On-demand rotational manipulation of microparticles and zebrafish larvae via orthogonally phased BAW acoustofluidics.

Rotational manipulation of microscale objects or living organisms is crucial for various applications in microsystems and biological engineering, especially in high-precision imaging. However, achieving precise rotation of individual biological samples at specific angles remains a challenge. This study introduces a novel and cost-effective acoustofluidic approach for on-demand rotation of microparticles and biological specimens, such as zebrafish larvae, to desired angles. The system consists of piezoelectric transducers arranged orthogonally on a structured glass capillary. By applying sinusoidal signals with a defined phase difference (φ) to these transducers, we can adjust the ultrasonic resonant field in the capillary's microchannel to rotate the acoustic pressure nodal plane at the cross-section. This rotation creates an acoustic radiation force that traps and aligns suspended objects along the rotated pressure node. Within a specific operational range, specimens are securely trapped along the channel axis and rotated at a controlled angle α relative to φ (following the relationship α ≈ φ/2), demonstrating stepwise rotational control. By dynamically adjusting the phase difference φ from 0 to 4π, we can achieve controlled full 360° rotation of a trapped object. Further parametric numerical studies are conducted to showcase the effectiveness of this technique at various operating parameters for the controlled rotational manipulation of objects suspended in a fluid. The use of a glass capillary and external piezoelectric transducers offers a smooth and biologically permissive environment, simplifying fabrication and showing significant potential for applications in micro-robotics, single-cell analysis, and organism-level studies in fields like developmental biology.