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Smart Magnetic Microrobots In article number 2200023, Warren C. Ruder and co‐workers present smart magnetic microrobot that learns to swim with deep reinforcement learning. This approach reveals a new strategy for microrobot manipulation in fluid environments similar to those in the human body, and thus has potential for medical impact in the future.

Microrobots In article number 2000256, Ada‐Ioana Bunea and co‐workers provide a critical overview of how microrobots can be manufactured and manipulated using light. The cover image shows blue structures printed in hard polymer and precisely manipulated by optical trapping with focused near‐infrared light, together with orange structures printed using soft, light‐responsive materials, which change shape in response to green light. Cover image drawn by Alexandre Wetzel.

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

Hydrogels with stimuli-responsive capabilities are gaining more and more attention nowadays with prospective applications in biomedical engineering, bioelectronics, microrobot, etc. We develop a photothermal responsive hydrogel based on N-isopropylacrylamide that achieved a fast and reversible deformation manipulated only by near-infrared (NIR) light. The hydrogel was fabricated by the projection micro stereolithography based 3D printing technique, which can rapidly prototype complex 3D structures. Furthermore, with the variation of the grayscale while manufacturing the hydrogel, the deformation of the hydrogel structure can be freely tuned within a few seconds by losing and absorbing water through adjusting the intensity and the irradiation direction of the NIR light, showing a potential application in ultra-fast object grabbing and transportation. The present study provides a new method for designing ultrafast photothermal responsive hydrogel based microrobot working in water.

Two-photon polymerization (TPP) is a cutting-edge micro/nanoscale three-dimensional (3D) printing technology based on the principle of two-photon absorption. TPP surpasses the diffraction limit in achieving feature sizes and excels in fabricating intricate 3D micro/nanostructures with exceptional resolution. The concept of 4D entails the fabrication of structures utilizing smart materials capable of undergoing shape, property, or functional changes in response to external stimuli over time. The integration of TPP and 4D printing introduces the possibility of producing responsive structures with micro/nanoscale accuracy, thereby enhancing the capabilities and potential applications of both technologies. This paper comprehensively reviews TPP-based 4D printing technology and its diverse applications. First, the working principles of TPP and its recent advancements are introduced. Second, the optional 4D printing materials suitable for fabrication with TPP are discussed. Finally, this review paper highlights several noteworthy applications of TPP-based 4D printing, including domains such as biomedical microrobots, bioinspired microactuators, autonomous mobile microrobots, transformable devices and robots, as well as anti-counterfeiting microdevices. In conclusion, this paper provides valuable insights into the current status and future prospects of TPP-based 4D printing technology, thereby serving as a guide for researchers and practitioners. Provide a comprehensive overview of two-photon polymerization (TPP)-based 4D printing technology and its applications. Introduce the working principle of TPP and its recent development. Present optional 4D printing materials for TPP technology. Summarize notable applications of TPP-based 4D printing technology at micro/nano scales. Discuss the following challenges and offer valuable insights and prospects into the current state of TPP-based 4D printing technology.

For robot swarm applications, accurate positioning is one of the most important requirements for avoiding collisions and keeping formations and cooperation between individuals. However, in some worst cases, the GNSS (Global Navigation Satellite System) signals are weak due to the crowd being in a swarm or blocked by a forest, mountains, and high buildings in the environment. Thus, relative localization is an indispensable way to provide position information for the swarm. In this paper, we review the status and development of relative localization. It is first assessed that relative localization to obtain spatio-temporal relationships between individuals is necessary to achieve the stable operation of the group. After analyzing typical relative localization systems and algorithms from the perspective of functionality and practicality, this paper concludes that the UWB-based (ultra wideband) system is suitable for the relative localization of robots in large-scale applications. Finally, after analyzing the current challenges in the field of fully distributed localization for robotic swarms, a complete mechanism encompassing the relative localization process and the relationship between local and global localization that can be a possible direction for future research is proposed.

After decades of development, microrobots have exhibited great application potential in the biomedical field, such as minimally invasive surgery, drug delivery, and bio‐sensing. Compared with conventional medical robotic systems, microrobots may be capable of reaching more narrow and vulnerable regions in the human body with minimal damage. However, limited by the small scale of microrobots, microprocessors, power supplies, and sensors can hardly be integrated on‐board. Thus, new strategies for the actuation and feedback for microrobots need to be explored. Furthermore, the open‐loop control method accomplished by operators may lack accuracy, and long‐duration operation could bring a severe physical challenge in many applications. Consequently, the automatic control of microrobots with the aid of control theories is developed to improve the control efficiency and precision. To further promote the automation level of microrobots, machine learning algorithms are expected to provide a solution to let microrobots adapt to more dynamic environments and undertake more complex medical tasks. Herein, a systematic introduction of the manipulation of microrobots from open‐loop to closed‐loop control is given in this review. It is envisioned that microrobots will play an important role in future biomedical applications. Microrobots have shown great potential in the biomedical field. To promote the application of microrobots in various scenarios, precise control with high autonomy level is necessary. In this review, state‐of‐the‐art research about control and autonomy of microrobots is given to provide a comprehensive introduction of microrobots for readers, and current challenges are summarized for the guidance of future research.

Metal-organic frameworks (MOFs) hold significant potential as vehicles for drug delivery due to their expansive specific surface area, biocompatibility, and versatile attributes. Concurrently, magnetically actuated micro/nano-robots (MNRs) offer distinct advantages, such as untethered and precise manipulation. The fusion of these technologies presents a promising avenue for achieving non-invasive targeted drug delivery. Here, we report a MOF-based magnetic microrobot swarm (MMRS) for targeted therapy. Our approach overcomes limitations associated with a single MNR, including limited drug loading and the risk of loss during manipulation. We select Zeolitic Imidazolate Framework-8 (ZIF-8) as the drug vehicle for its superior loading potential and pH-sensitive decomposition. Our design incorporates magnetic responsive components into the one-pot synthesis of Fe@ZIF-8, enabling collective behaviors under actuation. Tuning the yaw angle of alternating magnetic fields and nanoparticles’ amount, the MMRSs with controllable size achieve instantaneous transformation among different configurations, including vortex-like swarms, chain-like swarms, and elliptical swarms, facilitating adaptation to environmental variations. Transported to the subcutaneous T24 tumor site, the MMRSs with encapsulated doxorubicin (DOX) automatically degrade and release the drug, leading to a dramatic reduction of the tumor in vivo. Our investigation signifies a significant advancement in the integration of biodegradable MOFs into microrobot swarms, ushering in new avenues for accurate and non-invasive targeted drug delivery.

This paper presents a new strategy for simultaneous control of multiple magnetic Micro Robots (MRs) improving stability and robustness with respect to external disturbances. Independent control of multiple MRs, can enhance efficiency and allows for performing more challenging applications. In this study, we present a system consisting of a Helmholtz coil and 2N Permanent Magnets (PMs), rotated by servomotors, to control several MRs. We have also improved the system’s stability by adding a larger MR (stabilizer MR). This MR can be moved all around the workspace and works as a moving internal magnetic field source. Thanks to this moveable magnetic field, other MRs are more stable against environmental disturbances. By simulating simultaneous and independent control of multiple MRs, we demonstrate the advantages of using the stabilizer MR (more than 20 percent reduction in tracking error and control effort). In addition, we evaluate experimentally our proposed method to independently control the position of three MRs using a stabilizer MR demonstrating the efficacy of the strategy.