustic forces and fluid motion are then shown to produce different particle migration and trapping behaviors compared with those observed in Newtonian fluids. Finally, the study demonstrate the potential of this approach for biological applications through the focusing and enrichment of bacterial suspensions and the manipulation of cells in viscoelastic fluids. These results reveals that fluid properties can be used as an additional control parameter for acoustic manipulation, providing new opportunities for particle and cell focusing, trapping, separation, and concentration in microfluidic and biomedical applications.