The generation and characterisation of low fouling, uniform, gradient and micropatterned surfaces via plasma polymerisation

This thesis is focused on the generation, characterisation and application of PEG-like, low fouling surfaces deposited by plasma polymerisation of diethylene glycol dimethyl ether. The first part of the thesis focused on uniform films, where the ideal deposition parameters were identified for the fabrication of robust low fouling plasma polymer films, particularly with regards to the W/FM parameter by varying the plasma load power. A number of complimentary surface sensitive analytical tools were employed in film characterisation including, including XPS, NEXAFS and neutron reflectometry. A combination of these analytical techniques enabled us to determine that films deposited at lower load power retained a higher degree of monomer “PEG-like” functionality, particularly with regards to the ether content and these films displayed the most efficient low-fouling characteristics against BSA and lysozyme protein adsorption. Further to this, HeLa cell attachment was largely resisted by the lower-fouling higher ether containing plasma polymer surfaces. The use of neutron reflectometry in the analysis of the uniform plasma polymer films enabled us to further identify the densities and H content of the film, not otherwise determinable with XPS and ToF-SIMS. Using the scattering length densities we were also able to identify the full empirical formula of the plasma polymer films, where the lower load power that was shown to be most protein resistant (QCM-d) showed to have a chemical composition most similar to that of a typical PEG-grafted surface. The second part of the results component of the thesis was focused on the generation and characterisation of gradient PEG-like plasma polymer surfaces. These surfaces are ideal for the high throughput analysis of material-biological interactions, and were shown to be successful in the formation of chemical gradients of BSA, Lysozyme, IgG, human serum albumin (HAS) and fetal bovine serum (FBS). The gradient surfaces were analysed using complimentary techniques such as NEXAFS, XPS, synchrotron source gi FTIR microspectroscopy and ToF-SIMs and it was shown that more proteins adsorbed in regions of the gradients that displayed a lower ether and higher hydrocarbon and carbonyl content. Cell attachment was also investigated across the gradients, which appeared to be dictated by the adsorption of FBS which was present during the cell culture experiments. Time was shown to be a critical factor for the relative adsorption of FBS with the central region of the lower powered gradients showing to be FBS resistant (within XPS detection limits), while after a 24 hour adsorption period, proteins were measured across the entire length of the gradients. The generation and application of chemically micropatterned surfaces is discussed in the final results chapter of this thesis. By controlling the electrode geometry, we were able to deposit functional, chemically micro-patterned surfaces in one step using plasma polymerisation of diethylene glycol dimethyl ether. By etching patterned holes in the top, active electrode, and placing it to sit 1 mm above the substrate in the plasma reactor, variation to the plasma flow and resulting sheath leads to a low-fouling surrounding coating, while the patterned features (deposited under the holes of the electrode are more fragmented with a higher proportion of carbonyl and hydrocarbon species. The controlled spatial variation to surface chemistry was analysed and imaged using ToF-SIMS imaging and gi-FTIR microspectroscopy and the size and shape of the patterned features can be controlled with the design of the electrode. The biological applications of these chemically patterned surfaces was displayed by spatial control of protein (BSA) adsorption and cell (HeLa) attachment, as well as the spatial confinement of enzyme mediated self-assembled peptides