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Chemically driven micromotors display unpredictable trajectories due to the rotational Brownian motion interacting with the surrounding fluid molecules. This hampers the practical applications of these tiny robots, particularly where precise control is a requisite. To overcome the rotational Brownian motion and increase motion directionality, robots are often decorated with a magnetic composition and guided by an external magnetic field. However, despite the straightforward method, explicit analysis and modeling of their motion have been limited. Here, catalytic Janus micromotors are fabricated with distinct magnetizations and a controlled self-propelled motion with magnetic steering is shown. To analyze their dynamic behavior, a dynamic model that can successfully predict the trajectory of micromotors in uniform viscous flows in real time by incorporating a form of state-dependent-coefficient with a robust two-stage Kalman filter is theoretically developed. A good agreement is observed between the theoretically predicted dynamics and experimental observations over a wide range of model parameter variations. The developed model can be universally adopted to various designs of catalytic micro-/nanomotors with different sizes, geometries, and materials, even in diverse fuel solutions. Finally, the proposed model can be used as a platform for biosensing, detecting fuel concentration, or determining small-scale motors' propulsion mechanisms in an unknown environment., Advanced Intelligent Systems, 4 (11), ISSN:2640-4567

This research work mainly focuses on the study of the modeling and control of microrobotic systems in a biomedical context. So far, the use of magnetic actuation has been regarded as the most convenient approach for such achievements. Besides, the cardiovascular system allows to reach most parts of the human body and is then chosen as the main navigation route. This original topic is a rapidly expanding field whose ambition is to modernize current therapies by trying to improve therapeutic targeting while improving patient comfort. To achieve this goal, a good understanding of how microrobots evolve in the human body is an important step. The theoretical foundations and the physical laws that make it possible to describe the various phenomena which act on magnetic microrobots in vascular-like environments have thus been deeply studied. Methodologies for dealing with multiphysics approaches combining different sources of hypotheses and uncertainties have been developed. Great care has been taken in their validations by experimentation when possible, otherwise by numerical analysis. This helps to better understand the dominant dynamics, as well as the predominant parameters in the description of magnetic microrobots in a vascular-like environment. This makes it possible to efficiently characterize and predict their behaviors in a viscous flow and their responses to magnetic fields. On this basis, advanced navigation strategies have been developed. The navigation process can be divided into two stages. First, safe and efficient navigation paths are planned (off-line) based on the fast marching method (FMM). With the proposed navigation planning framework, different constraints and objectives can then be taken into account to obtain a truly feasible reference path. Second, control schemes that drive the magnetic microrobots along the planned reference path to the targeted location are synthesized. To do so, predictive and optimal control laws have been implemented. All the proposed models and navigation strategies have been evaluated through various experiments under different conditions with the platforms developed at the PRISME Laboratory., Ce travail traite principalement l'étude de la modélisation et du contrôle de systèmes microrobotiques dans un contexte biomédical. Jusqu'à présent, l'utilisation de l'actionnement magnétique est considérée comme l'approche la plus prometteuse pour de telles réalisations. Par ailleurs, le système cardiovasculaire permet d'atteindre la plupart des parties du corps humain et est alors choisi comme voie de navigation principale. Cette thématique originale est un domaine en pleine expansion dont l'ambition est de moderniser les thérapies actuelles en essayant d'améliorer le ciblage thérapeutique tout en améliorant le confort des patients. Pour atteindre cet objectif, une bonne compréhension du comportement des microrobots dans le corps humain est une étape importante. Les fondements théoriques et les lois de la physique permettant de décrire les différents phénomènes qui agissent sur les microrobots magnétiques dans des environnements de type vasculaire ont ainsi été étudiés en détails. Des méthodologies pour traiter des approches multiphysiques combinant différentes sources d'hypothèses et d'incertitudes ont été développées. Un grand soin a été apporté à leurs validations par l'expérimentation lorsque cela était possible, le cas échéant par des analyses numériques. Cela permet de mieux comprendre la dynamique dominante, ainsi que les paramètres prédominants dans la description des microrobots magnétiques. Cela permet de caractériser et de prédire efficacement leurs comportements dans un écoulement visqueux et leurs réponses aux champs magnétiques. Sur cette base, des stratégies de navigation avancées ont été développées. Le processus de navigation peut être divisé en deux étapes. Premièrement, des chemins de navigation sûrs et efficaces sont planifiés (hors ligne) sur la base de la méthode du _[fast marching]{lang=en .en}_ (FMM). Dans le cadre de la méthode de planification de la navigation proposée, différentes contraintes et objectifs peuvent être pris en compte pour obtenir un chemin de référence véritablement réalisable. Deuxièmement, des stratégies de commande guidant les microrobots magnétiques le long du chemin de référence jusqu'à l'emplacement ciblé sont synthétisées. Pour ce faire, des lois de commande prédictives et optimales ont été mises en œuvre. Tous les modèles et stratégies de navigation proposés ont été évalués à travers diverses expérimentations dans différentes conditions sur les plateformes développées au Laboratoire PRISME.

International audience; This paper introduces a two-dimensional autonomous navigation strategy of a 750 µm steel microrobot along a complex fluidic vascular network inside the bore of a clinical 3.0 T magnetic resonance imaging (MRI) scanner. To ensure successful magnetic resonance navigation (MRN) of a micro-robot along consecutive channels, the design of autonoumous navigation strategy is needed taking into account the major MRI technological constraints and physiological perturbations, e.g. non-negligible pulsatile flow, limitations on the magnetic gradient amplitude, MRI overheating, susceptibility artifacts uncertainties , and so on. An optimal navigation planning framework based on Pareto optimality is proposed in order to deal with this multiple-objective problem. Based on these optimal conditions, a dedicated control architecture has been implemented in an interventional medical platform for real-time propulsion, control and imaging experiments. The reported experiments suggest that the likelihood of controlling autonomously untethered 750 µm magnetic microrobots is rendered possible in a complex two-dimensional centimeter-sized vascular phantom. The magnetic microrobot traveled intricate paths at a mean velocity of about 4 mm s −1 with average tracking errors below 800 µm with limited magnetic gradients ±15 mT m −1 compatible with clinical MRI scanners. The experiments demonstrate that it is effectively possible to autonomously guide a magnetic microrobot using a conventional MRI scanner with only a software upgrade.

International audience; We report Au/Ru core–shell nanowire motors. These nanowires are fabricated using our previously developed electrodeposition-based technique, and their catalytic locomotion in the presence of H2O2 is investigated. Unlike conventional bimetallic nanowires that are self-electroosmotically propelled, our open-ended Au/Ru core–shell nanowires show both a noticeable decrease in rotational diffusivity and increase in motor speed with increasing nanowire length. Numerical modeling based on self-electroosmosis attributes decreases in rotational diffusivity to the formation of toroidal vortices at the nanowire tail, but fails to explain the speed increase with length. To reconcile this inconsistency, we propose a combined mechanism of self-diffusiophoresis and electroosmosis based on the oxygen gradient produced by catalytic shells. This mechanism successfully explains not only the speed increase of Au/Ru core–shell nanomotors with increasing length, but also the large variation in speed among Au/Ru, Au/Rh, and Rh/Au core–shell nanomotors. The possible contribution of diffusiophoresis to an otherwise well-established electroosmotic mechanism sheds light on future designs of nanomotors, at the same time highlighting the complex nature of nanoscale propulsion.

International audience; The propulsion of ferromagnetic objects by means of MRI gradients is a promising approach to enable new forms of therapy. In this work, necessary techniques are presented to make this approach work. This includes path planning algorithms working on MRI data, ferromagnetic artifact imaging and a tracking algorithm which delivers position feedback for the ferro-magnetic objects and a propulsion sequence to enable interleaved magnetic propulsion and imaging. Using a dedicated software environment integrating path-planning methods and real-time tracking, a clinical MRI system is adapted to provide this new functionality for controlled interventional targeted therapeutic applications. Through MRI-based sensing analysis, this paper aims to propose a framework to plan a robust pathway to enhance the navigation ability to reach deep locations in human body. The proposed approaches are validated with different experiments.

Treating Image Loss by Using the Vision/Motion Link: