There is considerable interest in the application of plasma polymerised acrylic acid (ppAAc) coatings due to their ability to enhance the adhesion of cells and proteins. An issue with this coating however it its stability in water and previous studies carried out using low pressure plasmas have demonstrated that high plasma powers are required to achieve water stable coatings. In this paper the use of both helium and air atmospheric plasmas are compared for the deposition of ppAAc coatings. The deposition studies were carried out on silicon wafer substrates using the PlasmaStream TM and PlasmaTreat TM plasma jet deposition systems respectively. The coatings were characterized using contact angle, FTIR, SEM, XPS, ellipsometry and optical profilometry. While both the helium and air plasmas were successful in the deposition of ppAAc coatings, the nm thick films deposited using the PlasmaTreat system exhibited significantly higher levels of water stability, probably due to a higher level of coating cross linking. Ellipsometry measurements demonstrated only a 0.2 nm reduction in the thickness of an 18 nm thick ppAAc coating, when immersed in an aqueous buffer solution for one hour. Protein attachment studies were carried out using a flow cell system, which was monitored using a spectroscopic ellipsometer. This study was carried out with Bovine Serum Albumin (BSA), Immunoglobulin G (IgG) and Fibrinogen (Fg) proteins. In all three cases increased levels of protein adhesion was observed for the ppAAc coating, compared to that obtained on the uncoated silicon wafer substrates.Keywords: Atmospheric Plasma, Thin Film, Nano-coatings, Surface Engineering, Protein Adhesion IntroductionControlling protein adhesion is an important issue affecting many different fields including bio-processing, medical device implants, biosensors, and drug delivery devices [1,2]. When the surface of a material interacts with a biological environment one of the initial interactions is through protein adhesion [3]. Amongst the factors influencing protein adsorption, are surface chemical functionality and morphology [4]. Amongst the techniques that have been investigated to modify the surfaces of polymers prior to protein adhesion studies have been micro patterning and monomer polymerisation by free radical solution, emulsion, grafting as well as plasma processes [5][6][7][8][9]. It has been demonstrated by a number of authors that plasma techniques enable both the surface functionality and morphology to be tailored [10,11]. This makes it possible to create a surface which will inhibit or enhance the rate of protein adhesion onto a biomaterial surface, without changing the properties of the bulk material [12].One surface chemistry that has received considerable attention for cell and protein adhesion has been acrylic acid. Surfaces containing this coating have been reported in applications ranging from platelet adhesion promotion [13], RGD peptide immobilisation [14], attachment of osteoblast-like [15], fibroblast [16] and keratinocyte [17]...
This study investigates protein adhesion on nm thick helium atmospheric plasma deposited quaternary ammonium salt (QAS) coatings. The adhesion of the proteins BSA, IgG and Fg was evaluated on coated and uncoated silicon wafer substrates. This study was carried out in PBS solution, under flow conditions using ellipsometry. The QAS was found to exhibit a low level of solubility in PBS over time (approx. 2 nm / hour). On addition of both the IgG and Fg proteins, it was found that a protective protein layer of 7 and 2 nm respectively was formed, which prevented further dissolution of the QAS. In contrast the 1 nm thick BSA protein layer, which formed on the QAS, was insufficiently thick to prevent the slow dissolution of the salt. It was concluded that the charge and structure of the protein influences its adhesion on the QAS surface. IntroductionA key issue affecting the performance of medical devices in the body is protein adhesion. [1,2] This is because proteins dictate how the cell interacts with the device surface.[3] Although there is a degree of inconsistency within the literature as to the factors influencing protein adsorption on a surface, it is believed that chemical functionality and topography are important factors. [4] Amongst the techniques that have been investigated to alter the surfaces of polymers in order to modify protein adhesion have been micro patterning and monomer polymerisation by free radical solution, emulsion, grafting as well as plasma processes. [5][6][7][8][9] The focus of this study is to investigate how a plasma polymerised quaternary ammonium salt (QAS) coating deposited onto a silicon wafer substrate influences protein adhesion.Worldwide consumption of quaternary ammonium compounds is estimated to be approximately 700,000 tons per annum.[10] Applications of these salts vary from surfactants, corrosion inhibitors and pesticides to personal care products and fabric softeners. [10][11][12] QAS coatings were selected for this study as they have also been reported to exhibit anti-bacterial and anti-fungal properties. [13,14] QAS surfaces have been shown to exhibit a high positive charge density, which exerts a strong electrostatic interaction with negatively charged bacteria. [15] It is reported that after the microbial cell adsorbs onto the coating surface through electrostatic interactions, the alkyl chain of the QAS, if of sufficient length, penetrates the microbial cell wall. This can disrupt the cytoplasmic membrane and release toxins that lead to necrosis. It is suggested that positively charged surfaces can tightly bind the adsorbed microbial cells and prevent their subsequent growth and proliferation, including biofilm formation.[16]There have been relatively few reports on the interaction between QAS surfaces and proteins.There have also been some inconsistencies between the adhesion results obtained by different authors. [17][18][19] It has been shown that quaternary ammonium based polymer coatings provide effective resistance against the non-specific adsorption of proteins ...
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