Helical Robot Research Articles

Learning automatic navigation control skills for miniature helical robots from human demonstrations

Magnetic micro-robotic technology holds immense potential for revolutionizing minimally invasive procedures, particularly in the realm of interventional medicine. The ability to effectively and precisely control micro-scale, magnetically actuated robots in real-world scenarios is important. Mastering this capability promises to elevate the precision and efficacy of medical interventions, thereby enhancing patient outcomes. Numerous methods were proposed in previous work and achieved significant progress. However, these efforts primarily focused on model-based strategies and control improvements, with little attention given to the manipulation of the surgeon. This paper presents an exploration of an imitation learning approach, leveraging extensive manual operation experiments, to replicate the task of robotic navigation in simulated vascular environments. The control strategies are directly acquired from experimental observations and encapsulated within a high-dimensional neural network, specifically a tailored variant of the Residual Network (ResNet). The robustness and effectiveness of our proposed methodology are validated through comprehensive experimentation. In automatic navigation trials, the average error spanned from 2.29 mm to 3.32 mm, leading to a mean trajectory deviation of approximately 2.92 mm. The average error rate is 31% lower than that observed in traditional model-based Proportional Integral Derivative (PID) controller (approximately 3.81 mm). In addition, the maximum error (4.87 mm) is 83% of that of the traditional method (5.85 mm). Our findings emphasize the viability and benefits of learning-based techniques in micro-robot control, paving the way for innovative control strategies in interventional surgeries applications.

Optomagnetic Coordination Helical Robot with Shape Transformation and Multimodal Motion Capabilities.

Soft robots with magnetic responsiveness exhibit diverse motion modes and programmable shape transformations. While the fixed magnetization configuration facilitates coupling control of robot posture and motion, it limits individual posture control to some extent. This poses a challenge in independently controlling the robot's transformation and motion, restricting its versatile applications. This research introduces a multifunctional helical robot responsive to both light and magnetism, segregating posture control from movements. Light fields assist in robot shaping, achieving a 78% maximum diameter shift. Magnetic fields guide helical robots in multimodal motions, encompassing rotation, flipping, rolling, and spinning-induced propulsion. By controlling multimodal locomotion and shape transformation on demand, helical robots gain enhanced flexibility. This innovation allows them to tightly grip and wirelessly transport designated payloads, showcasing potential applications in drug delivery, soft grippers, and chemical reaction platforms. The unique combination of structural design and control methods holds promise for intelligent robots in the future.

Development and verification of a micro magnetically guided helical robot with active locomotion and steering capabilities for guidewires

As a fundamental instrument in vascular interventional surgery, guidewires inherently face limitations when navigating through complex curved blood vessel bifurcations due to their deflection and the constraints of external pushing and twisting operations. To address this issue, this study proposes a micro magnetically guided helical robot comprising a cylindrical permanent magnet, a helical casing, a soft structure, and an interventional guidewire. The soft structure is employed to enhance the steering capability of the guidewire by reducing resistance caused by its deflection during steering. Furthermore, an additional helical casing with a permanent magnet is added at the head of the guidewire to enable active movement. The effectiveness of the experimental platform was validated using a T-shaped magnet, with a maximum error of less than 3°. A prototype of the magnetically guided robot was fabricated, and basic experiments were conducted in various liquid environments. Steering tests were performed in a 2D plane, demonstrating that with the assistance of the soft structure, the robot achieved an additional 32° of bending beyond the maximum initial bending degree, resulting in a maximum bending of 90°. Moreover, the active locomotion and steering capabilities of the magnetically guided robot were validated in various in vitro simulated blood vessels. The study effectively demonstrated the successful execution of selective steering motion, continuous steering motion, and large-angle bending motion by the robot, utilizing a variety of glycerin-filled tubing configurations, such as Y-shaped, Ω-shaped, and U-shaped tubing, as representative models to simulate iliac artery, aortic arch, and distal coronary arteries encountered in the femoral artery intervention pathway. These experiments confirmed the effectiveness of the proposed robot in enabling the guidewire to navigate through curved blood vessels.

Enhanced Tunneling Performance of Magnetic Helical Robots Utilizing Pecking Motion Generated by Alternating Rotating Magnetic Field

Magnetic helical robots (MHRs) actuated by an external magnetic field have been regarded as a possible application to treat occlusive vascular disease. We propose a pecking motion of an MHR to effectively tunnel an occlusive vascular lesion. The pecking motion is composed of a rotational driving motion and a linear impulsive motion of the MHR actuated by alternating rotating magnetic field (ARMF). The minimum magnetic flux density to synchronize the MHR to ARMF was mathematically determined from the equation of motion of the MHR and was experimentally verified. Finally, enhanced tunneling performance of the MHR with the pecking motion was verified by <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">in vitro</i> tunneling experiments with a pseudo-thrombus.

A biomimetic helical robot actuated by rotating magnetic field for targeted navigation and in situ prodrug activation to treat intestinal diseases

A biomimetic helical robot actuated by rotating magnetic field for targeted navigation and in situ prodrug activation to treat intestinal diseases

Resonance control method to suppress the self and mutual inductances of a 3-phase magnetic navigation system for fast drilling motion of micro helical robots

We developed a resonance control method to generate a high-speed rotating magnetic field in a three-phase magnetic navigation system composed of three electromagnets. The proposed resonance control method calculates the amplitudes and phases of voltages, while the capacitances suppressing the self and mutual inductances of the electromagnets to keep the currents and the magnitude of the rotating magnetic field constant, even if the frequency of the rotating magnetic field increases. Finally, we prototyped the three-phase magnetic navigation system and the variable capacitor module to validate the effectiveness of the proposed resonance control method experimentally.

A 5-D Large-Workspace Magnetic Localization and Actuation System Based on an Eye-in-Hand Magnetic Sensor Array and Mobile Coils

Simultaneous magnetic localization and actuation in a human-scale workspace are challenging but essential for medical applications such as whole gastrointestinal (GI) tract monitoring and blood clot clearance in the leg. In this article, we propose a 5-D magnetic localization and actuation system that can track and actuate magnetic robots in a cylindrical workspace with a diameter of 500 mm. Based on the eye-in-hand configuration of the sensor array and the flexibility of the mobile electromagnetic manipulation system (mEMS), we realize a high localization accuracy in a large workspace with only 25 sensors. Moreover, we design an accurate magnetic field modeling method that can attenuate the electromagnets’ hysteresis and provide a precise actuation field estimation. Taking advantage of the mobile sensor array, we developed a signal-quality-based tracking strategy (STS) that could improve the localization performance by adjusting the movement of the sensor array. The effectiveness and advantages of the proposed methods are verified by simulations and experiments. Results show that the STS could decrease 25% position root-mean-square error (RMSE). The resulting position RMSE and orientation RMSE are 2.02 mm and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${\mathrm {8.24}}^{\circ} $ </tex-math></inline-formula> , respectively. We experimentally prove the viability of the proposed strategy by propelling a magnetic helical robot through a 400-mm long 3-D twisted silicone phantom.

Electrical Optimization Method Based on a Novel Arrangement of the Magnetic Navigation System with Gradient and Uniform Saddle Coils.

The magnetic navigation system (MNS) with gradient and uniform saddle coils is an effective system for manipulating various medical magnetic robots because of its compact structure and the uniformity of its magnetic field and field gradient. Since each coil of the MNS was geometrically optimized to generate strong uniform magnetic field or field gradient, it is considered that no special optimization is required for the MNS. However, its electrical characteristics can be still optimized to utilize the maximum power of a power supply unit with improved operating time and a stronger time-varying magnetic field. Furthermore, the conventional arrangement of the coils limits the maximum three-dimensional (3D) rotating magnetic field. In this paper, we propose an electrical optimization method based on a novel arrangement of the MNS. We introduce the objective functions, constraints, and design variables of the MNS considering electrical characteristics such as resistance, current density, and inductance. Then, we design an MNS using an optimization algorithm and compare it with the conventional MNS; the proposed MNS generates a magnetic field or field gradient 22% stronger on average than that of the conventional MNS with a sevenfold longer operating time limit, and the maximum three-dimensional rotating magnetic field is improved by 42%. We also demonstrate that the unclogging performance of the helical robot improves by 54% with the constructed MNS.

Understanding Robustness of Magnetically Driven Helical Propulsion in Viscous Fluids Using Sensitivity Analysis

AbstractMagnetically‐actuated helical microrobots can propel themselves in fluids and tissues‐like mediums with a wide range of Reynolds numbers (Re). The properties of physiological fluids and input parameters vary in time and space and have a direct influence on their locomotion along prescribed paths. Therefore, understanding the response of microrobots to variations in rheological properties and input parameters become increasingly important to translate them into in vivo applications. Here, a physical framework is presented to understand and predict key parameters whose uncertainty affect certain state variables most. A six‐degree‐of‐freedom magneto‐hydrodynamic model is developed based on the resistive force theory (RFT) to predict the response of robots swimming through different fluids and examine their response during transitions into Newtonian–viscoelastic interfaces. Performance of the robot, while swimming in a fluid with a fixed viscosity, is quantified using sensitivity analysis based on the magneto‐hydrodynamic model. The numerical results show how abrupt changes in viscosity can affect their ability to rotate with the rotating field in synchrony. The sensitivity analysis shows that the states of the robot are mostly sensitive to variations in the actuation frequency. Open‐loop experiments are performed using a permanent‐magnet robotic system comprising a robotic arm and a rotating permanent magnet to actuate and control a helical robot at the Newtonian–Viscoelastic interface and validate the theoretical predictions of the RFT‐based sensitivity analysis.

Real-Time Ultrasound Doppler Tracking and Autonomous Navigation of a Miniature Helical Robot for Accelerating Thrombolysis in Dynamic Blood Flow.

Untethered small-scale robots offer great promise for medical applications in complex biological environments. However, challenges remain in the control and medical imaging of a robot for targeted delivery inside a living body, especially in flowing conditions (e.g., blood vessels). In this work, we report a strategy to autonomously navigate a miniature helical robot in dynamic blood flow under ultrasound Doppler imaging guidance. A magnetic torque and force-hybrid control approach is implemented, enabling the actuation of a millimeter-scale helical robot against blood flow under a rotating magnetic field with a controllable field gradient. Experimental results demonstrate that the robot (length 7.30 mm; diameter 2.15 mm) exhibits controlled navigation in vascular environments, including upstream and downstream navigation in flowing and pulsatile flowing blood with flow rates up to 24 mL/min (mean flow velocity: 14.15 mm/s). During navigation, the rotating robot-induced Doppler signals enable real-time localization and tracking in flowing and pulsatile flowing blood environments. Moreover, the robot can be selectively navigated along different paths by actively controlling the robot's orientation. We apply this autonomous strategy for localizing thrombus and accelerating thrombolysis rate. Compared with conventional tissue plasminogen activator (tPA) thrombolysis, the robot-enhanced shear stress and tPA convection near the clot-blood interface increase the unblocking and thrombolysis efficiency up to 4.8- and 3.5-fold, respectively. Such a medical imaging-guided navigation strategy provides simultaneous robot navigation and localization in complex dynamic biological environments, providing an intelligent approach toward real-time targeted delivery and diagnostic applications in vivo.

Guide-Wired Helical Microrobot for Percutaneous Revascularization in Chronic Total Occlusion in-Vivo Validation.

For the revascularization in small vessels such as coronary arteries, we present a guide-wired helical microrobot mimicking the corkscrew motion for mechanical atherectomy that enables autonomous therapeutics and minimizing the radiation exposure to clinicians. The microrobot is fabricated with a spherical joint and a guidewire. A previously developed external electromagnetic manipulation system capable of high power and frequency is incorporated and an autonomous guidance motion control including driving and steering is implemented in the prototype. We tested the validity of our approach in animal experiments under clinical settings. For the in vivo test, artificial thrombus was fabricated and placed in a small vessel and atherectomy procedures were conducted. The devised approach enables us to navigate the helical robot to the target area and successfully unclog the thrombosis in rat models in vivo. This technology overcomes several limitations associated with a small vessel environment and promises to advance medical microrobotics for real clinical applications while achieving intact operation and minimizing radiation exposures to clinicians. Advanced microrobot based on multi-discipline technology could be validated in vivo for the first time and that may foster the microrobot application at clinical sites.

Characterization of Helical Propulsion Inside In Vitro and Ex Vivo Models of a Rabbit Aorta.

In this work, the propulsion of a helical robot is experimentally characterized inside whole blood (in vitro model) and against the flowing streams of phosphate buffered saline (PBS) inside rabbit aorta (ex vivo model). The helical robot is magnetically actuated inside these models under the influence of rotating magnetic fields. The frequency response of the helical robot is characterized. Averaged speed is measured at actuation frequency of 8 Hz as 11.3 ± 0.52 (n = 5) and 7.45 ± 1.2 mm/s (n = 3) inside rabbit aorta and whole blood, respectively. The Speed of the robot inside rabbit aorta is characterized against flowing streams of PBS at flow rate of 90 ml/hr.

Magnetic localization and control of helical robots for clearing superficial blood clots.

This work presents an approach for the localization and control of helical robots during removal of superficial blood clots inside in vitro and ex vivo models. The position of the helical robot is estimated using an array of Hall-effect sensors and precalculated magnetic field map of two synchronized rotating dipole fields. The estimated position is used to implement closed-loop motion control of the helical robot using the rotating dipole fields. We validate the localization accuracy by visual feedback and feature tracking inside the in vitro model. The experimental results show that the magnetic localization of a helical robot with diameter of 1 mm can achieve a mean absolute position error of 2.35 ± 0.4 mm (n = 20). The simultaneous localization and motion control of the helical robot enables propulsion toward a blood clot and clearing at an average removal rate of 0.67 ± 0.47 mm3/min. This method is used to localize the helical robot inside a rabbit aorta (ex vivo model), and the localization accuracy is validated using ultrasound feedback with a mean absolute position error of 2.6 mm.

3D closed-loop swimming at low Reynolds numbers

In this paper, the mobility matrix of helical microswimmers is investigated to compute the magnetic torque as a function of the angular velocities of the helical robot to achieve a 3D path following in closed-loop. Thus, the helical swimmer kinematics are expressed in the Serret–Frenet frame considering the weight of the robot and lateral disturbances using the compensation inclination and direction angles, respectively. A new chained formulation is used to design a stable controller. The approach is simple and quite general and can be used for different non-holonomic autonomous systems. The 3D path following is validated by presenting experimental results using a scaled-up helical microswimmer actuated magnetically. Different trajectories were tested: a spatial straight line, a helix trajectory, and an inclined sinusoidal trajectory. Several conditions have been tested experimentally, namely: different velocity profiles, compensation inclination angles, liquid viscosities, control gains and boundary effects, and their impact on the performance of the path following. To illustrate the robustness and accuracy of the visual servo control to disturbances presenting in the environment such as the magnetic field gradient and boundary effects, it is compared with the open-loop control. The results show the robustness of the controller and a submillimetric accuracy during the path following.

The Influence of Mechanical Rubbing on the Dissolution of Blood Clots.

Mechanical rubbing of blood clots is a potential minimally-invasive method for clearing clogged blood vessels. In this work, we investigate the influence of the interaction of the tip of a helical robot with blood clots. This interaction enables the dissolution of the blood clot and the release of the entrapped red blood cells and platelets from its three-dimensional fibrin fiber network. We analyze the pre- and post-conditions of the blood clots following 40 minutes of mechanical rubbing, under the influence of a rotating magnetic field in the frequency range of 20 Hz to 45 Hz. Our measurements show that the weight of the blood clots is decreased by 22.5 ± 11.1% at frequency of 25 Hz. We also validate the influence of mechanical rubbing using cell count and spectrophotometric analysis on phosphate buffered saline samples past the robot and the clot. The maximum cell count is measured as 654 ± 108 × 104 cells/m1 and 54 ± 12 × 104 cells/m1, whereas the absorbance is measured as 4. 35 × 10-6 mol and 1. 05 × 10-6 mol under the influence of mechanical rubbing and without mechanical rubbing, respectively.

Mechanical Rubbing of Blood Clots Using Helical Robots Under Ultrasound Guidance

A simple way to mitigate the potential negative side-effects associated with chemical lysis of a blood clot is to tear its fibrin network via mechanical rubbing using a helical robot. Here, we achieve mechanical rubbing of blood clots under ultrasound guidance and using external magnetic actuation. Position of the helical robot is determined using ultrasound feedback and used to control its motion toward the clot, whereas the volume of the clots is estimated simultaneously using visual feedback. We characterize the shear modulus and ultimate shear strength of the blood clots to predict their removal rate during rubbing. Our in vitro experiments show the ability to move the helical robot controllably toward clots using ultrasound feedback with average and maximum errors of ${\text{0.84}\pm \text{0.41}}$ and 2.15 mm, respectively, and achieve removal rate of $-\text{0.614} \pm \text{0.303}$ mm $^{3}$ /min at room temperature ( ${\text{25}}^{\circ }$ C) and $-\text{0.482} \pm \text{0.23}$ mm $^{3}$ /min at body temperature (37 $^{\circ}$ C), under the influence of two rotating dipole fields at frequency of 35 Hz. We also validate the effectiveness of mechanical rubbing by measuring the number of red blood cells and platelets past the clot. Our measurements show that rubbing achieves cell count of $(\text{46} \pm \text{10.9}) \times \text{10}^{4}$ cell/ml, whereas the count in the absence of rubbing is $(\text{2} \pm \text{1.41}) \times \text{10}^{4}$ cell/ml, after 40 min.

The Rotation of Microrobot Simplifies 3D Control Inside Microchannels

This paper focuses on the control of rotating helical microrobots inside microchannels. We first use a 50 μm long and 5 μm in diameter helical robot to prove that the proximity of the channel walls create a perpendicular force on the robot. This force makes the robot orbit around the channel center line. We also demonstrate experimentally that this phenomenon simplifies the robot control by guiding it on a channel even if the robot propulsion is not perfectly aligned with the channel direction. We then use numerical simulations, validated by real experimental cases, to show different implications on the microrobot control of this orbiting phenomenon. First, the robot can be centered in 3D inside an in-plane microchannel only by controlling its horizontal direction (yaw angle). This means that a rotating microrobot can be precisely controlled along the center of a microfluidic channel only by using a standard 2D microscopy technology. Second, the robot horizontal (yaw) and vertical (pitch) directions can be controlled to follow a 3D evolving channel only with a 2D feedback. We believe this could lead to simplify imaging systems for the potential in vivo integration of such microrobots.

Development of a Helical Pole Climbing Robot with Underactuated Tendon-driven Arms

Development of a Helical Pole Climbing Robot with Underactuated Tendon-driven Arms

Magnetic Helical Robot for Targeted Drug-Delivery in Tubular Environments

We propose a novel magnetic helical robot (HR) that can helically navigate, release a drug to a target area, and generate a mechanical drilling motion to unclog tubular structures of the human body. The proposed HR is composed of two rotating cylindrical magnets (RMs), four fixed cylindrical magnets (FMs), and a helical body. The RMs can be rotated in different directions under two orthogonal external rotating magnetic fields (ERMF). Utilizing these ERMFs, we can generate various motions. The ERMF along the axis of the RMs can generate the drug-release motion, while the ERMF orthogonal to the axis of the RMs can generate navigating and drilling motions. On the other hand, the magnetic torque and the attractive magnetic force between RMs and FMs tightly seal the nozzles in the drug chamber. We analyze these magnetic torque and force of the magnets for the navigating, drug-release, and drilling motion. Especially, the drug-release motion utilizes an eccentric rotational motion of the RMs due to the attractive and repulsive magnetic force between RMs and FMs. This motion squeezes and discharges the drug through a nozzle. We designed the mechanical structure of the proposed HR considering the magnetic properties to achieve the proposed functions. Finally, we prototyped the HR and conducted several experiments to verify the navigating, drug-delivery and drilling capabilities of the HR. We also confirmed that drug-enhanced drilling could unclog the clogged area more effectively than the simple drilling motion.

Magnetic Navigation System Utilizing Resonant Effect to Enhance Magnetic Field Applied to Magnetic Robots

We propose a novel magnetic navigation system (MNS) with the resonant effect of an RLC circuit to generate large magnetic field in high frequency. The variable capacitors of the proposed MNS make it possible not only to change the resonant frequency of the RLC circuit, but also to maximize the output current without phase delay at variable resonant frequencies. The proposed MNS can compensate for the amplitude decrease and phase delay due to the inductance effect of a conventional MNS, while generating a uniform magnetic field with a wide range of rotating frequencies to effectively operate a helical robot in human blood vessels. For verification of the constructed MNS, we measured currents and magnetic fields at several resonant frequencies, and the experimental values corresponded well with the calculated values. We finally demonstrated that the proposed MNS substantially improves both moving and unclogging capabilities of a helical robot as compared to the conventional MNS.