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Plasma polymers from glycidol vapors are of interest for direct covalent grafting of molecules bearing amine or thiol groups. The question of whether pulsed plasma operation might lead to a higher surface density of epoxide groups and a higher density of grafted molecules is studied using the antifungal drug caspofungin. X-ray photoelectron spectroscopy and Time of flight-secondary ions mass spectrometry analysis followed by caspofungin grafting revealed that both continuous wave and pulsed plasmas led to surface epoxides but with higher densities upon pulsing. Investigations into stability suggested that glycidol plasma polymer coatings were still able to immobilize caspofungin after 2 years of storage, making them suitable for applications where grafting of molecules needs to be done immediately before usage of a device. Refereed/Peer-reviewed

Deposition chemistry from plasma is highly dependent on both the chemistry of the ions arriving at surfaces and the ion energy. Typically, when measuring the energy distribution of ions arriving at surfaces from plasma, it is assumed that the distributions are the same for all ionic species. Using ethyl acetate as a representative organic precursor molecule, we have measured the ion chemistry and ion energy as a function of pressure and power. We show that at low pressure (

Refereed/Peer-reviewed Plasma polymers have long been of interest as thin film coatings on biomedical devices and products, to generate desirable surface properties for favorable bio-interfacial interactions. Plasma polymers have also been used as platforms for the covalent immobilization of bioactive molecules. More recently, additional aspects have been investigated, such as selective prevention of adhesion of microbial pathogens, either via plasma polymers per se or including antimicrobial drugs. Plasma polymers have also been investigated for the release of silver ions and small organic molecules. Complementing low-pressure plasma approaches, processes at atmospheric pressure have attracted interest recently, including for nano/biocomposite coatings. This contribution reviews the use of plasma polymers for intended biomedical applications, with a focus on more recent topic areas.

Improved retention of desirable chemical structures during plasma polymerization requires rational tailoring of plasma-phase conditions. Using ethyl trimethylacetate, we studied the effects of pressure and power on the contribution of intact molecular ions to deposition and retention of ester groups. The abundance of protonated molecular ions in plasmas varies with pressure and power, but the functionality of plasma polymers, assessed by X-ray photoelectron spectroscopy and time-of-flight secondary ion mass spectrometry, is not correlated. Together with high ion flux, the ion energy distribution was found to be a key parameter and needs to be tailored to enable the soft landing of ions on the surface after traversing the sheath. The compromise between the abundance of ions and their energy distribution is optimal near the transition between the α and γ plasma phases. Refereed/Peer-reviewed

In the oral cavity, dental implants are exposed to an environment rich in various microbes that can produce infectious biofilms on the implant surface. Here we report the development of two distinct antimicrobial coatings that prevent biofilm formation by fungi or bacteria. The antimicrobial peptides Mel4 and caspofungin were immobilized on titanium surfaces through reactions with radicals embedded within a mechanically robust, ion-assisted plasma polymerized (PP) film. The immobilization does not require additional chemical reagents and is achieved by simply incubating the surfaces at room temperature in a buffer solution containing the antimicrobial agent. The antibiotic-functionalized surfaces were rigorously washed with hot sodium dodecyl sulphate (SDS) to remove physisorbed molecules, and analyzed by time of flight secondary ion mass spectrometry (ToF-SIMS), which revealed characteristic fragments of the peptides and provided strong evidence for the covalent nature of the binding between the molecules and the PP coating. Both Candida albicans and Staphylococcus aureus pathogens were significantly inhibited in their ability to colonize the surfaces and form biofilms. Our findings suggest that antimicrobial surfaces fabricated using ion-assisted plasma polymerization have great potential for coatings on biomedical devices where activity against fungal and bacterial pathogens is required. Refereed/Peer-reviewed

As some proteins are known to interact with sulfated and phosphated biomolecules such as specific glycosaminoglycans, this study derives from the hypothesis that sulfonate and phosphonate groups on solid polymer surfaces might cause specific interfacial interactions. Such surfaces were prepared by plasma polymerization of heptylamine (HA) and subsequent grafting of sulfonate or phosphonate groups via Michael-type addition of vinylic compounds. Adsorption of the proteins fibrinogen, albumin (HSA) and lysozyme on these functionalised plasma polymer surfaces was studied by XPS and quartz crystal microbalance with dissipation (QCM-D). It was also studied whether pre-adsorption with HSA would lead to a passivated surface against further adsorption of other proteins. XPS confirmed grafting of vinyl sulfonate and vinyl phosphonate onto the amine surface and showed that the proteins adsorbed to saturation at between 1 and 2 h. QCM-D showed rapid and irreversible adsorption of albumin on all three surfaces, while lysozyme could be desorbed with PBS to substantial extents from the sulfonated and phosphonated surfaces but not from the amine surface. Fibrinogen showed rapid initial adsorption followed by slower additional mass gain over hours. Passivation with albumin led to small and largely reversible subsequent adsorption of lysozyme, whereas with fibrinogen partial displacement yielded a mixed layer, regardless of the surface chemistry. Thus, protein adsorption onto these sulfonated and phosphonated surfaces is complex, and not dominated by electrostatic charge effects. Refereed/Peer-reviewed

In comparison with other chemistries, little has been reported on sulfur-containing plasma polymers; reasons include low volatility or high toxicity of monomers. Here, we report on plasma polymerization of dimethyl sulfoxide, by itself and its co-polymerization with 1,7-octadiene to generate S-containing plasma polymers. Results show dominance of S-S, S-H, and S-C with small percentages of SO and SO2. Upon storage in air there were no observable changes to the oxidation states of the S atoms in these plasma polymers, whereas the hydrocarbon component underwent oxidative changes. Methods were studied to oxidize the initial sulfur-containing surface groups, but approaches such as H2O2 treatment post-deposition and electrical biasing during deposition did not affect the oxidation states of the incorporated S. Refereed/Peer-reviewed

We report a systematic study of the plasma polymerization of ethyl α-bromoisobutyrate (EBIB) to produce thin film coatings capable of serving as ATRP initiation surfaces, for which they must contain α-bromoisobutyryl functional groups. In the deposition of polymeric coatings by plasma polymerization there generally occurs considerable fragmentation of precursor(“monomer”) molecules in the plasma; and the retention of larger structural elements is challenging, particularly when they are inherently chemically labile. Empirical principles such as low plasma power and low pressure are usually utilized. However, we show that the α-bromoisobutyryl structural moiety is labile in a plasma gas phase and in low pressure plasma conditions, below the collisional threshold, there is little retention. At higher pressure, in contrast, fragmentation of this structural motif appears to be reduced substantially, and coatings useful for ATRP initiation were obtained. Mass spectrometry analysis of the composition of the plasma phase revealed that the desired structural moiety can be retained through the plasma, if the plasma conditions are steered toward ions of the precursor molecule. Whereas at low pressure the plasma polymer assembles mainly from various neutral (radical) fragments, at higher pressure the deposition occurs from hyperthermal ions, among which the protonated intactmolecular ion is the most abundant. At higher pressure, a substantial population of ions has low kinetic energy, leading to “soft landing” and thus less fragmentation. This study demonstrates that relatively complex structural motifs in precursor molecule scan be retained in plasma polymerization if the chemical and physical processes occurring in the plasma phase are elucidated and controlled such that desirable larger structural elements play a key role in the film deposition. Refereed/Peer-reviewed

The attachment of pathogenic fungal cells onto materials surfaces, which is often followed by biofilm formation, causes adverse consequences in a wide range of areas. Here we have investigated the ability of thin film coatings from chlorinated molecules to deter fungal colonization of solid materials by contact killing of fungal cells reaching the surface of the coating. Coatings were deposited onto various substrate materials via plasma polymerization, which is a substrate-independent process widely used for industrial coating applications, using 1,1,2-trichloroethane as the process vapour. XPS surface analysis showed that the coatings were characterized by a highly chlorinated hydrocarbon polymer nature, with only a very small amount of oxygen incorporated. The activity of these coatings against human fungal pathogens was quantified using a recently developed, modified yeast assay and excellent antifungal activity was observed against Candida albicans and Candida glabrata. Plasma polymer surface coatings derived from chlorinated hydrocarbon molecules may therefore offer a promising solution to preventing yeast and mould biofilm formation on materials surfaces, for applications such as air conditioners, biomedical devices, food processing equipment, and others. Refereed/Peer-reviewed

This paper investigated the impacts of two deposition times (30 s, 60 s) and discharge powers (20 W, 50 W) on the resultant chemical and physical properties of plasma polymers (pp) formed using heptylamine (HA) or propionaldehyde (PA) monomers. Pinhole-free pp films were formed on all surfaces at deposition rates that varied according to both the time and power employed. XPS and ToF-SIMS analysis showed that power has a more of an effect than time on the chemical properties of the pp, which may be attributed to differences in monomer fragmentation and cross-linking. Mesenchymal stem cell (MSC) adhesion did not vary on the four different HApp surfaces, whereas a negative correlation between cell attachment and increasing plasma energy was observed on PApp surfaces. This suggests that the presence of oxygenated groups, particularly aldehyde and carboxylic groups, may have a dominant impact on MSC adhesion to these functional polymer substrates. Refereed/Peer-reviewed

Polyfunctional T cell responses are increasingly underpinning new and improved vaccination regimens. Studies of the nature and extent of these T cell responses may be facilitated if specific T cell populations can be assessed from mixed populations by ligand-mediated capture in a solid-state assay format. Accordingly, we report here the development of a novel strategy for the solid-state capture and real-time activation analyses of individual cognate T cells which utilizes a spontaneous self-assembly process for generating multimers of biotinylated class I major histocompatibility-peptide complex (MHCp) directly on the solid-state assay surface while also ensuring stability by covalent interfacial binding. The capture surface was constructed by the fabrication of multilayer coatings onto standard slides. The first layer was a thin polymer coating with surface aldehyde groups, onto which streptavidin was covalently immobilized, followed by the docking of multimers of biotinylated MHCp or biotinylated anti-CD45.1 monoclonal antibody. The high binding strength at each step of this immobilization sequence aims to ensure that artefacts such as (partial) detachment, or displacement by proteins from solution, would not interfere with the intended biological assays. The multilayer coating steps were monitored by X-ray photoelectron spectroscopy; data indicated that the MHCp proteins self-assembled in a multimeric form onto the streptavidin surface. Immobilized multimeric MHCp demonstrated the capacity to bind and retain antigen-specific T cells from mixed populations of cells onto the solid carrier. Furthermore, real-time confocal microscopic detection and quantification of subsequent calcium flux using paired fluorescent ratiometric probes facilitated the analysis of individual T cell response profiles, as well as population analyses using a combination of individual T cell events. Refereed/Peer-reviewed

Novel, highly chlorinated surface coatings were produced via a one-step plasma polymerization (pp) of 1,1,1-trichloroethane (TCE), exhibiting excellent antimicrobial properties against the vigorously biofilm-forming bacterium Staphylococcus epidermidis.

Not only bacteria but also fungal pathogens, particularly Candida species, can lead to biofilm infections on biomedical devices. By covalent grafting of the antifungal drug caspofungin, which targets the fungal cell wall, onto solid biomaterials, a surface layer can be created that might be able to provide long-term protection against fungal biofilm formation. Plasma polymerization of propionaldehyde (propanal) was used to deposit a thin (~20 nm) interfacial bonding layer bearing aldehyde surface groups that can react with amine groups of caspofungin to form covalent interfacial bonds for immobilization. Surface analyses by x-ray photoelectron spectroscopy and timeof-flight secondary ion mass spectrometry confirmed the intended grafting and uniformity of the coatings, and durability upon extended washing. Testing for fungal cell attachment and ensuing biofilm formation showed that caspofungin retained activity when covalently bound onto surfaces, disrupting colonizing Candida cells. Mammalian cytotoxicity studies using human primary fibroblasts indicated that the caspofungin-grafted surfaces were selective in eliminating fungal cells while allowing attachment and spreading of mammalian cells. These in vitro data suggest promise for use as antifungal coatings, for example, on catheters, and the use of a plasma polymer interlayer enables facile transfer of the coating method onto a wide variety of biomaterials and biomedical devices. Refereed/Peer-reviewed

Surfaces with micro- and nanometer-scale patterns have many potential applications, particularly in lifescience. This article reports on a versatile, straightforward, and inexpensive approach for the creation of chemical patterns using fabricated binary colloid crystals, consisting of small and large particles, as masks for the deposition of an amino-functionalised ultrathin film by plasma polymerization. After removal of the binary colloidal mask, the characterization techniques [scanning electron microscopy (SEM) and atomic force microscopy (AFM)] reveal a surface contrast that depicts an ability of the small particles to allow diffusion of the plasma to the substrate. A plasma-polymer film is created under the small particles and the region of substrate in direct contact with the large particle remains uncoated. Numerous types of patterns and feature heights can be produced with good fidelity over areas of several cm² by appropriate tuning of the binary colloid crystal mask morphology and the plasma-polymer deposition time. Finally, the amine groups of the patterned surface are used for covalent grafting poly(ethylene glycol) propionaldehyde (PEG-PALD) by reductive amination under conditions of reduced solubility to produce a patterned surface for directed adsorption of protein. AFM investigations show that the proteins are preferentially attached to the nanometer-scale regions of the pattern without PEG-PALD. Refereed/Peer-reviewed

Bacterial infections present an enormous problem causing human suffering and cost burdens to the healthcare systems worldwide. Herein we present several versatile strategies for controlled release of antibacterial agents which include silver ions as well as traditional antibiotics. At the heart of these release platforms is a thin film deposited by plasma polymerization. The use of plasma polymerization makes these strategies applicable to the surface of many types of medical devices since the technique for deposition of a polymer film from plasma in practically substrate independent. Refereed/Peer-reviewed

Ultrathin functional coatings deposited by plasma polymerization have utility in nano- and microtechnologies, however, until now very little has been reported to validate the widely held view that these coatings can be deposited onto any type of substrate, without substrate influence. In order to ascertain the role of the substrate in the early stages of plasma growth we address the growth rate and chemistry of plasma polymer coatings from two nitrogen- and two oxygen-containing monomers during the first stages of deposition onto gold and onto thiol MUA-coated gold surfaces. SPR thickness measurements and XPS analyzes indicate the substrate must be taken into account when ultrathin plasma polymer coatings are used for surface modification and we speculate on why this should be so. Refereed/Peer-reviewed

The preparation of thin film coatings with sulfonate and sulfate groups by plasma techniques is not straightforward due to limited volatility of suitable process vapours. We report a combination of plasma polymerisation and plasma treatment, treating heptylamine (HA-SO2) and 1, 7-octadiene (OD-SO2) plasma polymers with sulfur dioxide plasma. HA-SO 2 and OD-SO2 plasma polymer surfaces exhibited different compositions with the latter showing almost twice the amount of sulfur, as well as polysulfonate. Ageing of HA-SO2 plasma polymer surfaces in air or saline solution led to the disappearance of oligomers containing sulfonate and sulfate. Angle-dependent XPS analysis of HA-SO2 plasma polymers suggested that sulfur containing groups reptated into the plasma polymer upon storage after preparation. Refereed/Peer-reviewed

Free access via publisher's website. There is a need for coatings for biomedical devices and implants that can prevent the attachment of fungal pathogens while allowing human cells and tissue to appose without cytotoxicity. Here, the authors study whether a poly(2-hydroxyethylmethacrylate) (PHEMA) coating can suppress attachment and biofilm formation by Candida albicans and whether caspofungin terminally attached to surface-tethered polymeric linkers can provide additional benefits. The multistep coating scheme first involved the plasma polymerization of ethanol, followed by the attachment of α-bromoisobutyryl bromide (BiBB) onto surface hydroxyl groups of the plasma polymer layer. Polymer chains were grafted using surface initiated activators regenerated by electron transfer atom transfer radical polymerization with 2-hydroxyethylmethacrylate, yielding PHEMA layers with a dry thickness of up to 89 nm in 2 h. Hydroxyl groups of PHEMA were oxidized to aldehydes using the Albright–Goldman reaction, and caspofungin was covalently immobilized onto them using reductive amination. While the PHEMA layer by itself reduced the growth of C. albicans biofilms by log 1.4, the addition of caspofungin resulted in a marked further reduction by >4 log units to below the threshold of the test. The authors have confirmed that the predominant mechanism of action is caused by antifungal drug molecules that are covalently attached to the surface, rather than out-diffusing from the coating. The authors confirm the selectivity of surface-attached caspofungin in eliminating fungal, not mammalian cells by showing no measurable toxicity toward the myeloid leukaemia suspension cell line KG-1a.