Polymer Based Layer-by-Layer Antimicrobial Coatings

Abstract

In the face of the ever-relevant struggle against microbial pathogenesis and antibiotic resistance, continued development of novel approaches for the prevention of infection, thus circumventing need for treatment, are of deep importance. In this work, a series of model multilayer systems were created via layer-bylayer deposition and assessed for their antimicrobial activity against the Gram negative E. coli and the Gram positive S. aureus. Each multilayer system was comprised of repetitive units of either two components (bilayers) or three components (trilayers). Layer components constituted of synthetic polymers (Nafion, polyvinylpyrrolidone, and a methacrylate block copolymer), biomolecules (chitosan and lysozyme), along with oxides and nanoparticles (cerium oxide, graphene oxide, graphene quantum dots and carbon dots). An initial monolayer system was created using Nafion, a synthetic polymer with excellent mechanical properties, offering a stable foundation for subsequent layers. Multilayer systems were built upon this using various compounds in order to enhance antimicrobial activity. Through tailoring of multilayer components, systems could be taken from being more effective against a single type of bacteria to possessing equal activity against both Gram positive and negative bacteria, such as with the addition of lysozyme into a Nafion/ chitosan system. This addition bolstered activity against E. coli from 76.4% to 99.96%, matching the 99.98% activity against S. aureus. The Nafion itself could be substituted as a layer component with another synthetic polymer, with a GO/PVP system providing antimicrobial activity in a similar range to its Nafion/GO counterpart; 90.8% and 95.7% compared with 96.3% and 98.9% against E. coli and S. aureus respectively. QCM-D was used to control the deposition of each multilayer component, ensuring uniform layers and reproducibility. Biological properties were investigated using a qualitative haemotoxicity test, which found all systems to be non-haemotoxic, and circular dichroism to assess interactions between lysozyme and other compounds, which found Nafion to provide a heat stabilising effect on the enzyme. Physical properties were explored, using contact angle measurement to determine levels of hydrophobicity/ hydrophilicity, zeta surface potential measurements to assess interaction between layers, and AFM to measure surface roughness. Overall, all multilayer systems expressed excellent antimicrobial activity against the representative Gram positive and Gram negative species, with both favourable synergy and interchangeability between layer components. Layerby- layer deposition has shown itself to be a facile and effective method for the production of multilayer coatings with a range of physical and biological properties.