Papers

AVS2004 Session PS+BI-FrM: Plasmas in Bioscience

Friday, November 19, 2004 8:20 AM in Room 213C

Friday Morning

Start	Invited?	Item
8:20 AM		PS+BI-FrM-1 X-Ray and Neutron Reflectivity Studies of Plasma Polymer Coatings S.K. Øiseth (Consultant); P.G. Hartley, K.M. McLean (CSIRO Molecular Science, Australia); A Nelson, M James (Bragg Institute, Australia) Plasma polymer coatings adhere to and contour the surfaces of most organic and inorganic materials, and are attractive as surface chemical modification systems, since they offer both robustness and inherent surface chemical functionality for further surface chemical derivatisation. A variety of different techniques have been used to characterise the physico-chemical properties of surfaces of plasma polymer films. In many cases, however, it is also desirable to probe the internal structure of both modified and unmodified plasma polymer coatings in order to optimise their properties for a given application.. Reflectometry techniques are now becoming increasingly important in the characterization of nano-scale structured interfaces. X-ray reflectivity in particular is ideally suited to the study of the internal properties of layered film structures on surfaces, yielding data concerning sub surface structure and material properties. Neutron reflectivity meanwhile offers the ability to characterise surface layers in aqueous environments. In this study heptylamine and allylamine plasma polymer coatings were prepared on silicon wafers, and analysed using X-ray reflectometry before and after further surface modification procedures (e.g. adsorption of protein species from solution). Surface chemistry of the coatings was characterised using X-ray photoelectron spectroscopy (XPS). Atomic force microscopy (AFM) was also used to characterise both roughness and local film thickness at step-edges on the films. The excellent reflectivity data obtained demonstrate the suitability of plasma polymers for reflectivity studies (primarily due to their low surface roughness). Preliminary experiments on plasma polymer layers using neutron reflectivity are also described, which highlight the effect of surface hydration on layer properties.
8:40 AM		PS+BI-FrM-2 Angle Resolved XPS Characterisation of Plasma Polymerised Chemical Gradients K.L. Parry (Plasso Technology Ltd.); A.G. Shard (University of Sheffield, United Kingdom); R.G. White (Thermo Electron Corporation); J.D. Whittle (Plasso Technology Ltd.); A. Wright (Thermo Electron Corporation, United Kingdom) Well-defined chemical gradients are potentially important materials in a wide range of research activities. The surfaces of such materials can be derivatised with differing functional groups to provide spatially resolved surface chemical properties. Such surfaces can, for example, be used to immobilise biomolecules, which may become a route to producing novel biosensors. This study is concerned with chemical gradients within thin layers of plasma co-polymers deposited onto glass substrates. Continuous gradients of chemistry (hydrocarbon to either acid or amine) are produced by carefully programming the composition of the plasma monomer mixture while varying the area of the substrate exposed to the plasma. It will be shown that spatially resolved XPS is an ideal tool to determine the composition of the near surface region as a function of distance along the chemical gradient. Parallel angle resolved XPS provides additional information about the uniformity of the layer with depth. Such measurements can show, for example, surface enrichment of one of the functional groups in the co-polymer layer or variations in thickness along the chemical gradient. It is therefore possible to construct chemical state and thickness line scans or maps from the same ARXPS data set. Such data provide valuable information regarding the plasma co-polymer deposition process.
9:00 AM		PS+BI-FrM-3 Surface Characterization of Plasma Processed Bio-Functional Micro-Patterned Polymeric Surfaces A. Valsesia, M. Manso, M. Kormunda, P. Colpo, D. Gilliland, G. Ceccone, F. Rossi (EU-JRC-IHCP, Italy) The functionalization of the material surfaces is one of the major requirements for the control of the biological response and for the improvement of the biocompatibility. Among the functionalization techniques, PE-CVD is of high importance since the control of the film properties is achieved by an accurate modulation of the plasma processing parameters. PE-CVD allows the synthesis of a wide spectrum of bio-functional polymers: acid/base fouling surfaces (PAA, PAL) and super-hydrophilic anti-fouling surfaces (PEG, PEG-like coatings). Moreover the combination of plasma deposition and plasma etching techniques allows the formation of micro and nano-patterned surfaces with contrasted functionalities. In this work we have studied the plasma deposition of PAA (COOH functional), PAL (NH2 functional) and PEG-like (anti-fouling) layers. The chemical surface characterization of the films has been performed by XPS and TOF-SIMS and the surface free energies components have been calculated by Contact Angle in static and dynamic mode. QCM provided the evaluation of the mechanical stability of the samples in buffer solutions as well as the calculation of the bio-activity of the surfaces in proteins absorption experiments. The surface topography of the samples has been investigated by AFM. The micro-patterned surfaces have been characterized by TOF-SIMS and XPS in imaging mode, revealing the capability of the plasma processing techniques to produce chemically contrasted micrometric motives. The bio-response (protein absorption and cell adhesion) of the micro-patterned samples is under study.
9:20 AM		PS+BI-FrM-4 Plasma Sterilisation and De-pyrogenation of Surfaces: Review and Analysis of Mechanisms F. Rossi, R. De Mitri, M. Hasiwa (European Commission Joint Research Centre, Italy); S. Bobin, R. Eloy (Biomatech, France); T. Hartung (European Commission Joint Research Centre, Italy); P. Colpo (EU-JRC-IHCP, Italy) Mechanisms of plasma sterilisation are reviewed and analysed in terms of radiation induced desorption, UV radiation effects and etching. Different plasma discharges are analysed with Optical Emission Spectroscopy in order to find optimum conditions of UV emission and radicals production. Those effects are compared and related to effective sterilisation and depyrogenation rates obtained from the literature and experimentally on Bacillus subtilis and LPS. It is shown that UV emission is the major contribution for sterilisation and chemical etching for depyrogenation. SEM analysis of spores at different times of treatment show the degradation of the outer shell, as well as size and coverage reduction as the treatment duration increases. Effects of plasma on pyrogen is illustrated by AFM and ToF SIMS. A strategy for optimised sterilisation and depyrogenation treatment is proposed.
9:40 AM		PS+BI-FrM-5 Plasma Processes for Micro- and Nano-Patterning Biomedical Polymers P. Favia (University of Bari, Italy) Low pressure plasma processes can tune chemical composition, surface energy and topography of most substrates of biomedical interest in a well controlled way. Among the wide range of plasma-modification procedures, micro- and nano-patterning plasma-deposition processes of thin coatings are among the most interesting and novel technologies aimed to drive the behaviour of cells on surfaces. Two kind of plasma procedures will be described in this contribution, and some interesting in vitro tests will be discussed. The first one consists in the deposition of "cell-repulsive" coatings through physical masks to produce patterned surfaces; here "cell-adhesive" domains are alternated to non-adhesive ones. The second process involves the deposition of teflon-like coatings of CF_x chemical composition, including randomly distributed surface features with nanometric dimensions, which are peculiar of certain deposition conditions in modulated regime. Acknowledgments This research has been developed in the framework of the MIUR-FIRB RBNE01458S_006, COFIN '99 "Biomaterials with micro- and nano- structured surfaces" and 'NANOMED' QLKE-CT-2000 projects, whose financial contribution is gratefully acknowledged.
10:20 AM		PS+BI-FrM-7 Novel Plasma Modification of Microfluidic Devices for Control of Electroosmotic Flow E.R. Fisher, C.S. Henry, M.A. Boggs, I.T. Martin, Y. Liu, C.D. Garcia (Colorado State University) Microchip capillary electrophoresis (CE) is a widely used separation technique that combines the efficiency of CE with the portability of a microchip. Poly(dimethylsiloxane), PDMS, is often used to fabricate these microfluidic devices because it is inexpensive, has good optical properties, and the fabrication of complicated channel geometries is straightforward. Separations that occur in PDMS are based on the electroosmotic flow (EOF) within the channel. This, in turn, depends on the density of negatively charged groups on the PDMS surface, which is sensitive to both the pH of the solution and the sealing method (air plasma treatment, methanol). An additional issue is the hydrophobicity of the PDMS, which leads to the adsorption of hydrophobic analytes such as proteins during separations. The goal of this work is to treat PDMS with both non-depositing and depositing plasmas and fully characterize the altered surface chemistry, and its effects on EOF and separations. We have used depositing plasma systems to alter preassembled PDMS microchips, yielding novel surface chemistries. Plasma treated PDMS has been characterized using various surface analysis techniques, including contact angle measurements and XPS. XPS mapping shows that fluorocarbon (FC) plasma treatments permeate the channel via the reservoirs, not through the porous PDMS. Consequently, the reservoirs and channel are selectively coated with a FC film, resulting in reduced EOF. Conversely, plasma deposition of a hydrophilic hydrocarbon film yielded an increase in EOF. Selected coatings are stable over multiple EOF measurements. Separations conducted with treated chips evaluate biomolecule fouling characteristics. This is the first report of the modification of these devices via depositing plasma systems; plasma treatment of PDMS microchips has essentially been limited to O₂ or air plasmas to oxidize or cure the PDMS, for the enhancement of adhesion of PDMS to PDMS/glass.
10:40 AM		PS+BI-FrM-8 Thiol-Based Plasma Polymer Coatings as Platforms for Biosciences Applications P.G. Hartley, S.K. Øiseth, T.R. Gengenbach, G. Johnson, K.M. McLean (CSIRO Molecular Science, Australia) Radio frequency glow discharge plasma polymer coatings form robust thin films which contour and adhere strongly to the surfaces of polymeric and other materials. Their ability to modify surface properties, for example, to enhance biocompatibility or to introduce defined chemical functionalities at interfaces for the subsequent coupling of bioactive molecules have seen their widespread application in the field of biomaterials research. We report on the development of sulphur containing plasma polymers using ethanethiol as the feed monomer. In order to ascertain the influence of deposition conditions on the properties of the films, a range of protocols were employed. The films were characterised by X-ray photoelectron spectroscopy (XPS); atomic force microscopy; streaming potential and contact angle measurements. Since XPS data are not sufficiently specific to distinguish between similar carbon-sulphur functional groups (e.g. thiol vs. sulphides), the nature and density of the surface functionalities were quantified by using a thiol specific maleimide containing probe. The stability of the films was tested by assessing coating thickness and chemistry before and after autoclaving. The effects of ageing in air, particularly with respect to the chemical structure were monitored over several months. The incorporation of sulphur functionalities provide reproducible supports for the subsequent grafting of proteins and for the adhesion of gold nanoparticles. The coatings were also shown to act as supporters of cell attachment and growth.
11:00 AM		PS+BI-FrM-9 The Low Damage Surface Modification of the Self-assembled monolayer by the N₂ Neutral Beam Irradiation Y. Ishikawa (Tohoku University, Japan); T. Ishida (National institute of Advanced Industrial Science and Technology, Japan); S. Samukawa (Tohoku University, Japan) For the realization of future organic molecular devices, controlling surface property of molecular film, such as the electric properties of organic molecule, is quite important. To improve surface property of molecular film, fine surface modification method is highly expected. Thus, we propose the method for controlling the surface properties of organic films by applying plasma process. For this purpose, we used our nearly developed the neutral beam system.¹ The system could prevent the charged particles and ultraviolet photons, and only the neutral particles were irradiated to the substrates. In this study, we irradiated the N₂ neutral beam to the robust self-assembled monolayers (SAMs) made from terphenyls² on the gold substrate as the first attempt for neutral beam system to the organic molecular thin films. Energy of the N₂ neutral beams are at the highest 10 eV. We compared the X-ray photoelectron spectra of terphenyl SAMs before and after the N₂ beam irradiation. Then the C-N bonds were generated by the beam irradiation with maintaining the surfer molecular structure. This result indicates that the surface of the terphenyl SAMs would be replaced from carbon or hydrogen to nitrogen, and we can expect that the electric properties of the organic materials would be drastically changed by this method. ¹ S. Samukawa, K. Sakamoto, and K. Ichki: Jpn. J. Appl. Phys., Part 2 40, L779 (2001) ² T. Ishida, M. Sano, H. Fukushima, M. Ishida, and S. Sasaki: Langmuir, 18, 10496 (2002).