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The activation of zebrafish sperm is essential for advancing vertebrate research, including studies in germplasm physiology and cryopreservation. In this study, a magnetic microrobot-based micromixer is developed to maximize zebrafish sperm activation through uniform micromixing and precise hydrodynamic control. Three distinct configurations of the microfluidic channel, labeled Design I, II, and III, are proposed and employed to activate zebrafish sperm cells. These configurations are distinguished by the number of microrobots utilized and their specific placement within the microfluidic channel. The fluid shear rate induced by the microrobot's rotational motion is quantified to be 0.2 s⁻¹, falling within the lower range conducive to sperm activation. Meanwhile, zebrafish sperm activation percentage is observed to reach 88% within 10 s in an individual experiment. Additionally, the dynamics of sperm motility parameters, including VSL (straight-line velocity), VCL (curvilinear velocity), and LIN (linearity, VSL/VCL), are quantified to verify these results. The LIN value is observed to be 0.91 for Design III at the actuation time period of 10 s, indicating that the activated sperms are highly efficient and progressively motile. This study underscores the efficacy of microrobotic technologies in live cell manipulation, establishing a promising approach for future research. [ABSTRACT FROM AUTHOR]

Catalysis is a foundational pillar of modern synthetic chemistry, essential for countless industrial processes. Traditional catalysts are often static, either immobilized or dispersed in fluid media. The innovative concept of catalytic microrobots allows the introduction of self‐propelled and navigable catalyst particles that are engineered for dynamic and customizable catalysis. Catalytic microrobots are microscale devices with the inherent ability to move and swarm, designed to execute complex tasks in diverse environments, including biomedicine, and environmental remediation. Typically confined to aqueous media, their use in synthetic chemical reactions remains largely unexplored. Here, microrobots are presented as adaptable self‐propelled, self‐mixing micro‐catalysts for the Baeyer–Villiger oxidation, a key industrial process. Zeolite microstructures are tailored, outfitted with magnetic nanoparticles to create zeolite‐based microrobots (ZeoBOTs) that are maneuverable in magnetic fields. Uniquely, these ZeoBOTs are not limited to water but can operate in organic solvents, facilitating the Baeyer–Villiger oxidation in non‐aqueous conditions. Comparative analysis with static ZeoBOTs reveals that the dynamic, "on‐the‐fly" movement of the microrobots significantly enhances reaction yields. The findings herald a new era for synthetic chemistry, demonstrating the potential of microrobots as versatile catalysts beyond aqueous systems, and setting the stage for their broader application in synthetic processes. [ABSTRACT FROM AUTHOR]

This study investigates the dynamic fluctuations of pH caused by gastric acid secretion, a process of both biological and clinical significance, with microrobots. Abnormal patterns of acidity often indicate gastrointestinal diseases, underlying the importance of precise intragastric pH monitoring. Traditional methods using fluorescent probes face challenges due to their faint solid‐state fluorescence, limited target specificity, and accuracy. To overcome these obstacles, pH‐responsive fluorescent organic microparticles decorated with magnetite (Fe3O4) nanoparticles are engineered. These microrobots exhibit a unique fluorescence switching capability at a critical pH, enabling the monitoring of gastric acidity. The magnetic part of these microrobots ensures magnetic maneuverability to enable targeted navigation. The microrobots' fluorescence switching mechanism is elucidated through comprehensive spectroscopy, microscopy, and X‐ray diffraction analyses, revealing molecular‐level structural transformations upon interaction with gastric acid and antacids. These transformations, specifically protonation and deprotonation of the microrobots' fluorescent components, prompt a distinct fluorescence response correlating with pH shifts. In vitro and ex vivo experiments, simulating stomach conditions, confirm the microrobots' efficacy in pH‐responsive imaging. The results showcase the promising diagnostic potential of microrobots for gastrointestinal tract diseases, marking a significant advancement in imaging‐based medical diagnostics at targeted locations. [ABSTRACT FROM AUTHOR]

This paper presents a new strategy for simultaneous control of multiple magnetic Micro Robots (MRs) improving stability and robustness with respect to external disturbances. Independent control of multiple MRs, can enhance efficiency and allows for performing more challenging applications. In this study, we present a system consisting of a Helmholtz coil and 2N Permanent Magnets (PMs), rotated by servomotors, to control several MRs. We have also improved the system’s stability by adding a larger MR (stabilizer MR). This MR can be moved all around the workspace and works as a moving internal magnetic field source. Thanks to this moveable magnetic field, other MRs are more stable against environmental disturbances. By simulating simultaneous and independent control of multiple MRs, we demonstrate the advantages of using the stabilizer MR (more than 20 percent reduction in tracking error and control effort). In addition, we evaluate experimentally our proposed method to independently control the position of three MRs using a stabilizer MR demonstrating the efficacy of the strategy. [ABSTRACT FROM AUTHOR]

Electromagnetic actuation can support many fields of technology, such as robotics or biomedical applications. In this context, fully understanding the system behavior and proposing a low-cost package for feedback control is challenging. Modeling the electromagnetic force is particularly tricky because it is a nonlinear function of the actuated object's position and coil's current. Measuring in real time the position of the actuated object with the precision required for accurate motion control is also nontrivial. In this study, we propose a novel, cost-effective electromagnetic set-up to achieve position control via visual feedback. We actuated vertically and under different experimental conditions a 10 mm diameter steel ball hanging on a low-stiffness spring, demonstrating good tracking performance (the position error remained within ±0.5 mm, with a negligible phase delay in the best scenarios). The experimental results confirm the feasibility of the proposed set-up, which is characterized by minimum complexity and realized with off-the-shelf and cost-effective components. For these reasons, such a contribution helps to understand and apply electromagnetic actuation even further. [ABSTRACT FROM AUTHOR]

Magnetic fiber robots have revealed great potential for future minimally invasive robotic surgery. However, with the miniaturization of fiber robots, the integration of functional microtools at the distal end becomes extremely challenging, since it requires assembling multifunctional structures on the curved surfaces of fiber ends, which typically have very small curvature radii. In this study, a submillimeter fiber robot with integrated micro‐manipulation tool at the distal end is reported using a "Swiss roll" assembly strategy. This approach enables the one‐step assembly of multiscale structures (mm‐µm) from a 2D film to a 3D tool on the curved surface of the fiber robot. The multiscale structure consists of a millimeter‐scale (mm) magnetic thin film with integrated micrometer‐scale (µm) feature structures, which is inspired from the cat tongue covered by numerous little papillae. The fiber robot can perform multiple functions including endovascular clot grabbing, liquid delivery, and sampling under the manipulation of the magnetic field. The strategy provides a universal protocol for integrating and assembling functional components at the distal end of fiber robots, contributing significantly to the functionalization and miniaturization of interventional medical robots. [ABSTRACT FROM AUTHOR]

3D locomotion of magnetic microrobots requires at least one pair of coils per axis and 3D feedback of the position of the microrobot. This results in voluminous systems with high-power usage and a small working space, which require complex and expensive controllers. This study presents a single-coil magneto-electromagnetic system, comprising a parallel robot and coil, capable of precise 3D locomotion control of magnetic millirobots while requiring only feedback of the vertical position of the millirobot. The coil current creates a 2D magnetic trapping point in the horizontal plane, which depends on the position and orientation of the coil and toward which the millirobot moves, eliminating the need for position feedback at such plane. The vertical position of the millirobot is controlled by varying the coil current while receiving feedback from the vertical position of the millirobot. Feedbackless 2D control and 1-axis feedback 3D automatic control of magnetic millirobots are experimentally demonstrated, achieving higher speeds and similar position errors when compared to control systems with 3D position feedback. Furthermore, selective control of two millirobots is demonstrated by matching the region of maximum vertical magnetic force and the targeted millirobot, achieving selective levitation and control of such millirobots.

Magnetic microrobots can be miniaturized to a nanometric scale owing to their wireless actuation, thereby rendering them ideal for numerous biomedical applications. As a result, nowadays, there exist several mechano-electromagnetic systems for their actuation. However, magnetic actuation is not sufficient for implementation in biomedical applications, and further functionalities such as imaging and heating are required. This study proposes a multimodal electromagnetic system comprised of three pairs of Helmholtz coils, a pair of Maxwell coils, and a high-frequency solenoid to realize multimodal locomotion and heating control of magnetic microrobots. The system produces different configurations of magnetic fields that can generate magnetic forces and torques for the multimodal locomotion of magnetic microrobots, as well as generate magnetic traps that can control the locomotion of magnetic swarms. Furthermore, these magnetic fields are employed to control the magnetization of magnetic nanoparticles, affecting their magnetic relaxation mechanisms and diminishing their thermal properties. Thus, the system enables the control of the temperature increase of soft-magnetic materials and selective heating of magnetic microrobots at different positions, while suppressing the heating properties of magnetic nanoparticles located at undesired areas.

Magnetic microrobots have gained significant attention in the biomedical field due to their wireless actuation, strong controllability, fast response, and minimal impact on the environment. As the task complexity keeps increasing in the clinical applications of magnetic microrobots, more geometric structures and magnetization profiles have been included in the designs of magnetic microrobots, posing significant challenges to the fabrication of magnetic microrobots. Microassembly is a fabrication method that can create convoluted structures with small‐scale modules. It can accurately control the position and orientation of each magnetic module, resulting in a magnetic microrobot with arbitrary 3D geometries and magnetization profiles. This article reviews recent advanced assembly‐based fabrication methods of magnetic microrobots, including microassembly driven by contact mechanical forces and noncontact field forces. The principles, fabrication processes, and the advantages and disadvantages of each assembly‐based fabrication method are summarized. The existing challenges and future development of fabricating magnetic microrobots by assembly are discussed in detail. It is believed that this review will provide a methodological reference and inspire new ideas for manufacturing powerful magnetic microrobots in future biomedical applications. [ABSTRACT FROM AUTHOR]

Magnetic microrobots have gained significant attention in the biomedical field due to their wireless actuation, strong controllability, fast response, and minimal impact on the environment. As the task complexity keeps increasing in the clinical applications of magnetic microrobots, more geometric structures and magnetization profiles have been included in the designs of magnetic microrobots, posing significant challenges to the fabrication of magnetic microrobots. Microassembly is a fabrication method that can create convoluted structures with small‐scale modules. It can accurately control the position and orientation of each magnetic module, resulting in a magnetic microrobot with arbitrary 3D geometries and magnetization profiles. This article reviews recent advanced assembly‐based fabrication methods of magnetic microrobots, including microassembly driven by contact mechanical forces and noncontact field forces. The principles, fabrication processes, and the advantages and disadvantages of each assembly‐based fabrication method are summarized. The existing challenges and future development of fabricating magnetic microrobots by assembly are discussed in detail. It is believed that this review will provide a methodological reference and inspire new ideas for manufacturing powerful magnetic microrobots in future biomedical applications.

The use of global magnetic fields—typically produced by pairs of Maxwell and Helmholtz coils—offers the advantage of generating uniform magnetic fields and magnitude uniform gradient distributions over extensive volumes, while ensuring easy control. However, achieving selective control of multiple magnetic microrobots under such global fields remains problematic. In this study, we utilize a magnetic focus field generated by a pair of Maxwell coils to impede the magnetic torque-based movement of magnetic robots confined within channels. Although the magnetic field is null at the focus field’s center, it increases linearly in all directions. This exerts magnetic forces that push robots, which are situated away from the center, toward the channel walls. This not only restricts their positioning but also reduces their responsiveness to additional fields. By introducing uniform dc magnetic fields to the focus field, we can change the controlled robot. This mechanism for selective locomotion has been empirically validated with the selective movement of two helical magnetic robots and swarms of magnetic microparticles. Furthermore, leveraging the same focus field, we present a novel separation mechanism for magnetic particle swarms, enhancing the aforementioned selective locomotion mechanism. The practical implications of our proposed locomotion mechanism have been showcased in targeted delivery, drilling, and improved magnetic heating experiments.

Magnetically driven swimming microrobot is a typical one in the family of microrobots and they can achieve navigation and manipulation in low Reynolds number biomedical environments with an external magnetic drive strategy. This study reviews recent advances in material selection, structure design, fabrication techniques, drive control method, and applications for magnetically driven swimming microrobots. First, the materials used in magnetically driven swimming microrobots were introduced and the effect of material selection on performance was discussed. Second, structure design of swimming microrobots and manufacturing techniques are reviewed, followed by a discussion on the main advances in effective motion control, path planning, and path tracking. Then, the multi-applications of magnetically driven swimming microrobots including targeted drug delivery, cell manipulation, and minimally invasive surgery are summarized. Finally, the current challenges and future directions of the work on magnetically driven swimming microrobots are discussed.

Magnetic liquid-bodied microrobots (MRs) possess nearly infinite shape adaptivity. However, they currently confront the risk of structure instability/crushes during shape-morphing in tiny biological environments. This article reports that magnetic liquid metal (LM) MRs (LMMRs) show high structure stability and robust magnetic maneuverability. In this protocol, Fe nanoparticles are encapsulated inside less-than-10-μm LM microdroplets by establishing interfacial chemical potential barriers, yielding LMMRs. Their robust magnetic maneuverability originates from the magnetically controlled assembly of Fe nanoparticles inside LM and distinct liquid-solid interaction. With the self-adaptive shape-recovering capabilities even after 50% deformation, LMMRs can implement vertical climbing over walls up to 400% of its body length and traverse channels with the size of its two-thirds. The in vitro and in vivo experiments have both verified the effective magneto-mechanical stimulation of LMMRs upon neurons after their shape-adaptive crossing the blood-brain barrier under a driven magnetic field. Our work provides a promising strategy for wireless therapies with MRs by safely and effectively overcoming biological barriers.

Foodborne illnesses caused by Salmonella bacteria pose a significant threat to public health. It is still challenging to detect them effectively. Herein, biotemplated Janus disk-shaped magnetic microrobots (BJDMs) based on diatomite are developed for the highly efficient detection of Salmonella in milk. The BJDMs were loaded with aptamer, which can be magnetically actuated in the swarm to capture Salmonella in a linear range of 5.8 × 10 2 to 5.8 × 10 5 CFU/mL in 30 min, with a detection limit as low as 58 CFU/mL. In addition, the silica surface of BJDMs exhibited a large specific surface area to adsorb DNA from captured Salmonella, and the specificity was also confirmed via tests of a mixture of diverse foodborne bacteria. These diatomite-based microrobots hold the advantages of mass production and low cost and could also be extended toward the detection of other types of bacterial toxins via loading different probes. Therefore, this work offers a reliable strategy to construct robust platforms for rapid biological detection in practical applications of food safety.

Controlled microrobotic navigation in the vascular system can revolutionize minimally invasive medical applications, such as targeted drug and gene delivery. Magnetically controlled surface microrollers have emerged as a promising microrobotic platform for controlled navigation in the circulatory system. Locomotion of micrororollers in strong flow velocities is a highly challenging task, which requires magnetic materials having strong magnetic actuation properties while being biocompatible. The L10‐FePt magnetic coating can achieve such requirements. Therefore, such coating has been integrated into 8 µm‐diameter surface microrollers and investigated the medical potential of the system from magnetic locomotion performance, biocompatibility, and medical imaging perspectives. The FePt coating significantly advanced the magnetic performance and biocompatibility of the microrollers compared to a previously used magnetic material, nickel. The FePt coating also allowed multimodal imaging of microrollers in magnetic resonance and photoacoustic imaging in ex vivo settings without additional contrast agents. Finally, FePt‐coated microrollers showed upstream locomotion ability against 4.5 cm s−1 average flow velocity with real‐time photoacoustic imaging, demonstrating the navigation control potential of microrollers in the circulatory system for future in vivo applications. Overall, L10‐FePt is conceived as the key material for image‐guided propulsion in the vascular system to perform future targeted medical interventions. [ABSTRACT FROM AUTHOR]

Magnetic microrobots are vital tools for targeted therapy, drug delivery, and micromanipulation on cells in the biomedical field. In this paper, we report an automated control and path planning method of magnetic microrobots based on computer vision. Spherical microrobots can be driven in the rotating magnetic field generated by electromagnetic coils. Under microscopic visual navigation, robust target tracking is achieved using PID–based closed–loop control combined with the Kalman filter, and intelligent obstacle avoidance control can be achieved based on the dynamic window algorithm (DWA) implementation strategy. To improve the performance of magnetic microrobots in trajectory tracking and movement in complicated environments, the magnetic microrobot motion in the flow field at different velocities and different distribution obstacles was investigated. The experimental results showed that the vision-based controller had an excellent performance in a complex environment and that magnetic microrobots could be controlled to move to the target position smoothly and accurately. We envision that the proposed method is a promising opportunity for targeted drug delivery in biological research.

Mobile magnetic microrobots have been extensively used in a wide range of biomedical applications due to their numerous advantages. Magnetic microrobots in particular have been developed and shown great potential over the past two decades for the manipulation and migration of both single cells and cell aggregates. The efficient clearance of cell aggregates is crucial to prevent uncontrolled cell proliferation, tissue damage, and invasive surgeries, especially for those related to the vascular system. In this work, we showed cellular manipulation and mobility to achieve cellular clean up on Human Liver Cancer (HepG2) cells by using two types of untethered magnetic microrobots that are different in type and size. We performed the cellular clean up in the microchannel, which can demonstrate the closed working environment, and also on a glass slide to present an air-liquid interface. We showed that the microrobots could be able to move a cluster of cells in both conditions which could make them useful for sorting and separation applications. Furthermore, cell viability was assessed by using a trypan blue staining assay on HepG2 cells right after and 24 hours after microrobot actuation.

Faced with complex and diverse tasks, researchers seek to introduce stimuli-responsive materials into the field of microrobots. Magnetic helical microrobots based on shape-memory polymers demonstrate excellent locomotion capability and programmable shape transformations. However, the stimulation method of shape changes is still dependent on the rising of ambient temperature and lacks the ability to address individuals among multiple microrobots. In this paper, magnetic helical microrobots were prepared based on polylactic acid and Fe 3 O 4 nanoparticles, which demonstrated controlled locomotion under rotating magnetic fields and programmable shape changes in their length, diameter, and chirality. The transition temperature of shape recoveries was adjusted to a range above 37 °C. At 46 °C, helical microrobots had a fast shape change with a recovery ratio of 72% in a minute. The photothermal effect of Fe 3 O 4 nanoparticles under near-infrared laser can actuate the shape recovery rapidly, with a recovery ratio of 77% in 15 s and 90% in a minute. The stimulation strategy also allows addressing among multiple microrobots, or even within a single microrobot, selectively stimulating one or a part to change its shape. Combined with the magnetic field, laser-addressed shape changes were used for precise deployment and individual control of microrobots. Multiple microrobots can be enriched at the targeted point, heating the ambient temperature over 46 °C. The shape changes of internal parts of microrobots help them to grasp and assemble objects. Such microrobots have great potential in biomedicine and micromanipulation.

Recent development in technology and improvement of manufacturing tools have accelerated the use of microrobots (MRs) in numerous areas such as micro sensing and medical applications. The ability to control multiple MRs simultaneously and independently could lead to higher performance, and even make new applications possible. In this paper, we have proposed a system for simultaneous and independent control of the position of multiple MRs in a plane. The system consists of 2 N permanent magnets (PMs) with a circular arrangement in the plane around the workspace and a pair of Helmholtz coil to control N MRs. PMs are rotated by servomotors, and the coil aligns the orientation of the MRs normal to the plane. A sliding mode controller, as a robust approach, is designed to eliminate the undesired effects of disturbances and uncertainties. For this purpose, at each step, the required force for each MR is calculated based on the proposed controller, and corresponding angles of the PMs are computed analytically. The simultaneous control of multiple MRs is illustrated by simulation, and the performance of the system is discussed. Also, the position control of three MRs with dimensions of 250 µm, and a maximum speed of 330 µm/s is experimentally demonstrated. [ABSTRACT FROM AUTHOR]

Magnetic microrobots are vital tools for targeted therapy, drug delivery, and micromanipulation on cells in the biomedical field. In this paper, we report an automated control and path planning method of magnetic microrobots based on computer vision. Spherical microrobots can be driven in the rotating magnetic field generated by electromagnetic coils. Under microscopic visual navigation, robust target tracking is achieved using PID–based closed–loop control combined with the Kalman filter, and intelligent obstacle avoidance control can be achieved based on the dynamic window algorithm (DWA) implementation strategy. To improve the performance of magnetic microrobots in trajectory tracking and movement in complicated environments, the magnetic microrobot motion in the flow field at different velocities and different distribution obstacles was investigated. The experimental results showed that the vision-based controller had an excellent performance in a complex environment and that magnetic microrobots could be controlled to move to the target position smoothly and accurately. We envision that the proposed method is a promising opportunity for targeted drug delivery in biological research. [ABSTRACT FROM AUTHOR]