Disturbed flow is a hallmark of diseased vasculature, yet its influence on particle behavior under external actuation remains poorly understood. We uncover distinct behaviors of microparticles under disturbed flow when exposed to ultrasound, revealing selective trapping and aggregation phenomena that differ fundamentally between soft and rigid particles. Using microfluidic models of disturbed vascular flow, we show that microbubbles become trapped at the eye of vortices and self-assemble via ultrasound-induced forces. As clusters grow to a critical size, they are ejected and adhere to the wall opposite the ultrasound source, forming nuclei that progressively occupy aneurysm cavities—a mechanism that could enable targeted, noninvasive treatment. These findings reveal an unexplored interplay between ultrasound and hydrodynamic forces, offering a new strategy for ultrasound-guided therapeutic delivery in vascular disease.

Imitating the shape-encoded tactics of natural microswimmers—organisms that flip, roll, and rheotaxis through viscous fluids—could transform microfluidics, micromanufacturing, and targeted therapy. However, translating those geometric navigation cues into actively driven microrobots is an open, largely unexplored challenge. Here, inspired by the structure of sperm cells, we introduce a sound-propelled head-helix microparticle (“microrobot”) featuring an elliptical head and a spiral tail. This asymmetrical design interacts with the incident acoustic field, generating complex secondary flows that induce a torque, enabling the particle to reorient around its cross-section. The microparticle exhibits a preferred direction of propulsion and orientation when exposed to a traveling sound wave, reorienting if its initial alignment deviates from this preference. Both the preferred direction and orientation can be modulated by adjusting the sound frequency, and they further adapt to background flow fields in the environment. Furthermore, the microparticle exhibits rheotaxis-like motion, exhibiting wall-following motion with frequency-dependent sliding behavior. By moving towards the channel wall, it enters the region with the smallest flow velocities, allowing it to move antiparallel to the fluid. These findings contribute to the engineering of the trajectories of sound-propelled microparticles and to the development of next-generation microrobots for medical and other innovative applications.

Acoustically actuated soft matter offers potential for agile microscale manipulation, yet acoustic-soft matter interaction at the microscale remains poorly understood. Here, we explore the mechanism of ultrasound-soft matter interaction by developing a bio-inspired ultrasound-driven soft hydrogel microgripper. This exploration allows to delve deeper into the understanding of nonlinear dynamics, mode coupling, and energy transfer. The developed microgripper (≤ 120 µm) overcomes key challenges of existing grippers, including complex fabrication, reliance on additives or external wiring, rigid structures, slow or poorly controllable responses, and risks of sample damage or contamination. Interacting with acoustic actuation, soft microgrippers oscillate and deform, while adjusting acoustic parameters and microgrippers’ structures allows for programmable interactions. The optimized acoustic actuation of the soft microgripper enables precise, ultrafast (∼2 ms) gripping and handling of distinct delicate objects. This work advances the integration of soft matter with acoustic actuation especially at the microscale, offering a versatile, reliable, and scalable solution for microrobotics, targeted drug delivery, and lab-on-a-chip applications.