A Multifunctional Bioactive Nanoscale Coating Deposited by Atmospheric Pressure Plasma Polymerization of Peppermint Essential Oil

Implanted and indwelling medical devices remain challenged by infection, oxidative stress, and chronic inflammation, underscoring the need for multifunctional surface coatings to holistically address these complications. Peppermint essential oil is inherently antibacterial, antioxidant, and anti-inflammatory, yet its integration into stable, contact-active coatings is limited by fabrication constraints. Here, we present a one-step atmospheric pressure plasma polymerisation process that converts peppermint essential oil into a conformal, cross-linked coating that preserves precursor-derived functional groups that drive broad bioactivity. While the coating is substrate-independent, we evaluate its bioactive performance within the context of bladder catheterisation as a pilot application. It scavenges up to 90% of reactive species, reduces pro-inflammatory cytokine expression by up to 60%, and increases anti-inflammatory cytokines by up to 50%, while promoting macrophage polarisation toward an M2 phenotype. The coating exhibits intrinsic antibacterial activity, reducing viable bacteria by 90% (Live/Dead) and 70% (CFUs), attributed to membrane disruption of Gram-negative pathogens. In turn, this interaction potentiates the activity of colistin and levofloxacin, two antibiotics used in catheter-associated urinary tract infection management. Together, these findings establish a stable, multifunctional coating capable of mitigating infection, alleviating inflammation, and enhancing antibiotic performance, while offering a sustainable route for essential-oil-derived biomaterials.