Microrobot Research Articles

Dual-Responsive Nanorobot-Based Marsupial Robotic System for Intracranial Cross-Scale Targeting Drug Delivery.

Nanorobots capable of active movement are an exciting technology for targeted therapeutic intervention. However, the extensive motion range and hindrance of the blood-brain barrier impeded their clinical translation in glioblastoma therapy. Here, a marsupial robotic system constructed by integrating chemical/magnetic hybrid nanorobots (child robots) with a miniature magnetic continuum robot (mother robot) for intracranial cross-scale targeting drug delivery is reported. For primary targeting on macroscale, the continuum robot enters the cranial cavity through a minimally invasive channel (e.g., Ommaya device) in the skull and transports the nanorobots to pathogenic regions. Upon circumventing the blood-brain barrier, the released nanorobots perform secondary targeting on microscale to further enhance the spatial resolution of drug delivery. In vitro experiments against primary glioblastoma cells derived from different patients are conducted for personalized treatment guidance. The operation feasibility within organisms is shown in ex vivo swine brain experiments. The biosafety of the treatment system is suggested in in vivo experiments. Owing to the hierarchical targeting method, the targeting rate, targeting accuracy, and treatment efficacy have improved greatly. The marsupial robotic system offers a novel intracranial local therapeutic strategy and constitutes a key milestone in the development of glioblastoma treatment platforms.

3D Printable Micro/Macro Dual Driving Multipede Millirobot and Its Characterization for Multi-Locomotory Modes

Aiming at both high motion precision and high velocity is arduous in the development of miniature robots because of contradictory aspects between the precision and the velocity. In this article, we developed a simple three-dimensional printable micro/macro dual driving multipede millirobot to successfully satisfy both high precision and high velocity, by employing bio-inspired titled legs through the concept of anisotropic friction. Four locomotory modes (stick, stick-slip, pure-slip, and jumping) of the millirobot were carefully examined and effectively manipulated to switch micro and macro motions for high precision and high velocity, respectively. We investigated the effects of external conditions (mobile surface roughness and excitation waveform) and internal conditions (geometric parameters of driving legs) on the locomotory modes. The millirobot achieved a step resolution of 2 <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">μ</i> m in the micromotion and maximum mobile velocity of 800 mm/s in the macromotion. In addition, our millirobot can perform bi-directional motion (forward and backward) with quick return characteristics.

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.

Design of Flexible Bearing with Larger Inner Diameter

The flexible bearing is the kernel component of the cam wave generator. In precision transmission applications such as miniature robot joints, flexible bearings are required to have a smaller mass, lower moment of inertia, and larger inner diameter. Based on the theory of conventional rolling bearing, and by considering the working characteristics of flexible bearing for harmonic drive, this paper studies the influence law of structural parameters on the fatigue life of the flexible bearing; achieves a technical approach for expanding the bore size of the standard flexible bearing; and deduces the theoretical formulas applicable to the design of the flexible bearing. The new formula is utilized to improve the design parameters of the flexible bearing. The novel design with smaller diameter and more numbers of rolling elements can meet the above performance requirements compared to the conventional flexible bearing. Under the same conditions of radial deformation and materials used, finite element analysis results show that the maximum equivalent stress in the improved flexible bearing is smaller and that the novel design can meet the strength requirements of the harmonic drive.

Developments and Challenges of Miniature Piezoelectric Robots: A Review.

Miniature robots have been widely studied and applied in the fields of search and rescue, reconnaissance, micromanipulation, and even the interior of the human body benefiting from their highlight features of small size, light weight, and agile movement. With the development of new smart materials, many functional actuating elements have been proposed to construct miniature robots. Compared with other actuating elements, piezoelectric actuating elements have the advantages of compact structure, high power density, fast response, high resolution, and no electromagnetic interference, which make them greatly suitable for actuating miniature robots, and capture the attentions and favor of numerous scholars. In this paper, a comprehensive review of recent developments in miniature piezoelectric robots (MPRs) is provided. The MPRs are classified and summarized in detail from three aspects of operating environment, structure of piezoelectric actuating element, and working principle. In addition, new manufacturing methods and piezoelectric materials in MPRs, as well as the application situations, are sorted out and outlined. Finally, the challenges and future trends of MPRs are evaluated and discussed.It ishoped that this review will be of great assistance for determining appropriate designs and guiding future developments of MPRs, and provide a destination board to the researchers interested in MPRs.

Wireless Electrochemical Gel Actuators.

Soft actuators generate motion in response to external stimuli and are indispensable for soft robots, particularly future miniature robots with complex structure and motion. Similarly to conventional hard robots, electricity is suitable for the stimulation. However, previous electrochemical soft actuators require a tethered connection to a power supply, limiting their size, structure, and motion. Here, wireless electrochemical soft actuators composed of hydrogels and driven by bipolar electrochemistry are reported. Viologen, which dimerizes by one-electron reduction and dissociates by one-electron oxidation, is incorporated in the side chains of the gel networks and works as a reversible cross-link. Wireless and reversible electrochemical actuation of the hydrogels, i.e., muscle-like shrinking and swelling, is demonstrated at microscopic and even macroscopic scales.

Design of a Miniature Observation Robot for Light Emitting Diode Irradiation and Indocyanine Green Fluorescence-emission Guided Lymph Node Monitoring in Operating Rooms.

Typical surgical microscopes used for fluorescence-based lymph node detection experience limitations such as weight and restricted adjustability of the integrated light emitting diode (LED) and camera. This restricts the capture of detailed images of specific regions within the lesion. This study proposes a miniature observation robot design that offers adjustable working distance (WD) and rotational radius, along with zoom-in/zoom-out functionality. A five-degree-of-freedom manipulator was designed, with the end effector incorporating an LED and concave lens to widen the beam width for comprehensive lesion illumination. Additionally, a long-pass filter was integrated into the camera system to enhance image resolution. Experiments were conducted using a fluorescence-expressing phantom to evaluate the performance of the robot. Results demonstrated a captured image resolution of 9600 × 3240 pixels and a zoom-in/zoom-out capacity of up to 3.68 times. The proposed robot design is cost-effective and highly adjustable, enabling suitability for rapid and accurate detection of fresh lymph nodes during surgeries. The robot's capability to detect small lesions (<1cm), as validated by phantom tests, holds promise for the detection of minute lymph nodes.

Reactive wetting enabled anchoring of non-wettable iron oxide in liquid metal for miniature soft robot

Magnetic liquid metal (LM) soft robots attract considerable attentions because of distinctive immiscibility, deformability and maneuverability. However, conventional LM composites relying on alloying between LM and metallic magnetic powders suffer from diminished magnetism over time and potential safety risk upon leakage of metallic components. Herein, we report a strategy to composite inert and biocompatible iron oxide (Fe3O4) magnetic nanoparticles into eutectic gallium indium LM via reactive wetting mechanism. To address the intrinsic interfacial non-wettability between Fe3O4 and LM, a silver intermediate layer was introduced to fuse with indium component into AgxIny intermetallic compounds, facilitating the anchoring of Fe3O4 nanoparticles inside LM with improved magnetic stability. Subsequently, a miniature soft robot was constructed to perform various controllable deformation and locomotion behaviors under actuation of external magnetic field. Finally, practical feasibility of applying LM soft robot in an ex vivo porcine stomach was validated under in-situ monitoring by endoscope and X-ray imaging.

Using Footpad Sculpturing to Enhance the Maneuverability and Speed of a Robotic Marangoni Surfer.

From insects to arachnids to bacteria, the surfaces of lakes and ponds are teaming with life. Many modes of locomotion are employed by these organisms to navigate along the air-water interface, including the use of lipid-laden excretions that can locally change the surface tension of the water and induce a Marangoni flow. In this paper, we improved the speed and maneuverability of a miniature remote-controlled robot that mimics insect locomotion using an onboard tank of isopropyl alcohol and a series of servomotors to control both the rate and location of alcohol release to both propel and steer the robot across the water. Here, we studied the effect of a series of design changes to the foam rubber footpads, which float the robot and are integral in efficiently converting the alcohol-induced surface tension gradients into propulsive forces and effective maneuvering. Two designs were studied: a two-footpad design and a single-footpad design. In the case of two footpads, the gap between the two footpads was varied to investigate its impact on straight-line speed, propulsion efficiency, and maneuverability. An optimal design was found with a small but finite gap between the two pads of 7.5 mm. In the second design, a single footpad without a central gap was studied. This footpad had a rectangular cut-out in the rear to capture the alcohol. Footpads with wider and shallower cut-outs were found to optimize efficiency. This observation was reinforced by the predictions of a simple theoretical mechanical model. Overall, the optimized single-footpad robot outperformed the two-footpad robot, producing a 30% improvement in speed and a 400% improvement in maneuverability.

A hierarchical model for external electrical control of an insect, accounting for inter-individual variation of muscle force properties.

Cyborg control of insect movement is promising for developing miniature, high-mobility, and efficient biohybrid robots. However, considering the inter-individual variation of the insect neuromuscular apparatus and its neural control is challenging. We propose a hierarchical model including inter-individual variation of muscle properties of three leg muscles involved in propulsion (retractor coxae), joint stiffness (pro- and retractor coxae), and stance-swing transition (protractor coxae and levator trochanteris) in the stick insect Carausius morosus. To estimate mechanical effects induced by external muscle stimulation, the model is based on the systematic evaluation of joint torques as functions of electrical stimulation parameters. A nearly linear relationship between the stimulus burst duration and generated torque was observed. This stimulus-torque characteristic holds for burst durations of up to 500ms, corresponding to the stance and swing phase durations of medium to fast walking stick insects. Hierarchical Bayesian modeling revealed that linearity of the stimulus-torque characteristic was invariant, with individually varying slopes. Individual prediction of joint torques provides significant benefits for precise cyborg control.

Miniature soft jumping robots made by additive manufacturing

Abstract Fleets of insect-scale robots could navigate space-constrained environments for future applications in agriculture and maintenance. Long distance jumping expands the mobility of small robots. However, the performance of miniature jumpers is hindered by small-scale manufacturing processes and the limited library of design rules, materials, and actuators available at that scale. The intricate components in these robots are produced by manual assembly of miniature components, which imposes design constraints and causes mass inefficiency, reducing the overall system performance. Here, we combine bioinspired kinematic design, coiled artificial muscle actuators, and projection additive manufacturing (AM) to produce a monolithic elastomeric robot design. The fully elastomeric design, inspired by the kinematics of the locust jumping mechanism, can store elastic energy throughout the robot body before releasing it in the form of jumping kinetic energy, thus offering high energy storage density, miniaturization, and lightweight. Enabled by high-speed, production-grade AM, we designed and tested a fleet of 108 robot designs. The smallest tested robot has a length of 7.5 mm, a mass of 0.216 g, and jumps 60 times its body size in horizontal distance. A reduced-order model is developed to predict the compliant robot jumping distance, which agrees well with the experimental results. The jumping is driven by onboard coiled artificial muscles connected to a latch-triggering mechanism. Moreover, the robot can jump while carrying an integrated control system and power source to enable self-triggered jumping. A proof-of-concept motor-driven launch base is used to store large elastic energy in the robot. Overall, the combination of elastomeric AM, coiled artificial muscles, and an integrated triggering mechanism enables the production of fleets of high-performing miniature jumping robots.

Wireless Millimeter-Size Soft Climbing Robots with Omnidirectional Steerability on Tissue Surfaces.

Wirelessly actuated miniature soft robots actuated by magnetic fields that can overcome gravity by climbing soft and wet tissues are promising for accessing challenging enclosed and confined spaces with minimal invasion for targeted medical operation. However, existing designs lack the directional steerability to traverse complex terrains and perform agile medical operations. Here we propose a rod-shaped millimeter-size climbing robot that can be omnidirectionally steered with a steering angle up to 360 degrees during climbing beyond existing soft miniature robots. The design innovation includes the rod-shaped robot body, its special magnetization profile, and the spherical robot footpads, allowing directional bending of the body under external magnetic fields and out-of-plane motion of the body for delivery of medical patches. With further integrated bio-adhesives and microstructures on the footpads, we experimentally demonstrated inverted climbing of the robot on porcine gastrointestinal (GI) tract tissues and deployment of a medical patch for targeted drug delivery.

A programmable ferrofluidic droplet robot.

Soft miniature robots have wide potential applications in lab-on-a-chip and biomedical sciences due to their deformability, safety, and remarkable controllability. However, current ferrofluidic droplet robots have some problems, such as easy broken, limited motion range and high energy consumption. Therefore, the objective of this study is to propose a programmable ferrofluidic flexible droplet robot (PFDR) with control strategies for elongation, splitting and merging behaviors by designing an actuation system consisting of a row of electromagnets and a robotic arm or a coordinate robot. The PFDR can not only deform actively to prevent itself from breaking, but also deform passively to fit the profile of channels or tubes to move efficiently. The actuation system can make PFDR have larger motion range as well as lower energy consumption. The design concept and the operating principle of PFDR are presented. The magnetic actuation system is developed. The lag of PFDR is analyzed in theoretical and experimental ways. The splitting and merging behaviors are investigated and other functionalities are studied as well.

Design of CLARI: A Miniature Modular Origami Passive Shape‐Morphing Robot

Miniature robots provide unprecedented access to confined environments and show potential for applications such as search‐and‐rescue and high‐value asset inspection. The capability of body deformation further enhances the reachability of these small robots in cluttered terrains similar to those of insects and soft arthropods. Motivated by this concept, compliant legged articulated robotic insect (CLARI), an insect‐scale 2.59 g quadrupedal robot capable of body deformation, is presented. The robot, currently, with tethered electrical connections for power and control is manufactured using laminate fabrication and assembled using origami pop‐up techniques. To enable locomotion in multiple shape configurations, a novel body architecture comprising modular, actuated leg mechanisms, is designed. CLARI has eight independently actuated degrees of freedom driven by custom piezoelectric actuators, making it mechanically dextrous. Herein, open‐loop robot locomotion at multiple stride frequencies (1–10 Hz) is characterized using multiple gaits (trot, walk, etc.) in three different fixed body shapes (long, symmetric, wide) and the robot's capabilities are illustrated. Finally, preliminary results of CLARI locomoting with a compliant body in open terrain and through a laterally constrained gap, a novel capability for legged robots, is demonstrated. These results represent the first step toward achieving effective cluttered terrain navigation with adaptable compliant robots in real‐world environments.

Hydrogel muscles powering reconfigurable micro-metastructures with wide-spectrum programmability

Stimuli-responsive geometric transformations endow metamaterials with dynamic properties and functionalities. However, using existing transformation mechanisms to program a single geometry to transform into diverse final configurations remains challenging, imposing crucial design restrictions on achieving versatile functionalities. Here, we present a programmable strategy for wide-spectrum reconfigurable micro-metastructures using linearly responsive transparent hydrogels as artificial muscles. Actuated by the hydrogel, the transformation of micro-metastructures arises from the collaborative buckling of their building blocks. Rationally designing the three-dimensional printing parameters and geometry features of the metastructures enables their locally isotropic or anisotropic deformation, allowing controllable wide-spectrum pattern transformation with programmable chirality and optical anisotropy. This reconfiguration mechanism can be applied to various materials with a wide range of mechanical properties. Our strategy enables a thermally reconfigurable printed metalattice with pixel-by-pixel mapping of different printing powers and angles for displaying or hiding complex information, providing opportunities for encryption, miniature robotics, photonics and phononics applications.

Biomolecular Motor-Based Swarm Robot: An Innovation in Molecular Delivery

Biomolecular motor-based micro-sized robots have recently created an innovation in the field of science and technology as molecular transporters. Groups of these tiny robots can work substantially better than individual ones in terms of the transported distance and number or size of cargo. Site-specific molecular delivery, the main feature of these robots, has helped to improve the workability of robots in a more controllable manner.

Image-Integrated Magnetic Actuation Systems for Localization and Remote Actuation of Medical Miniature Robots: A Survey

Image-Integrated Magnetic Actuation Systems for Localization and Remote Actuation of Medical Miniature Robots: A Survey

Accuracy of on-site teleoperated milling with haptic assistance

PurposeIn bone surgery specialties, like orthopedics, neurosurgery, and oral and maxillofacial surgery patient safety and treatment success depends on the accurate implementation of computer-based surgical plans. Unintentional plan deviations can result in long-term functional damage to the patient. With on-site teleoperation, the surgeon operates a slave robot with a physically-decoupled master device, while being directly present at the operation site. This allows the surgeon to perform surgical tasks with robotic accuracy, while always remaining in the control loop.MethodsIn this study the master- and slave-side accuracy of an on-site teleoperated miniature cooperative robot (minaroHD) is evaluated. Master-side accuracy is investigated in a user study regarding scale factor, target feed rate, movement direction and haptic guidance stiffness. Scale factors are chosen to correspond to primarily finger, hand, and arm movements. Slave-side accuracy is investigated in autonomous milling trials regarding stepover, feed rate, movement direction, and material density.ResultsMaster-side user input errors increase with increasing target feed rate and scale factor, and decrease with increasing haptic guidance stiffness. Resulting slave-side errors decrease with increasing scale factor and are < 0.07 mm for optimal guidance parameters. Slave-side robot position errors correlate with the feed rate but show little correlation with stepover distance. For optimal milling parameters, the 95th percentile of tracked slave-side position error is 0.086 mm with a maximal error of 0.16 mm.ConclusionFor optimal guidance and milling parameters, the combined error of 0.23 mm is in the range of the dura mater thickness (< 0.27 mm) or mandibular canal wall (~ 0.85 mm). This corresponds to safety margins in high-demand surgical procedures like craniotomies, laminectomies, or decortication of the jaw. However, for further clinical translation, the performance and usability of on-site teleoperated milling must be further evaluated for real-life clinical application examples with consideration of all error sources in a computer-assisted surgery workflow.

VERTICAL MOTION OF MINIATURE WALKING ROBOTS. STATE OF THE PROBLEM REVIEW

The article reviews the state of the art of developing miniature walking robots for vertical movement due to friction forces between limbs and surface. In particular, special attention is paid to miniature walking robots - hexapods, as they have good stability and cross-country ability compared to other types of robots, both wheeled and tracked. Unlike other types of robots, hexapods can be fully autonomous. This makes them a potentially versatile tool for solving a variety of tasks in different areas, such as: 1) rescue operations - hexapods can penetrate destroyed buildings to assess the condition under the rubble, explore underwater spaces, and generally move in places where there is not enough space for movement and complex maneuvers; 2) military use - hexapods can clear mines, be used for reconnaissance or surveying, while saving lives due to the possibility of complete autonomy; 3) industrial applications - due to their maneuverability and cross-country ability, hexapod robots can become indispensable in quarries and construction sites where there are slopes, mountainous terrain, and generally where wheeled or tracked robots cannot easily move; 4) speleology - search and exploration of minerals inside caves, mines, etc; 5) accident response, in particular, in the nuclear power industry.&#x0D; Despite the long history of development and significant progress in this area, thanks to which many design solutions and modernizations are already known, the problem of vertical movement of small hexapod robots due to friction forces still remains unsolved.&#x0D; Existing developments are usually aimed at moving on surfaces by imitating the limbs of biological creatures (insects, animals, etc.), which allows robots to climb upwards thanks to an adhesive substance, grip the surface with mechanical claws, etc. Magnet and suction cup designs have also been known for a long time, but this solution requires a very powerful power source and is not universal.&#x0D; Therefore, one of the most promising areas of research is the vertical movement of hexapod robots due to friction forces between the limbs and the surface, since the robot remains autonomous and does not require special equipment and additional communication with a power source (compressor, etc.), and, more importantly, is able to move both on horizontal and vertical surfaces.&#x0D; At the moment, there are several examples of successful use of hexapods for vertical movement, but the review of works has shown that the problem of vertical movement of miniature hexapod robots remains relevant and requires further research and development. Existing achievements in this area give us hope that in the future we will demonstrate effective solutions to this problem and the widespread use of hexapods in various industries and science.

Tumbler‐Inspired Microneedle Containing Robots: Achieving Rapid Self‐Orientation and Peristalsis‐Resistant Adhesion for Colonic Administration

AbstractMicroneedle containing miniature robots offer a promising route for gastrointestinal administration since their capability of transmucosal delivery and controllable drug release. However, many challenges still lie ahead such as the intricate control modes, destitute systematic theory of the locomotion and adhesion behaviors, failure due to peristalsis and fluid flow, and risk of ileus. Herein, an untethered microneedle containing robots is designed for specific colonic administration, which can dispense with control systems, achieve fast self‐orientation and adhesion onto the mucosa (&lt;0.6 s), against physiology of peristalsis, and show low risks of obstruction. Further, the detachable layer between the microneedle and the robots can degrade under a time of 6 min, which ensures safely discharge under a small, excreted force of 20 mN induced by fluid flow. Through the optimism of microneedles, different drug release times can be achieved including 14 min, 2 days, 4 days, and 30 days, respectively. The in vivo experiments also demonstrate the effectiveness and feasibility of the robots. These robots can serve as a versatile platform to treat diseases such as chronic inflammation and cancer of the colon to minimize invasive surgical intervention and patient suffering.