Rolling microswarms along acoustic virtual walls

Abstract

Rolling is a ubiquitous transport mode utilized by living organisms and engineered systems. However, rolling at the microscale has been constrained by the requirement of a physical boundary to break the spatial homogeneity of surrounding mediums, which limits its prospects for navigation to locations with no boundaries. Here, in the absence of real boundaries, we show that microswarms can execute rolling along virtual walls in liquids, impelled by a combination of magnetic and acoustic fields. A rotational magnetic field causes individual particles to self-assemble and rotate, while the pressure nodes of an acoustic standing wave field serve as virtual walls. The acoustic radiation force pushes the microswarms towards a virtual wall and provides the reaction force needed to break their fore-aft motion symmetry and induce rolling along arbitrary trajectories. The concept of reconfigurable virtual walls overcomes the fundamental limitation of a physical boundary being required for universal rolling movements.

Micro/Nanorobotic Swarms: From Fundamentals to Functionalities

“…Because of the wall effect, i.e., the viscosity near a solid boundary is larger than that far from it, the swarm could roll along the wall. Moreover, using acoustic fields, virtual walls were created for guiding the motion of the rotating swarm . Without the virtual walls, the swarms rotated in the acoustic pressure nodes without making translation [Figure G­(i)].…”

“…Moreover, using acoustic fields, virtual walls were created for guiding the motion of the rotating swarm. 247 Without the virtual walls, the swarms rotated in the acoustic pressure nodes without making translation [Figure 5G(i)]. Once the virtual walls were generated, the swarms rolled and realized translation [Figure 5G(ii)].…”

Ultrasound Microrobots with Reinforcement Learning

“…further demonstrated a fundamentally new mechanism of rolling motion, i.e., rolling without dependence on real physical boundaries. [ 26 ] Dayton et al. utilized the acoustic radiation forces to concentrate microbubble contrast agents near a vessel wall in vivo.…”

“…[1] Zhang et al further demonstrated a fundamentally new mechanism of rolling motion, i.e., rolling without dependence on real physical boundaries. [26] Dayton et al utilized the acoustic radiation forces to concentrate microbubble contrast agents near a vessel wall in vivo. [41] Finally, an acoustic vortex beam and standing wavefield have been applied to manipulate micrometer-and millimeter-sized particles in vivo using phased-array and acoustic standing wavefield approaches.…”

“…Recently, ultrasoundbased propulsion has elicited considerable interest as an alternate means to generate propulsion and manoeuvre micro-and nanosized objects. [26][27][28][29][30][31][32][33][34][35][36][37] A brief overview of research in this area follows.…”