Magnetic Actuation System Research Articles

SPIONs mediated magnetic actuation promotes nerve regeneration by inducing and maintaining repair-supportive phenotypes in Schwann cells

BackgroundSchwann cells, the glial cells in the peripheral nervous system, are highly plastic. In response to nerve injury, Schwann cells are reprogrammed to a series of specialized repair-promoting phenotypes, known as repair Schwann cells, which play a pivotal role in nerve regeneration. However, repair Schwann cells represent a transient and unstable cell state, and these cells progressively lose their repair phenotypes and repair‐supportive capacity; the transience of this state is one of the key reasons for regeneration failure in humans. Therefore, the ability to control the phenotypic stability of repair Schwann cells is of great practical importance as well as biological interest.ResultsWe designed and prepared a type of fluorescent–magnetic bifunctional superparamagnetic iron oxide nanoparticles (SPIONs). In the present study, we established rat sciatic nerve injury models, then applied SPIONs to Schwann cells and established an effective SPION-mediated magnetic actuation system targeting the sciatic nerves. Our results demonstrate that magnetic actuation mediated by SPIONs can induce and maintain repair-supportive phenotypes of Schwann cells, thereby promoting regeneration and functional recovery of the sciatic nerve after crush injury.ConclusionsOur research indicate that Schwann cells can sense these external, magnetically driven mechanical forces and transduce them to intracellular biochemical signals that promote nerve regeneration by inducing and maintaining the repair phenotypes of Schwann cells. We hope that this study will provide a new therapeutic strategy to promote the regeneration and repair of injured peripheral nerves.Graphical

Thermoset Shape Memory Polymer Variable Stiffness 4D Robotic Catheters.

Variable stiffness catheters are typically composed of an encapsulated core. The core is usually composed of a low melting point alloy (LMPA) or a thermoplastic polymer (TP). In both cases, there is a need to encapsulate the core with an elastic material. This imposes a limit to the volume of variable stiffness (VS) material and limits miniaturization. This paper proposes a new approach that relies on the use of thermosetting materials. The variable stiffness catheter (VSC) proposed in this work eliminates the necessity for an encapsulation layer and is made of a unique biocompatible thermoset polymer with an embedded heating system. This significantly reduces the final diameter, improves manufacturability, and increases safety in the event of complications. The device can be scaled to sub‐millimeter dimensions, while maintaining a high stiffness change. In addition, integration into a magnetic actuation system allows for precise actuation of one or multiple tools.

Guiding Drug Through Interrupted Bloodstream for Potentiated Thrombolysis by C-Shaped Magnetic Actuation System In Vivo.

Fast and effective thrombolysis using tissue plasminogen activator (tPA) is limited by the poor delivery efficiency of thrombolytic drugs, which is induced by an interrupted bloodstream and delayed recanalization. Existing magnetic micro/nanodrug-loaded robots used for targeted thrombotic therapy are limited by the complexity of the clinical verification of nanodrugs and the limited space of magnetic actuation systems. Herein, a general drug delivery strategy based on mass transportation theory for thrombolysis is presented, and an open space C-shaped magnetic actuation system with laser location and ultrasound imaging navigation for in vivo evaluation is developed. tPA can be guided through an interrupted bloodstream to the thrombi by the locomotion of magnetic nanoparticle swarms (MNSs), thereby improving the thrombolysis efficacy. Notably, this strategy is able to quickly establish a life channel to achieve time-critical recanalization, which is typically inaccessible using native tPA. Both in vitro and in vivo thrombolysis experiments demonstrate that the thrombus lysis efficacy significantly increases after the application of the MNS under a rotating magnetic field. This study provides an anticipated C-shaped magnetic actuation system for in vivo validation and also presents a clinically feasible drug delivery strategy for targeted thrombolytic therapy with minimal systemic tPA exposure.

Magnetic Control of a Steerable Guidewire Under Ultrasound Guidance Using Mobile Electromagnets

Endovascular surgery has become a popular minimally invasive approach to diagnose and treat various vascular diseases. However, manipulating conventional passive guidewires and catheters still has technical challenges, such as long duration and undesired trauma. In addition, radiation exposure induced by commonly used fluoroscopic imaging has safety concerns. This letter presents a workflow that performs magnetic control of a steerable guidewire under ultrasound (US) guidance to address these issues. The designed magnetically steerable guidewire is fabricated by replica molding method, then a computational-efficient kinematic model is proposed to describe the relationship between the applied magnetic field and tip deformation. The constructed magnetic actuation system integrates three electromagnets and a US probe into a parallel mechanism, realizing large-workspace magnetic field generation and US feedback. Further, a motorized feeder is incorporated to provide the forward and backward motion of the guidewire. An autonomous control framework is proposed consisting of preoperative and intraoperative stages, through which the guidewire can be delivered to the targeted region automatically. Results show that the proposed kinematic model efficiently estimates the deformation of the guidewire. Furthermore, the overall procedure is experimentally validated on a phantom mimicking vascular structures. This letter provides a preliminary robotic solution to improve catheterization procedures by introducing magnetic actuation and US imaging.

Synthesis of magneto-responsive microswimmers for biomedical applications

Interest in untethered mini and micro-robots has shown a significant increase lately, especially magneto-responsive swimmers. In this study, a soft sub-millimeter sized swimmer and a magnetic actuation system was developed. An extrusion-based 3D printer was used to form swimmers with three different types of magnetic content, Fe micro flakes and nanoparticles, and Nd-Fe-B micro flakes, were incorporated into polymeric bounder material. Using milli- and micro-swimmers in biological environments demands the use of cyto-compatible materials that would disguise the magnetic materials from the immune system. In this study, particles were encapsulated in a gelatin-alginate-cellulose based hydrogel. Next, these microswimmers were steered along a path via the magnetic gradient created by a custom-made electromagnetic system. The base of the electromagnetic system was designed using a CAD computer program and three dimensionally (3D)-printed. Consisting of four independent solenoids, each two controlling the movement on an axis, the system was designed to move the microswimmers in a certain path. The solenoids were controlled by Arduino microcontroller board. The electrical current applied to the electromagnetic device in all the trials was 2 amperes, which generates a magnetic field in between 100 to 376 Gauss throughout the experiment area. Thus, a magnetic gradient from the center to the pole of the solenoid was established. The magnetic and chemical behavior of these materials were compared based on their magnetic responsiveness and 3d printability. Developed magneto-responsive microswimmers could be used in biomedical robotics and drug delivery applications.

The airborne inertially stabilized platform suspend by an axial-radial integrated active magnetic actuator system

IntroductionThe inertial stabilization platform (ISP) is widely used in the earth observation system to stably track the line of sight of the payload because it could isolate vibrations and angular motions of the aviation platform. Objectivesan active magnetic actuator (AMA) system integrating the axial and the radial control is used to levitate the azimuth gimbal to improve attitude stabilization precision and dynamic performance of the ISP, and then the dynamic model of azimuth gimbal is developed. MethodsThe magnetic force and the gimbal torque of the axial-radial integrated AMA system are investigated, and the attitude information of the suspended azimuth gimbal is measured. ResultsThe attitude stabilization precision of azimuth gimbal is confined at 0.02°, and the control bandwidth of the axial-radial integrated AMA system could exceed 100 Hz. Conclusionthe ISP with an axial-radial integrated AMA system has better attitude stabilization precision and wider control frequency than the pure mechanical ISP, so it is potential to be applied in the airborne remote sensing system to improve the measurement precision.

Magnetically Active Cardiac Patches as an Untethered, Non-Blood Contacting Ventricular Assist Device.

Patients suffering from heart failure often require circulatory support using ventricular assist devices (VADs). However, most existing VADs provide nonpulsatile flow, involve direct contact between the blood flow and the device's lumen and moving components, and require a driveline to connect to an external power source. These design features often lead to complications such as gastrointestinal bleeding, device thrombosis, and driveline infections. Here, a concept of magnetically active cardiac patches (MACPs) that can potentially function as non‐blood contacting, untethered pulsatile VADs inside a magnetic actuationsystem is reported. The MACPs, which are composed of permanent magnets and 3D‐printed patches, are attached to the epicardial surfaces, thus avoiding direct contact with the blood flow. They provide powerful actuation assisting native heart pumping inside a magnetic actuation system. In ex vivo experiments on a healthy pig's heart, it is shown that the ventricular ejection fractions are as high as 37% in the left ventricle and 63% in the right ventricle. Non‐blood contacting, untethered VADs can eliminate the risk of serious complications associated with existing devices, and provide an alternative solution for myocardial training and therapy for patients with heart failure.

3-D Visual Servoing of Magnetic Miniature Swimmers Using Parallel Mobile Coils

Untethered magnetic microrobots can be remotely controlled by dynamic magnetic fields. The ability to pass through complex and narrow regions makes them have great potential in biomedical applications. To date, various magnetic actuation systems and control methods have been developed to drive these tiny agents. However, steering their 3D locomotion at the human scale using electromagnetic systems is still challenging. In this regard, this article explores a closed-loop control strategy that guides swimming of magnetic microrobots at low Reynolds numbers in a large workspace. An eye-in-hand stereo-vision mobile-coil system is adopted to provide required dynamic magnetic fields and vision information. Both corkscrew-type and flexible-oar-type swimmers are analyzed, and a unified kinematic model is established. Based on the system and model, a triple-loop visual servoing scheme is proposed to fulfill simultaneous mechanism tracking and swimmer steering. Two different scaled-up untethered microrobots are employed in the path following experiment. Our prototype magnetic actuation system reaches a cylindrical workspace of diameter over 200 mm, and the mean error of path tracking is within 2 mm. These results provide a preliminary study for dexterous magnetic actuation of miniature robots for medical treatment.

Design and Real-Time Optimization for a Magnetic Actuation System With Enhanced Flexibility

In this article, a magnetic actuation system based on three mobile electromagnetic coils is designed and a control strategy for the system is proposed. Enhanced flexibility combined with optimization algorithms enables the system to satisfy various requirements in applications, such as avoiding collision between the coils and the obstructions within the workspace, placing the coils to optimal positions to enhance energy efficiency, generating wide varieties of magnetic field for complex tasks, and tracking the location of the robot with enlarged workspace. To reach that purpose, a model of the system is built for magnetic field calculation, and a real-time optimization algorithm based on particle swarm optimization combined with a collision detection algorithm is proposed and implemented to calculate optimal positions for coils and at the same time avoid collision. We fabricate a prototype system, named RoboMag, to prove the concept. Simulations and experiments on helical swimmer and soft robot are conducted to evaluate the performance. Compared with two conventional control strategies, the demanded currents for long-distance actuation are reduced by up to 62.7%. The calculation process is conducted in real time and the coils are able to avoid collision with the barriers inside the workspace during actuation. Moreover, generation and steering of a microrobotic swarm is demonstrated, showing the capability of the system in generating programmed dynamic fields for complicated tasks.

A New Type of Rotary Magnetic Actuator System Using Electromagnetic Vibration and Wheel

In recent years, large structures, such as bridges, which are a type of social infrastructure, have been constructed with increasing traffic volume. For this reason, inspection and maintenance of social infrastructures, such as large bridges and tanks, is important. In the present paper, a magnetic wheel actuator system capable of movement using a new principle of locomotion was proposed and tested. The experimental results indicated a maximum pulling force of 1.6 N. By on-off control of the attractive force of the magnetic wheel, the actuator system was demonstrated to be able to move on a step having a height of 10 mm. Furthermore, the proposed actuator system could freely rotate in horizontal and vertical planes of over angles of 360°.

Toward a Maneuverable Miniature Robotic Fish Equipped With a Novel Magnetic Actuator System

Most existing robotic fish have a large body size driven by servo motor system, while conventional small-sized actuators hardly generate a high swimming performance. This paper reports a miniature untethered robotic fish, whose body length is 69 mm. In particular, a newly designed magnetic actuator system (MAS) is equipped, which guarantees both small-sized dimension and flexibility of the robot. More specifically, the magnetic field generated by a permanent magnet is first investigated based on Biot–Savart law. Then, a novel tail-beating rhythm called magnetically actuated pulse width modulation (MAPWM) is modeled for the new actuator system. Further, an MAPWM-based control method is presented, in which the duty ratio of MAPWAM is innovatively utilized to realize the turning maneuvers for the first time. In addition, Lagrangian method is employed to establish the dynamic model to assess the MAPWM-based control method and the turning performance of the robotic fish. To further improve the maneuverability, the effect of a shape-variable caudal fin is analyzed based on computational fluid dynamics and the built dynamic model. Finally, combined with the MAS, the MAPWM-based control method, and the optimally selected caudal fin, extensive aquatic experiments are conducted on the robotic prototype. The results indicate that the developed miniature robotic fish achieves a considerably higher level of maneuverability in terms of turning radius when compared to swimming robots with equivalent dimensions.

A Manipulability Criterion for Magnetic Actuation of Miniature Swimmers With Flexible Flagellum

The use of untethered miniature swimmers is a promising trend, especially in biomedical applications. These swimmers are often operated remotely using a magnetic field commonly generated using fixed coils that can suffer from a lack of compactness and heating issues. The analysis of the swimming capabilities is still an ongoing topic of research. In this letter, we focus on the ability of a magnetic actuation system to operate the propulsion of miniature swimmers with flexible flagellum. As a first contribution, we present a new manipulability criterion to assess the ability of a magnetic actuation system to operate a swimming robot, i.e. to ensure a displacement in any desired direction with a fixed minimum speed. This criterion is developed thanks to an analogy with cable-driven parallel robots. As a second contribution, this manipulability criterion is exploited to identify the dexterous swimming workspace which can be used to design of new coil configurations as well as to highlight the possibilities of moving coil systems. A case study for a planar workspace surrounded by three coils is in particular carried out. The accompanying video illustrates the application of the proposed criterion in 3D, for a large number of coils.

A rotating permanent magnetic actuator for micropumping devices with magnetic nanofluids

In this study, a novel rotating permanent magnetic actuator (PMA) system is proposed to manipulate magnetic nanofluids to pump chemicals inside micro-sized channels with circular paths. The PMA consists of two permanent magnet pairs and a rotor-like structure. A semicircular-shaped microchannel with a square cross-section area is located at the top of the actuator in order to investigate the performance of the PMA. Fe3O4-water magnetic nanofluid is employed as a working fluid for the manipulation inside the microchannel. In the first stage of this work, a numerical survey is conducted to determine the most suitable angular distance between permanent magnets of a pair in terms of generated magnetic field form in the microchannel region and velocity distribution of magnetic nanofluid within the semicircular microchannel when the permanent magnets are stationary. Preliminary experiments are then carried out for the stationary permanent magnets to validate the predicted flow-field results. Performance tests for different PMA speeds (7.5–30 rpm) and particle concentrations (1%–3% by vol.) indicate that it is possible to manipulate the magnetic nanofluid inside the semicircular channel within a velocity range of 58.7–940 µm s−1, which corresponds to a flow rate range of 0.56–9.02 µL min−1. The results confirm that the proposed PMA system provides flow rate requirements in analytical microfluidic applications such as low flow drug delivery (1–10 µL min−1), cell sorting (6.1 µL min−1), and pathogen detection (3–5.83 µL min−1).

RectMag3D: A Magnetic Actuation System for Steering Milli/Microrobots Based on Rectangular Electromagnetic Coils

Milli/microrobots benefit from their small size and can perform minimally invasive surgery in a limited tissue space and eliminate the need for fine operations such as thrombus, which not only reduces trauma to patients but also shortens the recovery period after surgery. In order to realize motion control of the milli/microrobot at a small scale, the external magnetic field-based control method has a significant advantage of wireless connection, safety, and high efficiency compared to other external actuation ways. Aiming at the actuation of milli/microrobots in human tissue fluid during a medical operation, we designed a milli/microrobot magnetic actuation system called RectMag3D, which is based on rectangular electromagnetic coils. It can realize five-degree-of-freedom motion control of milli/microrobot in three-dimensional space. It has the advantage of the accurate modeling of a magnetic field from each rectangular coil. Therefore, accurate control can be achieved. In this paper, the design and modeling of the proposed system have been introduced. A linear programming algorithm has been applied to achieve fixed-point actuation and displacement actuation. Experiments show that the milli/microrobot can realize the steering and linear motion to the target point in any direction in the limited working space under the control of the magnetic actuation system.

Three-Dimensional Localization of a Robotic Capsule Endoscope Using Magnetoquasistatic Field

Recent research efforts regarding advanced Robotic Capsule Endoscopes (RCEs) have primarily focused on the development of actively locomotive endoscope capsules. However, accurate movement of an RCE inside the digestive organs remains a challenge that hinders the further development of an autonomous RCE that with applicability in clinical practice. To address this challenge, this study proposed and developed a novel three-dimensional (3D) location positioning method that is compatible with an RCE manipulated by an external magnetic actuation system. The developed localization methodology employed one embedded single-axis receiving coil (Rx) in the RCE and three external transmitting coils (Txs) placed under the clinical bed. The magnetic flux density obtained from the electromotive force at the Rx was applied to the solution of 3D nonlinear Biot–Savart equations and enabled the determination of the position of the Rx in relation to the corresponding magnetoquasistatic field source in the Tx. For implementation, this study developed: (1) an accurate mathematical model and volumetric analysis method for the magnetoquasistatic field by applying equipotential contour and surface mapping, (2) a method to determine the optimal Tx arrangement, and (3) a prototyped device and in-vitro validation of the feasibility of the 3D localization. In the helical trajectory tracking experiment, the device demonstrated an error of 2.03 ± 1.14 mm, and the feasibility in the clinical environment was verified through gastrointestinal phantom experiments. The proposed method will be further evaluated clinically for the retargeting and accurate localization of internal pathologies as well as the closed-loop control of an actively locomotive RCE.

The ARMM System: An Optimized Mobile Electromagnetic Coil for Non-Linear Actuation of Flexible Surgical Instruments

Automation of flexible surgical instruments requires the development of robotic technologies capable of small-scale power transmission. Magnetic actuation has successfully been used for that purpose. Nevertheless, current systems for magnetic actuation suffer from small workspaces or poor bandwidth of magnetic field control. In this work, we design, develop, and test a novel magnetic actuation system called Advanced Robotics for Magnetic Manipulation (ARMM). The ARMM system employs a 6 DoF mobile electromagnetic coil capable of generating prescribed magnetic fields and gradients. The mobile coil approach allows for easy scaling of the actuation workspace, which depends on the range of robotic arm, and in our case spans up to 1.3 m. Due to limited end-effector payload of the robotic arm used in the ARMM system, the mobile coil has been designed using an optimization routine. For a given mass and heat dissipation constraints, this routine provides the coil geometry that maximizes the average magnetic field generated in the target region. Since the Vacoflux core of the fabricated coil saturates within operational conditions, we propose an actuation strategy employing an online-updated iterative map technique. Using this map, the ARMM system allows for precise generation of prescribed magnetic fields and gradients at the point of interest, while taking into account the effects of the non-linearities due to core saturation. The strategy is validated experimentally, showing the average error of 2.34% for magnetic field and 7.20% for the magnetic field gradient.

Gradient-Enhanced Electromagnetic Actuation System With a New Core Shape Design for Microrobot Manipulation

Electromagnetic-based actuation is receiving increasing attention for driving microparticles, particularly for in vivo biomedical applications. In this article, we present a core shape design for electromagnetic coils to develop a magnetic gradient field-based actuation system that can enable microrobotic manipulation. Based on the mathematical model using the finite-element method, the shape of the iron core and the size of the probe are optimized, aiming to increase the gradient at the focused area. A thin disc is also attached to the end of the iron core for reducing the waste of magnetic field energy. Through this design, the magnetic field generated by the electromagnetic actuation system can be considerably enhanced to propel microrobots in the in vivo environments. The designed system is tested in different in vitro environments, including pure water, artificial cerebrospinal fluid, mouse blood, and a special environment with an extremely high viscosity coefficient. The system is also tested for driving microrobots in an in vivo environment, namely, zebrafish yolk. Experimental results effectively demonstrate the capacity of the designed platform in manipulating microrobots for in vitro and in vivo applications.

Magnetofection of Green Fluorescent Protein Encoding DNA-Bearing Polyethyleneimine-Coated Superparamagnetic Iron Oxide Nanoparticles to Human Breast Cancer Cells.

Gene therapy is a developing method for the treatment of various diseases. For this purpose, the search for nonviral methods has recently accelerated to avoid toxic effects. A strong alternative method is magnetofection, which involves the use of superparamagnetic iron oxide nanoparticles (SPIONs) with a proper organic coating and external magnetic field to enhance the localization of SPIONs at the target site. In this study, a new magnetic actuation system consisting of four rare-earth magnets on a rotary table was designed and manufactured to obtain improved magnetofection. As a model, green fluorescent protein DNA-bearing polyethyleneimine-coated SPIONs were used. Magnetofection was tested on MCF7 cells. The system reduced the transfection time (down to 1 h) of the standard polyethyleneimine transfection protocol. As a result, we showed that the system could be effectively used for gene transfer.

Modeling and Control of Magnetic Actuation Systems Based on Sensorless Displacement Information

This paper reveals the design and implementation of a magnetic actuation system (MAS) with noninvasive displacement measurement by current sensing only. A platform-independent MAS modeling methodology is utilized, describing the cross-coupled system behavior by the physical representation of mechanical and electromagnetic counterparts. An extended nonlinear inductor model is developed, demonstrating the challenging control task of displacement regulation. The inductor model facilitates the development of a combined current sensing methodology employing noninvasive displacement measurement. The combined sensor, based on adding a “shunt inductor” in series to the main actuator, performs both high-resolution displacement and dc current measurement with fast response and minimum losses. The MAS model and the combined sensor-based operation have been experimentally verified on a single-axis levitator prototype.

Active magnetic levitation and 3-D position measurement for a ball viscometer

Abstract. We present a new technique for 3-D position sensing and active magnetic levitation of a steel ball for use in a levitating ball viscometer. In order to achieve a stable levitation, a very sensitive positioning measurement system is mandatory. For this task the differential transformer principle was chosen to realize a 3-D position measurement. This leads to a purely magnetic sensor and actuator system without the need for other transducer types such as optical readout. The actuation utilizes power efficient switch-mode electronic circuitry which opens the possibility of upscaling the device, if demanded, for future applications. It is shown that this switch-mode actuation can be combined directly with the position measurement when special switching patterns are applied. A position resolution of ∼ 100 µm in all three axial directions at a sample rate of 476.19 Hz is achieved. For viscosity sensing, the steel ball is magnetically driven to orbital movements of variable revolution frequency of up to 2.5 Hz within a fluid chamber. The frequency response is analyzed and related to the shear viscosity of the fluid under test. As a proof of concept, measurements in various viscous liquids were performed with the prototype, showing promising results in the range of 1–10 mPa s. The principle may also be of interest for applications beyond viscosity sensing, such as fluid mixers, or as actuators in microfluidic devices.