Development of plasma polymer thin films for control of cell and microbe attachment

Functional plasma polymer films have gained increasing attention in recent decades to selectively modify the surface of biomaterials. Although many applications have been identified for plasma polymerisation, the fundamental aspects of plasma polymer film growth are still poorly understood. In this thesis, both the film growth mechanism and applications of the coatings to control cell and microbe attachment in vitro were investigated. The main part of the thesis focused on fabrication of diethylene glycol dimethyl ether (diglyme, DG) plasma polymer films via radio frequency glow discharge (RFGD) plasma polymerisation. By manipulation of process parameters, diglyme plasma polymer films (DGpp) could perform as low-fouling coatings that was similar to poly(ethylene glycol) (PEG) grafted layers. Systematic study on the effect of load powers to DGpp film chemistry was carried out. The surface chemistry of the synthesised films was studied by X-ray photoelectron spectroscopy (XPS) and near edge X-ray absorption fine structure (NEXAFS) spectroscopy. It was found that higher load power led to more fragmentation of the monomer, therefore less retention of ether functionality. The resultant films were used for protein adsorption, cell culture and microbe attachment studies in vitro. Films produced with high ether concentration generally were resistant to fouling, meanwhile, relatively low ether concentration allowed a higher quantity of protein adsorption, cell and microbe attachment. The DGpp films were very smooth in nature. They have been deposited onto amyloid fibril networks (AFNs) that have roughness greater than the film per se. The change in roughness resulted in differences in amount of cell attachment and spreading. The unique structure of the AFNs was still visible under atomic force microscopy (AFM) after DGpp deposition, thus a study to decipher the mechanism of film growth was conducted. During the deposition of the films, various substrates, such as silicon wafers, glass and polymers, were used to test the adhesion strength of DGpp films. On silicon wafers, the films were stable in atmospheric conditions but became patchy after immersion in water or cell culture solutions for prolonged times. In addition, it was found DGpp films were most stable on polymeric substrates but were easily delaminated from indium tin oxide (ITO) coated glass. The low adhesion strength on ITO glass was exploited further in this thesis to expose the substrate-film interface by peeling off the film using double-sided tape. This simple method allowed investigation of the chemistry of the DGpp films growth at the initial stage. Adhesion of plasma polymer film to the substrate depends on the interaction of gas phase species in the plasmas with the top surface of the material. In order to gain a better understanding of the interface mixing between plasma polymer films and polymeric substrates, DGpp films were deposited (under the same conditions) onto six types of plasma polymer films. Non-invasive methods, neutron and X-ray reflectometry (NR, XRR) were employed to characterise these bilayer constructs and showed changes in interfacial width depending on the base plasma polymer layer. Since the DGpp film was not very efficient in antimicrobial application for the long term, a new plasma polymer based route was selected to combat the infection problem of biomaterial surfaces. A brominated coating was produced using RFGD plasma polymerisation and modified with sodium azide to incorporate azide functionality onto the surface. The resultant coatings were tested in vitro against Staphylococcus epidermidis, Pseudomonas aeruginosa and Candida albicans. Excellent antimicrobial property was presented on azide immoblised surfaces. On the other hand, those coatings are compatible with HeLa cell culture and induced minimal lysis of human erythrocytes.