The linker-free covalent immobilization of polymers on surfaces has the potential to impart new properties and functions to surfaces for a wide range of applications. However, most current methods for the production of these surfaces involve multiple chemical steps and do not have a high degree of control over the chemical functionalities at the surface. A comprehensive study detailing the facile two-step covalent grafting of the antimicrobial peptide nisin onto polystyrene surfaces is reported. Functionalization is achieved using an atmospheric pressure plasma jet, and the reaction is monitored and compared with a standard wet chemical functionalization approach using a variety of analytical techniques. The reactive species produced by the atmospheric pressure plasma jet were analyzed by mass spectrometry and optical emission spectroscopy. The surface chemistry and topography of the functionalized surfaces were determined using contact angle measurements, Fourier infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy and atomic force microscopy respectively. Following surface analysis, the antimicrobial efficacy of the covalently grafted nisin against two major food borne pathogens (Staphylococcus aureus and Listeria monocytogenes) was assessed at two different pHs. The results demonstrated that a post-plasma treatment step after nisin deposition is required to covalently graft the peptide onto the surface. The covalent immobilization of nisin resulted in a significant reduction in bacterial counts within a short 30 minutes contact time. These surfaces were also significantly more antimicrobial compared to those prepared via a more traditional wet chemical approach indicating that the reported method could be a less expensive and less time consuming alternative.

The ability of nitric oxide (NO)-releasing polymer coatings to prevent biofilm formation is described. NO-releasing coatings on (poly(ethylene terephthalate) (PET) and silicone elastomer (SE)) were fabricated using aminosilane precursors. Pristine PET and SE were oxygen plasma treated, followed by immobilisation of two aminosilane molecules: N-(3-(trimethoxysilyl)propyl)diethylenetriamine (DET3) and N-(3-trimethoxysilyl)propyl)aniline (PTMSPA). N-diazeniumdiolate nitric oxide donors were formed at the secondary amine sites on the aminosilane molecules producing NO-releasing polymeric coatings. The NO payload and release were controlled by the aminosilane precursor, as DET3 has two secondary amine sites and PTMSPA only one. The antibacterial efficacy of these coatings was tested using a clinical isolate of Pseudomonas aeruginosa (PA14). All NO-releasing coatings in this study were shown to significantly reduce P. aeruginosa adhesion over 24 h with the efficacy being a function of the aminosilane modification and the underlying substrate. These NO-releasing polymers demonstrate the potential and utility of this facile coating technique for preventing biofilms for indwelling medical devices.

Nonhealing and chronic wounds represent a major problem for the quality of life of patients and have cost implications for healthcare systems. The pathophysiological mechanisms that prevent wound healing are usually multifactorial and relate to patient overall health and nutrition, vascularity of the wound bed, and coexisting infection/colonization. Bacterial infections are one of the predominant issues that can stall a wound, causing it to become chronic. Successful wound healing often depends on weeks or months of antimicrobial therapy, but this is problematic given the rise in multidrug-resistant bacteria. As such, alternatives to antibiotics are desperately needed to aid the healing of chronic, and even acutely infected wounds. Nitric oxide (NO) kills bacteria through a variety of mechanisms, and thus, bacteria have shown no tendency to develop resistance to NO as a therapeutic agent and therefore can be a good alternative to antibiotic therapy. In this paper, we report on the development of NO-releasing electrospun membranes fabricated from polycaprolactone (PCL)/gelatin blends and optimized to reduce bacterial infection. The NO payload in the membranes was directly related to the number of amines (and hence the amount of gelatin) in the blend. Higher NO payloads corresponded with a higher degree of antimicrobial efficacy. No cytotoxicity was observed for electrospun membranes, and an in vitro wound closure assay demonstrated closure within 16 h. The results presented here clearly indicate that these NO-releasing electrospun membranes hold significant promise as wound dressings due to their antimicrobial activity and biocompatibility.