A Magnetically Guided Self-Rolled Microrobot for Targeted Drug Delivery, Real-Time X-Ray Imaging, and Microrobot Retrieval

Material selection, preparation, driving and applications of light-driven micro/nano motors: a review

As an external energy stimulus, light possesses the advantageous qualities of being reversible, wireless and remotely maneuverable while driving the motion of micro and nano motors. Despite the extensive publication of articles on light-driven micro- and nano-motors (LDMNMs) over the past two decades, reviews that address LDMNMs in general, from material selection, design, preparation, driving to applications, remain scarce. Therefore, it is necessary to highlight the superiority of light as a stimulating energy source for driving MNMs, as well as to promote the continuous development of LDMNMs and give newcomers a more basic and comprehensive knowledge in this field. This present review focuses on advanced preparation methods for LDNMNs, and provides a comprehensive comparison of the advantages and limitations of various techniques. In addition, general design strategies for building asymmetric fields around LDMNMs are introduced, as well as a variety of photoactive materials, including photocatalytic, photothermal, and photoinduced isomerization materials. The existing propulsive mechanisms and kinematic behaviours of LDMNMs are described in detail, including photocatalytic oxidation, photothermal effects and photoinduced isomerization. The principles of the various drive mechanisms are also analysed in detail and their merits and shortcomings summarized. Finally, following a comprehensive review of the potential applications in biomedicine, environmental remediation and other fields, further perspectives on future developments are presented with a view to overcoming key challenges.

Asymmetric Laser Enabled High-Throughput Manufacturing of Multiform Magnetically Actuated Graphene-Based Robots for Various Water Depths

Achieving large-scale and facile manufacturing for diverse small-scale robots is critical in the field of small-scale robots. At present, conventional manufacturing methods have limitations in terms of efficiency, environmental friendliness, and operability. In particular, it is difficult to facilely process multiform small-scale robots through a single processing technology only. In this work, with the introduction of an asymmetric laser, multiforms of graphene, including powders, helical, and sheet, were successfully fabricated by simply adjusting laser processing parameters only. This allowed the development of multiform graphene-based robots capable of being actuated in various water depths, including underwater swarm, suspended helical, and floated sheet robots. Importantly, such robots can move smoothly in various trajectories under magnetic fields, including simple geometrical shapes and complicated words, demonstrating good maneuverability. Moreover, this manufacturing method enables the efficient production of multiform robots in different sizes, from 5 to 48 units, within 1 min. The proposed asymmetric laser technology is possible to provide a new means for manufacturing high-performance small-scale robots at high throughput.

Stochastic Dynamic Analysis of a Three-Tailed Helical Microrobot in Confined Spaces

This study investigates the complex dynamic behavior of three-tailed helical microrobots operating in confined spaces. A stochastic dynamic model has been developed to analyze the effects of input angular velocity, current, fluid viscosity, and channel width on their motion trajectories, velocity, mean squared displacement (MSD), and wobbling rate. The results indicate that Gaussian white noise exerts a dispersive driving effect on the motion characteristics of the microrobots, leading to a 49% reduction in their velocity compared to deterministic conditions. Additionally, the time required for microrobots to traverse from the initial position to the bifurcation point decreases by 65% when the current is increased and by 39% when the fluid viscosity is reduced. These findings underscore the importance of optimizing control parameters to effectively mitigate noise impacts, enhancing the practical performance of the microrobots in real-world applications. This research offers solid theoretical support and guidance for the deployment of microrobots in complex environments.

Magnetic Micro/nanorobots in Cancer Theranostics: From Designed Fabrication to Diverse Applications

Cancer poses a substantial threat and a serious challenge to public human health, driving the promotion of sophisticated technologies for cancer therapy. While conventional chemotherapy has bottlenecks such as low delivery efficiency, strong toxic side effects, and tumor enrichment barriers, magnetic micro/nanorobots (MNRs) emerge as promising therapeutic candidates that provide alternative strategies for cancer therapy. MNR is a kind of human-made machine that is micro- or nanosized, is reasonably designed, and performs command tasks through self-actuated or externally controlled propulsion mechanisms, which can be potentially applied in cancer theranostics. Here, this review first introduces the components that constitute a typical magnetic MNR, including the body part, the driving part, the control part, the function part, and the sensing part. Subsequently, this review elucidates representative fabrication methods to construct magnetic MNRs from top-down approaches to bottom-up approaches, covering injection molding, self-rolling, melt electrospinning writing, deposition, biotemplate method, lithography, assembling, 3D printing, and chemical synthesis. Furthermore, this review focuses on multiple applications of magnetic MNRs facing cancer diagnosis and treatment, encompassing imaging, quantification, drug release, synergy with typical therapies, cell manipulation, and surgical assistance. Then, this review systematically elaborates on the biocompatibility and biosafety of magnetic MNRs. Finally, the challenges faced by magnetic MNRs are discussed alongside future research directions. This review is intended to provide scientific guidance that may improve the comprehension and cognition of cancer theranostics through the platform of magnetic MNRs, promoting and prospering the practical application development of magnetic MNRs.

Advances in micro-/nanorobots for cancer diagnosis and treatment: propulsion mechanisms, early detection, and cancer therapy

In recent years, medical micro-/nanorobots (MNRs) have emerged as a promising technology for diagnosing and treating malignant tumors. MNRs enable precise, targeted actions at the cellular level, addressing several limitations of conventional cancer diagnosis and treatment, such as insufficient early diagnosis, nonspecific drug delivery, and chemoresistance. This review provides an in-depth discussion of the propulsion mechanisms of MNRs, including chemical fuels, external fields (light, ultrasound, magnetism), biological propulsion, and hybrid methods, highlighting their respective advantages and limitations. Additionally, we discuss novel approaches for tumor diagnosis, precision surgery, and drug delivery, emphasizing their potential clinical applications. Despite significant advancements, challenges such as biocompatibility, propulsion efficiency, and clinical translation persist. This review examines the current state of MNR applications and outlines future directions for their development, with the aim of enhancing their diagnostic and therapeutic efficacy and facilitating their integration into clinical practice.

Harnessing stimuli-responsive biomaterials for advanced biomedical applications

Cell behavior is intricately intertwined with the in vivo microenvironment and endogenous pathways. The ability to guide cellular behavior toward specific goals can be achieved by external stimuli, notably electricity, light, ultrasound, and magnetism, simultaneously harnessed through biomaterial-mediated responses. These external triggers become focal points within the body due to interactions with biomaterials, facilitating a range of cellular pathways: electrical signal transmission, biochemical cues, drug release, cell loading, and modulation of mechanical stress. Stimulus-responsive biomaterials hold immense potential in biomedical research, establishing themselves as a pivotal focal point in interdisciplinary pursuits. This comprehensive review systematically elucidates prevalent physical stimuli and their corresponding biomaterial response mechanisms. Moreover, it delves deeply into the application of biomaterials within the domain of biomedicine. A balanced assessment of distinct physical stimulation techniques is provided, along with a discussion of their merits and limitations. The review aims to shed light on the future trajectory of physical stimulus-responsive biomaterials in disease treatment and outline their application prospects and potential for future development. This review is poised to spark novel concepts for advancing intelligent, stimulus-responsive biomaterials.

Non-FFP-Based Magnetic Particle Imaging (NFMPI) with an Open-Type RF Coil System: A Feasibility Study

Active drug delivery systems for cancer therapy are gaining attention for their biocompatibility and enhanced efficacy compared to conventional chemotherapy and surgery. To improve precision in targeted drug delivery (TDD), actuating devices using external magnetic fields are employed. However, a key challenge is the inability to visually track magnetic drug carriers in blood vessels, complicating navigation to the target. Magnetic particle imaging (MPI) systems can localize magnetic carriers (MCs) but rely on bulky electromagnetic coils to generate a static magnetic field gradient, creating a field-free point (FFP) within the field of view (FOV). Also, additional coils are required to move the FFP across the FOV, limiting flexibility and increasing the system size. To address these issues, we propose a non-FFP-based, open-type RF coil system with a simplified structure composed of a Tx/Rx coil and a permanent magnet at the coil center, eliminating the need for an FFP. Furthermore, integrating a robotic arm for coil assembly enables easy adjustment of the FOV size and location. Finally, imaging tests with magnetic nanoparticles (MNPs) confirmed the system's ability to detect and localize a minimum mass of 0.3 mg (Fe) in 80 × 80 mm2.

Magnetically actuated cisplatin-loaded nanoparticle collectives enhance drug penetration for potentiated ovarian cancer chemotherapy

Chemotherapy is the main clinical treatment for ovarian cancer, but still faces challenges of low drug targeting efficiency and insufficient drug permeability. Drug-loaded nanoparticle collectives, which are actuated by magnetic field, could be targeted to a designated location and achieve targeted drug delivery. In this work, we report a strategy that utilizes magnetic mesoporous silica nanoparticles loaded with cis-diaminodichloroplatinum (Fe3O4@SiO2-CDDP) for targeted delivery of chemotherapeutic drugs and enhances penetration into deep tumors. The Fe3O4@SiO2-CDDP collectives actively moved to the target tumor site, and this movement was regulated by a magnetic actuation system. Under the action of a torque-force hybrid magnetic field (TFMF), Fe3O4@SiO2-CDDP could further penetrate into the interior of tumors and achieve pH-responsive drug release in the tumor environment. The feasibility of this strategy was verified in three-dimensional cell spheres in vitro and in a tumor-bearing mouse model in vivo. This magnetically actuated nanoparticle collectives enhanced drug penetration strategy provides a new paradigm for targeted drug delivery and potentiated tumor therapy.

Light-Driven Microrobots for Targeted Drug Delivery

As a new micromanipulation tool with the advantages of small size, flexible movement and easy manipulation, light-driven microrobots have a wide range of prospects in biomedical fields such as drug targeting and cell manipulation. Recently, microrobots have been controlled in various ways, and light field has become a research hotspot by its advantages of noncontact manipulation, precise localization, fast response, and biocompatibility. It utilizes the force or deformation generated by the light field to precisely control the microrobot, and combines with the drug release technology to realize the targeted drug application. Therefore, this paper provides an overview of light-driven microrobots with drug targeting to provide new ideas for the manipulation of microrobots. Here, this paper briefly categorizes the driving mechanisms and materials of light-driven microrobots, which mainly include photothermal, photochemical, and biological. Then, typical designs of light-driven microrobots with different driving mechanisms and control strategies for multiple physical fields are summarized. Finally, the applications of microrobots in the fields of drug targeting and bioimaging are presented as well as the future prospects of light-driven microrobots in the biomedical field are demonstrated.

Neurological insights into brain-targeted cancer therapy and bioinspired microrobots

Cancer, a multifaceted and pernicious disease, continuously challenges medicine, requiring innovative treatments. Brain cancers pose unique and daunting challenges due to the intricacies of the central nervous system and the blood-brain barrier. In this era of precision medicine, the convergence of neurology, oncology, and cutting-edge technology has given birth to a promising avenue - targeted cancer therapy. Furthermore, bioinspired microrobots have emerged as an ingenious approach to drug delivery, enabling precision and control in cancer treatment. This Keynote review explores the intricate web of neurological insights into brain-targeted cancer therapy and the paradigm-shifting world of bioinspired microrobots. It serves as a critical and comprehensive overview of these evolving fields, aiming to underscore their integration and potential for revolutionary cancer treatments.

Propulsion mechanisms of micro/nanorobots: a review

Micro/nanomotors (MNMs) are intelligent, efficient and promising micro/nanorobots (MNR) that can respond to external stimuli (e.g., chemical energy, temperature, light, pH, ultrasound, magnetic, biosignals, ions) and perform specific tasks. The MNR can adapt to different external stimuli and transform into various functional forms to match different application scenarios. So far, MNR have found extensive application in targeted therapy, drug delivery, tissue engineering, environmental remediation, and other fields. Despite the promise of MNR, there are few reviews that focus on them. To shed new light on the further development of the field, it is necessary to provide an overview of the current state of development of these MNR. Therefore, this paper reviews the research progress of MNR in terms of propulsion mechanisms, and points out the pros and cons of different stimulus types. Finally, this paper highlights the current challenges faced by MNR and proposes possible solutions to facilitate the practical application of MNR.

Advanced Design of Soft Robots with Artificial Intelligence

A comprehensive review focused on the whole systems of the soft robotics with artificial intelligence, which can feel, think, react and interact with humans, is presented. The design strategies concerning about various aspects of the soft robotics, like component materials, device structures, prepared technologies, integrated method, and potential applications, are summarized. A broad outlook on the future considerations for the soft robots is proposed.

In recent years, breakthrough has been made in the field of artificial intelligence (AI), which has also revolutionized the industry of robotics. Soft robots featured with high-level safety, less weight, lower power consumption have always been one of the research hotspots. Recently, multifunctional sensors for perception of soft robotics have been rapidly developed, while more algorithms and models of machine learning with high accuracy have been optimized and proposed. Designs of soft robots with AI have also been advanced ranging from multimodal sensing, human–machine interaction to effective actuation in robotic systems. Nonetheless, comprehensive reviews concerning the new developments and strategies for the ingenious design of the soft robotic systems equipped with AI are rare. Here, the new development is systematically reviewed in the field of soft robots with AI. First, background and mechanisms of soft robotic systems are briefed, after which development focused on how to endow the soft robots with AI, including the aspects of feeling, thought and reaction, is illustrated. Next, applications of soft robots with AI are systematically summarized and discussed together with advanced strategies proposed for performance enhancement. Design thoughts for future intelligent soft robotics are pointed out. Finally, some perspectives are put forward.

Study on Structural Design and Motion Characteristics of Magnetic Helical Soft Microrobots with Drug-Carrying Function

Magnetic soft microrobots have a wide range of applications in targeted drug therapy, cell manipulation, and other aspects. Currently, the research on magnetic soft microrobots is still in the exploratory stage, and most of the research focuses on a single helical structure, which has limited space to perform drug-carrying tasks efficiently and cannot satisfy specific medical goals in terms of propulsion speed. Therefore, balancing the motion speed and drug-carrying performance is a current challenge to overcome. In this paper, a magnetically controlled cone-helix soft microrobot structure with a drug-carrying function is proposed, its helical propulsion mechanism is deduced, a dynamical model is constructed, and the microrobot structure is prepared using femtosecond laser two-photon polymerization three-dimensional printing technology for magnetic drive control experiments. The results show that under the premise of ensuring sufficient drug-carrying space, the microrobot structure proposed in this paper can realize helical propulsion quickly and stably, and the speed of motion increases with increases in the frequency of the rotating magnetic field. The microrobot with a larger cavity diameter and a larger helical pitch exhibits faster rotary advancement speed, while the microrobot with a smaller helical height and a smaller helical cone angle outperforms other structures with the same feature sizes. The microrobot with a cone angle of 0.2 rad, a helical pitch of 100 µm, a helical height of 220 µm, and a cavity diameter of 80 µm achieves a maximum longitudinal motion speed of 390 µm/s.

Lightweight and drift-free magnetically actuated millirobots via asymmetric laser-induced graphene

Millirobots must have low cost, efficient locomotion, and the ability to track target trajectories precisely if they are to be widely deployed. With current materials and fabrication methods, achieving all of these features in one millirobot remains difficult. We develop a series of graphene-based helical millirobots by introducing asymmetric light pattern distortion to a laser-induced polymer-to-graphene conversion process; this distortion resulted in the spontaneous twisting and peeling off of graphene sheets from the polymer substrate. The lightweight nature of graphene in combine with the laser-induced porous microstructure provides a millirobot scaffold with a low density and high surface hydrophobicity. Magnetically driven nickel-coated graphene-based helical millirobots with rapid locomotion, excellent trajectory tracking, and precise drug delivery ability were fabricated from the scaffold. Importantly, such high-performance millirobots are fabricated at a speed of 77 scaffolds per second, demonstrating their potential in high-throughput and large-scale production. By using drug delivery for gastric cancer treatment as an example, we demonstrate the advantages of the graphene-based helical millirobots in terms of their long-distance locomotion and drug transport in a physiological environment. This study demonstrates the potential of the graphene-based helical millirobots to meet performance, versatility, scalability, and cost-effectiveness requirements simultaneously.

Magnetic Microrobots for In Vivo Cargo Delivery: A Review

Magnetic microrobots, with their small size and agile maneuverability, are well-suited for navigating the intricate and confined spaces within the human body. In vivo cargo delivery within the context of microrobotics involves the use of microrobots to transport and administer drugs and cells directly to the targeted regions within a living organism. The principal aim is to enhance the precision, efficiency, and safety of therapeutic interventions. Despite their potential, there is a shortage of comprehensive reviews on the use of magnetic microrobots for in vivo cargo delivery from both research and engineering perspectives, particularly those published after 2019. This review addresses this gap by disentangling recent advancements in magnetic microrobots for in vivo cargo delivery. It summarizes their actuation platforms, structural designs, cargo loading and release methods, tracking methods, navigation algorithms, and degradation and retrieval methods. Finally, it highlights potential research directions. This review aims to provide a comprehensive summary of the current landscape of magnetic microrobot technologies for in vivo cargo delivery. It highlights their present implementation methods, capabilities, and prospective research directions. The review also examines significant innovations and inherent challenges in biomedical applications.

Upstream mobility and swarming of light activated micromotors

Micromotors have been proposed for applications such as targeted drug delivery, thrombolysis, or sensing. However, single micrormotors are limited in the amount of payload they can deliver or force they can exert. Swarms of micromotors can overcome many of these challenges, however creating and controlling such swarms presents many challenges of its own. In particular, utilizing swarms in fluid flows is of significant importance for biomedical or lab-on-chip applications. Here, the upstream mobility and swarm formation of light driven micromotors in microchannel flows is demonstrated with maximum speeds around 0.1 mm s-1. Additionally, the light actuated microrobots operate in fairly low concentrations of hydrogen peroxide of approximately 1%. The micromotors form swarms at the boundary of the locally applied light pattern and the swarms can be moved by translating the light up or downstream.

System integration of magnetic medical microrobots: from design to control

Magnetic microrobots are ideal for medical applications owing to their deep tissue penetration, precise control, and flexible movement. After decades of development, various magnetic microrobots have been used to achieve medical functions such as targeted delivery, cell manipulation, and minimally invasive surgery. This review introduces the research status and latest progress in the design and control systems of magnetic medical microrobots from a system integration perspective and summarizes the advantages and limitations of the research to provide a reference for developers. Finally, the future development direction of magnetic medical microrobot design and control systems are discussed.

Preparation, Stimulus-Response Mechanisms and Applications of Micro/Nanorobots

Micro- and nanorobots are highly intelligent and efficient. They can perform various complex tasks as per the external stimuli. These robots can adapt to the required functional form, depending on the different stimuli, thus being able to meet the requirements of various application scenarios. So far, microrobots have been widely used in the fields of targeted therapy, drug delivery, tissue engineering, environmental remediation and so on. Although microbots are promising in some fields, few reviews have yet focused on them. It is therefore necessary to outline the current status of these microbots' development to provide some new insights into the further evolution of this field. This paper critically assesses the research progress of microbots with respect to their preparation methods, stimulus-response mechanisms and applications. It highlights the suitability of different preparation methods and stimulus types, while outlining the challenges experienced by microbots. Viable solutions are also proposed for the promotion of their practical use.

A glutathione-responsive PEGylated nanogel with doxorubicin-conjugation for cancer therapy

The complexity, degradability, and stability of drug delivery systems are crucial factors for clinical application. Herein, a glutathione (GSH)-responsive polyethylene glycol (PEG)ylated nanogel conjugated with doxorubicin (Dox) was prepared based on a linker with disulfide bonds, PEG, and Dox using a one-pot method. FT-IR and UV-vis analyses confirmed that all raw materials were incorporated in the Dox-conjugated nanogel structure. Dynamic light scattering (DLS) and transmission electron microscopy (TEM) results showed that the particle size of the Dox-conjugated nanogel was at the nanoscale and could be responsively disrupted in high GSH concentration. The in vitro accumulative Dox release rate from the nanogel reached 88% in PBS with 5 mg mL-1 GSH on day 4. Moreover, H22 cell viability and apoptosis experiments revealed that the nanogel effectively inhibited tumor cell growth. In vivo tracking and cell uptake experiments demonstrated that the nanogel accumulated and persisted in tumor tissues for 5 days and was distributed into cell nuclei at 6 h. Furthermore, H22-bearing mice experiments showed that the tumor size of the Dox-conjugated nanogel group was the smallest (287 mm3) compared to that of the free Dox (558 mm3) and 0.9% NaCl (2700 mm3) groups. Meanwhile, the body weight of mice as well as the H&E and TUNEL tissue section staining of organs and tumor tissues from the mice illustrated that the nanogel could significantly prevent side effects and induce tumor cell apoptosis. Taken together, compared with free Dox, the Dox-conjugated nanogel exhibited higher therapeutic efficacy and lower side effects in normal tissues, making it a potential novel nanomedicine for cancer.

Deep Reinforcement Learning Framework-Based Flow Rate Rejection Control of Soft Magnetic Miniature Robots

Soft magnetic miniature robots (SMMRs) have potential biomedical applications due to their flexible size and mobility to access confined environments. However, navigating the robot to a goal site with precise control performance and high repeatability in unstructured environments, especially in flow rate conditions, still remains a challenge. In this study, drawing inspiration from the control requirements of drug delivery and release to the goal lesion site in the presence of dynamic biofluids, we propose a flow rate rejection control strategy based on a deep reinforcement learning (DRL) framework to actuate an SMMR to achieve goal-reaching and hovering in fluidic tubes. To this end, an SMMR is first fabricated, which can be operated by an external magnetic field to realize its desired functionalities. Subsequently, a simulator is constructed based on neural networks to map the relationship between the applied magnetic field and robot locomotion states. With minimal prior knowledge about the environment and dynamics, a gated recurrent unit (GRU)-based DRL algorithm is formulated by considering the designed history state-action and estimated flow rates. In addition, the randomization technique is applied during training to distill the general control policy for the physical SMMR. The results of numerical simulations and experiments are illustrated to demonstrate the robustness and efficacy of the presented control framework. Finally, in-depth analyses and discussions indicate the potentiality of DRL for soft magnetic robots in biomedical applications.

Advances of nanomedicine in treatment of atherosclerosis and thrombosis

Atherosclerosis (AS) is a chronic inflammatory vascular disease. Myocardial ischemia originated from AS is the main cause of cardiovascular diseases, one of the major factors contributing to the global disease burden. AS is typically quiescent until occurrence of plaque rupture and thrombosis, leading to acute coronary syndrome and sudden death. Currently, clinical diagnostic techniques suffer from major pitfalls including lack of accuracy and specificity, which makes it rather difficult for drugs to directly target plaques to achieve therapeutic effect. Therefore, how to accurately diagnose and effectively intervene vulnerable AS plaques to achieve accurate delivery of drugs has become an urgent and evolving clinical problem. With the rapid development of nanomedicine and nanomaterials, nanotechnology has shown unique advantages in monitoring vulnerable plaques and thrombus and improving drug efficacy. Recent studies have shown that application of nanoparticle drug delivery system can booster the safety and effectiveness of drug therapy, and molecular imaging technology and nanomedicine also exhibit high clinical application potentials in disease diagnosis. Therefore, nanotechnology provides another promising avenue for diagnosis and treatment of AS and thrombosis, and has shown excellent performance in the development of targeted drug therapy and biomaterials. In this review, the research progress, challenges and prospects of nanotechnology in AS and thrombosis are discussed, expecting to provide new ideas for the prevention, diagnosis and treatment of AS and thrombosis.

Acoustic Trapping and Manipulation of Hollow Microparticles under Fluid Flow Using a Single-Lens Focused Ultrasound Transducer

Microparticle manipulation and trapping play pivotal roles in biotechnology. To achieve effective manipulation within fluidic flow conditions and confined spaces, it is necessary to consider the physical properties of microparticles and the types of trapping forces applied. While acoustic waves have shown potential for manipulating microparticles, the existing setups involve complex actuation mechanisms and unstable microbubbles. Consequently, the need persists for an easily deployable acoustic actuation setup with stable microparticles. Here, we propose the use of hollow borosilicate microparticles possessing a rigid thin shell, which can be efficiently trapped and manipulated using a single-lens focused ultrasound (FUS) transducer under physiologically relevant flow conditions. These hollow microparticles offer stability and advantageous acoustic properties. They can be scaled up and mass-produced, making them suitable for systemic delivery. Our research demonstrates the successful trapping dynamics of FUS within circular tubings of varying diameters, validating the effectiveness of the method under realistic flow rates and ultrasound amplitudes. We also showcase the ability to remove hollow microparticles by steering the FUS transducer against the flow. Furthermore, we present potential biomedical applications, such as active cell tagging and navigation in bifurcated channels as well as ultrasound imaging in mouse cadaver liver tissue.

Doxorubicin-Loaded Microrobots for Targeted Drug Delivery and Anticancer Therapy

Micro-sized magnetic particles (also known as microrobots [MRs]) have recently been shown to have potential applications for numerous biomedical applications like drug delivery, microengineering, and single cell manipulation. Interdisciplinary studies have demonstrated the ability of these tiny particles to actuate under the action of a controlled magnetic field that not only drive MRs in a desired trajectory but also precisely deliver therapeutic payload to the target site. Additionally, optimal concentrations of therapeutic molecules can also be delivered to the desired site which is cost-effective and safe especially in scenarios where drug dose-related side effects are a concern. In this study, MRs are used to deliver anticancer drugs (doxorubicin) to cancer cells and subsequent cell death is evaluated in different cell lines (liver, prostate, and ovarian cancer cells). Cytocompatibility studies show that MRs are well-tolerated and internalized by cancer cells. Doxorubicin (DOX) is chemically conjugated with MRs (DOX-MRs) and magnetically steered toward cancer cells using the magnetic controller. Time-lapsed video shows that cells shrink and eventually die when MRs are internalized by cells. Taken together, this study confirms that microrobots are promising couriers for targeted delivery of therapeutic biomolecules for cancer therapy and other non-invasive procedures that require precise control.

Plasma-Derived Nanoclusters for Site-Specific Multimodality Photo/Magnetic Thrombus Theranostics

Traditional thrombolytic therapeutics for vascular blockage are affected by their limited penetration into thrombi, associated off-target side effects, and low bioavailability, leading to insufficient thrombolytic efficacy. It is hypothesized that these limitations can be overcome by the precisely controlled and targeted delivery of thrombolytic therapeutics. A theranostic platform is developed that is biocompatible, fluorescent, magnetic, and well-characterized, with multiple targeting modes. This multimodal theranostic system can be remotely visualized and magnetically guided toward thrombi, noninvasively irradiated by near-infrared (NIR) phototherapies, and remotely activated by actuated magnets for additional mechanical therapy. Magnetic guidance can also improve the penetration of nanomedicines into thrombi. In a mouse model of thrombosis, the thrombosis residues are reduced by ≈80% and with no risk of side effects or of secondary embolization. This strategy not only enables the progression of thrombolysis but also accelerates the lysis rate, thereby facilitating its prospective use in time-critical thrombolytic treatment.

Rolling Helical Microrobots for Cell Patterning

Microrobots, untethered miniature devices capable of performing tasks at the microscale, have gained significant attention in the fields of robotics and biomedicine. These devices hold immense potential for various industrial and scientific applications, including targeted drug delivery and cell manipulation. In this study, we present a novel magnetic rolling helical microrobot specifically designed for bio-compatible cell patterning. Our microrobot incorporates both open-loop and closed-loop control mechanisms, providing flexible, precise, and rapid control for various applications. Through experiments, we demonstrate the microrobot's ability to manipulate cells by pushing them while rolling and arranging cells into desired patterns. This result is particularly significant as it has implications for diverse biological applications such as tissue engineering and organoid development. Moreover, we showcase the effectiveness of our microrobot in a closed-loop control system, where it successfully follows a predetermined path from an origin to a destination. The combination of cellular manipulation capabilities and trajectory-tracking performance underlines the versatility and potential of our magnetic rolling helical microrobot. The ability to control and navigate the microrobot with high precision opens up new possibilities for advanced biomedical applications. These findings contribute to the growing body of knowledge in microbotics and pave the way for further research and development in the field.

Biohybrid magnetic microrobots: An intriguing and promising platform in biomedicine

Biohybrid magnetic microrobots (BMMs) have emerged as an exciting class of microrobots and have been considered as a promising platform in biomedicine. Many microorganisms and body's own cells show intriguing properties, such as morphological characteristics, biosafety, and taxis abilities (e.g., chemotaxis, aerotaxis), which have made them attractive for the fabrication of microrobots. For remote controllability and sustainable actuation, magnetic components are usually incorporated onto these biological entities, and other functionalized non-biological components (e.g., therapeutic agents) are also included for specific applications. This review highlights the latest developments in BMMs with a focus on their biomedical applications. It starts by introducing the fundamental understanding of the propulsion system at the microscale in a magnetically driven manner, followed by a summary of diverse BMMs based on different microorganisms and body's own cells along with their relevant applications. Finally, the review discusses how BMMs contribute to the advancements of microrobots, the current challenges of using BMMs in practical clinical settings, and the future perspectives of this exciting field. STATEMENT OF SIGNIFICANCE: Biohybrid magnetic microrobots (BMMs), composed of biological entities and functional parts, hold great potential and serve as a novel and promising platform for biomedical applications such as targeted drug delivery. This review comprehensively summarizes the recent advancements in BMMs for biomedical applications, mainly focused on the representative propulsion modalities in a magnetically propelled manner and diverse designs of BMMs based on different biological entities, including microorganisms and body's own cells. We hope this review can provide ideas for the future design, development, and innovation of micro/nanorobots in the field of biomedicine.

Stimuli-Responsive Functional Micro-/Nanorobots: A Review

Stimuli-responsive functional micro-/nanorobots (srFM/Ns) are a class of intelligent, efficient, and promising microrobots that can react to external stimuli (such as temperature, light, ultrasound, pH, ion, and magnetic field) and perform designated tasks. Through adaptive transformation into the corresponding functional forms, they can perfectly match the demands depending on different applications, which manifest extremely important roles in targeted therapy, biological detection, tissue engineering, and other fields. Promising as srFM/Ns can be, few reviews have focused on them. It is therefore necessary to provide an overview of the current development of these intelligent srFM/Ns to provide clear inspiration for further development of this field. Hence, this review summarizes the current advances of stimuli-responsive functional microrobots regarding their response mechanism, the achieved functions, and their applications to highlight the pros and cons of different stimuli. Finally, we emphasize the existing challenges of srFM/Ns and propose possible strategies to help accelerate the study of this field and promote srFM/Ns toward actual applications.

Four-Dimensional-Printed Microrobots and Their Applications: A Review

Owing to their small size, microrobots have many potential applications. In addition, four-dimensional (4D) printing facilitates reversible shape transformation over time or upon the application of stimuli. By combining the concept of microrobots and 4D printing, it may be possible to realize more sophisticated next-generation microrobot designs that can be actuated by applying various stimuli, and also demonstrates profound implications for various applications, including drug delivery, cells delivery, soft robotics, object release and others. Herein, recent advances in 4D-printed microrobots are reviewed, including strategies for facilitating shape transformations, diverse types of external stimuli, and medical and nonmedical applications of microrobots. Finally, to conclude the paper, the challenges and the prospects of 4D-printed microrobots are highlighted.

Biodegradable Microrobots and Their Biomedical Applications: A Review

During recent years, microrobots have drawn extensive attention owing to their good controllability and great potential in biomedicine. Powered by external physical fields or chemical reactions, these untethered microdevices are promising candidates for in vivo complex tasks, such as targeted delivery, imaging and sensing, tissue engineering, hyperthermia, and assisted fertilization, among others. However, in clinical use, the biodegradability of microrobots is significant for avoiding toxic residue in the human body. The selection of biodegradable materials and the corresponding in vivo environment needed for degradation are increasingly receiving attention in this regard. This review aims at analyzing different types of biodegradable microrobots by critically discussing their advantages and limitations. The chemical degradation mechanisms behind biodegradable microrobots and their typical applications are also thoroughly investigated. Furthermore, we examine their feasibility and deal with the in vivo suitability of different biodegradable microrobots in terms of their degradation mechanisms; pathological environments; and corresponding biomedical applications, especially targeted delivery. Ultimately, we highlight the prevailing obstacles and perspective solutions, ranging from their manufacturing methods, control of movement, and degradation rate to insufficient and limited in vivo tests, that could be of benefit to forthcoming clinical applications.

In vivo applications of micro/nanorobots

Untethered robots in the size range of micro/nano-scale offer unprecedented access to hard-to-reach areas of the body. In these challenging environments, autonomous task completion capabilities of micro/nanorobots have been the subject of research in recent years. However, most of the studies have presented preliminary in vitro results that can significantly differ under in vivo settings. Here, we focus on the studies conducted with animal models to reveal the current status of micro/nanorobotic applications in real-world conditions. By a categorization based on target locations, we highlight the main strategies employed in organs and other body parts. We also discuss key challenges that require interest before the successful translation of micro/nanorobots to the clinic.

Assembly of Fillable Microrobotic Systems by Microfluidic Loading with Dip Sealing

Microrobots can provide spatiotemporally well-controlled cargo delivery that can improve therapeutic efficiency compared to conventional drug delivery strategies. Robust microfabrication methods to expand the variety of materials or cargoes that can be incorporated into microrobots can greatly broaden the scope of their functions. However, current surface coating or direct blending techniques used for cargo loading result in inefficient loading and poor cargo protection during transportation, which leads to cargo waste, degradation and non-specific release. Herein, a versatile platform to fabricate fillable microrobots using microfluidic loading and dip sealing (MLDS) is presented. MLDS enables the encapsulation of different types of cargoes within hollow microrobots and protection of cargo integrity. The technique is supported by high-resolution 3D printing with an integrated microfluidic loading system, which realizes a highly precise loading process and improves cargo loading capacity. A corresponding dip sealing strategy is developed to encase and protect the loaded cargo whilst maintaining the geometric and structural integrity of the loaded microrobots. This dip sealing technique is suitable for different materials, including thermal and light-responsive materials. The MLDS platform provides new opportunities for microrobotic systems in targeted drug delivery, environmental sensing, and chemically powered micromotor applications.

Multimodal collective swimming of magnetically articulated modular nanocomposite robots

Magnetically responsive composites can impart maneuverability to miniaturized robots. However, collective actuation of these composite robots has rarely been achieved, although conducting cooperative tasks is a promising strategy for accomplishing difficult missions with a single robot. Here, we report multimodal collective swimming of ternary-nanocomposite-based magnetic robots capable of on-demand switching between rectilinear translational swimming and rotational swimming. The nanocomposite robots comprise a stiff yet lightweight carbon nanotube yarn (CNTY) framework surrounded by a magnetic polymer composite, which mimics the hierarchical architecture of musculoskeletal systems, yielding magnetically articulated multiple robots with an agile above-water swimmability (~180 body lengths per second) and modularity. The multiple robots with multimodal swimming facilitate the generation and regulation of vortices, enabling novel vortex-induced transportation of thousands of floating microparticles and heavy semi-submerged cargos. The controllable collective actuation of these biomimetic nanocomposite robots can lead to versatile robotic functions, including microplastic removal, microfluidic vortex control, and transportation of pharmaceuticals.

Actuators for Implantable Devices: A Broad View

The choice of actuators dictates how an implantable biomedical device moves. Specifically, the concept of implantable robots consists of the three pillars: actuators, sensors, and powering. Robotic devices that require active motion are driven by a biocompatible actuator. Depending on the actuating mechanism, different types of actuators vary remarkably in strain/stress output, frequency, power consumption, and durability. Most reviews to date focus on specific type of actuating mechanism (electric, photonic, electrothermal, etc.) for biomedical applications. With a rapidly expanding library of novel actuators, however, the granular boundaries between subcategories turns the selection of actuators a laborious task, which can be particularly time-consuming to those unfamiliar with actuation. To offer a broad view, this study (1) showcases the recent advances in various types of actuating technologies that can be potentially implemented in vivo, (2) outlines technical advantages and the limitations of each type, and (3) provides use-specific suggestions on actuator choice for applications such as drug delivery, cardiovascular, and endoscopy implants.

Puffball-Inspired Microrobotic Systems with Robust Payload, Strong Protection, and Targeted Locomotion for On-Demand Drug Delivery

Microrobots are recognized as transformative solutions for drug delivery systems (DDSs) because they can navigate through the body to specific locations and enable targeted drug release. However, their realization is substantially limited by insufficient payload capacity, unavoidable drug leakage/deactivation, and strict modification/stability criteria for drugs. Natural puffballs possess fascinating features that are highly desirable for DDSs, including a large fruitbody for storing spores, a flexible protective cap, and environmentally triggered release mechanisms. This report presents a puffball-inspired microrobotic system which incorporates an internal chamber for loading large drug quantities and spatial drug separation, and a near-infrared-responsive top-sealing layer offering strong drug protection and on-demand release. These puffball-inspired microrobots (PIMs) display tunable loading capacities up to high concentrations and enhanced drug protection with minimal drug leakage. Upon near-infrared laser irradiation, on-demand drug delivery with rapid release efficiency is achieved. The PIMs also demonstrate translational motion velocities, switchable motion modes, and precise locomotion under a rotating magnetic field. This work provides strong proof-of-concept for a DDS that combines the superior locomotion capability of microrobots with the unique characteristics of puffballs, thereby illustrating a versatile avenue for development of a new generation of microrobots for targeted drug delivery.

Interactive and synergistic behaviours of multiple heterogeneous microrobots

Microrobots have been extensively studied for biomedical applications, and significant innovations and advances have been made in diverse aspects of the field. However, most studies have been based on individual microrobots with limited capabilities, constraining their scalability of functions for practical use. Here, we demonstrate the interactive and synergistic behaviours of multiple microrobots that are heterogeneous or incompletely homogeneous. A frequency-response theory is proposed where in a certain frequency range of an external rotating magnetic field (RMF), microrobots with dispersed and linearly aligned magnetic nanoparticles (MNPs) would exhibit similar and different behaviour, respectively. These microrobots rotate following the rotation of the external field, and such complete rotational motion is interrupted when the frequency exceeds a certain value, called the critical frequency (c_f), but such behaviour is more prominent in microrobots with linear MNPs. Upon further investigating the effect of various parameters on the c_f of the microrobots during the fabrication process, we find that heterogeneous microrobots with specific c_f values can be customized. In addition, experiments and simulations are combined to show the hydrodynamic behaviours around the rotating microrobots at different frequencies. Based on these findings, the interactive and synergistic behaviours of multiple microrobots are presented, which suggests great potential for the independent execution of multiple tasks or the synergistic performance of complex tasks and is significant for the future development of interactive synergistic microrobots in the biomedical field.

Multimodal Bubble Microrobot Near an Air-Water Interface

The development of multifunctional and robust swimming microrobots working at the free air-liquid interface has encountered challenge as new manipulation strategies are needed to overcome the complicated interfacial restrictions. Here, flexible but reliable mechanisms are shown that achieve a remote-control bubble microrobot with multiple working modes and high maneuverability by the assistance of a soft air-liquid interface. This bubble microrobot is developed from a hollow Janus microsphere (JM) regulated by a magnetic field, which can implement switchable working modes like pusher, gripper, anchor, and sweeper. The collapse of the microbubble and the accompanying directional jet flow play a key role for functioning in these working modes, which is analogous to a "bubble tentacle." Using a simple gamepad, the orientation and the navigation of the bubble microrobot can be easily manipulated. In particular, a speed modulation method is found for the bubble microrobot, which uses vertical magnetic field to control the orientation of the JM and the direction of the bubble-induced jet flow without changing the fuel concentration. The findings demonstrate a substantial advance of the bubble microrobot specifically working at the air-liquid interface and depict some nonintuitive mechanisms that can help develop more complicated microswimmers.

Contrast-enhanced ultrasound tracking of helical propellers with acoustic phase analysis and comparison with color Doppler

Medical microrobots (MRs) hold the potential to radically transform several interventional procedures. However, to guarantee therapy success when operating in hard-to-reach body districts, a precise and robust imaging strategy is required for monitoring and controlling MRs in real-time. Ultrasound (US) may represent a powerful technology, but MRs' visibility with US needs to be improved, especially when targeting echogenic tissues. In this context, motions of MRs have been exploited to enhance their contrast, e.g., by Doppler imaging. To exploit a more selective contrast-enhancement mechanism, in this study, we analyze in detail the characteristic motions of one of the most widely adopted MR concepts, i.e., the helical propeller, with a particular focus on its interactions with the backscattered US waves. We combine a kinematic analysis of the propeller 3D motion with an US acoustic phase analysis (APA) performed on the raw radio frequency US data in order to improve imaging and tracking in bio-mimicking environments. We validated our US-APA approach in diverse scenarios, aimed at simulating realistic in vivo conditions, and compared the results to those obtained with standard US Doppler. Overall, our technique provided a precise and stable feedback to visualize and track helical propellers in echogenic tissues (chicken breast), tissue-mimicking phantoms with bifurcated lumina, and in the presence of different motion disturbances (e.g., physiological flows and tissue motions), where standard Doppler showed poor performance. Furthermore, the proposed US-APA technique allowed for real-time estimation of MR velocity, where standard Doppler failed.

Single Coil Mechano-Electromagnetic System for the Automatic 1-Axis Position Feedback 3D Locomotion Control of Magnetic Robots and Their Selective Manipulation

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

Solid-Liquid State Transformable Magnetorheological Millirobot

Magnetically actuated soft millirobots (magneto-robot) capable of accomplishing on-demand tasks in a remote-control manner using noninvasive magnetic fields are of great interest in biomedical settings. However, the solid magneto-robots are usually restricted by the limited deformability due to the predesigned shape, while the liquid magneto-robots are capable of in situ shape reconfiguration but limited by the low stiffness and geometric instability due to the fluidity. Herein, we propose a magneto-active solid-liquid state transformable millirobot (named MRF-Robot) made from a magnetorheological fluid (MRF). The MRF-Robot can transform freely and rapidly between the Newtonian fluid in the liquid state upon a weak magnetic field (∼0 mT) and the Bingham plasticity in the solid state upon a strong magnetic field (∼100 mT). The MRF-Robot in the liquid state can realize diverse behaviors of large deformation, smooth navigation, in situ splitting, merging, and gradient pulling actuated by a weak magnetic field with a high gradient. The MRF-Robot in the solid state is distinguished for the controllable locomotion with reconfigured shapes and versatile object manipulations (including pull, push, and rotate the objects) driven by a strong magnetic field with a high gradient. Moreover, the MRF-Robot could continuously maneuver to accomplish diverse tasks in the comprehensive scenes and achieve liquid-drug delivery, thrombus clearance, and fluid-flow blockage in the phantom vascular model under magnetic actuation.

Shape-Tunable UV-Printed Solid Drugs for Personalized Medicine

Several recent advances have emerged in biotherapy and the development of personal drugs. However, studies exploring effective manufacturing methods of personal drugs remain limited. In this study, solid drugs based on poly(ethylene glycol)diacrylate (PEGDA) hydrogel and doxorubicin were fabricated, and their final geometry was varied through UV-light patterning. The results suggested that the final drug concentration was affected by the geometrical volume as well as the UV-light exposure time. The analysis of PEGDA showed no effect on the surrounding cells, indicating its high biocompatibility. However, with the addition of doxorubicin, it showed an excellent therapeutic effect, indicating that drugs inside the PEGDA structure could be successfully released. This approach enables personal drugs to be fabricated in a simple, fast, and uniform manner, with perfectly tuned geometry.

Delivery and actuation of aerosolized microbots

For disease of the lung, the physical key to effective inhalation-based therapy is size; too large (10's of μm) and the particles or droplets do not remain suspended in air to reach deep within the lungs, too small (subμm) and they are simply exhaled without deposition. μBots within this ideal low-μm size range however are challenging to fabricate and would lead to devices that lack the speed and power necessary for performing work throughout the pulmonary network. To uncouple size from structure and function, here we demonstrate an approach where individual building blocks are aerosolized and subsequently assembled in situ into μbots capable of translation, drug delivery, and mechanical work deep within lung mimics. With this strategy, a variety of pulmonary diseases previously difficult to treat may now be receptive to μbot-based therapies.

Magnetically controlled reversible shape-morphing microrobots with real-time X-ray imaging for stomach cancer applications

Stomach cancer is a global health concern as millions of cases are reported each year. In the present study, we developed a pH-responsive microrobot with good biocompatibility, magnetic-field controlled movements, and the ability to be visualized via X-ray imaging. The microrobot consisted of composite resin and a pH-responsive layer. This microrobot was found to fold itself in high pH environments and unfold itself in low pH environments. In addition, the neodymium (NdFeB) magnetic nanoparticles present inside the composite resin provided the microrobot with an ability to be controlled by a magnetic field through an electromagnetic actuation system, and the monomeric triiodobenzoate-based particles were found to act as contrast agents for real-time X-ray imaging. The doxorubicin coating on the microrobot's surface resulted in a high cancer-cell killing effect. Finally, we demonstrated the proposed microrobot under an ex vivo environment using a pig's stomach. Thus, this approach can be a potential alternative to targeted drug carriers, especially for stomach cancer applications.

Microrobotics for Precision Biofilm Diagnostics and Treatment

Advances in small-scale robotics and nanotechnology are providing previously unimagined opportunities for new diagnostic and therapeutic approaches with high precision, control, and efficiency. We designed microrobots for tetherless biofilm treatment and retrieval using iron oxide nanoparticles (NPs) with dual catalytic-magnetic functionality as building blocks. We show 2 distinct microrobotic platforms. The first system is formed from NPs that assemble into aggregated microswarms under magnetic fields that can be controlled to disrupt and retrieve biofilm samples for microbial analysis. The second platform is composed of 3-dimensional (3D) micromolded opacifier-infused soft helicoids with embedded catalytic-magnetic NPs that can be visualized via existing radiographic imaging techniques and controlled magnetically inside the root canal, uninterrupted by the soft and hard tissues surrounding the teeth in an ex vivo model. These microrobots placed inside the root canal can remove biofilms and be efficiently guided with microscale precision. The proof-of-concept paradigm described here can be adapted to target difficult-to-reach anatomical spaces in other natural and implanted surfaces in an automated and tether-free manner.

A Tissue Adhesion-Controllable and Biocompatible Small-Scale Hydrogel Adhesive Robot

Recently, the realization of minimally invasive medical interventions on targeted tissues using wireless small-scale medical robots has received an increasing attention. For effective implementation, such robots should have a strong adhesion capability to biological tissues and at the same time easy controlled detachment should be possible, which has been challenging. To address such issue, a small-scale soft robot with octopus-inspired hydrogel adhesive (OHA) is proposed. Hydrogels of different Young's moduli are adapted to achieve a biocompatible adhesive with strong wet adhesion by preventing the collapse of the octopus-inspired patterns during preloading. Introduction of poly(N-isopropylacrylamide) hydrogel for dome-like protuberance structure inside the sucker wall of polyethylene glycol diacrylate hydrogel provides a strong tissue attachment in underwater and at the same time enables easy detachment by temperature changes due to its temperature-dependent volume change property. It is finally demonstrated that the small-scale soft OHA robot can efficiently implement biomedical functions owing to strong adhesion and controllable detachment on biological tissues while operating inside the body. Such robots with repeatable tissue attachment and detachment possibility pave the way for future wireless soft miniature robots with minimally invasive medical interventions.

Stratified Disk Microrobots with Dynamic Maneuverability and Proton-Activatable Luminescence for in Vivo Imaging

Microrobots can expand our abilities to access remote, confined, and enclosed spaces. Their potential applications inside our body are obvious, e.g., to diagnose diseases, deliver medicine, and monitor treatment efficacy. However, critical requirements exist in relation to their operations in gastrointestinal environments, including resistance to strong gastric acid, responsivity to a narrow proton variation window, and locomotion in confined cavities with hierarchical terrains. Here, we report a proton-activatable microrobot to enable real-time, repeated, and site-selective pH sensing and monitoring in physiological relevant environments. This is achieved by stratifying a hydrogel disk to combine a range of functional nanomaterials, including proton-responsive molecular switches, upconversion nanoparticles, and near-infrared (NIR) emitters. By leveraging the 3D magnetic gradient fields and the anisotropic composition, the microrobot can be steered to locomote as a gyrating "Euler's disk", i.e., aslant relative to the surface and along its low-friction outer circumference, exhibiting a high motility of up to 60 body lengths/s. The enhanced magnetomotility can boost the pH-sensing kinetics by 2-fold. The fluorescence of the molecular switch can respond to pH variations with over 600-fold enhancement when the pH decreases from 8 to 1, and the integration of upconversion nanoparticles further allows both the efficient sensitization of NIR light through deep tissue and energy transfer to activate the pH probes. Moreover, the embedded down-shifting NIR emitters provide sufficient contrast for imaging of a single microrobot inside a live mouse. This work suggests great potential in developing multifunctional microrobots to perform generic site-selective tasks in vivo.

Evolving from Laboratory Toys towards Life-Savers: Small-Scale Magnetic Robotic Systems with Medical Imaging Modalities

Small-scale magnetic robots are remotely actuated and controlled by an externally applied magnetic field. These robots have a characteristic size ranging from several millimetres down to a few nanometres. They are often untethered in order to access constrained and hard-to-reach space buried deep in human body. Thus, they promise to bring revolutionary improvement to minimally invasive diagnostics and therapeutics. However, existing research is still mostly limited to scenarios in over-simplified laboratory environment with unrealistic working conditions. Further advancement of this field demands researchers to consider complex unstructured biological workspace. In order to deliver its promised potentials, next-generation small-scale magnetic robotic systems need to address the constraints and meet the demands of real-world clinical tasks. In particular, integrating medical imaging modalities into the robotic systems is a critical step in their evolution from laboratory toys towards potential life-savers. This review discusses the recent efforts made in this direction to push small-scale magnetic robots towards genuine biomedical applications. This review examines the accomplishment achieved so far and sheds light on the open challenges. It is hoped that this review can offer a perspective on how next-generation robotic systems can not only effectively integrate medical imaging methods, but also take full advantage of the imaging equipments to enable additional functionalities.

A Review of Microrobot's System: Towards System Integration for Autonomous Actuation In Vivo

Microrobots have received great attention due to their great potential in the biomedical field, and there has been extraordinary progress on them in many respects, making it possible to use them in vivo clinically. However, the most important question is how to get microrobots to a given position accurately. Therefore, autonomous actuation technology based on medical imaging has become the solution receiving the most attention considering its low precision and efficiency of manual control. This paper investigates key components of microrobot’s autonomous actuation systems, including actuation systems, medical imaging systems, and control systems, hoping to help realize system integration of them. The hardware integration has two situations according to sharing the transmitting equipment or not, with the consideration of interference, efficiency, microrobot’s material and structure. Furthermore, system integration of hybrid actuation and multimodal imaging can improve the navigation effect of the microrobot. The software integration needs to consider the characteristics and deficiencies of the existing actuation algorithms, imaging algorithms, and the complex 3D working environment in vivo. Additionally, considering the moving distance in the human body, the autonomous actuation system combined with rapid delivery methods can deliver microrobots to specify position rapidly and precisely.