Summary

Biofilm formation costs billions of dollars every year across a wide range of industries. On ship hulls, it has been estimated that a biofilm of just a few hundred microns yields an average 20% increase in fuel consumption. The food industry performs extensive chemical decontamination processes resulting in both environmental and financial costs, while bacterial infection results in the failure of biomedical devices, affects storage stability of microfluidic based bio-diagnostics and is the cause of numerous medical interventions. Attachment of bacterial cells is the critical first step in the chain of events leading to biofilms formation. Materials and surfaces that are able to prevent or limit the initial adhesion of bacteria are thus needed for a range of industrial applications.

Pure essential oil constituents are natural, non-synthetic materials that are environmentally friendly. Some of these constituents present inherently beneficial properties, such as antimicrobial and antifungal activity. Translation of the antimicrobial activity to surfaces requires methods for immobilising the bioactive components in a stable and active form.

The aim of this proof-of-concept project is to develop antimicrobial surface coatings from commercially available pure constituents of Australian essential oils including 1,8-cineole, citronellal, and citral (mixture of geranial and neral) using both plasma polymerisation and wet chemical routes. The antimicrobial activity of the coatings will be evaluated and compared to the activity of the oils. Through this project we aim to develop fabrication strategies that will enable the coating to be applied to any material that comes in contact with bacteria.

Program

New and Emerging Plant Industries

Research Organisation

Swinburne University of Technology

Objective Summary

The project aims to produce antimicrobial coatings from commercially available 1,8-cineole (1,8-epoxy-p-menthane), citronellal (3,7-dimethyl-6-octenal), and citral (3,7-dimethyl-2,6-octadienal). To achieve this, two parallel objectives have been developed:

Objective 1: Plasma polymerisation routes for depositing bioactive thin films from pure constituents. Initial studies will involve the development of plasma polymer films using pulsed deposition conditions. This will enable minimal monomer fragmentation, while ensuring that there is sufficient energy applied to create the necessary radicals and ions to form the polymer deposit. The addition of readily polymerised diluent monomer (1-7 octadiene) will also be explored for creating functionally active, stable films.

Objective 2: Wet chemical routes for immobilising pure constituents onto plasma polymers. This objective will explore wet chemical routes for applying the essential oils to the surfaces of plasma polymers using covalent coupling strategies and physical adsorption. Initial studies will focus on utilising hydrophobic/hydrophillic interactions between plasma polymers of either 1,7-octadiene or acrylic acid and the constituents, enabling dipping technologies to be explored as an effective and rapid coating method. Dependent on the chemistry of the constituent, specific covalent immobilisation strategies to enable coupling to plasma polymer films will also be developed, leading to improvements in the long-term stability of the coatings.

Thorough physical and chemical characterization of all fabricated surfaces will be performed. Biochemical assays, growth studies and laser confocal microscopy will be used to characterise the interactions and behaviours of bacteria on each of the modified materials and compare their performance to the topical application of the essential oils constituents.