Bioinspired reorientation strategies for application in micro/nanorobotic control

Engineers have recently been inspired by swimming methodologies of microorganisms in creating micro-/nanorobots for biomedical applications. Future medicine may be revolutionized by the application of these small machines in diagnosing, monitoring, and treating diseases. Studies over the past decade have often concentrated on propulsion generation. However, there are many other challenges to address before the practical use of robots at the micro-/nanoscale. The control and reorientation ability of such robots remain as some of these challenges. This paper reviews the strategies of swimming microorganisms for reorientation, including tumbling, reverse and flick, direction control of helical-path swimmers, by speed modulation, using complex flagella, and the help ofmastigonemes. Then, inspired by direction change in microorganisms,methods for orientation control for microrobots and possible directions for future studies are discussed. Further, the effects of solid boundaries on the swimming trajectories of microorganisms and microrobots are examined. In addition to propulsion systems for artificial microswimmers, swimming microorganisms are promising sources of control methodologies at the micro-/nanoscale

Magnetically Driven Micro and Nanorobots

Manipulation and navigation of micro and nanoswimmers in different fluid environments can be achieved by chemicals, external fields, or even motile cells. Many researchers have selected magnetic fields as the active external actuation source based on the advantageous features of this actuation strategy such as remote and spatiotemporal control, fuel-free, high degree of reconfigurability, programmability, recyclability, and versatility. This review introduces fundamental concepts and advantages of magnetic micro/nanorobots (termed here as "MagRobots") as well as basic knowledge of magnetic fields and magnetic materials, setups for magnetic manipulation, magnetic field configurations, and symmetry-breaking strategies for effective movement. These concepts are discussed to describe the interactions between micro/nanorobots and magnetic fields. Actuation mechanisms of flagella-inspired MagRobots (i.e., corkscrew-like motion and traveling-wave locomotion/ciliary stroke motion) and surface walkers (i.e., surface-assisted motion), applications of magnetic fields in other propulsion approaches, and magnetic stimulation of micro/nanorobots beyond motion are provided followed by fabrication techniques for (quasi)spherical, helical, flexible, wire-like, and biohybrid MagRobots. Applications of MagRobots in targeted drug/gene delivery, cell manipulation, minimally invasive surgery, biopsy, biofilm disruption/eradication, imaging-guided delivery/therapy/surgery, pollution removal for environmental remediation, and (bio)sensing are also reviewed. Finally, current challenges and future perspectives for the development of magnetically powered miniaturized motors are discussed

MRI-Based Communication with Untethered Intelligent Medical Microrobots

RESUME Les champs magnétiques présent dans un système clinique d’Imagerie par Résonance Magnétique (IRM) peuvent être exploités non seulement, afin d’induire une force de déplacement sur des microrobots magnétiques tout en permettant l’asservissement de leur position - une technique connue sous le nom de Navigation par Résonance Magnétique (NRM), mais aussi pour mettre en œuvre un procédé de communication. Pour des microrobots autonomes équipés de senseurs ayant un certain niveau d'intelligence et opérant à l'intérieur du corps humain, la puissance de transmission nécessaire pour communiquer des informations à un ordinateur externe par des méthodes présentement connues est insuffisante. Dans ce travail, une technique est décrite où une telle perte de puissance d'émission en raison de la mise à l'échelle de ces microrobots peut être compensée par le scanner IRM agissant aussi comme un récepteur très sensible. La technique de communication prend la forme d'une modification de la fréquence du courant électrique circulant le long d'une bobine miniature incorporé dans un microrobot. La fréquence du courant électrique peut être réglée à partir d'une entrée de seuil prédéterminée du senseur mis en place sur le microrobot. La fréquence devient alors corrélée à l’information de l’état du senseur recueilli par le microrobot et elle est déterminée en utilisant l'IRM. La méthode proposée est indépendante de la position et l'orientation du microrobot et peut être étendue à un grand nombre de microrobots pour surveiller et cartographier les conditions physiologiques spécifiques dans une région plus vaste à n’importe quelle profondeur à l'intérieur du corps.----------ABSTRACT The magnetic environment provided by a clinical Magnetic Resonance Imaging (MRI) scanner can be exploited to not only induce a displacement force on magnetic microrobots while allowing MR-tracking for serving control purpose or positional assessment - a technique known as Magnetic Resonance Navigation (MRN), but also for implementing a method of communication with intelligent microrobots. For untethered sensory microrobots having some level of intelligence and operating inside the body, the transmission power necessary to communicate information to an external computer via known methods is insufficient. In this work, a technique is described where such loss of transmission power due to the scaling of these microrobots can be compensated by the same MRI scanner acting as a more sensitive receiver. A communication scheme is implemented in the form of a frequency alteration in the electrical current circulating along a miniature coil embedded in a microrobot. The frequency of the electrical current could be regulated from a predetermined sensory threshold input implemented on the microrobot. Such a frequency provides information on the level of sensory information gathered by the microrobot, and it is determined using MR imaging. The proposed method is independent of the microrobot's position and orientation and can be extended to a larger number of microrobots for monitoring and mapping specific physiological conditions inside a larger region at any depths within the body

Challenges and attempts to make intelligent microswimmers

The study of microswimmers’ behavior, including their self-propulsion, interactions with the environment, and collective phenomena, has received significant attention over the past few decades due to its importance for various biological and medical applications. Microswimmers can easily access micro-fluidic channels and manipulate microscopic entities, enabling them to perform sophisticated tasks as untethered mobile microrobots inside the human body or microsize devices. Thanks to the advancements in micro/nano-technologies, a variety of synthetic and biohybrid microrobots have been designed and fabricated. Nevertheless, a key challenge arises: how to guide the microrobots to navigate through complex fluid environments and perform specific tasks. The model-free reinforcement learning (RL) technique appears to be a promising approach to address this problem. In this review article, we will first illustrate the complexities that microswimmers may face in realistic biological fluid environments. Subsequently, we will present recent experimental advancements in fabricating intelligent microswimmers using physical intelligence and biohybrid techniques. We then introduce several popular RL algorithms and summarize the recent progress for RL-powered microswimmers. Finally, the limitations and perspectives of the current studies in this field will be discussed

Current status and future application of electrically controlled micro/nanorobots in biomedicine

Using micro/nanorobots (MNRs) for targeted therapy within the human body is an emerging research direction in biomedical science. These nanoscale to microscale miniature robots possess specificity and precision that are lacking in most traditional treatment modalities. Currently, research on electrically controlled micro/nanorobots is still in its early stages, with researchers primarily focusing on the fabrication and manipulation of these robots to meet complex clinical demands. This review aims to compare the fabrication, powering, and locomotion of various electrically controlled micro/nanorobots, and explore their advantages, disadvantages, and potential applications

Embedded Energy Landscapes In Soft Matter For Micro-Robotics And Reconfigurable Structures

The ability to manipulate microscale objects with precision to form complex structures is central to the field of micro-robotics and to the realization of reconfigurable systems. Understanding and exploiting the forces that dominate at the microscale in complex environments pose major challenges and open untapped opportunities. This is particularly the case for micro-particles in soft milieu like fluid interfaces or nematic liquid crystalline fluids, which deform or reorganize around dispersed colloids or near bounding surfaces. These energetically costly deformations can be designed as embedded energy landscapes, a form of physical intelligence, to dictate emergent colloidal interactions. The fluid nature of these soft milieu allows colloids to move to minimize the free energy and externally forced robotic structures to re-write the embedded energy landscapes in the domain. Such physically intelligent systems are of great interest at the intersection of materials science and micro-robotics. Micro-particles on fluid interfaces deform the interface shape, migrate, and assemble to minimize the capillary energy. In the first part of my thesis, I design and fabricate a magnetic micro-robot as a mobile curvature source to interact with passive colloids on the water/oil interface. An analytical expression that includes both capillary and hydrodynamic interactions is derived and captures the main feature of experimental observations. I further demonstrate multiple micro-robotic tasks including directed assembly, cargo carrying, desired release and cargo delivery on the interface. Micro-particles in confined nematic liquid crystals (NLCs) distort the nematic director field, generating interactions. These interactions depend strongly on the colloids shape and surface chemistry, geometric frustration of director field and behavior of dynamic topological defects. To probe far-from-equilibrium dynamics, I fabricate a magnetic disk with hybrid anchoring. Upon controlled rotation, the disk’s companion defect undergoes periodic rearrangement, executing a complex swim stroke that propels disk translation. I study this new swimming modality in both high and low Ericksen number regimes. At high rotation rates, the defect elongates significantly adjacent to the disk, generating broken symmetries that allow steering of the disk. This ability is exploited in path planning. Thereafter, I design a four-armed micro-robot as a mobile distortion source to promote passive colloids assembly at particular sites via emergent interactions in NLCs whose strengths are characterized and found to be several orders of magnitude larger than thermal energies. While the strength of theses interactions allows colloidal cargo to be carried with the micro-robot during translation, it poses challenges for cargo release. We find that rotation of this micro-robot generates a complex dynamic defect-sharing event with colloidal cargo that spurs cargo release. Thereafter, I demonstrate the ability to exploit NLC elastodynamics to construct reconfigurable colloidal structures in a micro-robotics platform. At the colloidal scale, rotation dynamics are easier to generate, and this motivated me to exploit the topological swimming modality of the micro-robot. Using programmable rotating fields to direct the micro-robot’s motion, I achieve fully autonomous cargo manipulations including approach, assembly, transport and release. The ability to dynamically manipulate micro-particles and their structures in soft matter systems with embedded energy landscapes, as demonstrated in this thesis, creates new possibilities for micro-robotics and reconfigurable systems

Assembly Modulated by Particle Position and Shape: A New Concept in Self-Assembly

In this communication we outline how the bespoke arrangements and design of micron-sized superparamagnetic shapes provide levers to modulate their assembly under homogeneous magnetic fields. We label this new approach, ‘assembly modulated by particle position and shape’ (APPS). Specifically, using rectangular lattices of superparamagnetic micron-sized cuboids, we construct distinct microstructures by adjusting lattice pitch and angle of array with respect to a magnetic field. Broadly, we find two modes of assembly: (1) immediate 2D jamming of the cuboids as they rotate to align with the applied field (rotation-induced jamming) and (2) aggregation via translation after their full alignment (dipole-dipole assembly). The boundary between these two assembly pathways is independent on field strength being solely a function of the cuboid’s dimensions, lattice pitch, and array angle with respect to field—a relationship which we capture, along with other features of the assembly process, in a ‘phase diagram’. In doing so, we set out initial design rules to build custom made assemblies. Moreover, these assemblies can be made flexible thanks to the hinged contacts of their particle building blocks. This flexibility, combined with the superparamagnetic nature of the architectures, renders our assembly method particularly appropriate for the construction of complex actuators at a scale hitherto not possible

Analysis and Modeling of Magnetized Microswimmers: Effects of Geometry and Magnetic Properties

In recent years, much effort has been placed on development of microscale devices capable of propulsion in fluidic environments. These devices have numerous possible applications in biomedicine, microfabrication and sensing. One type of these devices that has drawn much attention among researchers is magnetic microswimmers--artificial microrobots that propel in fluid environments by being actuated using rotating external magnetic fields. This dissertation highlights our contribution to this class of microrobots. We address issues regarding fabrication difficulties arising from geometric complexities as well as issues pertaining to the controllability and adaptability of microswimmers.The majority of research in this field focuses on utilization of flexible or achiral geometries as inspired by microbiological organisms such as sperm and bacteria. Here, we set forth the minimum geometric requirements for feasible designs and demonstrate that neither flexibility nor chirality is required, contrary to biomimetic expectations. The physical models proposed in this work are generally applicable to any geometry and are capable of predicting the swimming behavior of artificial microswimmers with permanent dipoles. Through these models, we explain the wobbling phenomena, reported by experimentalists. Our model predicts the existence of multiple stable solutions under certain conditions. This leads to the realization that control strategies can be improved by adjusting the angle between the applied magnetic field and its axis of rotation. Furthermore, we apply our model to helical geometries which encompass the majority of magnetic microswimmers. We demonstrate the criterion for linear velocity-frequency response and minimization of wobbling motion. One approach to improve the adaptability of swimmers to various environments is to use modular units that can dynamically assemble and disassemble on-site. We propose a model to explain the docking process which informs strategies for successful assemblies. Most studies conducted so far are to elucidate permanent magnetic swimmers, but the literature is lacking on analysis of swimmers made of soft ferromagnetic materials. In this work, we develop a model for soft-magnetic microswimmers in the saturation regime in order to predict the swimming characteristics of these types of swimmers and compare to those of hard-magnetic swimmers

Silicon and Polymer Components for Microrobots

This dissertation presents the characterization and implementation of the first microfabrication process to incorporate high aspect ratio compliant polymer structures in-plane with traditional silicon microelectromechanical systems (MEMS). This discussion begins with in situ mechanical characterization of microscale polymer springs using silicon-on-insulator-MEMS (SOI-MEMS). The analysis compares microscale samples that were tested on-chip with macroscale samples tested using a dynamic mechanical analyzer. The results describe the effect of the processing steps on the polymer during fabrication and help to guide the design of mechanisms using polymers. Characterization of the dielectric breakdown of polymer thin films with thicknesses from 2 to 14 μm between silicon electrodes was also performed. The results demonstrate that there is a strong dependence of the breakdown field on both the electrode gap and shape. The breakdown fields ranged from 250 V/μm to 635 V/μm, depending on the electrode geometry and gap, approaching 10x the breakdown fields for air gaps of the same size. These materials were then used to create compliant all-polymer thermal and electrostatic microactuators. All-polymer thermal actuators demonstrated displacements as large at 100 μm and forces as high as 55 μN. A 1 mm long electrostatic dielectric elastomer actuator demonstrated a tip displacement as high as 350 μm at 1.1 kV with a electrical power consumption of 11μW. The actuators are fabricated with elastomeric materials, so they are very robust and can undergo large strains in both tension and bending and still operate once released. Finally, the compliant polymer and silicon actuators were combined in an actuated bio-inspired system. Small insects and other animals use a multitude of materials to realize specific functions, including locomotion. By incorporating compliant elastomer structures in-plane with traditional silicon actuators, compact energy storage systems based on elastomer springs for small jumping robots were demonstrated. Results include a 4 mm x 4 mm jumping mechanism that has reached heights of 32 cm, 80x its own height, and an on-chip actuated mechanism that has been used to propel a 1.4mg projectile over 7 cm