Microrobot Research Articles

Pangolin-inspired untethered magnetic robot for on-demand biomedical heating applications

Untethered magnetic miniature soft robots capable of accessing hard-to-reach regions can enable safe, disruptive, and minimally invasive medical procedures. However, the soft body limits the integration of non-magnetic external stimuli sources on the robot, thereby restricting the functionalities of such robots. One such functionality is localised heat generation, which requires solid metallic materials for increased efficiency. Yet, using these materials compromises the compliance and safety of using soft robots. To overcome these competing requirements, we propose a pangolin-inspired bi-layered soft robot design. We show that the reported design achieves heating > 70 °C at large distances > 5 cm within a short period of time <30 s, allowing users to realise on-demand localised heating in tandem with shape-morphing capabilities. We demonstrate advanced robotic functionalities, such as selective cargo release, in situ demagnetisation, hyperthermia and mitigation of bleeding, on tissue phantoms and ex vivo tissues.

Magnetic Liquid Metal Droplet Robot with Multifunction and High Output Force in Milli-Newton.

Magnetically actuated miniature robots have immeasurable potential in lab-on-a-chip and biomedical due to their ability to navigate in constrained space. However, current soft robots made by elastomers have limited functionalities and are prevented from very narrow environments such as channel much smaller than their size because of their non- or limited deformability. In this study, a soft and multifunctional robot based on liquid metal (magnetic liquid-metal droplet robot [MLDR]) with high output force is reported. It is fabricated by engulfing iron particles into a Galinstan droplet. By changing the shape and motion of permanent magnets, the MLDR can be reshaped and moved. The MLDR can also be split in batches and merged efficiently. It shows good softness and flexibility when navigating freely in a narrow channel, and thus can pass through a confined space smaller than its size easily. Furthermore, the MLDR can also push and spread the accumulated liquid in a desired path, and manipulate the motions of small objects well. Benefiting from the solidification-like phenomenon, an MLDR can output milli-Newton-level force much higher than the output force of ferrofluid droplet robots in micro-Newton level. The demonstrated capabilities of the MLDR are promising for the applications in lab-on-a-chip or biomedical devices.

In situ sensing physiological properties of biological tissues using wireless miniature soft robots.

Implanted electronic sensors, compared with conventional medical imaging, allow monitoring of advanced physiological properties of soft biological tissues continuously, such as adhesion, pH, viscoelasticity, and biomarkers for disease diagnosis. However, they are typically invasive, requiring being deployed by surgery, and frequently cause inflammation. Here we propose a minimally invasive method of using wireless miniature soft robots to in situ sense the physiological properties of tissues. By controlling robot-tissue interaction using external magnetic fields, visualized by medical imaging, we can recover tissue properties precisely from the robot shape and magnetic fields. We demonstrate that the robot can traverse tissues with multimodal locomotion and sense the adhesion, pH, and viscoelasticity on porcine and mice gastrointestinal tissues ex vivo, tracked by x-ray or ultrasound imaging. With the unprecedented capability of sensing tissue physiological properties with minimal invasion and high resolution deep inside our body, this technology can potentially enable critical applications in both basic research and clinical practice.

Electrodeposited Superhydrophilic-Superhydrophobic Composites for Untethered Multi-Stimuli-Responsive Soft Millirobots.

To navigate in complex and unstructured real-world environments, soft miniature robots need to possess multiple functions, including autonomous environmental sensing, self-adaptation, and multimodal locomotion. However, to achieve multifunctionality, artificial soft robots should respond to multiple stimuli, which can be achieved by multimaterial integration using facile and flexible fabrication methods. Here, a multimaterial integration strategy for fabricating soft millirobots that uses electrodeposition to integrate two inherently non-adherable materials, superhydrophilic hydrogels and superhydrophobic elastomers, together via gel roots is proposed. This approach enables the authors to electrodeposit sodium alginate hydrogel onto a laser-induced graphene-coated elastomer, which can then be laser cut into various shapes to function as multi-stimuli-responsive soft robots (MSRs). Each MSR can respond to six different stimuli to autonomously transform their shapes, and mimic flowers, vines, mimosas, and flytraps. It is demonstrated that MSRs can climb slopes, switch locomotion modes, self-adapt between air-liquid environments, and transport cargo between different environments. This multimaterial integration strategy enables creating untethered soft millirobots that have multifunctionality, such as environmental sensing, self-propulsion, and self-adaptation, paving the way for their future operation in complex real-world environments.

Biodegradable Magnetic Hydrogel Robot with Multimodal Locomotion for Targeted Cargo Delivery.

Recent strides in the development of untethered miniature robots have shown the advantages of diverse actuation methods, flexible maneuverability, and precise locomotion control, which has made miniature robots attractive for biomedical applications such as drug delivery, minimally invasive surgery, and disease diagnosis. However, biocompatibility and environmental adaptability are among the challenges for further in vivo applications of miniature robots due to the sophisticated physiological environment. Herein, we propose a biodegradable magnetic hydrogel robot (BMHR) that possesses precise locomotion with four stable motion modes, namely tumbling mode, precession mode, spinning-XY mode, and spinning-Z mode. Using a homemade vision-guided magnetic driving system, the BMHR can achieve flexible conversion between the different motion modes to cope with changes in complex environments, and its superior ability to cross obstacles is demonstrated. In addition, the transformation mechanism between different motion modes is analyzed and simulated. Benefiting from the diverse motion modes, the proposed BMHR has promising applications in drug delivery, showing remarkable effectiveness in targeted cargo delivery. The BMHR's biocompatible property, multimodal locomotion, and functionality with drug-loaded particles can provide a new perspective to combine miniature robots with biomedical applications.

Cooperative behavior of miniature magnetic swimmers in uniform magnetic fields

Magnetically powered miniature robots have received increasing attention for decades owing to their convenient navigation ability, noninvasive remote actuation, and diverse potential applications. Although various individual motions of magnetic miniature robots have been explored, mimicking group cooperation and synchronized coordination of natural intelligence remain challenging. Here, we introduce diverse cooperative behaviors between two magnetic miniature swimmers in uniform magnetic fields by tuning and composing their magnetic moments. The ability of these magnetic miniature swimmers to form dynamic steady states offers considerable promise for creating groups of machines that can perform cooperative tasks.

Design and Implementation of a Miniature Jellyfish-Inspired Robot

With the development of the global marine industry, the demand to investigate underwater environments using robots is increasing. Inspired by the unique structure and excellent swimming ability of <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Aurelia aurita</i> , a miniature jellyfish-inspired robot is developed. The robot comprises a headshell, six tentacles, a primary drive component, two flywheel steering components, a lightweight foam block, a dsPIC control system, and an energy supply component. The tentacles are covered with a 0.1-mm-thick silicone membrane and modeled in the shape of an umbrella. The membrane is driven by a gear motor to mimic the contraction and expansion of the interior cavity of a jellyfish; it exhibits the swimming behavior via water jet propulsion. Three-dimensional swimming is achieved by the flywheel steering components following the conservation of angular momentum. A built-in LoRa communication module (433 MHz) enables a robust, real-time connection between the robot and a terrestrial console. The small-sized, lightweight jellyfish robot has a diameter of 110 mm and a height of 140 mm; it weighs 318 g and achieves autonomous swimming with low power consumption. The robot can be used for underwater signal relay, environmental monitoring, and geological investigations.

An On-Wall-Rotating Strategy for Effective Upstream Motion of Untethered Millirobot: Principle, Design, and Demonstration

Untethered miniature robots that can access narrow and harsh environments in the body show great potential for future biomedical applications. Despite the many types of millirobot that have been developed, swimming against the fast blood flow remains a big challenge due to lack of the ability to stay still and the large fluidic resistance from blood. This article proposes an on-wall-rotating strategy and a streamlined millirobot to achieve effective upstream motion in the lumen. First, the principle of on-wall-rotating strategy and the dynamic motion model of the millirobot is established. Then, a critical safety angle <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\theta _{s}$</tex-math></inline-formula> is theoretically and experimentally analyzed for the safe and stable control of the robot. After that, a series of experiments are conducted to verify the proposed driving strategy. The results suggest that the robot is able to move at a speed of 5 mm/s against flow velocity of 138 mm/s, which is comparable to the blood flow of 2700 mm <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$^{3}$</tex-math></inline-formula> /s and several times faster than other reported driving strategies. This work offers a new strategy for the untethered magnetic robot construction and control for blood vessels, which would promote the application of millirobot for biomedical engineering.

A Minimalist Self-Localization Approach for Swarm Robots Based on Active Beacon in Indoor Environments.

When performing indoor tasks, miniature swarm robots are suffered from their small size, poor on-board computing power, and electromagnetic shielding of buildings, which means that some traditional localization methods, such as global positioning system (GPS), simultaneous localization and mapping (SLAM), and ultra-wideband (UWB), cannot be employed. In this paper, a minimalist indoor self-localization approach for swarm robots is proposed based on active optical beacons. A robotic navigator is introduced into a swarm of robots to provide locally localization services by actively projecting a customized optical beacon on the indoor ceiling, which contains the origin and the reference direction of localization coordinates. The swarm robots observe the optical beacon on the ceiling via a bottom-up-view monocular camera, and extract the beacon information on-board to localize their positions and headings. The uniqueness of this strategy is that it uses the flat, smooth, and well-reflective ceiling in the indoor environment as a ubiquitous plane for displaying the optical beacon; meanwhile, the bottom-up view of swarm robots is not easily blocked. Real robotic experiments are conducted to validate and analyze the localization performance of the proposed minimalist self-localization approach. The results show that our approach is feasible and effective, and can meet the needs of swarm robots to coordinate their motion. Specifically, for the stationary robots, the average position error and heading error are 2.41 cm and 1.44°; when the robots are moving, the average position error and heading error are less than 2.40 cm and 2.66°.

Nanobots for Medicinal Applications

The applications of nanotechnology have increased exponentially in the field of medicinal chemistry with the implementations of nanorobotics. Nanobots provide one of the most promising areas of nanotechnology spreading its roots to applications in various fields including medical imaging, drug delivery and even in the development of Nanobots have the advantages of small size, low weight, large thrust-to-weight ratio, high flexibility, and high sensitivity. The applications of nanobots are varied and are being explored in various fields. The aim of this review is to offer an overview to the emerging field of nanorobotics within medicinal chemistry and their applications for diagnosis, treatment and prevention of various diseases. It provides a comprehensive overview of the development of nanobots. The key components of the robots and the types of nanobots are discussed separately. The review also focuses on the disadvantages and the challenges in the development of nanobots for their specific causes. And finally, the efforts and measures that can bring us steps closer to the dream of catching up with our fantasies of developing tiny robots that could roam about inside our bodies, delivering drugs with unprecedented precision, and hunting down and destroying infected cells and most importantly science fiction becoming scientific fact are discussed.

Novel Concentric Magnetic Continuum Robot with Multiple Stiffness Modes for Potential Delivery of Nanomedicine

The utilisation of miniature robots has become essential in the domain of minimally invasive surgery and long-distance delivery of nanomedicine. Among these, the miniature magnetic continuum robot (MCR) stands out because of its simple structure and dexterity, which allow it to penetrate small cavities, transport specialised tools such as a laser, and deliver medications to support surgical treatment. Nevertheless, because of their soft bodies with a single stiffness, conventional MCRs have limited controllability when navigating through intricate cavities. To address this limitation, we propose a novel concentric magnetic continuum robot (C-MCR) comprising a concentric magnetic catheter with a guidewire having varying stiffness. The C-MCR allows substantial curvature bending owing to its difference in stiffness, and its detachable nature allows it to have four working modes to adapt to specific application requirements with improved stiffness controllability. Experiments demonstrate the ability of the C-MCR to navigate complex pathways and deliver nanomedicines over long distances to specific areas via its internal channels using a large homemade eight-coil electromagnetic system. The C-MCR offers promising application prospects for the long-distance delivery of tailored nanomedicines because of its simple operation, reduced risks, and larger attainable workspace.

Water Skating Miniature Robot Propelled by Acoustic Bubbles.

This paper presents a miniature robot designed for monitoring its surroundings and exploring small and complex environments by skating on the surface of water. The robot is mainly made of extruded polystyrene insulation (XPS) and Teflon tubes and is propelled by acoustic bubble-induced microstreaming flows generated by gaseous bubbles trapped in the Teflon tubes. The robot's linear motion, velocity, and rotational motion are tested and measured at different frequencies and voltages. The results show that the propulsion velocity is proportional to the applied voltage but highly depends on the applied frequency. The maximum velocity occurs between the resonant frequencies for two bubbles trapped in Teflon tubes of different lengths. The robot's maneuvering capability is demonstrated by selective bubble excitation based on the concept of different resonant frequencies for bubbles of different volumes. The proposed water skating robot can perform linear propulsion, rotation, and 2D navigation on the water surface, making it suitable for exploring small and complex water environments.

3D Printing of Multilayer Magnetic Miniature Soft Robots with Programmable Magnetization

Magnetically driven miniature soft robots exhibit fast and dexterous responses to an applied external magnetic field. With remote manipulation, controlled navigation of robots can be realized within hard‐to‐access spaces for potential use in the human body. Existing magnetic miniature soft robots using digital light processing are fabricated from planar sheets, and thus have limited shape transformations and locomotive behaviors. Herein, a multilayer 3D printing method is reported for patterning magnetic nanoparticles in ultraviolet (UV)‐curable polymer matrix. Various multilayer 3D structures within 10 mm in overall size are fabricated with controlled volumes at different parts, which outperform 2D folded shapes in terms of robustness and kinematic flexibility. By programming heterogeneous magnetization within discrete multilayer robot segments, magnetic torque‐induced shape changes including gripping, rolling, swimming, and walking are induced by a global actuation field. Stacked design features with minimum dimension of 200 μm and encoded magnetization with resolution of 350 μm can be realized in the printing process. Meanwhile, enhanced deformation flexibility and formation of orientation‐anchoring mechanisms are created by integrating multiple materials with distinct mechanical and magnetic properties, respectively, which enables the creation of versatile 3D multi‐material actuators.

Cyborg Cells: Bacteria with synthetic skeletons could be used as tiny robots.

Cyborg Cells: Bacteria with synthetic skeletons could be used as tiny robots.

Development of an Antihydropressure Miniature Underwater Robot With Multilocomotion Mode Using Piezoelectric Pulsed-Jet Actuator

The high-pressure environment of deep sea challenges the miniaturization of underwater robots due to assembly of anti-hydropressure devices for protecting electromagnetic motor. Here, inspired by the motion principle of jellyfish, a novel piezoelectric pulsed-jet actuator (PJA) was proposed as power source. Six PJAs were arranged crosswise to form an anti-hydropressure miniature cross-shaped underwater robot (CSUR) with dimensions of &#x03A6;10.9 &#x00D7; 6.3 cm³. The numerical simulation method was adopted to analyze the propulsion mechanism, optimize the structure and find the optimal frequency. A robot prototype was fabricated, and its motion performances were tested. The CSUR achieved floating, sinking, hovering motions in the vertical direction and linear, rotary, turning motions in the horizontal direction. The maximum linear velocity reached up to 47.8 mm&#x002F;s (0.43 BL&#x002F;s). The robot could move in high-pressure environment of 10 MPa, and the average velocity deviations under different water pressures were less than 10&#x0025;. Besides, the CSUR could move along S-shaped path to navigate around obstacles. The proposed robot performed merits of miniature structure, good adaptability of high-pressure environment, high agility and maneuverability. It is potential for the CSUR to be applied in exploring, mapping and sampling in narrow areas of deep sea.

A small legged robot for inspection purposes

StreszczenieThe paper deals with mobile robots with special emphasis on walking robots. A review of applications of particular types of mobile robots in various applications has been carried out. The validity of the use of walking robots in inspection tasks has been analyzed. A list of commercially available solutions has been presented and their parameters compared. A concept of a miniature walking robot for inspection tasks requiring operation in a confined space has been proposed. The design of the prototype, the structural solutions used, the system diagram and the structure of the control algorithms are presented. Conclusions and observations on the design process are presented. A set of modifications and solutions enabling the application of the robot in real inspection conditions have been proposed. The validity of the presented concept has been analyzed.

Path Planning and Navigation of Miniature Serpentine Robot for Bronchoscopy Application.

The miniature serpentine robot can be applied to NOTES (Natural Orifice Transluminal Endoscopic Surgery). In this paper, a bronchoscopy application is addressed. This paper describes the basic mechanical design and control scheme of this miniature serpentine robotic bronchoscopy. In addition, off-line backward path planning and real-time and in situ forward navigation in this miniature serpentine robot are discussed. The proposed backward-path-planning algorithm utilizes the 3D model of a bronchial tree constructed from the synthetization of medical images such as images from CT (Computed Tomography), MRI (Magnetic Resonance Imaging), or X-ray, to define a series of nodes/events backward from the destination, for example, the lesion, to the original starting point, for example, the oral cavity. Accordingly, forward navigation is designed to make sure this series of nodes/events shall be passed/occur from the origin to the destination. This combination of backward-path planning and forward navigation does not require accurate positioning information of the tip of the miniature serpentine robot, which is where the CMOS bronchoscope is located. Collaboratively, a virtual force is introduced to maintain the tip of the miniature serpentine robot at the center of the bronchi. Results show that this method of path planning and navigation of the miniature serpentine robot for bronchoscopy applications works.

A Perspective on Miniature Soft Robotics: Actuation, Fabrication, Control, and Applications

Soft robotics enriches the robotic functionalities by engineering soft materials and electronics toward enhanced compliance, adaptivity, and friendly human machine. This decade has witnessed extraordinary progresses and benefits in scaling down soft robotics to small scale for a wide range of potential and promising applications, including medical and surgical soft robots, wearable and rehabilitation robots, and unconstructed environments exploration. This perspective highlights recent research efforts in miniature soft robotics in a brief and comprehensive way in terms of actuation, powering, designs, fabrication, control, and applications in four sections. Section 2 discusses the key aspects of materials selection and structural designs for small‐scale tethered and untethered actuation and powering, including fluidic actuation, stimuli‐responsive actuation, and soft living biohybrid materials, as well as structural forms from 1D to 3D. Section 3 discusses the advanced manufacturing techniques at small scales for fabricating miniature soft robots, including lithography, mechanical self‐assembly, additive manufacturing, tissue engineering, and other fabrication methods. Section 4 discusses the control systems used in miniature robots, including off‐board/onboard controls and artificial intelligence‐based controls. Section 5 discusses their potential broad applications in healthcare, small‐scale objects manipulating and processing, and environmental monitoring. Finally, outlooks on the challenges and opportunities are discussed.

Amphibious Miniature Soft Jumping Robot with On-Demand In-Flight Maneuver.

In nature, some semiaquatic arthropods evolve biomechanics for jumping on the water surface with the controlled burst of kinetic energy. Emulating these creatures, miniature jumping robots deployable on the water surface have been developed, but few of them achieve the controllability comparable to biological systems. The limited controllability and agility of miniature robots constrain their applications, especially in the biomedical field where dexterous and precise manipulation is required. Herein, an insect-scale magnetoelastic robot with improved controllability is designed. The robot can adaptively regulate its energy output to generate controllable jumping motion by tuning magnetic and elastic strain energy. Dynamic and kinematic models are developed to predict the jumping trajectories of the robot. On-demand actuation can thus be applied to precisely control the pose and motion of the robot during the flight phase. The robot is also capable of making adaptive amphibious locomotion and performing various tasks with integrated functional modules.

Horizontal and Vertical Coalescent Microrobotic Collectives Using Ferrofluid Droplets.

Many artificial miniature robotic collectives have been developed to overcome the inherent limitations of inadequate individual capabilities. However, the basic building blocks of the reported collectives are mainly in the solid state, where the morphological boundaries of internal individuals are clear and cannot genuinely merge. Miniature robotic collectives based on liquid units still need to be explored; such on-demand mergeable swarm systems are advantageous for adapting to the changing external environment. Here, a strategy to achieve a coalescent collective system wepresented that exploits the ferrofluid droplets' splitting and coalescence properties to trigger the formation of horizontal multimodal and vertical gravity-resistant collectives and unveil pattern-enabled robotic functionalities. When subjected to a time-varying magnetic field, the droplet swarm exhibits a variety of morphologies ranging from horizontal collectives, including vortex-like, chain-like, and crystal-like patterns to vertical layer-upon-layer patterns. Using experiments and simulations, the formation and transformation of different morphological collectives are shown and their robust environmental adaptability are demonstrated. Potential applications of the multimodal droplet collectives are presented, including exploring an unknown environment, targeted object delivery, and fluid flow filtration in a lab-on-a-chip. This work may facilitate the design of microrobotic swarm systems and expand the range of materials for miniature robots.