Micro/nanoscale magnetic robots for biomedical applications

Magnetic small-scale robots are devices of great potential for the biomedical field because of the several benefits of this method of actuation. Recent work on the development of these devices has seen tremendous innovation and refinement toward ​improved performance for potential clinical applications. This review briefly details recent advancements in small-scale robots used for biomedical applications, covering their design, fabrication, applications, and demonstration of ability, and identifies the gap in studies and the difficulties that have persisted in the optimization of the use of these devices. In addition, alternative biomedical applications are also suggested for some of the technologies that show potential for other functions. This study concludes that although the field of small-scale robot research is highly innovative ​there is need for more concerted efforts to improve functionality and reliability of these devices particularly in clinical applications. Finally, further suggestions are made toward ​the achievement of commercialization for these devices

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

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

Study on Magnetic Control Systems of Micro-Robots

Magnetic control systems of micro-robots have recently blossomed as one of the most thrilling areas in the field of medical treatment. For the sake of learning how to apply relevant technologies in medical services, we systematically review pioneering works published in the past and divide magnetic control systems into three categories: stationary electromagnet control systems, permanent magnet control systems and mobile electromagnet control systems. Based on this, we ulteriorly analyze and illustrate their respective strengths and weaknesses. Furthermore, aiming at surmounting the instability of magnetic control system, we utilize SolidWorks2020 software to partially modify the SAMM system to make its final overall thickness attain 111 mm, which is capable to control and observe the motion of the micro-robot under the microscope system in an even better fashion. Ultimately, we emphasize the challenges and open problems that urgently need to be settled, and summarize the direction of development in this field, which plays a momentous role in the wide and safe application of magnetic control systems of micro-robots in clinic

Study and development of a magnetic steering system for microrobots

In a close future micro-scaled untethered robots might be able to access small spaces inside the human body, currently reachable only by using invasive surgical methods, thus revolutionizing future medicine. The aim of this Master Thesis work is to study and develop a system that can exploit static magnetic fields and gradients to steer purpose-developed microrobots. A concept of the device for the generation of magnetic fields is first elaborated, moving from the state-of-art systems based on Helmholtz and Maxwell coils, which can generate, respectively, nearly uniform magnetic fields and gradients. A uniform magnetic field can be used to orient a magnetic or magnetisable object, aligning it with the direction of the field, while a uniform magnetic gradient can be used to shift such an object. The developed system is formed by two coils in the Maxwell geometrical configuration and independently powered in order to generate a uniform magnetic gradient, a quasi-uniform magnetic field or a superimposition of the two, reducing the overall complexity of the hardware with respect to the systems also employing Helmholtz coils. An analytical model of the on-axis magnetic field generated by the device and a finite element model of the field in the workspace are developed. Three microrobot prototypes are then considered: a millimetre-sized NdFeB cylindrical permanent magnet, which allows to test the maximum performances of the developed device, a polymeric microbead, which is more compatible with biomedical applications but less reactive to magnetic fields than a permanent magnet, and a polymeric nanofilm, which allows to test the steering of very anisotropic shapes, both containing iron oxide nanoparticles. Models of their interaction with magnetic fields are presented. Furthermore, a model of the motion of the three prototypes employing the developed magnetic device is presented. The experimental set up is described, including the two coils and their support backing, the monitoring and powering circuitry and a software kit containing four graphical user interfaces for the calibration and validation of the system. After a set of trials performed for the calibration of the magnetic-field-generating device, the system is tested in steering the microrobot prototypes. The extrapolated data are compared to the behaviours predicted by the magnetic motion models. The abilities of the magnetic steering system and its main limits are finally examined, suggesting possible improvements of both the magnetic device and the microrobots in order to enhance their control and manipulation. In particular indications for developing the next-generation of wireless magnetically-actuated microrobots and the relative steering systems are extrapolated

Doctor of Philosophy

dissertationThis dissertation presents results documenting advancements on the control of untethered magnetic devices, such as magnetic \microrobots" and magnetically actuated capsuleendoscopes, motivated by problems in minimally invasive medicine. This dissertationfocuses on applying rotating magnetic elds for magnetic manipulation. The contributions include advancements in the way that helical microswimmers (devices that mimicthe propulsion of bacterial agella) are controlled in the presence of gravitational forces, advancements in ways that groups of untethered magnetic devices can be dierentiated and semi-independently controlled, advancements in the way that untethered magnetic device can be controlled with a single rotating permanent magnet, and an improved understanding in the nature of the magnetic force applied to an untethered device by a rotating magnet

Challenges of continuum robots in clinical context: a review

With the maturity of surgical robotic systems based on traditional rigid-link principles, the rate of progress slowed as limits of size and controllable degrees of freedom were reached. Continuum robots came with the potential to deliver a step change in the next generation of medical devices, by providing better access, safer interactions and making new procedures possible. Over the last few years, several continuum robotic systems have been launched commercially and have been increasingly adopted in hospitals. Despite the clear progress achieved, continuum robots still suffer from design complexity hindering their dexterity and scalability. Recent advances in actuation methods have looked to address this issue, offering alternatives to commonly employed approaches. Additionally, continuum structures introduce significant complexity in modelling, sensing, control and fabrication; topics which are of particular focus in the robotics community. It is, therefore, the aim of the presented work to highlight the pertinent areas of active research and to discuss the challenges to be addressed before the potential of continuum robots as medical devices may be fully realised

Characterisation and State Estimation of Magnetic Soft Continuum Robots

Minimally invasive surgery has become more popular as it leads to less bleeding, scarring, pain, and shorter recovery time. However, this has come with counter-intuitive devices and steep surgeon learning curves. Magnetically actuated Soft Continuum Robots (SCR) have the potential to replace these devices, providing high dexterity together with the ability to conform to complex environments and safe human interactions without the cognitive burden for the clinician. Despite considerable progress in the past decade in their development, several challenges still plague SCR hindering their full realisation. This thesis aims at improving magnetically actuated SCR by addressing some of these challenges, such as material characterisation and modelling, and sensing feedback and localisation. Material characterisation for SCR is essential for understanding their behaviour and designing effective modelling and simulation strategies. In this work, the material properties of commonly employed materials in magnetically actuated SCR, such as elastic modulus, hyper-elastic model parameters, and magnetic moment were determined. Additionally, the effect these parameters have on modelling and simulating these devices was investigated. Due to the nature of magnetic actuation, localisation is of utmost importance to ensure accurate control and delivery of functionality. As such, two localisation strategies for magnetically actuated SCR were developed, one capable of estimating the full 6 degrees of freedom (DOFs) pose without any prior pose information, and another capable of accurately tracking the full 6-DOFs in real-time with positional errors lower than 4~mm. These will contribute to the development of autonomous navigation and closed-loop control of magnetically actuated SCR

MicroBioRobots for Single Cell Manipulation

One of the great challenges in nano and micro scale science and engineering is the independent manipulation of biological cells and small man-made objects with active sensing. For such biomedical applications as single cell manipulation, telemetry, and localized targeted delivery of chemicals, it is important to fabricate microstructures that can be powered and controlled without a tether in fluidic environments. These microstructures can be used to develop microrobots that have the potential to make existing therapeutic and diagnostic procedures less invasive. Actuation can be realized using various different organic and inorganic methods. Previous studies explored different forms of actuation and control with microorganisms. Bacteria, in particular, offer several advantages as controllable micro actuators: they draw chemical energy directly from their environment, they are genetically modifiable, and they are scalable and configurable in the sense that any number of bacteria can be selectively patterned. Additionally, the study of bacteria inspires inorganic schemes of actuation and control. For these reasons, we chose to employ bacteria while controlling their motility using optical and electrical stimuli. In the first part of the thesis, we demonstrate a bio-integrated approach by introducing MicroBioRobots (MBRs). MBRs are negative photosensitive epoxy (SU8) microfabricated structures with typical feature sizes ranging from 1-100 μm coated with a monolayer of the swarming Serratia marcescens. The adherent bacterial cells naturally coordinate to propel the microstructures in fluidic environments, which we call Self-Actuation. First, we demonstrate the control of MBRs using self-actuation, DC electric fields and ultra-violet radiation and develop an experimentally-validated mathematical model for the MBRs. This model allows us to to steer the MBR to any position and orientation in a planar micro channel using visual feedback and an inverted microscope. Examples of sub-micron scale transport and assembly as well as computer-based closed-loop control of MBRs are presented. We demonstrate experimentally that vision-based feedback control allows a four-electrode experimental device to steer MBRs along arbitrary paths with micrometer precision. At each time instant, the system identifies the current location of the robot, a control algorithm determines the power supply voltages that will move the charged robot from its current location toward its next desired position, and the necessary electric field is then created. Second, we develop biosensors for the MBRs. Microscopic devices with sensing capabilities could significantly improve single cell analysis, especially in high-resolution detection of patterns of chemicals released from cells in vitro. Two different types of sensing mechanisms are employed. The first method is based on harnessing bacterial power, and in the second method we use genetically engineered bacteria. The small size of the devices gives them access to individual cells, and their large numbers permit simultaneous monitoring of many cells. In the second part, we describe the construction and operation of truly micron-sized, biocompatible ferromagnetic micro transporters driven by external magnetic fields capable of exerting forces at the pico Newton scale. We develop micro transporters using a simple, single step micro fabrication technique that allows us to produce large numbers in the same step. We also fabricate microgels to deliver drugs. We demonstrate that the micro transporters can be navigated to separate single cells with micron-size precision and localize microgels without disturbing the local environment