A Rapid and Uniform Magnetization Method for Fe3O4 Nanoparticles Assisted by Rotating Magnetic Fields for Microrobots.

Micro/nanorobots have garnered significant attention due to their potential applications in biomedical fields such as minimally invasive surgery, targeted drug delivery, and cell manipulation. Magnetic field actuation, as a non-invasive and highly biocompatible driving method, has become a research hotspot. However, traditional magnetic functionalization methods like magnetron sputtering suffer from complex processes, high costs, and poor biocompatibility. Meanwhile, the mixture method combining magnetic particles with photoresist is constrained by particle dispersion and molding quality. To address these challenges, this study developed a low-cost, rapid, efficient, uniform, and stable magnetic coating method for Fe3O4 nanoparticles. This technique utilizes a rotating magnetic field to rapidly transport and concentrate Fe3O4 nanoparticles around the photoresist microstructure, where the kinetic energy imparted by the magnetic field forcefully overcomes interfacial electrostatic repulsion, allowing strong van der Waals forces to drive their firm and uniform adhesion within 5 min. Systematic experiments demonstrate that this method exhibits outstanding performance in particle attachment uniformity, motion stability, durability, and biological environments. Its motion capabilities are comparable to those achieved by conventional magnetron sputtering, providing significant reference for the functional design and biomedical applications of magnetic micro/nanorobots.