Book Description

"It has been over a century since plasma polymers were discovered and since then they are investigated for numerous potential applications in many fields including electrical, optical and biomedical. Plasma based deposition techniques are dry processes with which a wide variety of substrate materials and objects with 3-dimensional geometries can be treated. The coatings are highly cross-linked, conformal and pin-hole free providing good barrier properties. Surface chemistries can easily be controlled and precursor gases are relatively inexpensive. These are a few reasons that make plasma polymers attractive, especially for biomedical applications such as cell and tissue culture, controlled drug release, anti-fouling coatings, biosensors and so on.In this thesis, application of nitrogen (N) based plasma polymer films is investigated, to regulate the adsorption of fibrinogen (Fg), a blood clotting protein, in light of achieving the long term goal of gaining control over blood coagulation, a useful criterion for studying aneurysm healing following an endovascular coiling procedure. In arriving at this main objective, several fundamental studies are first conducted to design a suitable set of coatings, which are produced using a low-pressure radio frequency (RF) glow discharge. In the first part of the thesis, a fundamental study on elucidating the characteristics of two distinct methods of producing N rich plasma polymer films is carried out, where the precursor types employed in each method are (i) single source precursors and (ii) precursor mixtures. A variety of characterisation tools are used to perform plasma diagnostics and thin film analyses, to understand the plasma-phase processes that result in coatings with specific functionalities. The second part of this work aims at producing plasma polymer coatings with a high amine content as well as high resistance to film dissolution in aqueous media. Owing to the increased controllability of N to C ratio in the gas phase and thereby, in the solid phase, which is the film, the second method of producing N based coatings is employed. This method involves using a functional group source gas, in this case ammonia, and a hydrocarbon (HC) precursor, in this case ethylene and/or 1,3-butadiene. Owing to the presence of two conjugated C-C double bonds, 1,3-butadiene is chosen to render better cross-linked coatings compared with those produced from ethylene, a common precursor used in many studies. Plasma deposition parameters varied in film optimisation are power, gas flow ratio and total gas flow rate. It is shown that butadiene based films, as required, yield a better compromise between amine content and water stability compared with that achieved by ethylene based films, under similar plasma deposition conditions. The final part of this project focuses on developing a series of plasma polymer films that can effectively promote Fg adsorption to varying extents. It commences with a continuation of the optimisation of coatings from the previous section. This is carried out by varying the deposition pressure, a crucial process parameter that greatly influences plasma polymerisation, and studying its effect on film properties such as the amine content, aqueous stability as well as affinity for Fg adsorption. Next, the influence of the type of N based coatings, defined by the HC precursor used for deposition, on Fg adsorption is investigated. An oxygen (O) rich and a platinum (Pt) coating are also included in the study. Finally, a subset of these coatings is chosen to monitor Fg adsorption in the presence of a second protein, human serum albumin (HSA). It is shown that the designed plasma polymer coatings could successfully regulate the adsorption of Fg with and without the presence of a high concentration of competing HSA, opening up the possibility for controlling blood coagulation, a useful concept to improve aneurysm healing following an endovascular coiling treatment. " --