Summary: A novel atmospheric‐pressure plasma‐polymerised thin film material has been deposited on various substrates using a pilot scale dielectric barrier discharge (DBD) reactor. Deposition kinetics and physico‐chemical characterisation data of nitrogen‐rich plasma‐polymerised ethylene (PPE:N) films, obtained using feed gas mixtures of N2 (ca. 10 slm) and C2H4 (ca. 10 sccm) are described. Nitrogen concentrations, [N], in the PPE:N films up to ca. 40% were determined by XPS; the concentrations of N‐functionality of greatest interest, primary amines, were determined by chemical derivatisation with 4‐trifluoromethylbenzaldehyde. The PPE:N films were further characterised by attenuated total reflectance infra‐red spectroscopy (ATR‐FTIR), contact angle goniometry, and atomic force microscopy (AFM). Square arrays of PPE:N “islands”, for example 30 μm in diameter repeated every 200 μm, were deposited on polymers, for example biaxially oriented poly(propylene) (BOPP), through specially‐prepared Kapton® polyimide masks. Cell culture experiments were then conducted on these micro‐patterned surfaces, using various cell types of interest in orthopaedics, for example growth plate and articular chondrocytes, or human U937 macrophages, the latter of which do not adhere to existing cell culture dishes. In all these cases the cells rapidly adhered and proliferated on the PPE:N islands, but not elsewhere on the polymer surfaces. In an effort to gain insight into cell adhesion mechanisms, adhesion of both macrophages and chondrocytes was tested against films with different [N] values. U‐937 macrophages adhered to films containing 25% or more [N], but not at all to films with lower values of [N], suggesting the existence of a “critical” value, [N]crit, necessary to induce cell adhesion.

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Mesenchymal stem cells (MSCs) are pluripotent progenitor cells with the ability to generate cartilage, bone, muscle, tendon, ligament, and fat. However, recent evidence indicates that a major drawback of current cartilage- and intervertebral disc-tissue engineering is that human MSCs isolated from some arthritic patients (a clinically relevant source of stem cells) express type X collagen (a marker of chondrocyte hypertrophy associated with endochondral ossification) and osteogenic markers. Some studies have attempted to use growth factors to inhibit type X collagen expression, but none has addressed the possible effect of the chemical composition of the substratum on chondrocyte hypertrophy and osteogenesis. Here, we examine the growth and differentiation potential of human MSCs cultured on nitrogen (N)-rich plasma polymer layers (N-doped plasma-polymerized ethylene, containing up to 36% nitrogen; PPE:N). We show that PPE:N almost completely suppresses the expression not only of type X collagen, but also of osteogenic marker genes such as alkaline phosphatase, bone sialoprotein, and osteocalcin. In contrast, neither aggrecan nor type I collagen expression were significantly affected. These results indicate that PPE:N coatings may be suitable surfaces for inducing MSCs to a chondrocyte or disc-like phenotype for tissue engineering of cartilage or intervertebral discs, in which hypertrophy and osteogenesis are suppressed.

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.

Back Cover: The cover illustration shows a schematic diagram of the dielectric barrier discharge system (top left) used to deposit plasma polymer films with high concentrations of nitrogen‐containing functional groups. Also shown are NEXAFS spectra (top right) and FTIR spectra (bottom left) used for semiquantitative analysis of nitrile functionalities (bottom right), where excellent agreement may be noted. Further details can be found in the article by P.‐L. Girard‐Lauriault, P. Desjardins, W. E. S. Unger,* A Lippitz, and M. R. Wertheimer* on page 631.

We investigated the ageing of amine-terminated self-assembled monolayers (amine-SAMs) on different silica substrates due to exposure to different ambient gases, pressures, and/or temperatures using time-of-flight secondary ion mass spectrometry (ToF-SIMS) with principal component analysis and complementary methods of surface analysis as X-ray photoelectron spectroscopy (XPS) and near edge X-ray absorption fine structure (NEXAFS). The goal of this study is to examine the durability of primary amine groups of amine-SAMs stored in a user laboratory prior to being used as supports for biomolecule immobilization and other applications. We prepared amine-SAMs on the native oxides of silicon wafers and glass slides using 3-aminopropyl triethoxysilane, by using optimized conditions such as anhydrous organic solvent and reaction time scale of hours to avoid multilayer growth. Selected commercial amine-SAM slides have been investigated, too. When the amine-SAMs are exposed to air, oxygen incorporation occurs, followed by formation of amide groups. The formation of oxygen species due to ageing was proved by ToF-SIMS, XPS, and NEXAFS findings such as CNO(-) secondary ion emission at m/z 42, observation of the N 1s HNC=O component peak at 400.2-400.3 eV in XPS, and, last but not least, by formation of a π*(HNC=O) resonance at 401 eV in the N K-edge X-ray absorption spectrum. It is concluded that the used multi-method approach comprising complementary ToF-SIMS, XPS, and NEXAFS analyses is well suited for a thorough study of chemical aspects of ageing phenomena of amine-SAM surfaces.

We present a new synchrotron X-ray photoelectron spectroscopy strategy for surface chemical analysis of materials. Our approach is based on the acquisition of photoelectron spectra at constant kinetic energies with the help of a tunable synchrotron X-radiation source. This ensures both constant and tunable information depth for all elements in a very thin organic layer. Many of the problems known to XPS depth profiling using laboratory equipment are thereby avoided. Using our methodology, the 95% information depth, z(95%), can be tuned down to about 0.7 nm in organic materials. The upper limit in our study at the HE-SGM monochromator dipole magnet beamline at the synchrotron radiation source BESSY II is about 4.3 nm. Elemental quantification is achieved through relative sensitivity factors (RSF) specific to the measurement conditions, determined either with the help of calculated photoionization cross sections and inelastic mean free paths or experimentally. The potential of the technique is demonstrated for the in-depth analysis of plasma deposited nitrogen-rich organic thin films used in biomedical applications.