Reconfigurable acoustic tweezers based on a programmable droplet array.

Conventional acoustic manipulation relies on either direct acoustic radiation force acting on particles or indirect methods using acoustic streaming generated by acoustic pressure fields to manipulate particles. While acoustic devices generating standing waves can create patterned arrangements of particles and cells, these methods are typically limited to producing regular arrays in static configurations. This study introduces a dynamic acoustic field modulation method to overcome these limitations, significantly enhancing manipulation flexibility. Crucially, the propagation of acoustic energy varies substantially at liquid-solid interfaces or gas-solid interfaces due to differences in acoustic impedance matching. To exploit this, we use a digital microfluidic chip (DMF) to manipulate droplets and generate a programmable droplet array via the electrowetting-on-dielectric effect. By utilizing the programmable droplet array, we dynamically alter the spatial distribution of the acoustic field from a bulk acoustic wave (BAW) device in real time and demonstrate this technique's capability for capturing and manipulating particles on demand. We believe this is a unique method to create acoustic tweezers with great flexibility and reconfigurability, which holds promising potential for advanced applications in micromanipulation, micro-assembly, and beyond.