Tilted-angle acoustofluidics for particle and cell manipulation: fundamentals, strategies, and outlook

Acoustofluidics enables contact-free and precise manipulation of particles and cells and has emerged as a powerful platform for a wide range of biological and medical applications. In acoustofluidic platforms, particles and cells can be manipulated using various device configurations, including cross-type, parallel-type, and tilted-angle layouts. Compared with conventional cross-type or parallel configurations, tilted-angle layouts introduce asymmetric force components that enable continuous and long-range lateral deflection of particles and cells, rendering such designs particularly advantageous for separation and sorting. The present review provides a comprehensive overview of tilted-angle acoustofluidic techniques for particle and cell manipulation, based on both surface and bulk acoustic waves, and offers a balanced assessment of the underlying principles, capabilities, and applications associated with these platforms. The paper first introduces the fundamental mechanisms of acoustic forces acting on micro-objects in tilted-angle configurations, followed by a systematic discussion of acoustofluidic strategies developed for key particle and cell manipulation tasks. Finally, current limitations and future prospects of tilted-angle acoustofluidics are critically discussed, outlining potential directions for advancing the field.