Fabrication of non-spherical microparticles with embedded chains of superparamagnetic iron oxide nanoparticles (SPIONs)

Designing microscale structures that respond predictably to external fields is critical for applications in directed assembly, adaptive materials, and biomedicine. Among available actuation methods, magnetic fields are particularly advantageous—they interact selectively with magnetic materials, offer orientational control, and exert relatively large forces and torques on microscale components. However, magnetic alignment is constrained by the longest magnetic axis of the structure. Because most fabrication methods produce materials in which magnetic and geometric axes coincide, such structures lack freedom for independent orientation and programmable magnetization. Here, we introduce a fabrication strategy that enables magnetization along arbitrary axes in microscale structures using superparamagnetic iron oxide nanoparticles (SPIONs). By applying a magnetic field to a SPION-doped photopolymer film, we induce chain-like assemblies that define a tunable magnetic axis. Subsequent photolithography builds particles around these chains in any orientation, decoupling magnetization and geometry. By varying the applied field and SPION concentration during fabrication, we precisely control the magnetic torque and response. Vector magnetometry measurements reveal how the particles respond to fields of different magnitudes and orientations. This approach establishes a versatile platform for engineering magnetically reconfigurable microsystems with programmable response.