The Method of Preparation Impacts the Performance of Poly(N-oxides) in Biological Applications

Biofilm formation is a major challenge in various areas such as healthcare, water treatment and manufacturing, contributing to persistent infections and equipment damage. Zwitterionic surface modifications, especially poly(N-oxides), are becoming increasingly important in this context due to their excellent hydration properties, which make them effective against microbial adhesion. Conventional methods for introducing poly(N-oxides) on surfaces involve the oxidation of tertiary amine-functionalized polymers with H₂O₂, a cost-efficient but potentially problematic approach due to residual H₂O₂ on the surface. This residual H₂O₂ can misrepresent the surface's true bioactivity, suggesting antibacterial properties that are not inherent to poly(N-oxides).

In this work, a highly sensitive dye-based assay was employed to quantify the release kinetics of H₂O₂ from N-oxide post-modified polyethylene (nonpolar) and polyamide (polar). Substantial H₂O₂ release was observed from both materials over 24 hours, with polyethylene releasing quantities four orders of magnitude greater than solvent-accessible N-oxides. These findings highlight the potential of residual H₂O₂ to distort biological assay outcomes. To overcome these limitations, a direct polymerization approach for N-(4-vinylbenzyl)-N,N-dimethyl-N-oxide was developed, eliminating the need for post-modification with H₂O₂. This method employed plasma-activation of the polymer substrate, styrene as a polymerizable unit, and a crosslinker to achieve stable hydrophilic modifications even on highly hydrophobic substrates like polyethylene. Microbiological testing with S. aureus and E. coli confirmed that N-oxide modified surfaces exhibited solely antiadhesive properties without bactericidal activity.

This study establishes a method for the polymerization of N-(4-vinylbenzyl)-N,N-dimethyl-N-oxide on polyethylene and polyamide base materials and highlights the pitfalls of H₂O₂ impurifications on poly(N-oxide) brush layers prepared by other synthetic protocols.