Universal Control for Micromotor Swarms with a Hybrid Sonoelectrode

Abstract

field actuation, enabling various sophisticated tasks accomplished. [9][10][11][12] However, it is usually restricted to the precise manipulations for a small number of micromotors. Indeed, many practical application scenarios, taking microfluidic analysis and ultratrace biological detection, for example, [13,14] require quickly steering the motion of numerous micromotors together to achieve higher throughput and capacity.The micromotor swarm is attractive due to its enhanced capacity for precise enrichment and reinforced adaption to diverse working environments, illuminating more prospective in active chemical and biological detections, etc. [15][16][17] The pioneering collective behaviors were conceptually exploited using the self-propelled catalytic micromotors, of which colonies and interactions for subcellular microrobots were enabled by chemical reactions. [18] Even though the catalytic decomposition could create sufficient energy to power self-organizations for microrobots, such unsustainable process is difficult to control and the collective swarming cannot be reversed. [19,20] Recently, external fields including optical [21,22] and magnetic [23,24] stimulus were employed to trigger micromotors mimicking the swarm behaviors of microorganisms in nature. In particular, dynamic clustering, schooling, and reversible explosion have been demonstrated on spherical or tubular micromotors, whereas specific material properties are strongly required. [25] On the other hand, the acoustic field has been emerging as an attractive power source due to its favorable controllability and ideal compatibility to micromotors with various configurations and components. [26][27][28] Most recently, self-generated large bubbles were applied to attract micromotors to organize dandelion-like microswarms and achieve ultrafast locomotion in the acoustic field, but only a limited number of micromotors could be collected to perform irreversible group swarming. [29] Recent achievements on ultrasensitive and rapid biosensing reveal that ultrasound-powered microrobot swarming is promising for Raman enhancement and trace-level protein detections, [30][31][32][33] but issues including control efficiency and versatility still need to be addressed. Consequently, facilely modulating swarming behaviors of massive micromotors remains an unmet challenge and the universal control strategy for different micromotor swarms is still lacking.

Review of Bubble Applications in Microrobotics: Propulsion, Manipulation, and Assembly

“…For example, microswimmers must rely on bubbles excited by an acoustic field (to provide a driving force) and magnetic field (to control the motion trajectory) [ 34 ]. Recently, the combination of bubble propulsion based on chemical reactions with acoustic [ 107 ] or magnetic fields [ 140 ] has become a research hotspot. The combination of multiple physical fields not only satisfies more complex and multifunctional applications, but also solves the problems and limitations of a single physical field.…”

“…When a large bubble core, generated via the fusion of multiple microbubbles, was excited and oscillated by ultrasound, these micromotor individuals gathered to it due to the locally intense acoustic field, to realize the dynamic assembly and cooperation of micromotors in a dandelion formation. Recently, Lu et al [ 107 ] controlled the release and collection of tubular micromotor swarms. Hydrogen bubbles were produced at the tip of the charged electrode.…”

“…( a ) Acoustic manipulation platform and sonoelectrode-enabled dual swarming modes including dispersion and aggregation. Adapted from Lu et al [ 107 ] with permission from John Wiley and Sons, Copyright 2021. ( b ) Fabrication and antibacterial process of Janus Ga/Zn micromotors.…”

Smart micro- and nanorobots for water purification

“…However, practical appli cations require swarms to adapt to environmental changes through selforganization and reconfigurability in shape and function. All these behaviours rely on physicochemical interactions between the robots [90][91][92][93] . For example, lightpowered magnetic microrobots sponta neously assemble into selfmotile 'snakelike' microchains owing to the particles' shapemodulated magnetic dipole-dipole interactions 94 .…”

Integrated Acoustic Chip for Culturing 3D Cell Arrays

“…Manipulation of biological particles by external field actuation has become common, enabling cell arraying and patterning at the microscale. − Active external fields (such as magnetism, ultrasound, , light, , electricity, , etc.) have potential in cell manipulation, and a series of effective methods have been developed. − Among them, acoustic force is a cell-friendly external field stimulus that can be used to manipulate cells in complex biological media. − Such acts of controlling cell assembly have led to the development of many microfluidic-based cell culture chips. − However, such devices have inherent limitations .…”