Stable and homogeneous SPION-infused Photo-Resins for 3D-printing magnetic hydrogels

3D printing of magnetic stimuli hydrogels has shown promise in low-resolution extrusion printing but integrating superparamagnetic iron oxide nanoparticles (SPION) into water-based photo-resins has posed challenges. Rapid agglomeration and sedimentation of SPION in photo-resins require continuous mixing during printing, leading to uneven nanoparticle (NP) distribution and inconsistent magnetic actuation. Here, we optimise the use of citric acid (CA) and l-sodium ascorbate (LA) as capping agents on the SPION's surface, before trialling them with photo-resins. Ultimately, we present a two-step approach to overcome these limitations, enabling high-resolution SLA-based 3D printing of hydrogels. By employing CA in both SPION and photo-resin preparation, we achieve a highly stable mixture that requires no agitation during printing, resulting in magnetically responsive hydrogels. This methodology can be applied to various photo-resin formulations, ensuring uniform NP distribution and enabling the 3D printing of stimuli-responsive materials for applications in soft robotics, aquatic micro-swimmers, and soft actuators. The breakthrough in stable and homogenous SPION-infused photo-resins has broad implications for tissue engineering, drug delivery, and regenerative medicine, offering novel biocompatible materials with resistance to stress and deformation. This approach can be extended to other NP with poor dispersion in hydrogels, paving the way for advanced functional materials in diverse applications.