Polypyrrole (PPy) coating concentration mediates electromagnetic coupling and oxidative protection for iron oxide core particles in biomedical applications

Abstract

While polypyrrole (PPy) coatings are known to enhance iron oxide nanoparticles' (IONPs') functional properties, the concentration-dependent interplay between electromagnetic coupling and oxidative protection remains challenging, due to their opposing dependence. In this study, we report a concentration-dependent strategy using PPy coatings to mediate this dual functionality in IONPs. Through micellar polymerisation, IONPs (50–100 nm) were coated with PPy at 10–50 mM concentrations. At 40 mM, conductivity peaked at 456 μS cm⁻¹, a 99% increase compared to that of bare IONPs. Electromagnetic characterization via vector network analysis (VNA) revealed maximum shielding effectiveness (SE_T = 1.36 dB) at the same concentration, primarily through the reflection mechanism. Cyclic voltammetry (CV) curves showed suppressed core oxidation for >30 mM coating concentration, due to the formation of a redox-buffering interface that reduced Fenton-like reactivity under acidic conditions. This oxidative shielding effect, coupled with maintained cytocompatibility (>80% cell viability at ≤2% w/v), provides critical insight into redox-safe design. Despite ∼25% reduction in saturation magnetisation, this reflects the intrinsic trade-off associated with surface functionalization, yet retaining applicability for magnetically guided biomedical applications. These findings provide a concentration-dependent framework for designing multifunctional fillers, which could be aimed at promoting cell alignment and bioelectronic responsiveness in ferromagnetic hydrogel systems, potentially for biomedical applications.