acoustofluidics

Acoustofluidics is a multidisciplinary field that uses acoustic waves to control fluids and suspended particles within microfluidic environments. It combines principles from acoustics, microfluidics, and materials science to enable contactless, label-free manipulation of cells, beads, and droplets, with potential applications in diagnostics, biology, and chemical processing.

The core physics involve ultrasound generated by piezoelectric transducers. In microchannels, standing acoustic waves create pressure nodes and antinodes, exerting acoustic radiation forces on particles that drive them toward nodes or antinodes depending on their properties. Viscous interactions between the fluid and channel walls also generate acoustic streaming, a secondary flow that can mix fluids or transport objects. Surface acoustic waves, produced on a piezoelectric substrate, can couple energy into the fluid to achieve similar effects in compact, chip-scale devices.

Common techniques include acoustophoresis, where particles migrate to specific regions of a channel under standing waves; acoustofluidic focusing and separation, which align or sort cells and beads by size, density, or mechanical properties; and SAW-based devices that use interdigital transducers to actuate fluids and particles. Additional methods exploit streaming for rapid mixing, pumping, or droplet manipulation within lab-on-a-chip platforms.

Applications span sample preparation, cell sorting and enrichment, and gentle, label-free handling of biological specimens. The ability to manipulate small volumes without reagents or physical contact makes acoustofluidics attractive for diagnostic workflows, single-cell analysis, and integrated microfluidic systems. Ongoing research aims to improve device integration, throughput, and compatibility with clinical environments.