One-Step Fabrication of Dual Optically/Magnetically Modulated Walnut-like Micromotor

Collective Molecular Machines: Multidimensionality and Reconfigurability

Molecular machines are key to cellular activity where they are involved in converting chemical and light energy into efficient mechanical work. During the last 60 years, designing molecular structures capable of generating unidirectional mechanical motion at the nanoscale has been the topic of intense research. Effective progress has been made, attributed to advances in various fields such as supramolecular chemistry, biology and nanotechnology, and informatics. However, individual molecular machines are only capable of producing nanometer work and generally have only a single functionality. In order to address these problems, collective behaviors realized by integrating several or more of these individual mechanical units in space and time have become a new paradigm. In this review, we comprehensively discuss recent developments in the collective behaviors of molecular machines. In particular, collective behavior is divided into two paradigms. One is the appropriate integration of molecular machines to efficiently amplify molecular motions and deformations to construct novel functional materials. The other is the construction of swarming modes at the supramolecular level to perform nanoscale or microscale operations. We discuss design strategies for both modes and focus on the modulation of features and properties. Subsequently, in order to address existing challenges, the idea of transferring experience gained in the field of micro/nano robotics is presented, offering prospects for future developments in the collective behavior of molecular machines.

Nano/Micromotors for Cancer Diagnosis and Therapy: Innovative Designs to Improve Biocompatibility

Nano/micromotors are artificial robots at the nano/microscale that are capable of transforming energy into mechanical movement. In cancer diagnosis or therapy, such "tiny robots" show great promise for targeted drug delivery, cell removal/killing, and even related biomarker sensing. Yet biocompatibility is still the most critical challenge that restricts such techniques from transitioning from the laboratory to clinical applications. In this review, we emphasize the biocompatibility aspect of nano/micromotors to show the great efforts made by researchers to promote their clinical application, mainly including non-toxic fuel propulsion (inorganic catalysts, enzyme, etc.), bio-hybrid designs, ultrasound propulsion, light-triggered propulsion, magnetic propulsion, dual propulsion, and, in particular, the cooperative swarm-based strategy for increasing therapeutic effects. Future challenges in translating nano/micromotors into real applications and the potential directions for increasing biocompatibility are also described.

Development of Microrobot with Optical Magnetic Dual Control for Regulation of Gut Microbiota

Microrobots have emerged as a promising precision therapy approach that has been widely used in minimally invasive treatments, targeted drug delivery, and wound cleansing, and they also offer a potential new method for actively modulating gut microbiota. Here, a double-faced microrobot was designed to carry gut bacteria via covalently immobilizing the antibodies, and a corresponding integrated optical and magnetic dual-driving control system was also developed for precise control of the microrobot. The microrobot utilizes magnetic microsphere as its core, with one side coated in gold, which serves as the optical receptor surface and the interface for bacterial attachment. The specific gut bacterium, S. cerevisiae, was immobilized on the gold-coated side using the corresponding antibodies. The dual-driving control system enables the precise modulation of gut bacteria by synergistically manipulating the microrobots' movement via the optical field and magnetic field. The feasibility of independent and coordinated control using optical fields and magnetic fields was validated through experimental and numerical simulation approaches. This work introduces a novel method for the precise modulation of gut microbiota, providing a new avenue for disease treatments based on gut bacteria.

Micro/nanorobots for remediation of water resources and aquatic life

Nowadays, global water scarcity is becoming a pressing issue, and the discharge of various pollutants leads to the biological pollution of water bodies, which further leads to the poisoning of living organisms. Consequently, traditional water treatment methods are proving inadequate in addressing the growing demands of various industries. As an effective and eco-friendly water treatment method, micro/nanorobots is making significant advancements. Based on researches conducted between 2019 and 2023 in the field of water pollution using micro/nanorobots, this paper comprehensively reviews the development of micro/nanorobots in water pollution control from multiple perspectives, including propulsion methods, decontamination mechanisms, experimental techniques, and water monitoring. Furthermore, this paper highlights current challenges and provides insights into the future development of the industry, providing guidance on biological water pollution control.

Smart micro- and nanorobots for water purification

Less than 1% of Earth's freshwater reserves is accessible. Industrialization, population growth and climate change are further exacerbating clean water shortage. Current water-remediation treatments fail to remove most pollutants completely or release toxic by-products into the environment. The use of self-propelled programmable micro- and nanoscale synthetic robots is a promising alternative way to improve water monitoring and remediation by overcoming diffusion-limited reactions and promoting interactions with target pollutants, including nano- and microplastics, persistent organic pollutants, heavy metals, oils and pathogenic microorganisms. This Review introduces the evolution of passive micro- and nanomaterials through active micro- and nanomotors and into advanced intelligent micro- and nanorobots in terms of motion ability, multifunctionality, adaptive response, swarming and mutual communication. After describing removal and degradation strategies, we present the most relevant improvements in water treatment, highlighting the design aspects necessary to improve remediation efficiency for specific contaminants. Finally, open challenges and future directions are discussed for the real-world application of smart micro- and nanorobots.

Tailoring Functional Micromotors for Sensing

Micromotors are identified as a promising candidate in the field of sensing benefiting from their capacity of autonomous movement. Here, a review on the development of tailoring micromotors for sensing is presented, covering from their propulsion mechanisms and sensing strategies to applications. First, we concisely summarize the propulsion mechanism of micromotors involving fuel-based propulsion and fuel-free propulsion introducing their principles. Then, emphasis is laid to the sensing stratagems of the micromotors including speed-based sensing strategy, fluorescence-based sensing strategy, and other strategies. We listed typical examples of different sensing stratagems. After that, we introduce the applications of micromotors in sensing fields including environmental science, food safety, and biomedical fields. Finally, we discuss the challenges and prospects of the micromotors tailored for sensing. We believe that this comprehensive review can help readers to catch the research frontiers in the field of sensing and thus to burst out new ideas.

Swarming Magnetically Navigated Indigo-Based Hydrophobic Microrobots for Oil Removal

Removal of oil is very important for environmental remediation when considering its negative impacts on living organisms and on the quality of water, groundwater, and soil. Here, we report on the application of hydrophobic magnetic hydrogen-bonded organic pigment-based microrobots for oil removal. The microrobots can be wirelessly navigated in a transversal rotating magnetic field, with full control of their trajectory. In addition, the velocity of magnetic microrobots can be easily controlled by changing the frequency. Due to their hydrophobic nature, the microrobots were able to enter droplets of spilled oil. Consequently, the navigation of the oil droplets was enabled in a magnetic field. Moreover, the microrobots captured within the oil droplets exhibited a swarm-like behavior; they collectively navigated toward further oil droplets that were collected and transferred to a desired location. This concept does not require the use of any additional fuel or surfactants, which is crucial for large-scale oil pollution treatment. Therefore, we believe that these microrobot swarms have great potential in remediating aqueous environments.

Micro/nanomotor technology: the new era for food safety control

Food poisoning caused by eating contaminated food remains a threat to global public health. Making the situation even worse is the aggravated global environmental pollution, which poses a major threat to the safety of agricultural resources. Food adulteration has been rampant owing to negligent national food safety regulations. The speed at which contaminated food is detected and disposed of determines the extent to which consumers' lives are safeguarded and agricultural economic losses are prevented. Micro/nanomotors offer a high-speed mobile loading platform that substantially increases the chemical reaction rates and, accordingly, exhibit great potential as alternatives to conventional detection and degradation techniques. This review summarizes the propulsion modes applicable to micro/nanomotors in food systems and the advantages of using micro/nanomotors, highlighting examples of their potential use in recent years for the detection and removal of food contaminants. Micro/nanomotors are an emerging technology for food applications that is moving toward mass production, simple preparation, and important functions.

Enzyme-powered micro- and nano-motors: key parameters for an application-oriented design

Nature has inspired the creation of artificial micro- and nanomotors that self-propel converting chemical energy into mechanical action. These tiny machines have appeared as promising biomedical tools for treatment and diagnosis and have also been used for environmental, antimicrobial or sensing applications. Among the possible catalytic engines, enzymes have emerged as an alternative to inorganic catalysts due to their biocompatibility and the variety and bioavailability of fuels. Although the field of enzyme-powered micro- and nano-motors has a trajectory of more than a decade, a comprehensive framework on how to rationally design, control and optimize their motion is still missing. With this purpose, herein we performed a thorough bibliographic study on the key parameters governing the propulsion of these enzyme-powered devices, namely the chassis shape, the material composition, the motor size, the enzyme type, the method used to incorporate enzymes, the distribution of the product released, the motion mechanism, the motion media and the technique used for motion detection. In conclusion, from the library of options that each parameter offers there needs to be a rational selection and intelligent design of enzymatic motors based on the specific application envisioned.

Encoding Manipulation of DNA-Nanoparticle Assembled Nanorobot Using Independently Charged Array Nanopores

During the past decades, scientists have developed different kinds of nanorobots based on various driving principles to realize controlled manipulation of them for potential applications like medical diagnosis and directed cargo delivery. In order to design a nanorobot with advantages of simple operation and precise control that can enrich the family of intelligent nanorobots, an encoding manipulation method is proposed to control the movement of a DNA-nanoparticle assembled nanorobot by combing electrophoresis and electroosmosis effect in independently charged array nanopores. The nanorobot is composed of one nanoparticle and one or two ssDNAs. ssDNAs act as the legs of the nanorobot. The selective ion transport through charged nanopores can induce cooperation and competition between the electroosmosis and electrophoresis, which is the main power to activate the nanorobot. Thus by simply switching the applied electric field and surface charge density of each nanopore which is defined as the encoded nanopore according to a predetermined strategy, the well-controlled encoding manipulation including capturing, releasing, jumping, and crawling of the nanorobot is realized in this work. The study is expected to realize its value in many interesting applications like drug delivery, nanosurgery, and so on in the near future.

Towards micromachine intelligence: potential of polymers

Inspired by the increasing desire to mimic the perfection of nature, micro- and nanorobots are triggering increasing interest among the scientific community. The development of such tiny machines that can autonomously perform specific and various tasks at a small scale has reached a high-level of complexity over the last 15 years although the transition from hard to soft self-propelled architectures has had the most profound impact. The use of organic components, such as polymers, is of particular interest to fulfill the lack of biocompatibility and biodegradability of inorganic-based microrobots. Additionally, the combination of self-powered micro- and nanorobots with some macromolecules' ability to be deformed and respond to external stimuli is an important topic. This review aims to critically assess the fundamental aspects of smart machines composed of polymers, examine recent advances in the combined systems at the micro- and nanoscale, and discuss the specific contribution of several polymer families. This review elucidates the role of smart polymers in the expanding field of intelligent micromachines.

Nature-inspired micro/nanomotors

Living things in nature have evolved with unique morphologies, structures, materials, behaviors, and functions to survive in complex natural environments. Nature has inspired the design ideas, preparation methods, and applications of versatile micro/nanomotors. This review summarizes diverse nature-inspired micro/nanomotors, which can be divided into five groups: (i) natural morphology-inspired micro/nanomotors, whose shapes are designed to imitate the morphologies of plants, animals, and objects in nature. (ii) Natural structure-inspired micro/nanomotors, which use structures from plants, red blood cells, and platelet cells as components of micro/nanomotors, or directly use sperm cells and microorganisms as the engines of micro/nanomotors. (iii) Natural behavior-inspired micro/nanomotors, which are proposed to mimic natural behaviors such as motion behavior, swarm behavior, and communication behavior between individuals. (iv) Micro/nanomotors inspired by both natural morphology and behavior. Nature makes it possible for synthetic micro/nanomotors to possess interesting morphologies, novel preparation methods, new propulsion modes, innovative functions, and broad applications. The nature-inspired micro/nanomotors could provide a promising platform for various practical fields.

Self-/Magnetic-Propelled Catalytic Nanomotors Based on a Janus SPION@PEG-Pt/PCL Hybrid Nanoarchitecture: Single-Particle versus Collective Motions

In this paper, we synthesized superparamagnetic iron oxide nanoparticles (NPs) functionalized with (3-aminopropyl)triethoxysilane (Fe₃O₄@APTES). The synthesized NPs were coated with succinic anhydride (Fe₃O₄@COOH) in the next step. Half the surface of the NPs was shielded with wax microparticles via the Pickering emulsion technique, and the unshielded side was covered with poly(ethylene glycol) methyl ether. Platinum nanoparticles (Pt NPs) were deposited between PEG chains by the oxidation-reduction method through an in situ procedure to obtain a metal-polymer composite. These deposited Pt NPs have the potential to catalyze the decomposition of hydrogen peroxide at the surface of Janus nanomotors (JNMs). After de-waxing of the NPs, Irgacure 2959 (as the initiator) was reacted with the bare side of the NPs to provide the opportunity to grow poly(ε-caprolactone) (PCL) chains on the surface of the nanomotors through the "grafting from" method. The diffusion coefficient and velocity of the JNMs (before and after the PCL reaction) in the aqueous solution of 1, 2, 3, 5, and 10% (w/w) hydrogen peroxide and in the presence of different concentrations of NaCl solutions (0, 5, and 10% (w/v)) were investigated by mean square displacement analysis for single-particle or collective motions of JNMs. In addition, the simultaneous effect of an external magnetic field and the NaCl concentration on the movement direction of JNMs was also evaluated in the presence of hydrogen peroxide (10%). Increasing the ionic strength through NaCl addition permits the JNMs to move with relatively lower amounts of fuel [i.e., 2% (w/w)]. The collective motion investigation of the JNMs showed the highest speed in the media with 10% (w/w) hydrogen peroxide and 5% (w/v) NaCl solution (about 1215.78 μm²/s) due to the surfactant effect of the Janus architecture.

Polymeric Micro/Nanomotors and Their Biomedical Applications

Since their naissance in the 2000s, various micro or nanomotors with powerful functions have been proposed. Among them, polymer-based micro or nanomotors stand out for the easy processing and facile functionalization, holding immense potential for bioapplications. In this review, fabrication of polymer-based micro or nanomotors and their applications in biomedical areas are covered. Classic manufacturing approaches as well as cutting-edge techniques are discussed with representative works highlighted. Current challenges and future prospects are presented in the hope of pointing new research directions to facilitate practical translations of micro/nanomotors.

Micro/nano-machines for spilled-oil cleanup and recovery: A review

High-efficiency, safe and economically viable nano-engineered platforms for oil spill cleanup and recovery are of great importance. This review takes account of the concept of nanomotors and micromotors and their most advancements in use for oil spill treatment. The fundamental facets of artificial micro- and nano-machines/nanobots/nanomotors (MNMs) are first documented, followed by the most recent influencing developments in chemical engineering approaches toward their specific utilizations. The surface chemistry of these MNMs, their behaviors in different water matrices and their roles in the removal of oil are examined, revealing great rooms for improvement. The strategies for surface and structural modification of these tiny machines toward enhancing their reactivity in the removal of oil and coupled tasking are discussed in details, highlighting the significance of fit-for-duty design and tailored fabrication. The engineering limitations and practical implementation barriers of this emerging technology and how it can be overcome are also considered. Finally, some engineering boundaries and perspectives of this fast-evolving field are proposed at the end.

Magnetically Driven Micro and Nanorobots

Manipulation and navigation of micro and nanoswimmers in different fluid environments can be achieved by chemicals, external fields, or even motile cells. Many researchers have selected magnetic fields as the active external actuation source based on the advantageous features of this actuation strategy such as remote and spatiotemporal control, fuel-free, high degree of reconfigurability, programmability, recyclability, and versatility. This review introduces fundamental concepts and advantages of magnetic micro/nanorobots (termed here as “MagRobots”) as well as basic knowledge of magnetic fields and magnetic materials, setups for magnetic manipulation, magnetic field configurations, and symmetry-breaking strategies for effective movement. These concepts are discussed to describe the interactions between micro/nanorobots and magnetic fields. Actuation mechanisms of flagella-inspired MagRobots (i.e., corkscrew-like motion and traveling-wave locomotion/ciliary stroke motion) and surface walkers (i.e., surface-assisted motion), applications of magnetic fields in other propulsion approaches, and magnetic stimulation of micro/nanorobots beyond motion are provided followed by fabrication techniques for (quasi-)spherical, helical, flexible, wire-like, and biohybrid MagRobots. Applications of MagRobots in targeted drug/gene delivery, cell manipulation, minimally invasive surgery, biopsy, biofilm disruption/eradication, imaging-guided delivery/therapy/surgery, pollution removal for environmental remediation, and (bio)sensing are also reviewed. Finally, current challenges and future perspectives for the development of magnetically powered miniaturized motors are discussed.

Visible-Light-Driven Water-Fueled Ecofriendly Micromotors Based on Iron Phthalocyanine for Highly Efficient Organic Pollutant Degradation

The light-driven micromotor has been demonstrated to have great potential in the environmental remediation field. However, it is still challenging to develop highly efficient, ecofriendly, and visible-light-powered micromotors for organic pollutant degradation. In this paper, we report an ecofriendly micromotor based on iron phthalocyanine (FePc) and gelatin, which exhibits the visible-light-driven self-propulsion behavior using water fuel based on the photocatalytic reaction and self-diffusiophoresis mechanism. Fast motion behavior is observed which induces the rapid agitation of the solution. This, together with the excellent photocatalytic activity, makes the FePc-based micromotor highly efficient when utilized in the degradation of organic pollutants with a normalized reaction rate constant of 2.49 × 10^-2 L m^-2 s^-1, which is by far the fastest and is far superior than the stationary counterpart. The external fuel-free propulsion and the high efficiency in pollutant degradation make the current micromotor potentially attractive for environmental remediation.

Controlled Group Motion of Anisotropic Janus Droplets Prepared by One-Step Vortex Mixing

In living systems, highly efficient biological micromotors are fascinating and crucial to the maintenance and regulation of normal functions. Inspired by this, solid colloid motors with controlled movements were recently developed for diverse applications. However, to meet the requirements of more elaborate functionalities, the development of droplet-based micromotors, which feature with appealing advantages such as deformability, encapsulation capability, and biocompatibility, is demanding. Herein, responsive Janus droplets with intrinsic magnetic anisotropy were fabricated, taking advantage of the traditional one-step vortex mixing that guarantees large-scale production. Furthermore, the size range of the droplets can be easily extended continuously from hundreds of micrometers down to tens of nanometers. What is more appealing, directed in situ group motions that include alignment, rotation, and transfer of the Janus droplets prepared were successfully realized and precisely controlled by using an external magnetic field. These collective motions induced excellent performances in pollutant adsorption and separation, switchable conductivities, and the size grading. Such scalable, simple, and controllable strategy can expand the application of Janus emulsions to complicated fields of microreactors, microsensors, and environmental regulation.

Bubble-propelled micromotors based on hierarchical MnO2 wrapped carbon nanotube aggregates for dynamic removal of pollutants

Water pollution is currently an urgent public health and environmental issue. Bubble-propelled micromotors might offer an effective approach for dealing with environmental contamination. Herein, we present the synthesis of multi-walled carbon nanotube (MWCNT)/manganese dioxide (MnO₂) micromotors based on MWCNT aggregates as microscale templates by a simple one-step hydrothermal procedure. The morphology, composition, and structure of the obtained MWCNT/MnO₂ micromotors were characterized in detail. The MnO₂ nanoflakes formed a catalytic layer on the MWCNT backbone, which promoted effective bubble evolution and propulsion at remarkable speeds of 359.31 μm s⁻¹. The bubble velocity could be modulated based on the loading of MnO₂ nanoflakes. The rapid movement of these MWCNT/MnO₂ catalytic micromotors resulted in a highly efficient moving adsorption platform, which considerably enhanced the effectiveness of water purification. Dynamic adsorption of organic dyes by the micromotors increased the degradation rate to approximately 4.8 times as high as that of their corresponding static counterparts. The adsorption isotherms and adsorption kinetics were also explored. The adsorption mechanism was well fitted by the Langmuir model, following pseudo-second-order kinetics. Thus, chemisorption of Congo red at the heterogeneous MnO₂ wrapped microimotor surface was the rate determining step. The high propulsion speed and remarkable decontamination efficiency of the MWCNT/MnO₂ micromotors indicate potential for environmental contamination applications.

Water pollution is currently an urgent public health and environmental issue.

Micromotors as "Motherships": A Concept for the Transport, Delivery, and Enzymatic Release of Molecular Cargo via Nanoparticles

Nano/micromotors based on biodegradable and biocompatible polymers represent a progressively developing group of self-propelled artificial devices capable of delivering biologically active compounds to target sites. The majority of these machines are micron sized, and biologically active compounds are simply attached to their surface. Micron-sized devices cannot enter cells, but they provide rapid velocity, which scales down with the size of the device; nanosized devices can enter cells, but their velocity is negligible. An advanced hierarchical design of the micro/nanodevices is an important tool in the development of functional biocompatible transport systems and their implementation in real in vivo applications. In this work, we demonstrate a "mothership" concept, whereby self-propelled microrobots transport smaller cargo-carrying nanorobots that are released by enzymatic degradation.

Graphene quantum dot based micromotors: a size matter

Low dimensional 0D graphene quantum dots are used for the preparation of micromotors with higher yield compared to graphene micromotors.