Search

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 microrobots are propelled by magnetic fields or magnetic field gradients generated by electromagnetic systems. Generally, 3D Helmholtz coils systems are used for microrobot propulsion, because of their low power consumption, ease of manufacture, and ease of control, for which, only three power supplies are required. Systems of this kind can only generate uniform magnetic fields, which limits their range of applications. However, generating both uniform magnetic fields and gradients typically requires more coils and power supplies, resulting in large expensive energy-intensive systems with complicated control algorithms. Although the aforementioned systems can control magnetic robots with up to 6 degrees of freedom (DOFs), most existing applications at the micro/nanoscale only require 2 rotational DOFs and 1 translational DOF. Here, we propose a new control system capable of producing 3D uniform magnetic fields with 3 DOFs and 3D gradients with 1 DOF. With this system, one pair of coils in a traditional 3D Helmholtz coil system is modified, to enable independent control of the individual coils directing a selected axis, while the configuration of the remaining two pairs of coils is unchanged. This results in a control system with low power consumption, and a simple control algorithm that can be easily applied to existing 3D Helmholtz systems, as it only requires the addition of a power supply. In combination with the developed system, we also propose a new control algorithm applicable to both permanently and temporarily magnetized microrobots, and verify this experimentally.

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]

Mobile microrobots with shape morphing capability show great advantages for conducting tasks in complex environments. Combination of magnetically driven locomotion and stimuli‐responsive shape morphing is an effective strategy to realize these microrobots. However, most existing microrobots fabricated by the combination strategy are of low locomotion efficiency due to the limited amount of magnetic material loaded. Herein, a novel scheme for coating the magnetic nanoparticles (NPs) on the surface of microrobot is proposed to increase the magnetic material loading amount. Theoretical analyses demonstrate that, below a critical size at microscale, surface coating NPs can load more magnetic material than embedding NPs into the volume due to the high surface area‐to‐volume ratio. Microrobots with both shape morphing and enhanced magnetically driven locomotion are fabricated by coating magnetic NPs on the surface of stimuli‐responsive hydrogel microstructures. It is experimentally demonstrated that surface coating ensures that the microstructure has not only an efficient locomotion but also an excellent deformability. A four‐claw microgripper is fabricated, which is smaller and has higher magnetically driven locomotion speed than the most existing shape morphing microrobots. This microgripper demonstrating carrying and delivery capabilities is of immediate interest to microobject manipulation and minimally invasive surgery.

Mobile microrobots with shape morphing capability show great advantages for conducting tasks in complex environments. Combination of magnetically driven locomotion and stimuli‐responsive shape morphing is an effective strategy to realize these microrobots. However, most existing microrobots fabricated by the combination strategy are of low locomotion efficiency due to the limited amount of magnetic material loaded. Herein, a novel scheme for coating the magnetic nanoparticles (NPs) on the surface of microrobot is proposed to increase the magnetic material loading amount. Theoretical analyses demonstrate that, below a critical size at microscale, surface coating NPs can load more magnetic material than embedding NPs into the volume due to the high surface area‐to‐volume ratio. Microrobots with both shape morphing and enhanced magnetically driven locomotion are fabricated by coating magnetic NPs on the surface of stimuli‐responsive hydrogel microstructures. It is experimentally demonstrated that surface coating ensures that the microstructure has not only an efficient locomotion but also an excellent deformability. A four‐claw microgripper is fabricated, which is smaller and has higher magnetically driven locomotion speed than the most existing shape morphing microrobots. This microgripper demonstrating carrying and delivery capabilities is of immediate interest to microobject manipulation and minimally invasive surgery. [ABSTRACT FROM AUTHOR]

In recent years, magnetism has gained an enormous amount of interest among researchers for actuating different sizes and types of bio/soft robots, which can be via an electromagnetic‐coil system, or a system of moving permanent magnets. Different actuation strategies are used in robots with magnetic actuation having a number of advantages in possible realization of microscale robots such as bioinspired microrobots, tetherless microrobots, cellular microrobots, or even normal size soft robots such as electromagnetic soft robots and medical robots. This review provides a summary of recent research in magnetically actuated bio/soft robots, discussing fabrication processes and actuation methods together with relevant applications in biomedical area and discusses future prospects of this way of actuation for possible improvements in performance of different types of bio/soft robots. [ABSTRACT FROM AUTHOR]

Wireless magnetic microrobots are envisioned to revolutionize minimally invasive medicine. While many promising medical magnetic microrobots are proposed, the ones using hard magnetic materials are not mostly biocompatible, and the ones using biocompatible soft magnetic nanoparticles are magnetically very weak and, therefore, difficult to actuate. Thus, biocompatible hard magnetic micro/nanomaterials are essential toward easy‐to‐actuate and clinically viable 3D medical microrobots. To fill such crucial gap, this study proposes ferromagnetic and biocompatible iron platinum (FePt) nanoparticle‐based 3D microprinting of microrobots using the two‐photon polymerization technique. A modified one‐pot synthesis method is presented for producing FePt nanoparticles in large volumes and 3D printing of helical microswimmers made from biocompatible trimethylolpropane ethoxylate triacrylate (PETA) polymer with embedded FePt nanoparticles. The 30 μm long helical magnetic microswimmers are able to swim at speeds of over five body lengths per second at 200 Hz, making them the fastest helical swimmer in the tens of micrometer length scale at the corresponding low‐magnitude actuation fields of 5–10 mT. It is also experimentally in vitro verified that the synthesized FePt nanoparticles are biocompatible. Thus, such 3D‐printed microrobots are biocompatible and easy to actuate toward creating clinically viable future medical microrobots.

Wireless magnetic microrobots are envisioned to revolutionize minimally invasive medicine. While many promising medical magnetic microrobots are proposed, the ones using hard magnetic materials are not mostly biocompatible, and the ones using biocompatible soft magnetic nanoparticles are magnetically very weak and, therefore, difficult to actuate. Thus, biocompatible hard magnetic micro/nanomaterials are essential toward easy‐to‐actuate and clinically viable 3D medical microrobots. To fill such crucial gap, this study proposes ferromagnetic and biocompatible iron platinum (FePt) nanoparticle‐based 3D microprinting of microrobots using the two‐photon polymerization technique. A modified one‐pot synthesis method is presented for producing FePt nanoparticles in large volumes and 3D printing of helical microswimmers made from biocompatible trimethylolpropane ethoxylate triacrylate (PETA) polymer with embedded FePt nanoparticles. The 30 μm long helical magnetic microswimmers are able to swim at speeds of over five body lengths per second at 200 Hz, making them the fastest helical swimmer in the tens of micrometer length scale at the corresponding low‐magnitude actuation fields of 5–10 mT. It is also experimentally in vitro verified that the synthesized FePt nanoparticles are biocompatible. Thus, such 3D‐printed microrobots are biocompatible and easy to actuate toward creating clinically viable future medical microrobots. [ABSTRACT FROM AUTHOR]

Developing microrobots with multiple deformabilities has become extremely challenging due to the lack of materials that are soft enough at the microscale level and the inability to be reconfigured after fabrication. In this study, it is aimed to prove that liquid microrobots composed of ferrofluid droplets are inherently deformable and they can be controlled, individually or in aggregate, with multiple programmable deformabilities. For example, the liquid‐microrobot monomer (LRM) can pass through narrow channels via elongation and achieve scaling via splitting and coalescence. LRMs can also reassemble into various kinds of functional liquid‐robot aggregates, such as microsticks, micropies, microtrains, microkayaks, and microrollingpins. Thus, they can respond to multi‐terrain surfaces or perform various complex tasks. Moreover, the authors' physics‐based theoretical model demonstrates dynamic self‐assembly and group behavior of a multiple LRM system, which is conducive to investigating the mechanisms behind it. These ferrofluid droplet robots provide novel solutions for some potential applications, such as untethered micromanipulation and targeted cargo delivery. [ABSTRACT FROM AUTHOR]

Magnetically actuated mobile microrobots can access distant, enclosed, and small spaces, such as inside microfluidic channels and the human body, making them appealing for minimally invasive tasks. Despite their simplicity when scaling down, creating collective microrobots that can work closely and cooperatively, as well as reconfigure their formations for different tasks, would significantly enhance their capabilities such as manipulation of objects. However, a challenge of realizing such cooperative magnetic microrobots is to program and reconfigure their formations and collective motions with under-actuated control signals. This article presents a method of controlling 2D static and time-varying formations among collective self-repelling ferromagnetic microrobots (100 μ m to 350 μ m in diameter, up to 260 in number) by spatially and temporally programming an external magnetic potential energy distribution at the air–water interface or on solid surfaces. A general design method is introduced to program external magnetic potential energy using ferromagnets. A predictive model of the collective system is also presented to predict the formation and guide the design procedure. With the proposed method, versatile complex static formations are experimentally demonstrated and the programmability and scaling effects of formations are analyzed. We also demonstrate the collective mobility of these magnetic microrobots by controlling them to exhibit bio-inspired collective behaviors such as aggregation, directional motion with arbitrary swarm headings, and rotational swarming motion. Finally, the functions of the produced microrobotic swarm are demonstrated by controlling them to navigate through cluttered environments and complete reconfigurable cooperative manipulation tasks. [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.

Cell-carrying magnet-driven microrobots are easily affected by blood flow or body fluids during transportation in the body, and thus cells often fall off from the microrobots. To reduce the loss of loaded cells, we developed a microrobot with a bioactive nanostructured titanate surface (NTS), which enhances cell adhesion. The microrobot was fabricated using 3D laser lithography and coated with nickel for magnetic actuation. Then, the microrobot was coated with titanium for the external generation of an NTS through reactions in NaOH solution. Enhanced cell adhesion may be attributed to the changes in the surface wettability of the microrobot and in the morphology of the loaded cells. An experiment was performed on a microfluidic chip for the simulation of blood flow environment, and result revealed that the cells adhered closely to the microrobot with NTS and were not obviously affected by flow. The cell viability and protein absorption test and alkaline phosphatase activity assay indicated that NTS can provide a regulatory means for improving cell proliferation and early osteogenic differentiation. This research provided a novel microrobotic platform that can positively influence the behaviour of cells loaded on microrobots through surface nanotopography, thereby opening up a new route for microrobot cell delivery.

A microrobot system comprising an untethered tumbling magnetic microrobot, a two-degree-of-freedom rotating permanent magnet, and an ultrasound imaging system has been developed for in vitro and in vivo biomedical applications. The microrobot tumbles end-over-end in a net forward motion due to applied magnetic torque from the rotating magnet. By turning the rotational axis of the magnet, two-dimensional directional control is possible and the microrobot was steered along various trajectories, including a circular path and P-shaped path. The microrobot is capable of moving over the unstructured terrain within a murine colon in in vitro, in situ, and in vivo conditions, as well as a porcine colon in ex vivo conditions. High-frequency ultrasound imaging allows for real-time determination of the microrobot’s position while it is optically occluded by animal tissue. When coated with a fluorescein payload, the microrobot was shown to release the majority of the payload over a 1-h time period in phosphate-buffered saline. Cytotoxicity tests demonstrated that the microrobot’s constituent materials, SU-8 and polydimethylsiloxane (PDMS), did not show a statistically significant difference in toxicity to murine fibroblasts from the negative control, even when the materials were doped with magnetic neodymium microparticles. The microrobot system’s capabilities make it promising for targeted drug delivery and other in vivo biomedical applications.

Soft, untethered microrobots composed of biocompatible materials for completing micromanipulation and drug delivery tasks in lab-on-a-chip and medical scenarios are currently being developed. Alginate holds significant potential in medical microrobotics due to its biocompatibility, biodegradability, and drug encapsulation capabilities. Here, we describe the synthesis of MANiACs—Magnetically Aligned Nanorods in Alginate Capsules—for use as untethered microrobotic surface tumblers, demonstrating magnetically guided lateral tumbling via rotating magnetic fields. MANiAC translation is demonstrated on tissue surfaces as well as inclined slopes. These alginate microrobots are capable of manipulating objects over millimeter-scale distances. Finally, we demonstrate payload release capabilities of MANiACs during translational tumbling motion.

Wireless capsule endoscopy ( WCE) is a powerful tool for medical screening and diagnosis, where a small capsule is swallowed and moved by means of natural peristalsis and gravity through the human gastrointestinal ( GI) tract. The camera-integrated capsule allows for visualization of the small intestine, a region which was previously inaccessible to classical flexible endoscopy. As a diagnostic tool, it allows to localize the sources of bleedings in the middle part of the gastrointestinal tract and to identify diseases, such as inflammatory bowel disease (Crohn's disease), polyposis syndrome, and tumors. The screening and diagnostic efficacy of the WCE, especially in the stomach region, is hampered by a variety of technical challenges like the lack of active capsular position and orientation control. Therapeutic functionality is absent in most commercial capsules, due to constraints in capsular volume and energy storage. The possibility of using body-exogenous magnetic fields to guide, orient, power, and operate the capsule and its mechanisms has led to increasing research in Magnetically Guided Capsule Endoscopy ( MGCE). This work shortly reviews the history and state-of-art in WCE technology. It highlights the magnetic technologies for advancing diagnostic and therapeutic functionalities of WCE. Not restricting itself to the GI tract, the review further investigates the technological developments in magnetically guided microrobots that can navigate through the various air- and fluid-filled lumina and cavities in the body for minimally invasive medicine. [ABSTRACT FROM AUTHOR]

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.

It is important to fabricate biocompatible and chemical-resistant microstructures that can be powered and controlled without a tether in fluid environment for applications when contamination must be avoided, like cell manipulation, and applications where connecting the power source to the actuator would be cumbersome, like targeted delivery of chemicals. In this work, a novel fabrication method was described to encapsulate magnetic composite into pure SU-8 structures, enabling the truly microscale ferromagnetic microrobots biocompatible and chemical resistant. The microrobots were developed using the simple multilayer photolithography that allows us to mass produce and were actuated contact-free by external magnetic field to complete micromanipulations of micro-objects. The microrobots were actuated moving along a preplanned path to transport a glass microsphere object at an approximately average speed of 1.1 mm/sec and can be operated to rotate, aim at targets and collect objects. [ABSTRACT FROM PUBLISHER]

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.

In this paper, we have developed an approach for independent autonomous navigation of multiple microrobots under the influence of magnetic fields and validated it experimentally. We first developed a heuristics based planning algorithm for generating collision-free trajectories for the microrobots that are suitable to be executed by an available magnetic field. Second, we have modeled the dynamics of the microrobots to develop a controller for determining the forces that need to be generated for the navigation of the robots along the trajectories at a suitable control frequency. Next, an optimization routine is developed to determine the input currents to the electromagnetic coils that can generate the required forces for the navigation of the robots at the controller frequency. We then validated our approach by simulating an electromagnetic system that contains an array of sixty-four magnetic microcoils designed for generating local magnetic fields suitable for simultaneous independent actuation of multiple microrobots. Finally, we prototyped an mm-scale version of the system and present experimental results showing the validity of our approach. [ABSTRACT FROM AUTHOR]

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]

In this paper, we have developed an approach for independent autonomous navigation of multiple microrobots under the influence of magnetic fields and validated it experimentally. We first developed a heuristics based planning algorithm for generating collision-free trajectories for the microrobots that are suitable to be executed by an available magnetic field. Second, we have modeled the dynamics of the microrobots to develop a controller for determining the forces that need to be generated for the navigation of the robots along the trajectories at a suitable control frequency. Next, an optimization routine is developed to determine the input currents to the electromagnetic coils that can generate the required forces for the navigation of the robots at the controller frequency. We then validated our approach by simulating an electromagnetic system that contains an array of sixty-four magnetic microcoils designed for generating local magnetic fields suitable for simultaneous independent actuation of multiple microrobots. Finally, we prototyped an m m -scale version of the system and present experimental results showing the validity of our approach.

Microrobots have been investigated in recent years with the objective of discovering applications in the biomedical industry. The selective control of multiple microrobots is a challenging task; however, such control would allow for the dexterous manipulation of microscale objects. In this paper, we present a novel control method for the selective actuation of microrobots using only an external magnetic field. Such selective actuation of microrobots can be achieved by combining two types of external magnetic field rotations and two microrobotic designs, one with a bar-shaped head and the other with a cross-shaped head. After the type of rotation is chosen, the bar-shaped or the cross-shaped head can be individually actuated or both of them can be actuated simultaneously. To demonstrate the feasibility of the proposed method, millimeter-sized prototypes were fabricated and their individual actuation was successfully demonstrated in silicone oil. The prototypes showed the ability to swim in silicone oil (viscosity: 100 cSt) with a synchronized frequency of up to 0.25 Hz. This result suggests that the proposed method can be used in water at high input frequencies while taking the scaling effect into consideration. Hence, this method is expected to have many practical applications. [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]

Cell-carrying magnet-driven microrobots are easily affected by blood flow or body fluids during transportation in the body, and thus cells often fall off from the microrobots. To reduce the loss of loaded cells, we developed a microrobot with a bioactive nanostructured titanate surface (NTS), which enhances cell adhesion. The microrobot was fabricated using 3D laser lithography and coated with nickel for magnetic actuation. Then, the microrobot was coated with titanium for the external generation of an NTS through reactions in NaOH solution. Enhanced cell adhesion may be attributed to the changes in the surface wettability of the microrobot and in the morphology of the loaded cells. An experiment was performed on a microfluidic chip for the simulation of blood flow environment, and result revealed that the cells adhered closely to the microrobot with NTS and were not obviously affected by flow. The cell viability and protein absorption test and alkaline phosphatase activity assay indicated that NTS can provide a regulatory means for improving cell proliferation and early osteogenic differentiation. This research provided a novel microrobotic platform that can positively influence the behaviour of cells loaded on microrobots through surface nanotopography, thereby opening up a new route for microrobot cell delivery. [ABSTRACT FROM AUTHOR]

A microrobot system comprising an untethered tumbling magnetic microrobot, a two-degree-of-freedom rotating permanent magnet, and an ultrasound imaging system has been developed for in vitro and in vivo biomedical applications. The microrobot tumbles end-over-end in a net forward motion due to applied magnetic torque from the rotating magnet. By turning the rotational axis of the magnet, two-dimensional directional control is possible and the microrobot was steered along various trajectories, including a circular path and P-shaped path. The microrobot is capable of moving over the unstructured terrain within a murine colon in in vitro, in situ, and in vivo conditions, as well as a porcine colon in ex vivo conditions. High-frequency ultrasound imaging allows for real-time determination of the microrobot's position while it is optically occluded by animal tissue. When coated with a fluorescein payload, the microrobot was shown to release the majority of the payload over a 1-h time period in phosphate-buffered saline. Cytotoxicity tests demonstrated that the microrobot's constituent materials, SU-8 and polydimethylsiloxane (PDMS), did not show a statistically significant difference in toxicity to murine fibroblasts from the negative control, even when the materials were doped with magnetic neodymium microparticles. The microrobot system's capabilities make it promising for targeted drug delivery and other in vivo biomedical applications. [ABSTRACT FROM AUTHOR]

Soft, untethered microrobots composed of biocompatible materials for completing micromanipulation and drug delivery tasks in lab-on-a-chip and medical scenarios are currently being developed. Alginate holds significant potential in medical microrobotics due to its biocompatibility, biodegradability, and drug encapsulation capabilities. Here, we describe the synthesis of MANiACs—Magnetically Aligned Nanorods in Alginate Capsules—for use as untethered microrobotic surface tumblers, demonstrating magnetically guided lateral tumbling via rotating magnetic fields. MANiAC translation is demonstrated on tissue surfaces as well as inclined slopes. These alginate microrobots are capable of manipulating objects over millimeter-scale distances. Finally, we demonstrate payload release capabilities of MANiACs during translational tumbling motion. [ABSTRACT FROM AUTHOR]

Microhelices with unique three-dimensional (3D) helical structures have attracted great attention due to applications in various fields, especially magnetic microhelices can be applied as microrobots for removal of clogging substance in microchannels, cargo transport, cell manipulation, and so on. Here, a facile and flexible strategy is developed to controllably fabricate microhelices with droplet microfluidics. On-flow fabrication of microhelices is simply achieved by generating monodisperse droplets first, transforming the spherical droplets into helical templates subsequently due to the liquid rope coiling effect, followed by polymerizing monomers in the templates via on-line UV irradiation and then degrading the shells of helical fibers. Benefitting from the flexible controllability of microfluidics, the morphologies of microhelices can be precisely controlled by adjusting the flow rates of fluids and the structures of microfluidic devices. Functional microhelices can be easily prepared by introducing functional components or elements into inner fluids. By introducing magnetic nanoparticles into inner fluids, magnetic microhelices are easily fabricated as microrobots that featured with magnetic-field-driven corkscrew-like motion for efficient cargo transport and removal of clogging substance in microchannels. This novel microfabrication method allows a precise morphological control and easy functionalization of microhelices, providing a flexible and versatile strategy for fabricating designer functional microhelices for diverse applications.

Biocompatibility and high responsiveness to magnetic fields are fundamental requisites to translate magnetic small-scale robots into clinical applications. The magnetic element iron exhibits the highest saturation magnetization and magnetic susceptibility while exhibiting excellent biocompatibility characteristics. Here, a process to reliably fabricate iron microrobots by means of template-assisted electrodeposition in 3D-printed micromolds is presented. The 3D molds are fabricated using a modified two-photon absorption configuration, which overcomes previous limitations such as the use of transparent substrates, low writing speeds, and limited depth of field. By optimizing the geometrical parameters of the 3D molds, metallic structures with complex features can be fabricated. Fe microrollers and microswimmers are realized that demonstrate motion at ≈20 body lengths per second, perform 3D motion in viscous environments, and overcome higher flow velocities than those of "conventional 3D printed helical microswimmers." The cytotoxicity of these microrobots is assessed by culturing them with human colorectal cancer (HCT116) cells for four days, demonstrating their good biocompatibility characteristics. Finally, preliminary results regarding the degradation of iron structures in simulated gastric acid liquid are provided., (© 2019 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Magnetic microrobots can be actuated in fuel-free conditions and are envisioned for biomedical applications related to targeted delivery and therapy in a minimally invasive manner. However, mass fabrication of microrobots with precise propulsion performance and excellent therapeutic efficacy is still challenging, especially in a predictable and controllable manner. Herein, we propose a facile technique for mass production of magnetic microrobots with multiple functions using Spirulina ( Sp.) as biotemplate. Core-shell-structured Pd@Au nanoparticles (NPs) were synthesized in Sp. cells by electroless deposition, working as photothermal conversion agents. Subsequently, the Fe 3 O 4 NPs were deposited onto the surface of the obtained (Pd@Au)@ Sp. particles via a sol-gel process, enabling them to be magnetically actuated. Moreover, the anticancer drug doxorubicin (DOX) was loaded on the (Pd@Au)/Fe 3 O 4 @ Sp. microrobots, which endows them with additional chemotherapeutic efficacy. The as-prepared biohybrid (Pd@Au)/Fe 3 O 4 @ Sp.-DOX microrobots not only possess efficient propulsion performance with the highest speed of 526.2 μm/s under a rotating magnetic field but also have enhanced synergistic chemo-photothermal therapeutic efficacy. Furthermore, they can be structurally disassembled into individual particles under near-infrared (NIR) laser irradiation and exhibit pH- and NIR-triggered drug release. These intriguing properties enable the microrobots to be a very promising and efficient platform for drug loading, targeted delivery, and chemo-photothermal therapy.