Robotic-Assisted Acoustic Vortex Tweezers

Teng Li

Abstract

Acoustic tweezers, as a precise contactless object manipulation strategy, have shown great promise for engineering, biology, and chemistry research, such as controlling microrobots, handling delicate bioparticles (e.g., exosomes and cells), transporting hazardous reagent droplets, forming self-assemblies of colloidal materials, and arranging nanomaterials for composite fabrication. Compared to various other contactless manipulation methods—such as optical, electrical, magnetic, and acoustic techniques—acoustic tweezers have been attracting increasing attention in recent years. While other methods rely on an object’s optical, electrical, or magnetic properties, the success of acoustic tweezers depends only on the object’s compressibility and acoustic impedance. Moreover, acoustic tweezers offer multiple appealing features, including biocompatibility, the ability to penetrate barriers (e.g., tissue, glass, petri dishes, etc.), and the ability to manipulate a variety of objects with different sizes and material properties (e.g., soft, hard, gaseous, and liquid samples). However, traditional acoustic tweezers are mainly based on acoustic standing waves to generate a low acoustic radiation force node for object trapping and manipulation, which limits the translation distance of trapped objects to only several wavelengths. Additionally, most acoustic tweezers operate within microfluidic channels, with a complex actuation setup, which limits integration with other biomedical and biochemical workflows in a wide range of related research fields.
To address these limitations, we developed an acoustic vortex-based tweezers system capable of high-resolution, multi-degree-of-freedom, multifunctional, and programmable acoustic manipulation. This system generates an acoustic vortex beam with a helical wavefront spinning around a phase singularity, creating a donut-shaped acoustic intensity field at the beam center. This intensity pattern forms a uniform acoustic radiation potential well, enabling stable object trapping and manipulation. By adjusting the focal length of the focused acoustic beam, our system creates a contraction neck near the focal point, where the narrowed concentration provides an axial force for 3D acoustic manipulation. The helical wavefront of the acoustic vortex beam also exerts coherent orbital angular momentum on trapped objects, enabling rotational control. By adjusting the beam’s chirality, we achieve tunable chirality in acoustic manipulation, allowing both clockwise and counterclockwise control. Furthermore, integrating this acoustic holographic vortex-based device into a multi-DOF robotic-assisted system significantly broadens the application range of our methodology. Serving as an advanced end-effector, the acoustic vortex device enhances the capabilities of a traditional robotic arm. In this work, we demonstrated 4-DOF manipulation of single objects, through-biological-barrier manipulation, and ultrasound imaging-assisted acoustic tweezers.