Nanoscale iodophoric poly(vinyl amide) coatings for the complexation and release of iodine for antimicrobial surfaces

Abstract

Wound infection exacerbated by multidrug-resistant (MDR) bacteria has necessitated the need for wound dressing materials with embedded antimicrobial property to prevent the development of chronic wounds. Iodine (I2), typically as a poly(vinyl pyrrolidone)-I2 (PVP–I) complex, is a widely used antiseptic agent in wound care owing to its efficacy, safety, and low probability to cause further resistance. Despite extensive research on PVP–I formulations, there is potentially a large selection of poly(vinyl amide)s that have remained largely unexplored as iodophoric materials, particularly as coatings for wound dressings and medical devices. Therefore, in this study we prepared a series of stable, cross-linked poly(vinyl amide) coatings via plasma polymerization and studied their structure–property relationships for the complexation and release of I2. Plasma polymerized poly(N-vinyl-2-pyrrolidone) (pPVP), poly(N-methyl-N-vinylacetamide) (pPMVA) and poly(N-vinylcaprolactam) (pPVCl) nanoscale coatings were prepared with uniform thicknesses of 330–340 nm and low surface roughness. Complexation of I2 as polyiodides resulted in a significant increase in the pPVCl coating thickness in phosphate buffered saline (PBS), consistent with the Hofmeister effect. Raman spectroscopy confirmed that the I2 was complexed exclusively as the triiodide ion (I3-) in all coatings, which was confirmed by synchrotron X-ray photoelectron spectroscopy (XPS) experiments. Nuclear magnetic resonance (NMR) spectroscopy of poly(vinyl amides) was employed to further prove that the complexing species was hydrogen triiodide (HI3). The loading of I2 species increased from pPVP < pPMVA < pPVCl, with percentage elemental compositions of 1.3, 1.8, and 2.9%, respectively, which correlated with the extent of nitrogen loss during polymerization and oxidation, and was also in agreement with determined negative zeta potential values. However, quantification of the released I2 species over 5 h showed that the greatest release was observed from pPMVA (121.3 µg.cm−2), with pPVP (77.4 µg.cm−2) and pPVCl (74.6 µg.cm−2) releasing a similar amount, highlighting that I2 release from poly(vinyl amide) coatings is a function of the loading and composition of the polymer, not just the I2 complexing amide motif. The I2 complexed pPMVA coated wound dressings were highly effective against Gram-negative Pseudomonas aeruginosa and Gram-positive Staphylococcus aureus, the two major strains associated with wound infection, reducing bacterial viability by up to 4 and 7 (log10 reduction) orders of magnitude. Overall, the poly(vinyl amide) coatings are promising iodophors for the prevention and treatment of wound infections.