Low‐pressure plasma co‐polymerisation of binary gas mixtures of ethylene and ammonia was investigated in order to deposit N‐rich plasma polymer coatings for biomedical applications. Deposition kinetics and relevant surface characteristics were investigated as a function of r.f. power, gas pressure, and NH3/C2H4 ratio. Physico‐chemical properties of the coatings were determined by surface‐sensitive techniques: for example, total nitrogen concentrations up to 40 at.‐% were measured by XPS, while those of primary amines were determined by chemical derivatisation followed by XPS analysis. L‐PPE:N films were further characterised by UV‐vis and IR spectroscopic ellipsometry and by CAG.

Summary: The wavelength‐dependent vacuum ultraviolet (VUV) photolysis of several polymers, low density polyethylene (LDPE), biaxially oriented poly(propylene) (BOPP), atactic polystyrene (PS), and poly(methyl methacrylate) (PMMA), was studied by irradiation in vacuum with the well‐characterized emissions from four different resonant or excimer VUV sources. These lamps comprise radiofrequency (r.f.) discharges in different noble gases, such as krypton, xenon (at low pressures, producing near‐monochromatic resonant line radiations), xenon excimer (at “high” pressure), and a deuterium/argon mixture (producing a broad‐band emission). VUV‐induced mass loss (ablation or etching) was monitored in situ by quartz crystal microbalance measurements. Following irradiation, samples were analysed by ATR‐FTIR and XPS, to evaluate near‐surface structural changes (e.g., creation of unsaturation, cross‐linking) resulting from the VUV‐initiated bond scissions and radical‐creation reactions. PMMA was the most readily ablatable polymer, whereas the mass loss of BOPP was higher than that of LDPE, regardless of the irradiation wavelength, λ. All polymers were found to form double bonds, with the exception of PS, which is rather stable, probably due to energy dissipation by fluorescence.Formation of double bonds in a) vinyl‐, b) vinylidene‐, and c) vinylene‐like unsaturated groups, as a function of the radiation dose, D, for KrL (▪), XeL (▴), and D2Ar‐irradiated (•) PMMA.magnified imageFormation of double bonds in a) vinyl‐, b) vinylidene‐, and c) vinylene‐like unsaturated groups, as a function of the radiation dose, D, for KrL (▪), XeL (▴), and D2Ar‐irradiated (•) PMMA.

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Film samples of two very pure polyolefins, low-density polyethylene (LDPE) and biaxially oriented polypropylene (BOPP), were surface-modified by vacuum ultraviolet (VUV) photochemistry in low-pressure ammonia. The influence of experimental conditions such as wavelength and intensity (photon flux) of the VUV radiation, ammonia pressure, and treatment duration, as well as the mechanisms involved in the surface modification were discussed. Changes in the surface energy and chemistry were investigated using suitable techniques like contact angle goniometry (surface energy) measurements, X-ray photoelectron spectroscopy (XPS), attenuated total reflectance infrared spectroscopy, and time-of-flight secondary ion mass spectroscopy. We show that chemically bonded nitrogen concentrations [N], up to 25%, can be achieved on the polymer surfaces by VUV photochemistry, and that N is predominantly bonded as amine groups, thus leading to an important increase in the surface energy of treated samples. Finally, XPS, surface energy measurements, and atomic force microscopy were used to characterize possible degradation of the polymer surfaces during the VUV treatments.

We present a two-fold study designed to elucidate the adhesion mechanism of human U937 monocytes on novel N-rich thin films deposited by plasma- and VUV photo-polymerisation, so-called "PVP:N" materials. It is shown that there exist sharply-defined ("critical") surface-chemical conditions that are necessary to induce cell adhesion. By comparing the film chemistries at the "critical" conditions, we demonstrate the dominant role of primary amines in the cell adhesion mechanism. Quantitative real-time RT-PCR experiments using U937 cells that had adhered to PVP:N materials for up to 24 h are presented. The adhesion induces a transient expression of cytokines, markers of macrophage activation, as well as a more sustained expression of PPAR gamma and ICAM-I.