Magnetic-responsive hydrogels as composite smart materials: preparation, applications and challenges

Magnetic-responsive hydrogels (MRHs) combine hydrogel networks with magnetic particles, enabling remote actuation, magnetothermal conversion, and multifunctional responses. However, their performance is highly dependent on particle composition, size, loading, dispersion, particle-polymer interactions, crosslinking density, and fabrication conditions, making their design and characterization complex. Moreover, systematic relationships among preparation, interfacial modification, structure-property regulation, and application performance remain insufficiently understood. To address these issues, this review summarizes the preparation, modification, properties, and applications of MRHs from a preparation-interface-property-application perspective. Firstly, soft- and hard-magnetic hydrogels are classified and compared. Next, blending, in situ precipitation, and covalent bonding are discussed with emphasis on particle dispersion, retention, interfacial stability, and mechanical performance. Furthermore, surface modification, mechanical reinforcement, and the effects of particle characteristics, loading, and crosslinking density on magnetic, swelling, mechanical, magnetothermal, and biological properties are analyzed. Finally, applications in biomedicine, environmental remediation, actuation and sensing, and emerging engineering fields are reviewed together with challenges in nanoparticle leakage, fatigue, magnetic-field dosimetry, biodegradation, reproducibility, sterilization, and scale-up. Overall, this review provides guidance for the rational design and practical development of MRHs.