Label-free microcargo delivery and controllable release in complex fluidic environments based on autonomous magnetic...

Magnetic microswarms exhibit great potential for targeted delivery because of their excellent controllability and environmental adaptability. Enabling label-free cargo delivery and controllable release while endowing microswarms with resistance to environmental disturbances is key to expanding their application scope. In this study, we present a label-free microcargo delivery strategy based on a magnetic microswarm actuated by a magnetic tweezers system. In this approach, high-frequency magnetic fields enable autonomous cargo capture, while low-frequency fields trigger controlled release, forming a simple yet effective frequency-switching mechanism. Owing to the high-intensity magnetic field produced by the magnetic tweezers system, the microswarm exhibits significantly improved anti-interference capability, ensuring stable transport even under dynamic flow conditions. Leveraging visual feedback, the microswarm autonomously captures and stably transports various microscale cargos, including polystyrene microspheres and cell spheroids up to 400 µm in diameter. In complex structures and flowing fluid environments, microswarms that carry cargo successfully resist fluid impacts and achieve autonomous navigation. Furthermore, the controllable release of nonmagnetic cargos is realized through a frequency-switching mechanism. When a microswarm carries multiple cargos, small cargos are usually discharged first, indicating the potential of this release mechanism to sequentially release multiple cargos. This strategy circumvents the risks associated with permanent magnetic labeling and enhances the microswarm's anti-interference capability, providing essential technical support for the practical translation and clinical application of magnetic microrobots.