Trajectory tracking of microrobots presents a significant challenge in biomedical research applications such as drug delivery and artery unclogging. Microrobots are inherently subject to uncertainties and unmodeled dynamics, complicating their control. Additionally, the overheating of coils in the electromagnetic actuation system can limit controller performance. In this paper, we propose an observer-based optimal control strategy for microrobots, where the desired trajectory is generated online by means of a joystick. The control law addresses the problem of coils overheating by minimizing energy consumption while achieving trajectory tracking despite uncertainties and unmodeled dynamics. For practical implementation, we introduce a modified nonlinear extended state observer to estimate the entire state of the microrobot. Analytical tuning approaches for the control law and observer are developed usingD-pole placement technique and Kharitonov’s theorem. This solution is an alternative to the use of cooling systems, which require more energy consummation and often reduce the performance of the controller. The tracking performance of the proposed control strategy is evaluated through simulation and experimental tests on a dedicated platform. Both simulation and practical results demonstrate the effectiveness of the developed control strategy.

One approach to control drug delivery in the cochlea is to use a magnetic microrobot powered by externally applied magnetic fields. However, it is necessary to integrate a localization system to ensure the precise navigation of the microrobot in the cochlear canal. To avoid integrating a clinical imaging modality for the navigation of microrobots in the cochlea, we propose in this work the application of magnetic sensors to localize the magnetic microrobot. In our method, we propose a real-time localization system based only on two sensors to keep a precise localization of the spherical magnetic microrobot. The first sensor measures both the magnetic field of the environment and the magnetic field generated by the microrobot (localization sensor). The second sensor (surrounding sensor) is placed away from the localization sensor, this sensor measures the magnetic field of the environment, which will be subtracted from the signal of the localization sensor to determine the value of the magnetic field of the microrobot. We have proposed a new magnetic sensor calibration method and a robust localization algorithm for precise localization of the microrobot. The experiments demonstrate the effectiveness of the designed system and show the precision of the proposed localization strategy.

This paper presents a novel permanent magnets based actuator capable of injecting and 2D wireless control the motion of an untethered microrobot. The actuator is obtained with a simple, but an effective arrangement of four permanent magnets. Its novelty is that it creates local maxima of the magnetic field magnitude in a planar workspace. This results in a convergence point for magnetic microrobots that are in its influence zone. Trapping microrobots in the local maxima makes their open-loop guidance possible, even in presence of reasonable perturbations. Actually, open-loop control is the only way to achieve some drug delivery when there are no sensors to provide us a feedback on the microrobot's positions. With the proposed actuator, the workspace is reduced, the movement is simplified and the actuator orientation is not needed anymore. Experimental results are provided in the paper to show the soundness of the proposed actuator design.

This paper presents a novel design of four permanent magnet based actuator for magnetic drug targeting of therapeutic microrobots. Drugs are transported through therapeutic magnetic boluses composed of magnetic particles controlled by magnetic gradients. In this study, to maximize the effect of the treatment and minimize adverse effects on the patient, a magnetic actuator have been developed to wirelessly control microrobots in a fluidic environment using four external magnets. Experimental validation is carried using the robotic arm Fanuc LR Mate 200iD to demonstrate the steerability of the magnetic microrobots under different trajectory constraints in viscous fluidic environment.

This work presents a method to guide microrobots by positioning a magnetic actuator using hybrid vision system. The used actuator mounted at a robot end-effector creates local maxima of the magnetic field magnitude, which results in an attractive point for microrobots in its influence zone. The hybrid vision system serves to control the actuator position through the robotic platform to make the trapped microrobot undergo a planned trajectory. In first validation results, the particle driving is achieved in open loop with no adjustment with respect to the planned trajectory. Such scheme can be used in the case where the microrobot position can not be measured in real time. The second validation results deal with the case of microrobot positioning by visual servoing. This can be used in the case where recovering microrobot position is possible, for example in eye treatment.

The use ofrobotic devices for drug delivery in sensitive area of the human body is an innovative and reliable solution. Most of them use magnetics fields, to steer micro-nano-robots into diseases locations. In this study, we use a magnetic actuator based on two permanent magnets as an end-effector of a robotic manipulator. The actuator offers the possibility to generate both pushing and pulling forces on the magnetic actuator axis in an open-loop control way. We describe in this paper the robotic drug delivery strategy that we implemented in a 6 degree of freedom robotic manipulator to push and to steer a magnetic microparticle from the round window to the apex of the human cochlea. Different experiments have been conducted in order to demonstrate the effectiveness and robustness of the navigation proposed strategy on a human phantom cochlea. The results demonstrate clearly that precise and reliable drug administration is rendered possible.

For actuating the magnetic microrobots, two types of magnetic actuation technologies have been used during the last past years. These magnetic technologies may be either electromagnetic coils or permanent magnets based systems. This second solution is not the most used by researchers, because of the difficulties to control the magnetic force. In this paper we propose a magnetic actuator prototype based on permanent magnets. In addition to the magnets, the actuator is also composed of a mechanical structure. This structure is used for positioning the permanent magnets, which allows to control the magnetic force generated by the actuator. We demonstrated in simulation and experimentally confirmed the ability of this actuator to generate both pushing and pulling forces.

The magnetic particles actuated by an external magnetic field present a promising solution as drug carrier at the inner ear (cochlea). This technique allows non-invasive drug delivery with minimal hydraulic force and very high precision. In this work, magnetic prototyping platform for intra cochlear drug delivery procedure is proposed. This platform is composed by magnetic actuator mounted on a robot end-effector and an hybrid vision system. The latter consists of a camera to control the position of magnetic actuator, two microscopes to recover the position of the magnetic particles and the 3D structure of the cochlea. The hybrid vision system allows real-time tracking of magnetic particles inside the artificial cochlea. The accuracy of the drug delivery strategy depends strongly on the calibration of the vision system. In this paper a method to calibrate the hybrid vision system is proposed and validated with experimental results.

This paper presents an optimal control strategy for navigation of multiple magnetic microbeads for future drug targeting applications. To transport the drugs, we use therapeutic magnetic microbeads as navigable agents controlled by magnetic gradients. The main difficulty is to control independently each therapeutic agent along a trajectory with the same magnetic gradient fields. This study proposes an optimal control methodology to control a group of different therapeutic agents at desired states. Based on a dynamic model of group of magnetic microbeads, controllability and observability conditions are formulated and simulated. Based on the proposed theoretical analysis a linear quadratic with integral action control (LQI) has been chosen to be applied to the microbeads system. Finally, an experimental investigation is carried out in millimeter-sized fluidic artery vessels to demonstrate the controllability and stability of two magnetic microbeads under different velocity and trajectory constraints with a laminar viscous fluidic environment.

This paper presents an optimal design strategy for magnetic targeting of therapeutic drugs. In this study, to maximize the effect of the treatment and minimize adverse effects on the patient, mathematical models have been developed to find the number and the size of the boluses with respect to the growth of a tumor. Using these models, control strategies are developed to establish a schedule that allows the physician to administer the medication while respecting borne by the patient doses. To transport the drugs, we use therapeutic magnetic boluses composed of magnetic particle aggregates as navigable agents controlled by magnetic gradients. Based on the optimal design of the bolus, an experimental investigation is carried out in millimeter-sized fluidic artery vessels to demonstrate the steerability of the magnetic bolus under different velocity, shear-stress and trajectory constraints with a laminar viscous fluidic environment.

This paper has presented a new vision-based force-sensing framework that allows to characterize the forces applied on a magnetic microrobot in an endovascular-like environment. Especially, unlike common approaches used with optical microscopy where orthographic projection model are used, we consider in this paper the weak-perspective model. The proposed vision-based force characterization allows to retrieve the three dimensional (3D) translational velocities and accelerations of a microrobot viewed from a digital microscope. Hence, thanks to the dynamic model the external forces are estimated on-line. The framework was applied and validated for a magnetic microrobot navigating in a viscous flow. Experimental results in two different environments illustrate the efficiency of the proposed method.

Magnetic microrobotics was nowadays one of the most advanced technique to reach deep locations in human body for future biomedical applications. Different magnetic microrobot designs were proposed, such as bead pulling or microswimmers. In this paper, the use of chain-like of magnetic N-microspheres was investigated to enable new kind of motions and applications. An accurate theoretical model of chain-like magnetic microbeads navigating in viscous fluidic environments is described. Thus, the behavior of such microrobot was analyzed for different number of microspheres (ranging from N = 2 to 5). The efficiency of the proposed technique was demonstrated experimentally in a microfluidic vessel phantom to mimic atherosclerosis disease leading to plaque formation that fully occluded a vasculature.

Navigating in bodily fluids to perform targeted diagnosis and therapy has recently raised the problem of robust control of magnetic microrobots under real endovascular conditions. Various control approaches have been proposed in the literature but few of them have been experimentally validated. In this paper, we point out the problem of navigation controllability of magnetic microrobots in high viscous fluids and under pulsatile flow for endovascular applications. We consider the experimental navigation along a desired trajectory, in a simplified millimeter-sized arterial bifurcation, operating in fluids at the low-Reynolds-number regime where viscous drag significantly dominates over inertia. Different viscosity environments are tested under a systolic pulsatile flow compatible with heart beating. The control performances in terms tracking, robustness and stability are then experimentally demonstrated.

This paper presents real-time MRI-based control of a ferromagnetic microcapsule for endovascular navigation. The concept was studied for future development of microdevices designed to perform minimally invasive interventions in remote sites accessible through the human cardiovascular system. A system software architecture is presented illustrating the different software modules to allow navigation of a microdevice in blood vessels, namely: (i) vessel path planner, (ii) magnetic gradient steering, (iii) tracking and (iv) closed-loop navigation control. First, the position recognition of the microrobot into the blood vessel is extracted using Frangi vesselness filtering from the pre-operation images. Then, a set of minimal trajectory is predefined, using FMM, to guide the microrobot from the injection point to the tumor area through the anarchic vessel network. Based on the pre-computed path, a GPC is proposed for robust time-multiplexed navigation along a 2D path in presence of pulsative flow. The simulation results suggest the validation of the proposed image processing and control algorithms. A series of disturbances introduced in the presence and absence of closed-loop control affirms the robustness and effectiveness of this predictive control system.