Supramolecular Adaptive Nanomotors with Magnetotaxis Behavior

Motion control of chemically powered colloidal motors

Chemically powered colloidal motors can convert chemical energy into directional mechanical movement, making them promising for applications such as targeted drug delivery, environmental decontamination, and precision disease treatment. However, their self-propulsion is constantly disrupted by random Brownian motion, making precise control under low Reynolds number conditions highly challenging. This review provides a brief overview of the three main propulsion mechanisms of chemically powered colloidal motors. It also summarizes recent advances in motion control, including speed regulation and trajectory navigation. Finally, we discuss future directions for achieving more precise motion control. We hope this review will inspire further research on developing more effective and practical control strategies for colloidal motors.

Polymersome-based nanomotors: preparation, motion control, and biomedical applications

Polymersome-based nanomotors represent a cutting-edge development in nanomedicine, merging the unique vesicular properties of polymersomes with the active propulsion capabilities of synthetic nanomotors. As a vesicular structure enclosed by a bilayer membrane, polymersomes can encapsulate both hydrophilic and hydrophobic cargoes. In addition, their physical-chemical properties such as size, morphology, and surface chemistry are highly tunable, which makes them ideal for various biomedical applications. The integration of motility into polymersomes enables them to actively navigate biological environments and overcome physiological barriers, offering significant advantages over passive delivery platforms. Recent breakthroughs in fabrication techniques and motion control strategies, including chemically, enzymatically, and externally driven propulsion, have expanded their potential for drug delivery, biosensing, and therapeutic interventions. Despite these advancements, key challenges remain in optimizing propulsion efficiency, biocompatibility, and in vivo stability to translate these systems into clinical applications. In this perspective, we discuss recent advancements in the preparation and motion control strategies of polymersome-based nanomotors, as well as their biomedical-related applications. The molecular design, fabrication approaches, and nanomedicine-related utilities of polymersome-based nanomotors are highlighted, to envisage the future research directions and further development of these systems into effective, precise, and smart nanomedicines capable of addressing critical biomedical challenges.

Breaking Through Physiological Barriers: Nanorobotic Strategies for Active Drug Delivery

Self-propelled micro/nanomotors (MNMs) represent a groundbreaking advancement in precision drug delivery, offering potential solutions to persistent challenges such as systemic toxicity, limited bioavailability, and nonspecific distribution. By transforming various energy sources into mechanical motion, MNMs are able to autonomously navigate through complex physiological environments, facilitating targeted delivery of therapeutic agents to previously inaccessible regions. However, to achieve efficient in vivo drug delivery, biomedical MNMs must demonstrate their ability to overcome crucial physiological barriers encompassing mucosal surfaces, blood flow dynamics, vascular endothelium, and cellular membrane. This review provides a comprehensive overview of the latest strategies developed to address these obstacles while also analyzing the broader challenges and opportunities associated with clinical translation. Our objective is to establish a solid foundation for future research in medical MNMs by focusing on enhancing drug delivery efficiency and advancing precision medicine, ultimately paving the way for practical theragnostic applications and wider clinical adoption.

Catalytic Nanoparticles in Biomedical Applications: Exploiting Advanced Nanozymes for Therapeutics and Diagnostics

Catalytic nanoparticles (CNPs) as heterogeneous catalyst reveals superior activity due to their physio-chemical features, such as high surface-to-volume ratio and unique optical, electric, and magnetic properties. The CNPs, based on their physio-chemical nature, can either increase the reactive oxygen species (ROS) level for tumor and antibacterial therapy or eliminate the ROS for cytoprotection, anti-inflammation, and anti-aging. In addition, the catalytic activity of nanozymes can specifically trigger a specific reaction accompanied by the optical feature change, presenting the feasibility of biosensor and bioimaging applications. Undoubtedly, CNPs play a pivotal role in pushing the evolution of technologies in medical and clinical fields, and advanced strategies and nanomaterials rely on the input of chemical experts to develop. Herein, a systematic and comprehensive review of the challenges and recent development of CNPs for biomedical applications is presented from the viewpoint of advanced nanomaterial with unique catalytic activity and additional functions. Furthermore, the biosafety issue of applying biodegradable and non-biodegradable nanozymes and future perspectives are critically discussed to guide a promising direction in developing span-new nanozymes and more intelligent strategies for overcoming the current clinical limitations.

Urease-powered nanobots for radionuclide bladder cancer therapy

Bladder cancer treatment via intravesical drug administration achieves reasonable survival rates but suffers from low therapeutic efficacy. To address the latter, self-propelled nanoparticles or nanobots have been proposed, taking advantage of their enhanced diffusion and mixing capabilities in urine when compared with conventional drugs or passive nanoparticles. However, the translational capabilities of nanobots in treating bladder cancer are underexplored. Here, we tested radiolabelled mesoporous silica-based urease-powered nanobots in an orthotopic mouse model of bladder cancer. In vivo and ex vivo results demonstrated enhanced nanobot accumulation at the tumour site, with an eightfold increase revealed by positron emission tomography in vivo. Label-free optical contrast based on polarization-dependent scattered light-sheet microscopy of cleared bladders confirmed tumour penetration by nanobots ex vivo. Treating tumour-bearing mice with intravesically administered radio-iodinated nanobots for radionuclide therapy resulted in a tumour size reduction of about 90%, positioning nanobots as efficient delivery nanosystems for bladder cancer therapy.

Programmable Compartment Networks by Unraveling the Stress-Dependent Deformation of Polymer Vesicles

Nanocontainers that can sense and respond to environmental stimuli like cells are desirable for next-generation delivery systems. However, it is still a grand challenge for synthetic nanocontainers to mimic or even surpass the shape adaption of cells, which may produce novel compartments for cargo loading. Here, this work reports the engineering of compartment network with a single polymer vesicle by unraveling osmotic stress-dependent deformation. Specifically, by manipulating the way in exerting the stress, sudden increase or gradual increase, polymer vesicles can either undergo deflation into the stomatocyte, a bowl-shaped vesicle enclosing a new compartment, or tubulation into the tubule of varied length. Such stress-dependent deformation inspired us to program the shape transformation of polymer vesicles, including tubulation, deflation, or first tubulation and then deflation. The coupled deformation successfully transforms the polymer vesicle into the stomatocyte with tubular arms and a network of two or three small stomatocytes connected by tubules. To the author's knowledge, these morphologies are still not accessed by synthetic nanocontainers. This work envisions that the network of stomatocytes may enable the loading of different catalysts to construct novel motile systems, and the well-defined morphology of vesicles helps to define the effect of morphology on cellar uptake.

Application of micro/nanorobot in medicine

The development of micro/nanorobots and their application in medical treatment holds the promise of revolutionizing disease diagnosis and treatment. In comparison to conventional diagnostic and treatment methods, micro/nanorobots exhibit immense potential due to their small size and the ability to penetrate deep tissues. However, the transition of this technology from the laboratory to clinical applications presents significant challenges. This paper provides a comprehensive review of the research progress in micro/nanorobotics, encompassing biosensors, diagnostics, targeted drug delivery, and minimally invasive surgery. It also addresses the key issues and challenges facing this technology. The fusion of micro/nanorobots with medical treatments is poised to have a profound impact on the future of medicine.

Antibacterial micro/nanomotors: advancing biofilm research to support medical applications

Multi-drug resistant (MDR) bacterial infections are gradually increasing in the global scope, causing a serious burden to patients and society. The formation of bacterial biofilms, which is one of the key reasons for antibiotic resistance, blocks antibiotic penetration by forming a physical barrier. Nano/micro motors (MNMs) are micro-/nanoscale devices capable of performing complex tasks in the bacterial microenvironment by transforming various energy sources (including chemical fuels or external physical fields) into mechanical motion or actuation. This autonomous movement provides significant advantages in breaking through biological barriers and accelerating drug diffusion. In recent years, MNMs with high penetrating power have been used as carriers of antibiotics to overcome bacterial biofilms, enabling efficient drug delivery and improving the therapeutic effectiveness of MDR bacterial infections. Additionally, non-antibiotic antibacterial strategies based on nanomaterials, such as photothermal therapy and photodynamic therapy, are continuously being developed due to their non-invasive nature, high effectiveness, and non-induction of resistance. Therefore, multifunctional MNMs have broad prospects in the treatment of MDR bacterial infections. This review discusses the performance of MNMs in the breakthrough and elimination of bacterial biofilms, as well as their application in the field of anti-infection. Finally, the challenges and future development directions of antibacterial MNMs are introduced.

Strategies in design of self-propelling hybrid micro/nanobots for bioengineering applications

Micro/nanobots are integrated devices developed from engineered nanomaterials that have evolved significantly over the past decades. They can potentially be pre-programmed to operate robustly at numerous hard-to-reach organ/tissues/cellular sites for multiple bioengineering applications such as early disease diagnosis, precision surgeries, targeted drug delivery, cancer therapeutics, bio-imaging, biomolecules isolation, detoxification, bio-sensing, and clearing up clogged arteries with high soaring effectiveness and minimal exhaustion of power. Several techniques have been introduced in recent years to develop programmable, biocompatible, and energy-efficient micro/nanobots. Therefore, the primary focus of most of these techniques is to develop hybrid micro/nanobots that are an optimized combination of purely synthetic or biodegradable bots suitable for the execution of user-defined tasks more precisely and efficiently. Recent progress has been illustrated here as an overview of a few of the achievable construction principles to be used to make biomedical micro/nanobots and explores the pivotal ventures of nanotechnology-moderated development of catalytic autonomous bots. Furthermore, it is also foregrounding their advancement offering an insight into the recent trends and subsequent prospects, opportunities, and challenges involved in the accomplishments of the effective multifarious bioengineering applications.

Progress on Physical Field-Regulated Micro/Nanomotors for Cardiovascular and Cerebrovascular Disease Treatment

Cardiovascular and cerebrovascular diseases (CCVDs) are two major vasculature-related diseases that seriously affect public health worldwide, which can cause serious death and disability. Lack of targeting effect of the traditional CCVD treatment drugs may damage other tissues and organs, thus more specific methods are needed to solve this dilemma. Micro/nanomotors are new materials that can convert external energy into driving force for autonomous movement, which can not only enhance the penetration depth and retention rates, but also increase the contact areas with the lesion sites (such as thrombus and inflammation sites of blood vessels). Physical field-regulated micro/nanomotors using the physical energy sources with deep tissue penetration and controllable performance, such as magnetic field, light, and ultrasound, etc. are considered as the emerging patient-friendly and effective therapeutic tools to overcome the limitations of conventional CCVD treatments. Recent efforts have suggested that physical field-regulated micro/nanomotors on CCVD treatments could simultaneously provide efficient therapeutic effect and intelligent control. In this review, various physical field-driven micro/nanomotors are mainly introduced and their latest advances for CCVDs are highlighted. Last, the remaining challenges and future perspectives regarding the physical field-regulated micro/nanomotors for CCVD treatments are discussed and outlined.

Recent progress of micro/nanomotors to overcome physiological barriers in the gastrointestinal tract

Oral administration is a convenient administration route for gastrointestinal disease therapy with good patient compliance. But the nonspecific distribution of the oral drugs may cause serious side effects. In recent years, oral drug delivery systems (ODDS) have been applied to deliver the drugs to the gastrointestinal disease sites with decreased side effects. However, the delivery efficiency of ODDS is tremendously limited by physiological barriers in the gastrointestinal sites, such as the long and complex gastrointestinal tract, mucus layer, and epithelial barrier. Micro/nanomotors (MNMs) are micro/nanoscale devices that transfer various energy sources into autonomous motion. The outstanding motion characteristics of MNMs inspired the development of targeted drug delivery, especially the oral drug delivery. However, a comprehensive review of oral MNMs for the gastrointestinal diseases therapy is still lacking. Herein, the physiological barriers of ODDS were comprehensively reviewed. Afterward, the applications of MNMs in ODDS for overcoming the physiological barriers in the past 5 years were highlighted. Finally, future perspectives and challenges of MNMs in ODDS are discussed as well. This review will provide inspiration and direction of MNMs for the therapy of gastrointestinal diseases, pushing forward the clinical application of MNMs in oral drug delivery.

Nanorobot-Mediated Synchronized Neuron Activation

Interactions between active materials lead to collective behavior and even intelligence beyond the capability of individuals. Such behaviors are prevalent in nature and can be observed in animal colonies, providing these species with diverse capacities for communication and cooperation. In artificial systems, however, collective intelligence systems interacting with biological entities remains unexplored. Herein, we describe black (B)-TiO2@N/Au nanorobots interacting through photocatalytic pure water splitting-induced electrophoresis that exhibit periodic swarming oscillations under programmed near-infrared light. The periodic chemical-electric field generated by the oscillating B-TiO2@N/Au nanorobot swarm leads to local neuron activation in vitro. The field oscillations and neurotransmission from synchronized neurons further trigger the resonance oscillation of neuron populations without synaptic contact (about 2 mm spacing), in different ways from normal neuron oscillation requiring direct contact. We envision that the oscillating nanorobot swarm platforms will shed light on contactless communication of neurons and offer tools to explore interactions between neurons.

Light-Triggered Mechanical Disruption of Extracellular Barriers by Swarms of Enzyme-Powered Nanomotors for Enhanced Delivery

Targeted drug delivery depends on the ability of nanocarriers to reach the target site, which requires the penetration of different biological barriers. Penetration is usually low and slow because of passive diffusion and steric hindrance. Nanomotors (NMs) have been suggested as the next generation of nanocarriers in drug delivery due to their autonomous motion and associated mixing hydrodynamics, especially when acting collectively as a swarm. Here, we explore the concept of enzyme-powered NMs designed as such that they can exert disruptive mechanical forces upon laser irradiation. The urease-powered motion and swarm behavior improve translational movement compared to passive diffusion of state-of-the-art nanocarriers, while optically triggered vapor nanobubbles can destroy biological barriers and reduce steric hindrance. We show that these motors, named Swarm 1, collectively displace through a microchannel blocked with type 1 collagen protein fibers (barrier model), accumulate onto the fibers, and disrupt them completely upon laser irradiation. We evaluate the disruption of the microenvironment induced by these NMs (Swarm 1) by quantifying the efficiency by which a second type of fluorescent NMs (Swarm 2) can move through the cleared microchannel and be taken up by HeLa cells at the other side of the channel. Experiments showed that the delivery efficiency of Swarm 2 NMs in a clean path was increased 12-fold in the presence of urea as fuel compared to when no fuel was added. When the path was blocked with the collagen fibers, delivery efficiency dropped considerably and only depicted a 10-fold enhancement after pretreatment of the collagen-filled channel with Swarm 1 NMs and laser irradiation. The synergistic effect of active motion (chemically propelled) and mechanical disruption (light-triggered nanobubbles) of a biological barrier represents a clear advantage for the improvement of therapies which currently fail due to inadequate passage of drug delivery carriers through biological barriers.

Collective Behaviors of Active Matter Learning from Natural Taxes Across Scales

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

Controlled propulsion of micro/nanomotors: operational mechanisms, motion manipulation and potential biomedical applications

Inspired by natural mobile microorganisms, researchers have developed micro/nanomotors (MNMs) that can autonomously move by transducing different kinds of energies into kinetic energy. The rapid development of MNMs has created tremendous opportunities for biomedical fields including diagnostics, therapeutics, and theranostics. Although the great progress has been made in MNM research, at a fundamental level, the accepted propulsion mechanisms are still a controversial matter. In practical applications such as precision nanomedicine, the precise control of the motion, including the speed and directionality, of MNMs is also important, which makes advanced motion manipulation desirable. Very recently, diverse MNMs with different propulsion strategies, morphologies, sizes, porosities and chemical structures have been fabricated and applied for various uses. Herein, we thoroughly summarize the physical principles behind propulsion strategies, as well as the recent advances in motion manipulation methods and relevant biomedical applications of these MNMs. The current challenges in MNM research are also discussed. We hope this review can provide a bird's eye overview of the MNM research and inspire researchers to create novel and more powerful MNMs.

Micro-Nano Motors with Taxis Behavior: Principles, Designs, and Biomedical Applications

As a novel mobile nanodevice, micro-nano motors (MNMs) can convert the energy of the surrounding environment into mechanical motion. With this unique ability, they promise revolutionary potential in bio-applications including precise drug delivery, bio-sensing, and noninvasive surgery. Yet for practically reaching the target and fulfilling these tasks in dynamically changing bio-environment, environment adaptivity beyond propulsion is important yet challenging. MNMs with taxis behavior/autonomous target-seeking ability offer a desirable solution. These motors can adaptively move to the target location and complete the task. Thanks to the persistent efforts of researchers, tactic MNMs have shown automatic navigation to target under various energy fields, not only in static environments, but also in shear rheological conditions that simulate blood flow. Therefore, tactic motors with self-targeting capability lay a concrete foundation for targeted drug delivery, cell transplantation, and thrombus ablation. This review systematically presents the moving principle, design, and biological applications of tactic MNMs under different energy fields. Through in-depth analysis of state-of-art progress, the obstacles of the field and possible solutions are discussed. With the continuous innovation and breakthroughs of multi-disciplinary researchers, MNMs with taxis behavior are expected to provide a revolutionary solution for cancer and other major diseases in the biomedical field.

Core-Shell Structured Micro-Nanomotors: Construction, Shell Functionalization, Applications, and Perspectives

The successful integration of well-designed micro-nanomotors (MNMs) with diverse functional systems, such as, living systems, remote actuation systems, intelligent sensors, and sensing systems, offers many opportunities to not only endow them with diverse functionalization interfaces but also bring augmented or new properties in a wide variety of applications. Core-shell structured MNM systems have been considered to play an important role in a wide range of applications as they provide a platform to integrate multiple complementary components via decoration, encapsulation, or functionalization into a single functional system, being able to protect the active species from harsh environments, and bring improved propulsion performance, stability, non-toxicity, multi-functionality, and dispersibility, etc., which are not easily available from the isolated components. More importantly, the hetero-interfaces between individual components within a core-shell structure might give rise to boosted or new physiochemical properties. This review will bring together these key aspects of the core-shell structured MNMs, ranging from advanced protocols, enhanced/novel functionalities arising from diverse functional shells, to integrated core-shell structured MNMs for diverse applications. Finally, current challenges and future perspectives for the development of core-shell structured MNMs are discussed in term of synthesis, functions, propulsions, and applications.

The dynamics of chemically propelled dimer motor on a pinning substrate

The dynamics of self-propelled micro-motors, in a thin fluid film containing an attractive substrate, is investigated by means of a particle-based simulation. A chemically powered sphere dimer, consisting of a...

Multifunctional micro/nanomotors as an emerging platform for smart healthcare applications

Self-propelling micro- and nano-motors (MNMs) are emerging as a multifunctional platform for smart healthcare applications such as biosensing, bioimaging, and targeted drug delivery with high tissue penetration, stirring effect, and rapid drug transport. MNMs can be propelled and/or guided by chemical substances or external stimuli including ultrasound, magnetic field, and light. In addition, enzymatically powered MNMs and biohybrid micromotors have been developed using the biological components in the body. In this review, we describe emerging MNMs focusing on their smart propulsion systems, and diagnostic and therapeutic applications. Finally, we highlight several MNMs for in vivo applications and discuss the future perspectives of MNMs on their current limitations and possibilities toward further clinical applications.

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.

Recent progress of biomimetic motions-from microscopic micro/nanomotors to macroscopic actuators and soft robotics

Motion is a basic behavioral attribute of organisms, and it is a behavioral response of organisms to the external environment and internal state changes. Materials with switchable mechanical properties are widespread in living organisms and play crucial roles in the motion of organisms. Therefore, significant efforts have been made toward mimicking such architectures and motion behaviors by making full use of the properties of stimulus-responsive materials to design smart materials/machines with specific functions. In recent years, the biomimetic motions based on micro/nanomotors, actuators and soft robots constructed from smart response materials have been developed gradually. However, a comprehensive discussion on various categories of biomimetic motions in this field is still missing. This review aims to provide such a panoramic overview. From nano-to macroscales, we summarize various biomimetic motions based on micro/nanomotors, actuators and soft robotics. For each biomimetic motion, we discuss the driving modes and the key functions. The challenges and opportunities of biomimetic motions are also discussed. With rapidly increasing innovation, advanced, intelligent and multifunctional biomimetic motions based on micro/nanomotors, actuators and soft robotics will certainly bring profound impacts and changes for human life in the near future.

Deep Penetration of Nanolevel Drugs and Micrometer-Level T Cells Promoted by Nanomotors for Cancer Immunochemotherapy

The ability of nanomotors to promote the deep penetration of themselves and the loaded drugs in diseased tissues has been proposed and confirmed. However, whether such motion behavior of the nanomotors can also promote deep penetration of micrometer-sized immune cells in the diseased microenvironment, which is important for the immunotherapy of some diseases, has not been mentioned. Herein, we construct a nitric oxide (NO)-driven nanomotor that can move in the tumor microenvironment, focusing on its motion behavior and the role of NO, the beneficial product released during movement from this kind of nanomotor, in regulating the infiltration behavior and activity of immune cells. It can be found that the drug-loaded nanomotors with both NO-releasing ability and motility can promote the normalization of the tumor vasculature system and the degradation of the intrinsic extracellular matrix (ECM), which can significantly improve the tumor infiltration ability of T cells in vivo. The efficiency of T-cell infiltration in tumor tissue in vivo increased from 2.1 to 28.2%. Both subcutaneous and intraperitoneal implantation tumor models can validate the excellent antitumor effect of drug-loaded NO-driven nanomotors. This combination of motility of the power source from nanomotors and their physiological function offers a design idea for therapeutic agents for the future immunotherapy of many diseases.

Multilobed Magnetic Liposomes Enable Remotely Controlled Collection, Transport, and Delivery of Membrane-Soluble Cargos to Vesicles and Cells

Lipid bilayers are the basic structural components of all living systems, forming the membranes of cells, sub-cellular organelles, and extracellular vesicles. A class of man-made lipidic vesicles called multilobed magnetic liposomes (MMLs) is reported in this work; these MMLs possess a previously unattained combination of features owing to their unique multilobe structure and composition. MMLs consist of a central cluster of lipid-coated magnetic iron oxide nanoparticles that lend them a magnetophoretic velocity comparable to the most efficient living microswimmers. Multiple liposome-like lobes protrude from the central region; these can incorporate both water-soluble and lipid-soluble molecular payloads at high carrying capacity and exchange the incorporated substances with the membranes of both artificial and live cells by the contact diffusion mechanism. The size of MMLs is controllable in the range of 200-800 nm. Their functionality is demonstrated by completing a model mission where MMLs are remotely controlled to collect, transport, and deliver a cargo to live cells.

From shaping to functionalization of micro-droplets and particles

The structure of microdroplet and microparticle is a critical factor in their functionality, which determines the distribution and sequence of physicochemical reactions. Therefore, the technology of precisely tailoring their shape is requisite for implementing the user demand functions in various applications. This review highlights various methodologies for droplet shaping, classified into passive and active approaches based on whether additional body forces are applied to droplets to manipulate their functions and fabricate them into microparticles. The passive approaches cover batch emulsification, solvent evaporation and diffusion, micromolding, and microfluidic methods. In active approaches, the external forces, such as electrical and magnetic fields or optical lithography, are applied to microdroplets. Special attention is also given to latest technologies using microdroplets and microparticles, especially in the fields of biological, optical, robotic, and environmental applications. Finally, this review aims to address the advantages and disadvantages of the introduced approaches and suggests the direction for further development in this field.

Supramolecular nanomotors with "pH taxis" for active drug delivery in the tumor microenvironment

Self-propelled nanomotors demonstrating autonomous motion in biologically relevant fuel are currently being studied to overcome the use of external physical or chemical stimuli as precise delivery agents. In this context, the tumor microenvironment (TME) with slightly acidic pH is used for developing cargo-releasing artificial systems triggered by such conditions. However, there is still a need for fabrication of smart nanomotors that can sense the acidic pH prevalent in the TME rather than using an external fuel source for selective activation and thereafter migrating towards tumors for active drug delivery. Herein, supramolecular assembly-based nanomotors are fabricated by in-situ grown CaCO3 nanoparticles and studied for their motility behaviour in endogenously generated acidic pH by HeLa cells and further exploited as an active delivery vehicle for DOX molecules to the cells for their anticancer efficacy. The nanomotors are activated in slightly acidic pH showcasing "pH taxis" towards tumor cells without the need for any sophisticated/complicated technologies or an external fuel source for active and targeted delivery of drugs.

Self-Propelled Micro/Nanomotors for On-Demand Biomedical Cargo Transportation

Micro/nanomotors (MNMs) are miniaturized machines that can perform assigned tasks at the micro/nanoscale. Over the past decade, significant progress has been made in the design, preparation, and applications of MNMs that are powered by converting different sources of energy into mechanical force, to realize active movement and fulfill on-demand tasks. MNMs can be navigated to desired locations with precise controllability based on different guidance mechanisms. A considerable research effort has gone into demonstrating that MNMs possess the potential of biomedical cargo loading, transportation, and targeted release to achieve therapeutic functions. Herein, the recent advances of self-propelled MNMs for on-demand biomedical cargo transportation, including their self-propulsion mechanisms, guidance strategies, as well as proof-of-concept studies for biological applications are presented. In addition, some of the major challenges and possible opportunities of MNMs are identified for future biomedical applications in the hope that it may inspire future research.

Autonomous Motion of Bubble-Powered Carbonaceous Nanoflask Motors

We report a carbonaceous nanomotor with a characteristic flask-like hollow structure that can autonomously move under the propulsion of oxygen bubbles. The carbonaceous nanoflask (CNF) motor was fabricated by encapsulating platinum nanoparticles (Pt NPs) into the hollow cavity of the CNF. The internally encapsulated Pt NPs act as catalysts to decompose hydrogen peroxide (H₂O₂) fuel into oxygen bubbles. The generated oxygen bubbles recoil the motion of the CNF motors. Besides, the velocity of CNF motors can be controlled by adjusting the concentration of the H₂O₂ solution. The motion velocity increases with the increase of H₂O₂ concentration, up to 109.25 μm s^-1 at 10% H₂O₂. This study provides important implications for understanding the motion behaviors of nanomotors with an internal cavity, and the self-propelled CNF motors as smart carrier systems have potential applications in the future.

Medical micro/nanorobots in complex media

Medical micro/nanorobots have received tremendous attention over the past decades owing to their potential to be navigated into hard-to-reach tissues for a number of biomedical applications ranging from targeted drug/gene delivery, bio-isolation, detoxification, to nanosurgery. Despite the great promise, the majority of the past demonstrations are primarily under benchtop or in vitro conditions. Many developed micro/nanoscale propulsion mechanisms are based on the assumption of a homogeneous, Newtonian environment, while realistic biological environments are substantially more complex. Moving toward practical medical use, the field of micro/nanorobotics must overcome several major challenges including propulsion through complex media (such as blood, mucus, and vitreous) as well as deep tissue imaging and control in vivo. In this review article, we summarize the recent research efforts on investigating how various complexities in biological environments impact the propulsion of micro/nanoswimmers. We also highlight the emerging technological approaches to enhance the locomotion of micro/nanorobots in complex environments. The recent demonstrations of in vivo imaging, control and therapeutic medical applications of such micro/nanorobots are introduced. We envision that continuing materials and technological innovations through interdisciplinary collaborative efforts can bring us steps closer to the fantasy of "swallowing a surgeon".

[Application of self-propelled micro-/nanomotors in active targeted drug delivery]

As a new type of micro-/nanomachines, self-propelled micro-/nanomotors (MNMs) can convert chemical or external energies from the surrounding environment into mechanical forces to produce autonomous motion. The ability of autonomous movement allows these MNMs to move actively to the targeted locations, and thus confers great potentials on the MNMs for applications in biomedicine, especially in drug delivery. MNMs have been shown to effectively load therapeutic payloads for active delivery to the disease site, which greatly improves the therapeutic efficacy and reduces side effects compared with the traditional nanodrugs. In this review, we provide an overview of different propulsion mechanisms of MNMs, including chemical propulsion based on redox reaction and external field propulsion driven by external energy such as light, magnetic field, electric field and ultrasound, followed by a review of the recent progress in active drug delivery based on MNMs in the past decade. We also discuss the current challenges and future perspectives of the application of the MNMs.

A Review on Artificial Micro/Nanomotors for Cancer-Targeted Delivery, Diagnosis, and Therapy

Micro/nanomotors have been extensively explored for efficient cancer diagnosis and therapy, as evidenced by significant breakthroughs in the design of micro/nanomotors-based intelligent and comprehensive biomedical platforms. Here, we demonstrate the recent advances of micro/nanomotors in the field of cancer-targeted delivery, diagnosis, and imaging-guided therapy, as well as the challenges and problems faced by micro/nanomotors in clinical applications. The outlook for the future development of micro/nanomotors toward clinical applications is also discussed. We hope to highlight these new advances in micro/nanomotors in the field of cancer diagnosis and therapy, with the ultimate goal of stimulating the successful exploration of intelligent micro/nanomotors for future clinical applications.

Tadpole-like Unimolecular Nanomotor with Sub-100 nm Size Swims in a Tumor Microenvironment Model

Inspired by the natural motors capable of performing multiple tasks in complex living environments, synthetic nanomotors emerge as a potential vehicle for revolutionizing biomedical processes. Yet current motors suffer from decreased and even completely hindered motion in a complex physiological environment, shadowing the future of this booming field. To address this problem, a unimolecular nanomotor based on molecular bottlebrush (MBB) of sub-100 nm size is reported. This motor is constructed precisely via controlled radical polymerization and click chemistry and propelled with biocompatible catalase. Such a molecular nanomotor possesses tadpole-like asymmetry and is able to overcome Brownian motion, and demonstrates strong directional propulsion (linear and coiled cyclic trajectories) in a viscous tumor microenvironment gel model at an ultralow hydrogen peroxide level of 2 mM (0.006%). In addition, the molecular nanomotor exhibits superior stability in serum containing cell medium and good biocompatibility in blood. Such molecular bottlebrush based nanomotors may represent a unique platform for overcoming the tissue penetration barrier.

Self-Propulsion Strategies for Artificial Cell-Like Compartments

Reconstitution of life-like properties in artificial cells is a current research frontier in synthetic biology. Mimicking metabolism, growth, and sensing are active areas of investigation; however, achieving motility and directional taxis are also challenging in the context of artificial cells. To tackle this problem, recent progress has been made that leverages the tools of active matter physics in synthetic biology. This review surveys the most significant achievements in designing motile cell-like compartments. In this context, strategies for self-propulsion are summarized, including, compartmentalization of catalytically active particles, phoretic propulsion of vesicles and emulsion droplet motion driven by Marangoni flows. This work showcases how the realization of motile protocells may impact biomedical engineering while also aiming at answering fundamental questions in locomotion of prebiotic cells.

Microswimmers with Heat Delivery Capacity for 3D Cell Spheroid Penetration

Micro- and nanoswimmers are a fast emerging concept that changes how colloidal and biological systems interact. They can support drug delivery vehicles, assist in crossing biological barriers, or improve diagnostics. We report microswimmers that employ collagen, a major extracellular matrix (ECM) constituent, as fuel and that have the ability to deliver heat via incorporated magnetic nanoparticles when exposed to an alternating magnetic field (AMF). Their assembly and heating properties are outlined followed by the assessment of their calcium-triggered mobility in aqueous solution and collagen gels. It is illustrated that the swimmers in collagen gel in the presence of a steep calcium gradient exhibit fast and directed mobility. The experimental data are supported with theoretical considerations. Finally, the successful penetration of the swimmers into 3D cell spheroids is shown, and upon exposure to an AMF, the cell viability is impaired due to the locally delivered heat. This report illustrates an opportunity to employ swimmers to enhance tissue penetration for cargo delivery via controlled interaction with the ECM.

Nano-and Micromotors Designed for Cancer Therapy

Research on nano- and micromotors has evolved into a frequently cited research area with innovative technology envisioned for one of current humanities' most deadly problems: cancer. The development of cancer targeting drug delivery strategies involving nano-and micromotors has been a vibrant field of study over the past few years. This review aims at categorizing recent significant results, classifying them according to the employed propulsion mechanisms starting from chemically driven micromotors, to field driven and biohybrid approaches. In concluding remarks of section 2, we give an insight into shape changing micromotors that are envisioned to have a significant contribution. Finally, we critically discuss which important aspects still have to be addressed and which challenges still lie ahead of us.

Nanocatalytic Medicine

Catalysis and medicine are often considered as two independent research fields with their own respective scientific phenomena. Promoted by recent advances in nanochemistry, large numbers of nanocatalysts, such as nanozymes, photocatalysts, and electrocatalysts, have been applied in vivo to initiate catalytic reactions and modulate biological microenvironments for generating therapeutic effects. The rapid growth of research in biomedical applications of nanocatalysts has led to the concept of "nanocatalytic medicine," which is expected to promote the further advance of such a subdiscipline in nanomedicine. The high efficiency and selectivity of catalysis that chemists strived to achieve in the past century can be ingeniously translated into high efficacy and mitigated side effects in theranostics by using "nanocatalytic medicine" to steer catalytic reactions for optimized therapeutic outcomes. Here, the rationale behind the construction of nanocatalytic medicine is eludicated based on the essential reaction factors of catalytic reactions (catalysts, energy input, and reactant). Recent advances in this burgeoning field are then comprehensively presented and the mechanisms by which catalytic nanosystems are conferred with theranostic functions are discussed in detail. It is believed that such an emerging catalytic therapeutic modality will play a more important role in the field of nanomedicine.

Biocompatibility of artificial micro/nanomotors for use in biomedicine

The advent of micro/nanomotors (MNMs) has shed light on the innovation of active biomedical systems or devices that might bring revolutionary solutions to traditional biomedical strategies. In spite of development beyond expectation over the last decade with a fair number of proof-of-concept demonstrations, the in vivo practical application of MNMs for clinical use is still in its infancy. The biocompatibility of MNMs is the first consideration before realizing practicality, taking into account the complicated interactions between the self-propelled MNMs and biological systems. Therefore, in this review, we focused on the biocompatibility of MNMs with regard to the fabrication materials and propulsion mechanisms by means of in-depth discussions on the advantages and limitations of MNMs for operating under physiological conditions. The future prospective and suggestions on the development of MNMs toward practical biomedical applications will also be proposed.

Fuel-Free Micro-/Nanomotors as Intelligent Therapeutic Agents

There are many efficient biological motors in Nature that perform complex functions by converting chemical energy into mechanical motion. Inspired by this, the development of their synthetic counterparts has aroused tremendous research interest in the past decade. Among these man-made motor systems, the fuel-free (or light, magnet, ultrasound, or electric field driven) motors are advantageous in terms of controllability, lifespan, and biocompatibility concerning bioapplications, when compared with their chemically powered counterparts. Therefore, this review will highlight the latest biomedical applications in the versatile field of externally propelled micro-/nanomotors, as well as elucidating their driving mechanisms. A perspective into the future of the micro-/nanomotors field and a discussion of the challenges we need to face along the road towards practical clinical translation of external-field-propelled micro-/nanomotors will be provided.

Nanoparticle-Regulated Semiartificial Magnetotactic Bacteria with Tunable Magnetic Moment and Magnetic Sensitivity

Micro-/nanomotors are widely used in micro-/nanoprocessing, cargo transportation, and other microscale tasks because of their ability to move independently. Many biological hybrid motors based on bacteria have been developed. Magnetotactic bacteria (MTB) have been employed as motors in biological systems because of their good biocompatibility and magnetotactic motion in magnetic fields. However, the magnetotaxis of MTB is difficult to control due to the lack of effective methods. Herein, a strategy that enables control over the motion of MTB is presented. By depositing synthetic Fe₃ O₄ magnetic nanoparticles on the surface of MTB, semiartificial magnetotactic bacteria (SAMTB) are produced. The overall magnetic properties of SAMTB, including saturation magnetization, residual magnetization, and blocking temperature, are regulated in a multivariate and multilevel fashion, thus regulating the magnetic sensitivity of SAMTB. This strategy provides a feasible method to manoeuvre MTB for applications in complex fluid environments, such as magnetic drug release systems and real-time tracking systems. Furthermore, this concept and methodology provide a paradigm for controlling the mobility of micro-/nanomotors based on natural small organisms.

Active, Autonomous, and Adaptive Polymeric Particles for Biomedical Applications

Nature's motors are complex and efficient systems, which are able to respond to many different stimuli present in the cell. Nanomotors for biomedical applications are designed to mimic nature's complexity; however, they usually lack biocompatibility and the ability to adapt to their environment. Polymeric vesicles can overcome these problems due to the soft and flexible nature of polymers. Herein we will highlight the recent progress and the crucial steps needed to fabricate active and adaptive motor systems for their use in biomedical applications and our approach to reach this goal. This includes the formation of active, asymmetric vesicles and the incorporation of a catalyst, together with their potential in biological applications and the challenges still to overcome.

Glucose-Fueled Micromotors with Highly Efficient Visible-Light Photocatalytic Propulsion

Synthetic micro/nanomotors fueled by glucose are highly desired for numerous practical applications because of the biocompatibility of their required fuel. However, currently all of the glucose-fueled micro/nanomotors are based on enzyme-catalytic-driven mechanisms, which usually suffer from strict operation conditions and weak propulsion characteristics that greatly limit their applications. Here, we report a highly efficient glucose-fueled cuprous oxide@N-doped carbon nanotube (Cu₂O@N-CNT) micromotor, which can be activated by environment-friendly visible-light photocatalysis. The speeds of such Cu₂O@N-CNT micromotors can reach up to 18.71 μm/s, which is comparable to conventional Pt-based catalytic Janus micromotors usually fueled by toxic H₂O₂ fuel. In addition, the velocities of such motors can be efficiently regulated by multiple approaches, such as adjusting the N-CNT content within the micromotors, glucose concentrations, or light intensities. Furthermore, the Cu₂O@N-CNT micromotors exhibit a highly controllable negative phototaxis behavior (moving away from light sources). Such motors with outstanding propulsion in biological environments and wireless, repeatable, and light-modulated three-dimensional motion control are extremely attractive for future practical applications.

Intelligent Micro/nanomotors with Taxis

Micro/nanomotors (MNMs) are micro/nanoscale devices that can convert energy from their surroundings into autonomous motion. With this unique ability, they may revolutionize application fields ranging from active drug delivery to biological surgeries, environmental remediation, and micro/nanoengineering. To complete these applications, MNMs are required to have a vital capability to reach their destinations. Employing external fields to guide MNMs to the targets is common and effective way. However, in application scenarios where targets are generally unknown or dynamically change, MNMs must possess the capability of self-navigation or self-targeting. Taking advantage of tactic movements toward or away from signal sources, numerous intelligent MNMs with self-navigation or self-targeting have been demonstrated and attracted much attention during the past few years. In this Account, we elucidate the intelligent response mechanisms of such tactic MNMs, which are summarized as two main models. One is that local vector fields, including those of chemical concentration gradients, gravity, flows, and magnetic fields existing in systems, achieve the overall alignment of asymmetric MNMs via aligning torques, directing the MNMs to swim toward or away from the signal sources. Another is that isotropic MNMs may produce propulsion forces with direction solely determined by the local vector field regardless of their Brownian rotations. Then we discuss and highlight the recent progress in tactic MNMs, including chemotactic, phototactic, rheotactic, gravitactic, and magnetotactic motors. Artificial chemotactic MNMs can be designed with different morphologies and compositions if asymmetric reactions are associated with chemical concentration gradients. In these systems, asymmetric phoretic slip flows are induced, leading to torques that enable the anisotropic particles to align and exhibit chemotaxis. For phototactic MNMs, light irradiation establishes asymmetric fields surrounding the motors via light-induced chemical reactions or physical effects to generate phototactic motion. Shape-asymmetric MNMs reorient in natural fluid flows because of torques applied by the flows, inducing rheotactic movements. MNMs with either the centroid or magnetic components distributed asymmetrically maintain orientation under the torque triggered by gravity or magnetic forces, generating tactic motions. In the end, we envision the future development of synthetic tactic MNMs, including enhancement of the sensitivity of motors to target signals, increasing the diversity of chemical motor systems, and combining multiple mechanisms to endow the tactic motors with multiple functionality. By highlighting the current achievements and offering our perspective on tactic MNMs, we look forward to inspiring the emergence of the next generation of intelligent MNMs with taxis.

Composite Multifunctional Micromotors from Droplet Microfluidics

Inspired by natural biological machines, lots of effort has been invested in developing artificially functional micromotors which can convert energy into movement for carrying out tasks in diverse areas. Here, we present a capillary microfluidic system with dual inner injections for one-step generation of composite structured polymer micromotors with two distinct cores of platinum (Pt) nanoparticle-integrated and iron oxide (Fe₃O₄) nanoparticle-dispersed hydrogels. Because the flow rates of the prepolymerized fluids can be precisely tuned in the microfluidics, the diameters of the micromotors as well as the sizes and numbers of the inner cores can be well tailored to optimize the parameters of the resultant micromotors. When exposed to a hydrogen peroxide (H₂O₂) medium, the Pt-integrated cores of the micromotors could provide propulsion by expelling bubbles produced from the catalytic decomposition of H₂O₂, while the Fe₃O₄-dispersed cores could impart magnetic guidance for the micromotors. Benefiting from the close cooperation of these two types of cores, the micromotors were imparted with a strong propulsion and prominent recyclability for the delivery of both microscale and macroscale objects. These results manifest that this kind of composite micromotor has great diversity in various applications.

A Supramolecular Approach to Nanoscale Motion: Polymersome-Based Self-Propelled Nanomotors

Autonomous micro- and nanoscale systems have revolutionized the way scientists look into the future, opening up new frontiers to approach and solve problems via a more bioinspired route. However, to achieve systems with higher complexity, superior output control, and multifunctionality, an in-depth study of the different factors that affect micro- and nanomotor behavior is crucial. From a fundamental perspective, the mechanical response of micro- and nanomotors still requires further study in order to have a better understanding of how exactly these systems operate and the different mechanisms of motion that can be combined into one system to achieve an optimal response. From a design engineering point of view, compatibility, degradability, specificity, sensitivity, responsiveness, and efficiency of the active systems fabricated to this point have to be addressed, with respect to the potential of these devices for biomedical applications. Nonetheless, optimizing the system with regards to all these areas is a challenging task with the micro- and nanomotors studied to date, as most of them consist of materials or designs that are unfavorable for further chemical or physical manipulation. As this new field of self-powered systems moves forward, the need for motor prototypes with different sizes, shapes, chemical functionalities, and architectures becomes increasingly important and will define not only the way active systems are powered, but also the methods for motor fabrication. Bottom-up supramolecular approaches have recently emerged as great candidates for the development of active structures that allow for chemical or physical functionalization, shape transformation, and compartmentalization, in a structure that provides a soft interface to improve molecular recognition and cell uptake. Our group pioneers the use of supramolecular structures as catalytically propelled systems via the fabrication of stomatocyte or tubular-shaped motors capable of displaying active motion in a substrate concentration-dependent fashion. This behavior demonstrates the potential of bottom-up assemblies for powering motion at the micro- or nanoscale, with a system that can be readily tuned and controlled at the molecular level. In this Account, we highlight the steps we have taken in order to understand and optimize the design of catalytically powered polymersome-based motors. Our research has been focused on addressing the importance of motor architecture, motion activation, direction control, and biological integration. While our work supports the feasibility of supramolecular structures for the design of active systems, we strongly believe that we are still in the initial stages of unveiling the full potential of supramolecular chemistry in the micro- and nanomotor field. We look forward to using this approach for the development of multifunctional and stimuli-responsive systems in the near future.