Magnetic Microrobots Research Articles

Magnetic Microrobots Fabricated by Photopolymerization and Assembly.

Magnetic soft microrobots have great potential to access narrow spaces and conduct multiple tasks in the biomedical field. Until now, drug delivery, microsurgery, disease diagnosis, and dredging the blocked blood vessel have been realized by magnetic soft microrobots invivo or invitro. However, as the tasks become more and more complex, more functional units have been embedded in the body of the developed magnetic microrobots. These magnetic soft microrobots with complex designed geometries, mechanisms, and magnetic orientation are now greatly challenging the fabrication of the magnetic microrobots. In this paper, we propose a new method combining photopolymerization and assembly for the fabrication of magnetic soft microrobots. Utilizing the micro-hand assembly system, magnetic modules with different shapes and materials are firstly arrayed with precise position and orientation control. Then, the developed photopolymerization system is employed to fix and link these modules with soft materials. Based on the proposed fabrication method, 3 kinds of soft magnetic microrobots were fabricated, and the fundamental locomotion was presented. We believe that the presented fabrication strategy could help accelerate the clinical application of magnetic microrobots.

Fish-like magnetic microrobots for microparts transporting at liquid surfaces.

Magnetic microrobots have tremendous potential applications due to their wireless actuation and fast response in confined spaces. Herein, inspired by fish, a magnetic microrobot working at liquid surfaces was proposed in order to transport microparts effectively. Different from other fish-like robots propelled by flexible caudal fins, the microrobot is designed as a simple sheet structure with a streamlined shape. It is fabricated monolithically utilizing polydimethylsiloxane doped with magnetic particles. The unequal thicknesses of different parts of the fish shape enable the microrobot to move faster via a liquid level difference around the body under an oscillating magnetic field. The propulsion mechanism is investigated through theoretical analysis and simulations. The motion performance characteristics are further characterized through experiments. It is interesting to find that the microrobot moves in a head-forward mode when the vertical magnetic field component is upward, whereas it moves in a tail-forward mode when the component is downward. Relying on the modulation of capillary forces, the microrobot is able to capture and deliver microballs along a given path. The maximum transporting speed can reach 1.2 mm s-1, which is about three times the microball diameter per second. It is also found that the transporting speed with the microball is much higher than that of the microrobot alone. The reason for this is that when the micropart and microrobot combine, the increased asymmetry of the liquid surfaces caused by the forward movement of the gravity center can increase the forward driving force. The proposed microrobot and the transporting method are expected to have more applications in micromanipulation fields.

Magnetic Microrobots with Folate Targeting for Drug Delivery.

Untethered microrobots can be used for cargo delivery (e.g., drug molecules, stem cells, and genes) targeting designated areas. However, it is not enough to just reach the lesion site, as some drugs can only play the best therapeutic effect within the cells. To this end, folic acid (FA) was introduced into microrobots in this work as a key to mediate endocytosis of drugs into cells. The microrobots here were fabricated with biodegradable gelatin methacryloyl (GelMA) and modified with magnetic metal-organic framework (MOF). The porous structure of MOF and the hydrogel network of polymerized GelMA were used for the loading of enough FA and anticancer drug doxorubicin (DOX) respectively. Utilizing the magnetic property of magnetic MOF, these microrobots can gather around the lesion site with the navigation of magnetic fields. The combination effects of FA targeting and magnetic navigation substantially improve the anticancer efficiency of these microrobots. The result shows that the cancer cells inhibition rate of microrobots with FA can be up to 93%, while that of the ones without FA was only 78%. The introduction of FA is a useful method to improve the drug transportation ability of microrobots, providing a meaningful reference for further research.

Combined three dimensional locomotion and deformation of functional ferrofluidic robots

Magnetic-controlled ferrofluidic robots demonstrate exceptional precision in efficiently navigating complex 3D paths, which enhances their applicability across diverse fields, including medicine, micromanipulation, and bioengineering.

ModMag: A modular magnetic micro-robotic manipulation device

Electromagnetic systems have been used extensively for the control of magnetically actuated objects, such as in microrheology and micro- robotics research. Therefore, optimizing the design of such systems is highly desirable. Some of the features that are lacking in most cur- rent designs are compactness, portability, and versatility. Portability is especially relevant for biomedical applications in which in vivo or in vitro testing may be conducted in locations away from the laboratory microscope. This document describes the design, fabrication, and imple- mentation of a compact, low-cost, versatile, and user-friendly device (the ModMag) capable of controlling multiple electromagnetic setups, includ- ing a two-dimensional 4-coil configuration, a 3-dimensional Helmholtz configuration, a 2-dimensional magnetic tweezer configuration, and a piezoelectric transducer for producing acoustic waves. All electronics for powering the systems are contained in a compact 10″x6”x3” case, which includes a 10″ touchscreen. A graphical user interface provides additional ease of use. The system can also be controlled remotely, allowing for more flexibility and the ability to interface with other software running on the remote computer such as proprietary camera software. Aside from the software and circuitry, we also describe the design of the electromagnetic coil setups and provide examples of the use of the ModMag in experiments.•Low cost and portable magnetic micro-robot manipulation device•Compatible with the 3 most common coil configurations (traditional, Helmholtz, tweezer)

Eliminating waste with waste: transforming spent coffee grounds into microrobots for water treatment.

Water pollutants such as oil spills, industrial dyes, and microplastics threaten public health and aquatic ecosystems. There are considerable challenges in removing water contaminants using traditional methods. Several studies have been conducted in recent years to develop effective water purification materials. Despite this, the mass production of most materials is extremely challenging because they involve multiple intricate steps and sophisticated equipment. Herein, we report the facile synthesis of spent coffee ground (SCG)-derived magnetic microrobots, which we dub "CoffeeBots", to remove oil, organic dyes, and microplastic pollution from contaminated seawater. In order to meet eco-friendly, high-yield and low-cost requirements, iron oxide nanoparticles (IONPs) were deposited on biodegradable SCGs using green chemistry. The IONPs on CoffeeBots facilitate magnetic navigation and recycling, microswarm assembly, and ease of retrieval after water remediation tasks. CoffeeBots' intrinsic surface hydrophobicity enables efficient on-the-fly capture and removal of oil droplets and microplastics from contaminated water with remote magnetic guidance. CoffeeBots were also functionalized with ascorbic acid (AA@CoffeeBots) to remove methylene blue (MB) dye contaminants from polluted seawater. SCGs and AA act as bioadsorbent and reducing agent, respectively, for MB dye removal whereas magnetic propulsion enhances mixing and accelerates MB decolorization. These CoffeeBots can be recycled numerous times for removing oil spills, organic dyes, and microplastics from the seawater. CoffeeBots hold considerable potential as sustainable, recyclable, and low-cost remediation agents for water treatment in the near future.

Ultrasound-Guided Wired Magnetic Microrobot With Active Steering and Ejectable Tip

Interventional therapy is popular in modern surgical procedures for the treatment of vascular diseases. However, it remains challenging to smoothly steer the guidewire/catheter into distal tortuous lumen environments. In this article, a wired magnetic microrobot (WMM) is proposed for approaching hard-to-reach regions. The WMM consists of a commercial guidewire and an assembled tip module, which has two working modalities with a magnetically triggered switch. The tethered mode has high efficiency and reliability, where the forward–backward motion is controlled by the feeding device and the steering motion is actuated by the directional external magnetic field. The untethered mode has enhanced flexibility, where the ejected helical bullet is wirelessly propelled by the rotating external magnetic field. A homemade actuation system is adopted for large-workspace magnetic control and medical imaging-based feedback. Targeted scanning is conducted based on real-time segmentation of the vessel region in ultrasound (US) images and estimation of the vascular distribution. Both transverse and longitudinal views are used for visual tracking under different modes. With the proposed system, the WMM can be navigated in a 3-D tubular structure over a distance of 1000 mm, and the whole procedure can be performed under US imaging monitoring.

Fabrication of three-lobed magnetic microrobots for cell transportation.

Mobile microrobots have the potential to transform medical treatments based on therapeutic delivery. Specifically, microrobots are promising candidates for cell transportation in cell-based therapies. Despite recent progress in cellular manipulation by microrobots, there is a significant need to design and fabricate microrobots to advance the field further. In this work, we present a facile approach to manufacturing three-lobed microrobots by a bench-top procedure. The microrobots are actuated by a harmless magnetic field which makes them biofriendly. Chemically, these microrobots are made of organosilica. The microrobots showed equally good control in both the open-loop and closed-loop settings. The three-lobed microrobots have two modes of motion during the open-loop control experiments. We employed these two modes for single-cell transportation. Our results show that the three-lobed microbots are very promising for cell transportation in a fluid.

Magnetic Hydrogel Microrobots as Insecticide Carriers for In Vivo Insect Pest Control in Plants.

The cost of insect pests to human society exceeds USD70 billion per year worldwide in goods, livestock, and healthcare services. Therefore, pesticides are needed to prevent insect damage despite the secondary effects of these chemical agents on non-target organisms. Chemicals encapsulation into carriers is a promising strategy to improve their specificity. Hydrogel-based microrobots show enormous potential as chemical carriers. Herein, hydrogel chitosan magnetic microrobots encapsulating ethyl parathion (EP)-CHI@Fe3 O4 are used to efficiently kill mealworm larvae (Tenebrio molitor). The mechanism takes advantage of pH-responsive chitosan degradation at Tenebrio molitor midgut pH to efficiently deliver pesticide into the mealworm intestinal tract in just 2h. It is observed that under a transversal rotating magnetic field, mealworm populations show higher mortality after 30min compared to free pesticide. This example of active pesticide carriers based on soft microrobots opens new avenues for microrobots applications in the agrochemical field as active chemical carriers.

Effects of applied potential, initial gap, and megasonic vibrations on the localized electrochemical deposition of Ni-Co microcolumns

This study demonstrates the localized electrochemical deposition (LECD) of nickel–cobalt (Ni-Co) alloy microcolumns and investigates the effects of the experimental parameters on the deposition process. The results revealed that the applied potential significantly affected the surface morphology, deposition rate, and compositions of the Ni-Co microcolumns. Although a high potential significantly improved the deposition rate of the microcolumns, the deterioration of the surface morphologies of the microcolumns was observed. The microcolumns were also deposited at different initial gaps, and smoother surface morphologies were achieved with a relatively larger initial gap. The addition of megasonic vibrations was shown to significantly increase the deposition rate, due to the accelerated ion mass transfer and bubble elimination. Furthermore, the compositions of deposited samples confirmed the anomalous co-deposition behavior of Ni-Co alloys. This study lays the experimental groundwork for potential applications such as micro actuators and magnetic helical microrobots.

An On‐Demand Microrobot with Building Block Design for Flow Manipulation

AbstractThe ability to precisely maneuver miniature objects in flow through a well‐controlled manner is envisaged to have an extensive impact in micro manipulation for profound medical and biological applications. In this work, the magnetic microrobots are fabricated by employing a distinct block‐to‐block approach in which the microrobotic structures are developed using several magnetic and nonmagnetic blocks. To demonstrate the on‐board control strategies of the microrobots, two distinct modes of motion are introduced and actuated with the aid of the developed in‐house electromagnetic system. To delve into the physics of microrobot locomotion, theoretical and numerical investigations are performed that further provide practical relevance for extensive applications with profound reliability. A mixing task is conducted to elucidate the enriched controllability of the microrobot in furnishing an on‐demand flow agitation function with high efficiency. Furthermore, the directions of such mixing are engineered using the proposed modes of motion which can unlock the possibilities to precisely control the directional inhomogeneities of the fluids encountered in diversely microfluidic systems. Aside from it, the multidimensional controllability of the microrobot motions exhibiting distinct flow behaviors is further demonstrated to precisely disperse the particles suspended in the fluid medium. Subsequently, such behaviors combined with the adaptive modes of microrobot motion can be potentially employed as one of the strategies to prevent the fouling problems encountered in several microfluidic applications. The presented work provides the feasible functions of the microrobots where they can play a pivotal role in dampening their functional limitations inherent in dynamic environment, and pave to emerge as fully autonomous microrobots for future engineering applications.

Fabrication of Bilayer Magnetically Actuated L-Shaped Microrobot Based on Chitosan via Photolithography.

Magnetically actuated microrobots showed increasing potential in various fields, especially in the biomedical area, such as invasive surgery, targeted cargo delivery, and treatment. However, it remains a challenge to incorporate biocompatible natural polymers that are favorable for practical biomedical applications. In this work, bilayer magnetic microrobots with an achiral planar design were fabricated using a biocompatible natural polymer and Fe3O4 nanoparticles through the photolithography by applying the layer-by-layer method. The microrobots consisted of a magnetic bottom layer and a photo-crosslinked chitosan top layer. The SEM results showed that the microrobot processed the L-shaped planar structure with the average width, length, and thickness of 99.18 ± 5.11 μm, 189.56 ± 11.37 μm, and 23.56 ± 4.08 μm, respectively. Moreover, microrobots actuated using a three-dimensional (3D) Helmholtz coil system was characterized and reached up to an average maximum velocity of 325.30 μm/s and a step-out frequency of 14 Hz. Furthermore, the microrobots exhibited excellent cell biocompatibility towards L929 cells in the CCK-8 assay. Therefore, the development of bi-layered chitosan-based microrobots offers a general solution for using magnetic microrobots in biomedical applications by providing an easy-to-fabricate, highly mobile microrobotic platform with the incorporation of biocompatible natural polymers for enhanced biocompatibility.

Swarming Magnetic Microrobots for Pathogen Isolation from Milk.

Bovine mastitis produced by Staphylococcus aureus (S. aureus) causes major problems in milk production due to the staphylococcal enterotoxins produced by this bacterium. These enterotoxins are stable and cannot be eradicated easily by common hygienic procedures once they are formed in dairy products. Here, magnetic microrobots (MagRobots) are developed based on paramagnetic hybrid microstructures loaded with IgG from rabbit serum that can bind and isolate S. aureus from milk in a concentration of 3.42 104 CFU g-1 (allowable minimum level established by the United States Food and Drug Administration, FDA). Protein A, which is present on the cell wall of S. aureus, selectively binds IgG from rabbit serum and loads the bacteria onto the surface of the MagRobots. The selective isolation of S. aureus is confirmed using a mixed suspension of S. aureus and Escherichia coli (E. coli). Moreover, this fuel-free system based on magnetic robots does not affect the natural milk microbiota or add any toxic compound resulting from fuel catalysis. This system can be used to isolate and transport efficiently S. aureus and discriminate it from nontarget bacteria for subsequent identification. Finally, this system can be scaled up for industrial use in food production.

2D Magnetic Manipulation of a Micro-Robot in Glycerin Using Six Pairs of Magnetic Coils.

This paper demonstrates the control system of a single magnetic micro-robot driven by combined coils. The combined coils consist of three pairs of Helmholtz coils and three pairs of Maxwell coils. The rotating magnetic field, gradient magnetic field, and combined magnetic field model of the combined coils were analyzed. To make the output magnetic field quickly converge to the reference point without steady-state error, the discrete-time optimal controller was designed based on the auto disturbance rejection technology. We have designed a closed-loop controller based on a position servo. The control system includes the position control and direction control of the micro-robot. To address problems with slow sampling frequency in visual feedback and inability to feed real-time position back to the control system, a Kalman filter algorithm was used to predict the position of the micro-robot in two-dimensional space. Simulations and experiments were carried out based on the proposed structure of combined coils and control scheme. The experimental results demonstrated the uniformity and excellent dynamic performance of the generated magnetic field.

Magnetic Systems for Regenerative Medicine

Magnetic Systems for Regenerative Medicine

Soft Magnetic Microrobots for Photoactive Pollutant Removal.

"Soft" robotics based on hydrogels appears as an alternative to the traditional technology of "hard" robotics. Soft microrobots are employed for drug delivery and cell manipulation. This work develops magnetic hydrogel-based microrobots using chitosan (CHI) as the body of the micromotor and Fe3 O4 nanoparticles to allow for its magnetic actuation. In addition, ZnO nanoparticles are incorporated inside the CHI body of the microrobot to act as an active component for pollutants photodegradation. CHI@Fe3 O4 -ZnO microrobots are used for the efficient photodegradation of persistent organic pollutants (POPs). The high absorption of CHI hydrogel enhances the POP photodegradation, degrading it 75% in just 30min. The adsorption-degradation and magnetic properties of CHI@Fe3 O4 -ZnO microrobots are used in five cycles while maintaining up to 60% photodegradation efficiency. The proof-of-concept present in this work represents a simple way to obtain soft microrobots with magnetic actuation and photodegradation functionalities for several water purification applications.

Biohybrid Magnetic Microrobots for Tumor Assassination and Active Tissue Regeneration.

Magnetic microrobots have attracted increasing research interest for diverse biomedical applications, such as targeted therapy and tissue regeneration. However, multifunctional microrobots with complex morphology at the microscale are urgently needed to be fabricated, actively controlled, and functionalized. In this study, the chrysanthemum pollen-derived biohybrid magnetic microrobots (CDBMRs) with spiny protrusion, hollow cavity, and porous surface structure were proposed for tumor assassination and active tissue regeneration. By exquisitely designing the sequential treatment process, CDBMRs were fabricated and the innate morphology of pollen templates was well preserved. Under magnetic field, CDBMR exhibited various individual and collective behaviors. CDBMRs were utilized for synergetic tumor treatment by the combination of magnetically controlled physical assassination and active drug delivery. Meanwhile, CDBMRs showed excellent ability for active cell delivery and tissue regeneration, which was further proved by enhanced osteogenesis ability. By making full use of the natural morphology of pollen grains, the biohybrid microrobots presented a promising strategy for effective tumor therapeutics and tissue regeneration.

Detachable electromagnetic actuation system for inverted microscope and its function in motion control of microrobots

In recent years, magnetic microrobots have shown unique advantages and exciting prospects in many application fields. However, the motion mechanism, driving force and imaging effect of magnetic microrobots still need to be further studied and improved. These factors are related to the design of magnetic actuation systems and the manufacturing of microrobots. This paper presents a new structural design involving detachable electromagnetic coils for developing a combinable magnetic actuation system that can be integrated with inverted microscopes for microrobot research. A maximum magnetic field intensity of 20 mT and uniform working space of 10 mm × 10 mm are achieved by applying coil parameter optimization and the yoke design. Furthermore, a dumbbell microrobot, which is symmetrical along its length axis, and a moon microrobot, which is asymmetric along its length axis, are fabricated and their motion characteristics are compared. The dumbbell microrobot exhibits reversible switching of three motion modes, whereas the motion of the moon microrobot exhibits the obvious drift. These dumbbell and moon microrobots are successfully controlled to move along a square path and a labyrinth path respectively, thus verifying the control performance of the magnetic actuation system.

Modeling and Estimation of Self-Phoretic Magnetic Janus Microrobot With Uncontrollable Inputs

This study theoretically investigates the modeling of spherical catalytic self-phoretic magnetic Janus microrobot (MJR) evolving in uniform viscous flow. A 2-D state-space representation of the MJR is developed, exhibiting a state-dependent-coefficient (SDC) form. To evaluate the consistency of the modeling formalism, a dual Kalman filter (DKF) methodology is employed with respect to experimental results when unknown parameters or uncontrollable inputs are considered. In fact, the self-phoretic thrust mechanism and the magnetodynamics of the MJR are not well-known. SDC-DKF is implemented, and we find that there is good agreement between the dynamics computed from our theoretical predictions and the experimental observations in a wide range of model parameter variations.

Self-Propelled Magnetic Dendrite-Shaped Microrobots for Photodynamic Prostate Cancer Therapy.

Photocatalytic micromotors that exhibit wireless and controllable motion by light have been extensively explored for cancer treatment by photodynamic therapy (PDT). However, overexpressed glutathione (GSH) in the tumor microenvironment can down-regulate the reactive oxygen species (ROS) level for cancer therapy. Herein, we present dendrite-shaped light-powered hematite microrobots as an effective GSH depletion agent for PDT of prostate cancer cells. These hematite microrobots can display negative phototactic motion under light irradiation and flexible actuation in a defined path controlled by an external magnetic field. Non-contact transportation of micro-sized cells can be achieved by manipulating the microrobot's motion. In addition, the biocompatible microrobots induce GSH depletion and greatly enhance PDT performance. The proposed dendrite-shaped hematite microrobots contribute to developing dual light/magnetic field-powered micromachines for the biomedical field.