Jiangfan Yu

Magnetic Actuation Based Motion Control for Microrobots: An Overview

Untethered, controllable, mobile microrobots have been proposed for numerous applications, ranging from micro-manipulation, in vitro tasks (e.g., operation of microscale biological substances) to in vivo applications (e.g., targeted drug delivery; brachytherapy; hyperthermia, etc.), due to their small-scale dimensions and accessibility to tiny and complex environments. Researchers have used different magnetic actuation systems allowing custom-designed workspace and multiple degrees of freedom (DoF) to actuate microrobots with various motion control methods from open-loop pre-programmed control to closed-loop path-following control. This article provides an overview of the magnetic actuation systems and the magnetic actuation-based control methods for microrobots. An overall benchmark on the magnetic actuation system and control method is also discussed according to the applications of microrobots.

Multifunctional biohybrid magnetite microrobots for imaging-guided therapy

A biohybrid microrobot with one-step fabrication provides multiple functions for imaging-guided therapy. Magnetic microrobots and nanorobots can be remotely controlled to propel in complex biological fluids with high precision by using magnetic fields. Their potential for controlled navigation in hard-to-reach cavities of the human body makes them promising miniaturized robotic tools to diagnose and treat diseases in a minimally invasive manner. However, critical issues, such as motion tracking, biocompatibility, biodegradation, and diagnostic/therapeutic effects, need to be resolved to allow preclinical in vivo development and clinical trials. We report biohybrid magnetic robots endowed with multifunctional capabilities by integrating desired structural and functional attributes from a biological matrix and an engineered coating. Helical microswimmers were fabricated from Spirulina microalgae via a facile dip-coating process in magnetite (Fe3O4) suspensions, superparamagnetic, and equipped with robust navigation capability in various biofluids. The innate properties of the microalgae allowed in vivo fluorescence imaging and remote diagnostic sensing without the need for any surface modification. Furthermore, in vivo magnetic resonance imaging tracked a swarm of microswimmers inside rodent stomachs, a deep organ where fluorescence-based imaging ceased to work because of its penetration limitation. Meanwhile, the microswimmers were able to degrade and exhibited selective cytotoxicity to cancer cell lines, subject to the thickness of the Fe3O4 coating, which could be tailored via the dip-coating process. The biohybrid microrobots reported herein represent a microrobotic platform that could be further developed for in vivo imaging–guided therapy and a proof of concept for the engineering of multifunctional microrobotic and nanorobotic devices.

On-Demand Disassembly of Paramagnetic Nanoparticle Chains for Microrobotic Cargo Delivery

Paramagnetic nanoparticles are considered as attractive building blocks, particularly for robotic delivery of drugs. Although paramagnetic nanoparticles can be effectively gathered and transported using external magnetic fields, the disassembly process is yet to be fully investigated to avoid the formation of aggregations. In this paper, we report a novel method of controllable disassembly of paramagnetic nanoparticle chains using a predefined dynamic magnetic field. The dynamic field is capable of performing spreading and fragmentation of the particle chains simultaneously. Using the magnetic dipole–dipole repulsive forces, the final area covered by the particle chains swells up to 545% of the initial area. The final length distribution presents a strong relationship with the frequency of the dynamic field in deionized (DI) water and two kinds of biofluids. An analytical model of phase lag is proposed, which shows good agreement with the experimental results. Furthermore, we also present an assembly process using a rotating magnetic field, indicating that the assembly disassembly process is reversible. In addition, batch-cargo delivery of polystyrene microbeads using the nanoparticle chains as swarm-like nanorobots is demonstrated.

Pattern generation and motion control of a vortex-like paramagnetic nanoparticle swarm

Controlling a swarm of microrobots with external fields is one of the major challenges for untethered microrobots. In this work, we present a new method to generate a vortex-like paramagnetic nanoparticle swarm (VPNS) from dispersed nanoparticles with a diameter of 500 nm, using rotating magnetic fields. The VPNS exhibits a dynamic-equilibrium structure, in which the nanoparticles perform synchronized motions. The mechanisms of the pattern-generation process are analyzed, simulated, and validated by experiments. By tuning the rotating frequency of the input magnetic field, the pattern of a VPNS changes accordingly. Analytical models for estimating the areal change of the pattern are proposed, and they have good agreement with the experimental data. Moreover, reversible merging and splitting of vortex-like swarms are demonstrated and investigated. Serving as a mobile robotic end-effector, a VPNS is capable of making locomotion by tuning the pitch angle of the actuating rotating field. With a small pitch angle, e.g. 2°, the whole swarm moves as an entity, and the shape of the pattern remains intact. In addition, the trapping forces of VPNSs are verified, showing the critical input parameters of the magnetic field that affect the morphology of the swarm. Finally, we demonstrate that VPNSs pass through curved and branched channels with high positioning precision, and the access rates for targeted delivery are over 90%, which are significantly higher than those in the cases of particle swarms moving with tumbling motions.

Mobile paramagnetic nanoparticle-based vortex for targeted cargo delivery in fluid

Microrobots are considered as potential candidates for targeted delivery of cargos, drugs and even energy with high precision. One interesting phenomenon is their collective behaviour actuated by dynamic fields, which is yet to be adequately studied. Herein, we report a novel method of using millions of magnetic nanoparticles to generate a dynamic-equilibrium particle-based vortex, which can manipulate multiple cargos simultaneously at the microscale. The governing physical laws of the generation of a particle-based vortex are explained and the experimental results are presented. The high effectiveness of this micro-vortex-based method of particle gathering is testified. Moreover, the vortex can be navigated near a solid surface in a controlled manner. The velocity and morphology of the mobile vortices with different pitch angles are investigated, showing that the vortex moving with small pitch angles is capable of maintaining the original shape and coverage area. Collecting and transporting multiple polystyrene (PS) microbeads into a channel using the vortex are also demonstrated. This method allows us to perform micromanipulation using the collective behaviour of nanoparticles and to develop new strategies for the formation and control of the microrobotic swarm.

Steering micro-robotic swarm by dynamic actuating fields

We present a general solution for steering microrobotic swarm by dynamic actuating fields. In our approach, the motion of micro-robots is controlled by changing the actuating direction of a field applied to them. The time-series sequence of actuating fields directions can be computed automatically. Given a target position in the domain of swarm, a governing field is first constructed to provide optimal moving directions at every points. Following these directions, a robot can be driven to the target efficiently. However, when working with a crowd of micro-robots, the optimal moving directions on different agents can contradict with each other. To overcome this difficulty, we develop a novel steering algorithm to compute a statistically optimal actuating direction at each time frame. Following a sequence of these actuating directions, a crowd of micro-robots can be transported to the target region effectively. Our steering strategy of swarm has been verified on a platform that generates magnetic fields with unique actuating directions. Experimental tests taken on aggregated magnetic micro-particles are quite encouraging.

Magnetic control of AMB-1 magnetotactic bacteria for micromanipulation

Remotely actuated microrobots have the potential for biomedical applications such as targeted drug/cell delivery and biomanipulation. In this paper, we report the magnetic control of magnetotactic bacteria (MTB), i.e. AMB-1, using a low-strength uniform magnetic field and their performance for pick-and-place of magnetic microparticles in fluid. Furthermore, we demonstrate the assembly of several individual microparticles and the transportation using an AMB-1 bacterium. The force and torque generated by the AMB-1 are investigated. In addition, the assembled microparticles transported by the helical-shaped bacteria exhibits a dynamic helical pattern when they are propelled by the bacterium with a corkscrew motion. In addition, we demonstrate the disassembly of an individual microparticle payload from an AMB-1. The study on magnetic control of the AMB-1 bacteria and the dynamics of the transported microparticles pave the way for micromanipulation using AMB-1 bacteria.

Characterising of mobile vortex-like paramagnetic nanoparticle swarm: From a single vortex to multiple vortices

Paramagnetic nanoparticles actuated by external magnetic fields with effective and fast responses, can serve as microrobotic end-effectors with great potential for targeted delivery of drugs. In this paper, we report that using a rotating magnetic field, suspended paramagnetic particles are gathered into a vortex-like swarm. Moreover, by increasing the rotating frequency of the magnetic fields, multiple swarms are generated. The navigation of the vortex-like swarm is realised by tuning the pitch angle of the rotating field. In addition, using the nanoparticle swarm, the pick-and-place manipulation of a batch of polystyrene (PS) microbeads are demonstrated.