Magnetic microrobot swarms collectively perform tasks in a confined environment through multimode transformation and locomotion.

Swimming biohybrid microsized robots (e.g., bacteria- or sperm-driven microrobots) with self-propelling and navigating capabilities have become an exciting field of research, thanks to their controllable locomotion in hard-to-reach areas of the body for noninvasive drug delivery and treatment. However, current cell-based microrobots are susceptible to immune attack and clearance upon entering the body. Here, we report a neutrophil-based microrobot (“neutrobot”) that can actively deliver cargo to malignant glioma in vivo. The neutrobots are constructed through the phagocytosis of Escherichia coli membrane-enveloped, drug-loaded magnetic nanogels by natural neutrophils, where the E. coli membrane camouflaging enhances the efficiency of phagocytosis and also prevents drug leakage inside the neutrophils. With controllable intravascular movement upon exposure to a rotating magnetic field, the neutrobots could autonomously aggregate in the brain and subsequently cross the blood-brain barrier through the positive chemotactic motion of neutrobots along the gradient of inflammatory factors. The use of such dual-responsive neutrobots for targeted drug delivery substantially inhibits the proliferation of tumor cells compared with traditional drug injection. Inheriting the biological characteristics and functions of natural neutrophils that current artificial microrobots cannot match, the neutrobots developed in this study provide a promising pathway to precision biomedicine in the future.

Significance: This work proposes reconfigurable multifunctional ferrofluid droplets as soft robots to overcome the limitation of existing magnetically actuated miniature soft robots based on elastomers, i.e., they cannot navigate inside very clustered and constrained spaces and reconfigure their shapes in situ for diverse tasks, due to limited deformability and predesigned shapes. We propose a fundamental mechanism of controlling reconfigurable large deformation (e.g., splitting) and coordinated motions of multiple ferrofluid droplets by programming external magnetic fields spatiotemporally. We employ this mechanism to achieve multiple functionalities, including on-demand liquid-cargo delivery, morphing for efficient and versatile manipulation of delicate objects, and programmable fluidic-mixing function, potentially enabling unprecedented functionalities in lab/organ-on-a-chip, fluidics, bioengineering, and medical device applications, beyond magnetically actuated elastomer-based soft robots.

Magnetic miniature soft robots have shown great potential for facilitating biomedical applications by minimizing invasiveness and possible physical damage. However, researchers have mainly focused on fixed-size robots, with their active locomotion accessible only when the cross-sectional dimension of these confined spaces is comparable to that of the robot. Here, we realize the scale-reconfigurable miniature ferrofluidic robots (SMFRs) based on ferrofluid droplets and propose a series of control strategies for reconfiguring SMFR’s scale and deformation to achieve trans-scale motion control by designing a multiscale magnetic miniature robot actuation (M ³ RA) system. The results showed that SMFRs, varying from centimeters to a few micrometers, leveraged diverse capabilities, such as locomotion in structured environments, deformation to squeeze through gaps, and even reversible scale reconfiguration for navigating sharply variable spaces. A miniature robot system with these capabilities combined is promising to be applied in future wireless medical robots inside confined regions of the human body.

Magnetic helical robots (MHRs) have shown notable potential for targeted therapy. However, traditional fabrication methods are usually complex and expensive, and the prepared MHR’s locomotion is monotonous with limited capacity. Here, we present a cost-effective, customizable, and scalable fabrication craft of MHR, via using bent needle tips to engrave helical structures onto polymethyl methacrylate substrates and incorporating nanoparticle alignment strategies to create ferrofluidic helical miniature robots (FHMRs) with cross-scale size scopes. We then propose strategic magnetic driving methods that enable FHMRs with five powerful motion modes for negotiating various application scenarios. Experimental results show that FHMRs can move flexibly and effectively simulate thrombus removal within a vascular model by integrating multiple motion modes. Furthermore, modified FHMRs can swiftly deliver drugs to targeted areas, with the capability for phased release on surfaces of wrinkled physiological tissues. These advancements highlight the considerable potential of FHMRs for future applications in the biomedical field.

Microrobot swarms have powerful functions and reconfigurable collective behaviors, which enable them to be a possible way to completely solve the low execution efficiency and poor practicability of a single microrobot. However, some general deficiencies hinder the advancement of research in the application of microrobot swarms. For example, the limited number of individuals and the tiny spatial size make the current microrobot swarms too insignificant to meet practical needs. To release these restrictions, we designed a hybrid-style magnetic actuation control system that integrates the electromagnetic coils and permanent magnet. This hybrid-style actuation system can generate customized magnetic fields spatiotemporally, including powerful rotating and gradient magnetic fields, which enables the emergence of a large-scale magnetic microrobot swarm (LMMS) under the coupling effect of the magnetic field and gradient. Besides, the LMMS based on ferrofluid droplets is studied to verify the actuation system's feasibility, with a series of control strategies being proposed accordingly and the performance of the actuation system being discussed theoretically by mathematical models. Finally, physical or simulation experiments were carried out on these bases, demonstrating that the aforementioned method can realize the controllable emergence, dispersion, and locomotion of the LMMS with excellent manipulation ability and maneuverability.