Paskert, A. | bioRxiv Science

bioRxiv2025

Bioinspired Geometry-Encoded Rheotactic Navigation of Sound-Driven Microrobots

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.

bioengineering↗

bioRxiv2023

An Acoustically Controlled Microrobot Modelled on Spirochete Bacteria

As a next-generation toolkit, microrobots can transform a wide range of fields, including micromanufacturing, electronics, microfluidics, tissue engineering, and medicine. While still in their infancy, acoustically actuated wireless microrobots are becoming increasingly attractive, as acoustic control can generate large propulsive forces, requires relatively simple microrobot design, and does not entail complex manipulation systems. However, the interaction of acoustics with microstructure geometry is poorly understood to date, and its study is necessary for developing next-generation acoustically powered microrobots. We present here a mass-manufactured acoustically driven helical microrobot capable of locomotion using a fin-like double-helix microstructure. This microrobot responds to sound stimuli and mimics the spiral motion of natural microswimmers such as spirochetes. The asymmetric double helix interacts with the incident acoustic field, inducing a propulsion torque that causes the microrobot to rotate around its long axis. Moreover, our microrobot has the unique feature of its directionality being switchable by simply tuning the acoustic frequency. We demonstrate this locomotion in 2D and 3D artificial vasculatures using a single sound source. Since ultrasound is widely used as an imaging modality in clinical settings, our robotic system can integrate seamlessly into practice; thus, our findings could contribute to the development of next-generation smart microrobots. One-Sentence SummaryWe present an acoustically driven helical microrobot capable of corkscrew-like locomotion using a double-helix microstructure.

bioengineering↗