In situ multi-material μCLIP for fabricating Fe₃O₄/HEMA-based magnetic miniature devices with large deformation

Micro-continuous liquid interface production (μCLIP) enables high-speed and high-precision fabrication of magnetic microstructures by reducing resin residence time and suppressing particle settling. However, achieving large and reliable deformation remains challenging due to the high stiffness of conventional single-material prints and poor interfacial bonding between soft hydrogel and magnetic components. Here we present a multi-material μCLIP process with in situ vat exchange, utilising a homogeneously doped Fe₃O₄/HEMA photopolymer to improve interfacial chemical continuity. The HEMA hydrogel showed a modulus drop from 1154.9 MPa (dry) to 0.21 MPa (swollen), enabling large reversible deformation while maintaining printing precision. Among five Fe₃O₄/HEMA formulations (0–10 wt%), 7.5 wt% HEMA in the Fe₃O₄/HEMA magnetic resin achieved optimal interfacial bonding, increasing tensile strength by 2.3 times and elongation by 3.1 times compared with the undoped resin. A cantilever and a compact magnetic aperture of 6.5 mm in diameter were fabricated to validate the approach. The aperture achieved a 69.4% increase in opening diameter (from 1.60 to 2.71 mm) under a 120 mT magnetic field, confirming reliable multi-material coupling and controllable actuation. This strategy provides an effective pathway toward multi-material magnetic devices with reliable interfacial integration and accurate motion control in optical and soft robotic systems.