tPA-anchored nanorobots for in vivo arterial recanalization at submillimeter-scale segments.

Micro/nanorobots provide a promising approach for intravascular therapy with high precision. However, blood vessel is a highly complex system, and performing interventional therapy in those submillimeter segments remains challenging. While micro/nanorobots can enter submillimeter segments, they may still comprise nonbiodegradable parts, posing a considerable challenge for post-use removal. Here, we developed a retrievable magnetic colloidal microswarm, composed of tPA-anchored Fe3O4@mSiO2 nanorobots (tPA-nbots), to archive tPA-mediated thrombolysis under balloon catheter-assisted magnetic actuation with x-ray fluoroscopy imaging system (CMAFIS). By deploying tPA-nbot transcatheter to the vicinity of the thrombus, the tPA-nbot microswarms were magnetically actuated to the blood clot at the submillimeter vessels with high precision. After thrombolysis, the tPA-nbots can be retrieved via the CMAFIS, as demonstrated in ex vivo organ of human placenta and in vivo carotid artery of rabbit. The proposed colloidal microswarm provides a promising robotic tool with high spatial precision for enhanced thrombolysis with low side effects.

Multimode microdimer robot for crossing tissue morphological barrier.

Swimming microrobot energized by magnetic fields exhibits remotely propulsion and modulation in complex biological experiment with high precision. However, achieving high environment adaptability and multiple tasking capability in one configuration is still challenging. Here, we present a strategy that use oriented magnetized Janus spheres to assemble the microdimer robots with two magnetic distribution configurations of head-to-side configuration (HTS-config) and head-to-head configuration (HTH-config), achieving performance of multiple tasks through multimode transformation and locomotion. Modulating the magnetic frequency enables multimode motion transformation between tumbling, rolling, and swing motion with different velocities. The dual-asynchronization mechanisms of HTS-config and HTH-config robot dependent on magnetic dipole-dipole angle are investigated by molecular dynamic simulation. In addition, the microdimer robot can transport cell crossing morphological rugae or complete drug delivery on tissues by switching motion modes. This microdimer robot can provide versatile motion modes to address environmental variations or multitasking requirements.

Collective Behaviors of Active Matter Learning from Natural Taxes Across Scales.

Taxis orientation is common in microorganisms, and it provides feasible strategies to operate active colloids as small-scale robots. Collective taxes involve numerous units that collectively perform taxis motion, whereby the collective cooperation between individuals enables the group to perform efficiently, adaptively, and robustly. Hence, analyzing and designing collectives is crucial for developing and advancing microswarm toward practical or clinical applications. In this review, natural taxis behaviors are categorized and synthetic microrobotic collectives are discussed as bio-inspired realizations, aiming at closing the gap between taxis strategies of living creatures and those of functional active microswarms. As collective behaviors emerge within a group, the global taxis to external stimuli guides the group to conduct overall tasks, whereas the local taxis between individuals induces synchronization and global patterns. By encoding the local orientations and programming the global stimuli, various paradigms can be introduced for coordinating and controlling such collective microrobots, from the viewpoints of fundamental science and practical applications. Therefore, by discussing the key points and difficulties associated with collective taxes of different paradigms, this review potentially offers insights into mimicking natural collective behaviors and constructing intelligent microrobotic systems for on-demand control and preassigned tasks.

Endoscope-assisted magnetic helical micromachine delivery for biofilm eradication in tympanostomy tube.

Occlusion of the T-tube (tympanostomy tube) is a common postoperative sequela related to bacterial biofilms. Confronting biofilm-related infections of T-tubes, maneuverable and effective treatments are still challenging presently. Here, we propose an endoscopy-assisted treatment procedure based on the wobbling Fe2O3 helical micromachine (HMM) with peroxidase-mimicking activity. Different from the ideal corkscrew motion, the Fe2O3 HMM applies a wobbling motion in the tube, inducing stronger mechanical force and fluid convections, which not only damages the biofilm occlusion into debris quickly but also enhances the catalytic generation and diffusion of reactive oxygen species (ROS) for killing bacteria cells. Moreover, the treatment procedure, which integrated the delivery, actuation, and retrieval of Fe2O3 HMM, was validated in the T-tube implanted in a human cadaver ex vivo. It enables the visual operation with ease and is gentle to the tympanic membrane and ossicles, which is promising in the clinical application.

A Robot Platform for Highly Efficient Pollutant Purification.

In this study, we propose a highly efficient robot platform for pollutant adsorption. This robot system consists of a flapping-wing micro aircraft (FWMA) for long-distance transportation and delivery and cost-effective multifunctional Janus microrobots for pollutant purification. The flapping-wing micro air vehicle can hover for 11.3 km with a flapping frequency of approximately 15 Hz, fly forward up to 31.6 km/h, and drop microrobots to a targeted destination. The Janus microrobot, which is composed of a silica microsphere, nickel layer, and hydrophobic layer, is used to absorb the oil and process organic pollutants. These Janus microrobots can be propelled fast up to 9.6 body lengths per second, and on-demand speed regulation and remote navigation are manageable. These Janus microrobots can continuously carry oil droplets in aqueous environments under the control of a uniform rotating magnetic field. Because of the fluid dynamics induced by the Janus microrobots, a highly efficient removal of Rhodamine B is accomplished. This smart robot system may open a door for pollutant purification.

Decoupling and Reprogramming the Wiggling Motion of Midge Larvae Using a Soft Robotic Platform.

The efficient motility of invertebrates helps them survive under evolutionary pressures. Reconstructing the locomotion of invertebrates and decoupling the influence of individual basic motion are crucial for understanding their underlying mechanisms, which, however, generally remain a challenge due to the complexity of locomotion gaits. Herein, a magnetic soft robot to reproduce midge larva's key natural swimming gaits is developed, and the coupling effect between body curling and rotation on motility is investigated. Through the authors' systematically decoupling studies using programmed magnetic field inputs, the soft robot (named LarvaBot) experiences various coupled gaits, including biomimetic side-to-side flexures, and unveils that the optimal rotation amplitude and the synchronization of curling and rotation greatly enhance its motility. The LarvaBot achieves fast locomotion and upstream capability at the moderate Reynolds number regime. The soft robotics-based platform provides new insight to decouple complex biological locomotion, and design programmed swimming gaits for the fast locomotion of soft-bodied swimmers.

Propulsion Gait Analysis and Fluidic Trapping of Swinging Flexible Nanomotors.

Micro- and nanomachines as feasible agents to exploit the microworld have attracted extensive research interest, particularly in the manipulation of soft nanorobots at small scales. Herein, we propose a model for regulating the motion of a swinging flexible nanomotor (SFN) driven by an oscillating magnetic field. Multisegments of an SFN are synthesized from nickel, gold, and porous silver. The coupling of magnetic actuation and the swinging pattern of SFNs are studied to reveal their mobility. Additionally, an optimal frequency occurs from the coupling of magnetic torque and structural deformation, rather than the simply considered step-out phenomenon. Meanwhile, a fluidic trapping region is formulated alongside the SFN. Such a trapping region is demonstrated by trapping a living neutrophil and accomplishing in vitro transportation using fluidic mediation. On-demand cargo delivery can be realized using a programmable magnetic field, and SFNs can be recycled with ease after manipulation owing to environmental concerns. In this study, we demonstrated the properties of SFNs that are useful bases for their customization and control. These flexible nanomotors may have the potential to promote drug delivery and biomedical operations in noncontact modes.

Magnetic Microswarm Composed of Porous Nanocatalysts for Targeted Elimination of Biofilm Occlusion.

Biofilm is difficult to thoroughly cure with conventional antibiotics due to the high mechanical stability and antimicrobial barrier resulting from extracellular polymeric substances. Encouraged by the great potential of magnetic micro-/nanorobots in various fields and their enhanced action in swarm form, we designed a magnetic microswarm consisting of porous Fe3O4 mesoparticles (p-Fe3O4 MPs) and explored its application in biofilm disruption. Here, the p-Fe3O4 MPs microswarm (p-Fe3O4 swarm) was generated and actuated by a simple rotating magnetic field, which exhibited the capability of remote actuation, high cargo capacity, and strong localized convections. Notably, the p-Fe3O4 swarm could eliminate biofilms with high efficiency due to synergistic effects of chemical and physical processes: (i) generating bactericidal free radicals (•OH) for killing bacteria cells and degrading the biofilm by p-Fe3O4 MPs; (ii) physically disrupting the biofilm and promoting •OH penetration deep into biofilms by the swarm motion. As a demonstration of targeted treatment, the p-Fe3O4 swarm could be actuated to clear the biofilm along the geometrical route on a 2D surface and sweep away biofilm clogs in a 3D U-shaped tube. This designed microswarm platform holds great potential in treating biofilm occlusions particularly inside the tiny and tortuous cavities of medical and industrial settings.

Light-Triggered Catalytic Performance Enhancement Using Magnetic Nanomotor Ensembles.

Micro/nanomachines have attracted extensive attention in the biomedical and environmental fields for realizing functionalities at small scales. However, they have been rarely investigated as active nanocatalysts. Heterogeneous nanocatalysts have exceptional reusability and recyclability, and integration with magnetic materials enables their recovery with minimum loss. Herein, we propose a model active nanocatalyst using magnetic nanomotor ensembles (MNEs) that can degrade contaminants in an aqueous solution with high catalytic performance. MNEs composed of a magnetite core coated with gold nanoparticles as the nanocatalyst can rotate under the action of a programmable external field and carry out rapid reduction of 4-nitrophenol (4-NP). The hydrogen bubbles generated in the catalytic reaction provide random perturbations for the MNEs to travel in the reaction solution, resulting in uniform processing. The reduction can be further boosted by irradiation with near-infrared (NIR) light. Magnetic field induces the rotation of the MNEs and provides microstirring in the catalysis. Light enhances the catalytic activity via the photothermal effect. These MNEs are also capable of moving to the targeted region through the application of a programmable magnetic field and then process the contaminant in the targeted region. We expect that such magnetic MNEs may help better in applying active heterogeneous nanocatalysts with magnetic field and light-enhanced performance in industrial applications due to their advantages of low material cost and short reaction time.

Light-Driven Hovering of a Magnetic Microswarm in Fluid.

Swarm behaviors are nature's strategies for performing cooperative work, and extensive research has been aimed at emulating these strategies in engineering systems. However, the implementation of vertical motion and construction of a 3D structure are still challenging. Herein, we propose a simple strategy for creating a hybrid-driven paramagnetic tornado-like microswarm in an aqueous solution by integrating the use of a magnetic field and light. The precession of a magnetic field results in in-plane rotation, and light promotes the conversion of a planar microswarm to a microswarm tornado, thus realizing the transition from 2D to 3D patterns. This 3D microswarm is capable of performing reversible, vertical mass transportation. The reconfigurable collective behavior of the swarm from 2D to 3D motion consists of rising, hovering, oscillation, and landing stages. Moreover, this 3D tornado-like microswarm is capable of controlling the chemical reaction rate of the liquid in which it is deployed, for example, the degradation of methylene blue. The experimental results unveil that the tornado-like microswarm can enhance the overall degradation while holding the reactant nearby and inside it because of the flow difference between near and far regions of the microswarm tornado. Furthermore, by applying an oscillating magnetic field, the 3D microswarm can process the trapped methylene blue for on-demand degradation. The microswarm tornado is demonstrated to provide a method for collective vertical transportation and inspire ideas for mimicking 3D swarm behaviors in order to apply the functional performance to biomedical, catalytic, and micro-/nanoengineering applications.

Bubble-Assisted Three-Dimensional Ensemble of Nanomotors for Improved Catalytic Performance.

Combining catalysts with active colloidal matter could keep catalysts from aggregating, a major problem in chemical reactions. We report a kind of ensemble of bubble-cross-linked magnetic colloidal swarming nanomotors (B-MCS) with enhanced catalytic activity because of the local increase of the nanocatalyst concentration and three-dimensional (3D) fluid convection. Compared with the two-dimensional swarming collective without bubbles, the integral rotation was boosted because of the dynamic dewetting and increased slip length caused by the continuously ejected tiny bubbles. The bubbles cross-link the nanocatalysts and form stack along the vertical axis, generating the 3D network-like B-MCS ensemble with high dynamic stability and low drag resistance. The generated B-MCS ensemble exhibits controllable locomotion performance when applying a rotating magnetic field. Benefiting from locally increased catalyst concentration, good mobility, and 3D fluidic convection, the B-MCS ensemble offers a promising approach to heterogeneous catalysis.

On-Demand Coalescence and Splitting of Liquid Marbles and Their Bioapplications.

Coalescence and splitting of liquid marbles (LMs) are critical for the mixture of precise amount precursors and removal of the wastes in the microliter range. Here, the coalescence and splitting of LMs are realized by a simple gravity-driven impact method and the two processes are systematically investigated to obtain the optimal parameters. The formation, coalescence, and splitting of LMs can be realized on-demand with a designed channel box. By selecting the functional channels on the device, gravity-based fusion and splitting of LMs are performed to mix medium/drugs and remove spent culture medium in a precise manner, thus ensuring that the microenvironment of the cells is maintained under optimal conditions. The LM-based 3D stem cell spheroids are demonstrated to possess an approximately threefold of cell viability compared with the conventional spheroid obtained from nonadhesive plates. Delivery of the cell spheroid to a hydrophilic surface results in the in situ respreading of cells and gradual formation of typical 2D cell morphology, which offers the possibility for such spheroid-based stem cell delivery in regenerative medicine.