MRI-Based Tumour Targeting Enhancement with Magnetotactic Bacterial Carriers

RÉSUMÉ Le cancer constitue la première cause de mortalité au Québec, avec 20,000 décès estimés par année. Parmi tous les patients atteints du cancer, une grande proportion pourrait profiter de l’avancement technologique en ce qui concerne le transport de médicaments. En effet, l’un des meilleurs moyens d’augmenter l’efficacité d’un médicament contre le cancer, tout en réduisant sa toxicité sur les cellules saines, est de le diriger vers la tumeur et de le maintenir à cet endroit jusqu’à ce qu’un effet thérapeutique se produise. Le transport ciblé de médicaments vers la tumeur peut considérablement améliorer l’efficacité thérapeutique, surtout si le transporteur est capable d’atteindre les zones nécrotiques et se répartir uniformément dans la zone à traiter. Les bactéries, de par leur motilité, sont d’excellents candidats pour une telle application, surtout qu’elles peuvent aussi être facilement fonctionnalisées. Ainsi, la recherche sur le traitement du cancer utilisant des bactéries s’est imposée comme une approche prometteuse surtout qu’elle pallie à une limitation majeure de la chimiothérapie et de la radiothérapie en permettant le traitement des zones anaérobies. Alors que des laboratoires à travers le monde tentent de fabriquer des systèmes miniatures en se basant sur le modèle bactérien, nous avons opté pour l’utilisation des bactéries qui existent dans la nature. Notre stratégie a été de trouver un système biologique ayant les caractéristiques essentielles (e.x. diamètre total de moins de deux micromètres, force de poussée de plus de 4 pN, etc.) et de concentrer nos efforts à identifier une interface et une méthode permettant son contrôle pour des fins de ciblages thérapeutiques dans les lésions tumorales. Nous avons identifié les bactéries magnétotactiques de type MC-1 comme le meilleur transporteur potentiel de médicaments pour le ciblage du cancer. Les MC-1 sont à la fois dirigeables par champs magnétiques et anaérobies, ce qui leur donne un grand avantage par rapport aux bactéries traditionnellement utilisées pour le ciblage du cancer. Le ciblage du cancer avec des bactéries exploite le plus souvent l’affinité des bactéries anaérobies à la région nécrotique faible en oxygène de la tumeur. Certes, ce ciblage manque de spécificité et un des problèmes le plus reconnu est la nécessité d’injecter une forte dose de bactéries pour assurer une croissance de celles-ci à l’intérieur de la tumeur. Ceci n’est pas le cas avec les MC-1 car elles sont à la fois anaérobies et magnétotactiques grâce à une chaîne de nanoparticules d’environ 70 nanomètres de diamètre, formant une sorte de « nano-boussole » magnétique à----------ABSTRACT Magnetotactic Bacteria (MTB) are being explored as potential drug transporters to solid tumours. The MTB’s active motility combined with magnetotaxism (their ability to swim following the direction of a magnetic field) offer new and potentially more accurate solutions in delivering drugs to tumours. In fact, the flagella bundles of the MC-1 bacteria (with an overall ideal cell diameter of approximately 50% the diameter of the tiniest human blood vessels) provide 4.0 to 4.7pN of thrust force for propulsion (roughly 10 times the value of many other well-known flagellated bacteria). Since there are no existing methods or technologies capable of inducing an equivalent force on a carrier of appropriate size for traveling inside a tumour’s microvasculature, live microorganisms are considered as a viable option. Many of the parameters in a tumour microenvironment, such as malformed angiogenesis capillaries, heterogeneous blood flow, and high interstitial pressure, hinder the delivery of blood-borne drugs to the affected area. Active motility might prove to be helpful in bypassing these limitations and may facilitate the uniform distribution of the drug in the targeted area. An MTB navigation technique that allows targeting without prior knowledge of the exact architecture of the vessels network has been developed. This navigation technique exploits both the ability of the MTB to swim following an imposed magnetic field and their random, continuous motion at low magnetic fields. Firstly, a focused magnetic field on the target sets the overall direction of the bacteria. Then, as the bacteria approach the targeted zone, the intensity of the magnetic field is decreased, which allows better bacteria repartition by exploiting their free motion. An additional approach that enhances MTB targeting relies on modulating the magnetic field direction in time, while keeping the magnetic field lines pointed toward the target. Navigation experiments in complex micro-channel networks highlight this process, where the successful targeting of bacteria is demonstrated when an appropriate magnetic field algorithm is applied, especially when it takes into account the nature of the channel network. Tridimensional control and navigation of MTB is also possible with the same technique through proper powering of the magnetic coils. In fact, by controlling their magnetic environment, it is possible to form a swarm of MTB, control its size and position within a given volume using a computer program

Magnet-targeted delivery and imaging

Magnetic nanoparticles, in combination with applied magnetic fields, can non-invasively focus delivery of small-molecule drugs and human cells to specific regions of the anatomy. This emerging technology could solve one of the main challenges in therapy development: delivery of a high concentration of the therapeutic agent to the target organ or tissue whilst reducing systemic dosing and off-target side effects. Several challenges, however, must be met before this technology can be applied either effectively or safely in the clinic to augment therapies. Multiple nanoparticle features interact to influence the efficiency of magnet-targeted delivery, and so their design will have a large influence on the success of therapeutic targeting. Iron oxide core size and composition affect the type and strength of magnetism, and thus the amount of force that can be applied by an external magnetic field, while particle behaviour within biological systems can be affected by particle size and coating. Preclinical researchers have investigated the use of magnetic targeting-based therapies across a wide range of conditions, and positive results have been reported for both cell and drug delivery applications. Furthermore, magnetic resonance imaging (MRI) can non-invasively monitor the success of targeted delivery—providing high-resolution anatomical information on particle location in preclinical and clinical contexts. In this chapter, we provide a basic introduction to the physical principles behind magnetic targeting technology, relevant design features of nanoparticles and magnetic targeting devices, an overview of preclinical and clinical applications, and an introduction to imaging magnetic particles in vivo

Design and Implementation of Electromagnetic Actuation System to Actuate Micro/NanoRobots in Viscous Environment

The navigation of Micro/Nanorobots (MNRs) with the ability to track a selected trajectory accurately holds significant promise for different applications in biomedicine, providing methods for diagnoses and treatments inside the human body. The critical challenge is ensuring that the required power can be generated within the MNR. Furthermore, ensuring that it is feasible for the robot to travel inside the human body with the necessary power availability. Currently, MNRs are widely driven either by exogenous power sources (light energy, magnetic fields, electric fields, acoustics fields, etc.) or by endogenous energy sources, such as chemical interaction energy. Various driving techniques have been established, including piezoelectric as a driving source, thermal driving, electro-osmotic force driven by biological bacteria, and micro-motors powered by chemical fuel. These driving techniques have some restrictions, mainly when used in biomedicine. External magnetic fields are another potential power source of MNRs. Magnetic fields can permeate deep tissues and be safe for human organisms. As a result, magnetic fields’ magnetic forces and moments can be applied to MNRs without affecting biological fluids and tissues. Due to their features and characteristics of magnetic fields in generating high power, they are naturally suited to control the electromagnetically actuated MNRs in inaccessible locations due to their ability to go through tiny spaces. From the literature, it can be inferred from the available range of actuation technologies that magnetic actuation performs better than other technologies in terms of controllability, speed, flexibility of the working environment, and far less harm may cause to people. Also, electromagnetic actuation systems may come in various configurations that offer many degrees of freedom, different working mediums, and controllability schemes. Although this is a promising field of research, further simulation studies, and analysis, new smart materials, and the development and building of new real systems physically, and testing the concepts under development from different aspects and application requirements are required to determine whether these systems could be implemented in natural clinical settings on the human body. Also, to understand the latest development in MNRs and the actuation techniques with the associated technologies. Also, there is a need to conduct studies and comparisons to conclude the main research achievements in the field, highlight the critical challenges waiting for answers, and develop new research directions to solve and improve the performance. Therefore, this thesis aims to model and analyze, simulate, design, develop, and implement (with complete hardware and software integration) an electromagnetic actuation (EMA) system to actuate MNRs in the sixdimensional (6D) motion space inside a relatively large region of interest (ROI). The second stage is a simulation; simulation and finite element analysis were conducted. COMSOL multi-physics software is used to analyze the performance of different coils and coil pairs for Helmholtz and Maxwell coil configurations and electromagnetic actuation systems. This leads to the following.: • Finite element analysis (FEA) demonstrates that the Helmholtz coils generate a uniform and consistent magnetic field within a targeted ROI, and the Maxwell coils generate a uniform magnetic gradient. • The possibility to combine Helmholtz and Maxwell coils in different space dimensions. With the ability to actuate an MNR in a 6D space: 3D as a position and 3D as orientation. • Different electromagnetic system configurations are proposed, and their effectiveness in guiding an MNR inside a mimicked blood vessel environment was assessed. • Three pairs of Helmholtz coils and three pairs of coils of Maxwell coils are combined to actuate different size MNRs inside a mimicked blood vessel environment and in 6D. Based on the modeling results, a magnetic actuation system prototype that can control different sizes MNRs was conceived. A closed-loop control algorithm was proposed, and motion analysis of the MNR was conducted and discussed for both position and orientation. Improved EMA location tracking along a chosen trajectory was achieved using a PID-based closed-loop control approach with the best possible parameters. Through the model and analysis stage, the developed system was simulated and tested using open- and closed-loop circumstances. Finally, the closedloop controlled system was concluded and simulated to verify the ability of the proposed EMA to actuate an MN under different trajectory tracking examples with different dimensionality and for different sizes of MNRs. The last stage is developing the experimental setup by manufacturing the coils and their base in-house. Drivers and power supplies are selected according to the specifications that actuate the coils to generate the required magnetic field. Three digital microscopes were integrated with the electromagnetic actuation system to deliver visual feedback aiming to track in real-time the location of the MNR in the 6D high viscous fluidic environment, which leads to enabling closed-loop control. The closed-loop control algorithm is developed to facilitate MNR trajectory tracking and minimize the error accordingly. Accordingly, different tests were carried out to check the uniformity of the magnetic field generated from the coils. Also, a test was done for the digital microscope to check that it was calibrated and it works correctly. Experimental tests were conducted in 1D, 2D plane, and 3D trajectories with two different MNR sizes. The results show the ability of the proposed EMA system to actuate the two different sizes with a tracking error of 20-45 µm depending on the axis and the size of the MNR. The experiments show the ability of the developed EMA system to hold the MNR at any point within the 3D fluidic environment while overcoming the gravity effects. A comparison was made between the results achieved (in simulation and physical experiments) and the results deduced from the literature. The comparison shows that the thesis’s outcomes regarding the error and MNR size used are significant, with better performance relative to the MNR size and value of the error

The behaviour of magnetotactic bacteria in changing magnetic fields

Die Beobachtung des Verhaltens von magnetotaktischen Bakterien (MTB) in wechselndeMagnetfeldern kann signifikante direkte und indirekte Informationen offenlegen über deren Merkmale und physiologische Eigenschaften. Sowohl Einzel- als auchMassenanalyse wurden in der vorliegenden Studie durchgeführt. Die Einzelzell-Experimente wurden in einem mikrofluidischen Chip mitmaßgefertigtem Design durchgeführt, in welchem die MTB fokussiert werden konnten während einMagnetfeld mittels eines permanentenMagneten angelegt wurde, welcher unter demMikroskoptisch befestigt war. Beobachtungen und Aufnahme der Reaktionen erlaubte eine offline-Analyse der Bewegungsbahnen. Diese Auswertung zeigte, dass die Zellen unterschiedlich reagierten auf Variation derMagnitude derMagnetfeldstärke. DesWeiteren konnte durch Simulationen und Experimente aufgezeigt werden, dass der Widerstand der MTB unterschätzt wurde, was zu zusätzlichen makroskopische Experimenten führte, um eine Verbindung von morphologischer Eigenschaften und Rotationswiderstandsprofilen darzulegen. Diese Experimente wurden durchgeführt in einem Gefäßmit Silikonöl unter Verwendung verschiedener 3D-gedruckter Modelle von verschiedenen ellipsoid- und spirillum-basierenden Morphologien. Die Modelle begründeten sich auf Elektronenmikroskop-Abbildungen von tatsächlichen MTB. Die Auswertung dieser Experimente konnte zur Aufklärung beitragen, dass Eigenschaften der MTB nicht in existierende Modelle des Rotationswiderstandes berücksichtigt werden. Die Massenanalyse wurde durchgeführt in einem maßangefertigtem Optischen-Dichte-Messer, spezifisch hergestellt umMagnetfeld-Orientierungen mit Photospektrometrie zu kombinieren. Von diesen Beobachtungen konnte der magnetische Gehalt von einer MTB-Kultur und Einzelproben abgeleitet werden, sowohl absolut als auch relativ. Zusätzlich wurde die Reaktionszeit einer verwendeten Charge gemessen werden umdenmagnetischen dipol-Moment mit dem Rotationswiderstand zu korrelieren. Dies erlaubte eine Unterscheidung zwischen verschiedenen Qualitäten und Quantitäten von Kulturen, als auch Langzeit- und kontinuierliche Beobachtung desWachstumsverhaltens von diesen. Trotz des Auffindens neuer Eigenschaften durch welche eine genauere Berechnung von Rotationswiderstandsprofilen möglich wurde bleibt die Länge eines Objekts weiterhin der dominierende Faktor im Zusammenspiel von magnetischem Drehmoment und Rotationswiderstandskraft. UnserModell erlaubt eine genauere Vorhersage des Rotationswiderstandes von Objekten mit ähnlichen Formen wie MTB in Schleichender Strömung als auch Zuständen von geringen Reynoldszahlen.The observation of behaviour of magnetotactic bacteria (MTB) in changing magnetic fields can give significant direct and indirect information about their traits and biophysical properties. Both single and bulk experiment and analysis were performed in this study. The single cel experimentswere performed inside custommicrofluidic chips designed to keep the MTB in focus, while a magnet field was applied using a permanent magnet mounted under a microscope stage. Observation and recording of the response allowed for off-line analysis of the trajectories. This analysis has shown that the cells respond differently to varyingmagnitudes of magnetic field strength. Furthermore, from simulations and experiments we have found that the drag of the MTB had been underestimated, which lead to additional macroscopic experiments relating morphological traits to more rotational drag profiles. These experiments were done in a vat of silicone oil using 3D-printed models of varying spheroid- and spirillum-based morphologies. The models were based on scanning electron microscope images of actualMTB. Analysis of these experiments elucidated the contribution of traits not included in existing models for rotational drag. The bulk analysis was performed in a custom made optical density meter, specifically designed to combine magnetic field orientations with photo spectrometry. From our observation we could derive the magnetic response, both absolute and relative, of a given culture or sample of MTB. Additionally, the response time of a given batch could also be measured, relating the magnetic dipole moment with the rotational drag. This allowed distinguishing between different quality and quantity of cultures, as well as long termand continuous observation of a culture in growth. In spite of having found new traits by which one can more accurately calculate the rotational drag profile, the length of an object still remains the dominate factor when balancing magnetic torque and drag force. Our model does allow for predicting more accurately the rotational drag of objects with shapes similar toMTB in Stokes flow or under low Reynolds number conditions

Conception et fabrication d'un microrobot sans fil autonome opérant dans un milieu aqueux

RÉSUMÉ Il existe plusieurs définitions du mot « robot ». L’une d’elles définit un robot comme un dispositif qui peut se déplacer et réagir à une excitation pour exécuter une ou plusieurs tâches dédiées. Un tel robot est pourvu d’une certaine forme d’intelligence ou d’un programme qui exécute ces tâches automatiquement sans l’intervention humaine. De plus, sa conception sera influencée par l’environnement dans lequel il évolue et par les fonctions qui doivent lui être intégrées pour effectuer des tâches prédéfinies. En microrobotique, le principal obstacle dans la miniaturisation des robots intelligents sans fil est d’obtenir la source de puissance nécessaire pour supporter les quatre fonctions de base (intelligence, détection, communication, actuation ou déplacement), malgré les contraintes d’espace. Deux approches principales peuvent être envisagées pour réduire les dimensions du robot, soit l’augmentation de la capacité de réception et de conversion énergétique, soit la diminution du besoin en énergie électrique.----------ABSTRACT There are several definitions of the word “robot”. One of them defines a robot as a device which can move and react to a stimulus to execute one or more dedicated tasks. Such a robot is endowed with a certain form of intelligence or a program which executes automatically without human intervention. Moreover, the design of a robot will be influenced by the environment in which it moves and by the functions which must be integrated to carry out some preset tasks. In microrobotics, a major difficulty during the miniaturization of intelligent wireless robots is to feed them with power to support the four basic functions (intelligence, sensors, communication, actuation or displacement) while meeting volume constraints. Therefore, two principal approaches can be considered to reduce the robot dimensions. The first would be to increase the reception capacity and energy conversion. The second would be to decrease the electrical power requirements