Hybrid Microdiscs for Magnetically Induced Non‐Cytotoxic Thermal Actuation and Programmable Biomolecule Delivery

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Abstract
A modular microfabrication strategy is presented for developing multifunctional magnetic microdiscs (MDs) with structural control and tunable composition. Combining photolithography with layer‐by‐layer assembly, this approach enables the fabrication of perfectly flat microdiscs with nanometric thickness. By selecting distinct lithographic methods, the disc diameter is tailored to modulate cellular interaction: large discs (≈18 µm) remain at the cell surface, while smaller ones (≈1.5 µm) are readily internalized. This dimensional tunability defines whether the platform operates extracellularly or intracellularly. Both microdisc types show excellent biocompatibility (at 4 MD‐18/cell and 3000 MD‐1.5/cell) and deliver spatially confined, non‐cytotoxic heating (AFM = 677 kHz, 25 mT, 1 h). These features support their use not for thermal ablation but for magnetothermal stimulation or enhanced molecular delivery. The fabrication method allows independent control of the inorganic thin film, polymeric layers, magnetic nanoparticle (MNP) content, and biomolecular payloads. Integrating Fe 3 O 4 MNPs of optimized size and shape maximizes magnetic responsiveness. Additionally, BSA‐loaded microdiscs are fabricated to illustrate the system's potential for programmable biomolecule delivery using the HCT116 cell line. Time‐lapse assays reveal efficient uptake dynamics, with protein loading influencing internalization. These hybrid MDs combine adjustable design and predictable uptake, offering strong potential for next‐generation magnetically actuated biomedical strategies.

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