High-precision delivery of microrobots at the whole-body scale is of considerable importance for efforts toward targeted therapeutic intervention. However, vision-based control of microrobots, to deep and narrow spaces inside the body, remains a challenge. Here, we report a soft and resilient magnetic cell microrobot with high biocompatibility that can interface with the human body and adapt to the complex surroundings while navigating inside the body. We achieve time-efficient delivery of soft microrobots using an integrated platform called endoscopy-assisted magnetic actuation with dual imaging system (EMADIS). EMADIS enables rapid deployment across multiple organ/tissue barriers at the whole-body scale and high-precision delivery of soft and biohybrid microrobots in real time to tiny regions with depth up to meter scale through natural orifice, which are commonly inaccessible and even invisible by conventional endoscope and medical robots. The precise delivery of magnetic stem cell spheroid microrobots (MSCSMs) by the EMADIS transesophageal into the bile duct with a total distance of about 100 centimeters can be completed within 8 minutes. The integration strategy offers a full clinical imaging technique–based therapeutic/intervention system, which broadens the accessibility of hitherto hard-to-access regions, by means of soft microrobots.

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.

We report fluorescent magnetic spore–based microrobots for remote sensing of C. diff toxins in clinical stool supernatants.

Ferromagnetic particles (FMPs) have attracted a large amount of attention for tumor treatment in recent decades in the form of magnetic hyperthermia and thermoablation therapies. Previous research has commonly focused on the improvement of the specific loss power and the increase in the particle concentration to enhance the heating temperature during hyperthermia. Instead of magnetic hyperthermia with passive particles, here a feasible approach of using reconfigurable swarms of ferromagnetic colloidal particles is reported to realize enhanced local hyperthermia. The concentration of the particle swarm can be tuned up to 500% of the original particle concentration via reversible pattern transformation, i.e., shrinking and swelling. The FMP swarms with a controllable pattern size show their potential for directed energy delivery and offer a new strategy for realizing a highly localized heating effect using a low dose of the active FMPs.

Magnetic microrobotics has undergone approximately 20 years of development, and the robotics and control communities have contributed significant theoretical and practical results to the motion control aspects of this field. This article introduces fundamental motion principles covering individual, multiagent, and swarm control and critically reviews the state of the art along with representative results. It then describes closed-loop control (an important part of this field), including the system structure, current motion planning and control methods, and current feedback approaches. As the development of motion control in magnetic microrobotics is far from complete, especially for swarm control, its current limitations are discussed. Finally, we conclude with several challenges and future research directions. Expected final online publication date for the Annual Review of Control, Robotics, and Autonomous Systems, Volume 4 is May 3, 2021. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.