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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

Plasma polymerization of (2,2,6,6-tetramethylpiperidin-1-yl)oxyl (TEMPO) yields thin films containing stable nitroxide radicals that have properties analogous to that of nitric oxide (NO) without short lifetimes. This property gives TEMPO films a wide variety of potential applications. Typically, control of the final film chemistry is difficult and the plasma discharge conditions must be tailored to in order to maximize the retention of these nitroxide groups during the polymerization and deposition process. In this study, plasma diagnostics and surface analysis of the deposited films were carried out to determine the optimal plasma conditions for the retention of nitroxide groups. These techniques included energy-resolved mass spectrometry, heated planar probe ion current measurements, deposition rate measurements, and x-ray photoelectron spectroscopy (XPS). Results show that operating the plasma with a combination of low input powers and high pressures produces a collisional discharge in which fragmentation of the TEMPO molecule is suppressed, leading to good retention of nitroxide groups. Ion energy distribution functions and quartz crystal microbalance measurements support the soft landing theory of ion deposition on the substrate within this γ-mode, in which the flux of low energy, soft landed ions form the primary contribution to film growth. XPS analysis of deposited polymers shows 75.7% retention of N - O groups in the polymer films deposited in a 25 Pa 5 W discharge. © 2020 Author(s).

Functionalizing medical devices with polypeptides to enhance their performance has become important for improved clinical success. The extracellular matrix (ECM) adhesion protein vitronectin (VN) is an effective coating, although the chemistry used to attach VN often reduces its bioactivity. In vivo, VN binds the ECM in a sequence-dependent manner with heparan sulfate (HS) glycosaminoglycans. We reasoned therefore that sequence-based affinity chromatography could be used to isolate a VN-binding HS fraction (HS9) for use as a coating material to capture VN onto implant surfaces. Binding avidity and specificity of HS9 were confirmed by enzyme-linked immunosorbent assay (ELISA) and surface plasmon resonance (SPR)-based assays. Plasma polymerization of allylamine (AA) to tissue culture-treated polystyrene (TCPS) was then used to capture and present HS9 as determined by radiolabeling and ELISA. HS9-coated TCPS avidly bound VN, and this layered surface supported the robust attachment, expansion, and maintenance of human pluripotent stem cells. Compositional analysis demonstrated that 6-O- and N-sulfation, as well as lengths greater than three disaccharide units (dp6) are critical for VN binding to HS-coated surfaces. Importantly, HS9 coating reduced the threshold concentration of VN required to create an optimally bioactive surface for pluripotent stem cells. We conclude that affinity-purified heparan sugars are able to coat materials to efficiently bind adhesive factors for biomedical applications. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 106B: 1887-1896, 2018.

We explore how to configure an argon atmospheric-pressure plasma jet for enhancing its production of hydrogen peroxide (H2O2) in deionised water (DIW). The plasma jet consists of a quartz tube of 1.5 mm inner diameter and 3 mm outer diameter, with an upstream internal needle electrode (within the tube) and a downstream external cylindrical electrode (surrounding the tube). The plasma is operated by purging argon through the glass tube and applying a sinusoidal AC voltage to the internal needle electrode at 10 kV (peak–peak) with a frequency of 23.5 kHz. We study how the following operational parameters influence the production rate of H2O2 in water: tube length, inter-electrode separation distance, distance of the ground electrode from the tube orifice, distance between tube orifice and the DIW, argon flow rate and treatment time. By examining the electrical and optical properties of the plasma jet, we determine how the above operational parameters influence the major plasma processes that promote H2O2 generation through electron-induced dissociation reactions and UV photolysis within the plasma core and in the plasma afterglow; but with a caveat being that these processes are highly dependent on the water vapour content from the argon gas supply and ambient environment. We then demonstrate how the synergistic action between H2O2 and other plasma generated molecules at a plasma induced low pH in the DIW is highly effective at decontaminating common wound pathogens Gram-positive Staphylococus aureus and Gram-negative Pseudomonas aeruginosa. The information presented in this study is relevant in the design of medical plasma devices where production of plasma reactive species such as H2O2 at physiologically useful concentrations is needed to help realise the full clinical potential of the technology.

Skin has a remarkable capacity for regeneration; however, with an ever aging population, there is a growing burden to the healthcare system from chronic wounds. Novel therapies are required to address the problems associated with nonhealing chronic wounds. Novel wound dressings that can encourage increased reepithelialization could help to reduce the burden of chronic wounds. A suite of chemically defined surfaces have been produced using plasma polymerization, and the ability of these surfaces to support the growth of primary human skin cells has been assessed. Additionally, the ability of these surfaces to modulate cell migration and morphology has also been investigated. Keratinocytes and endothelial cells were extremely sensitive to surface chemistry showing increased viability and migration with an increased number of carboxylic acid functional groups. Fibroblasts proved to be more tolerant to changes in surface chemistry; however, these cells migrated fastest over amine-functionalized surfaces. The novel combination of comprehensive chemical characterization coupled with the focus on cell migration provides a unique insight into how a material's physicochemical properties affect cell migration. Refereed/Peer-reviewed

Plasma polymerization was used to coat a melt electrospun polycaprolactone scaffold to improve cell attachment and organization. Plasma polymerization was performed using an amine containing monomer, allylamine, which then allowed for the subsequent immobilization of biomolecules, i.e., heparin and fibroblast growth factor-2. The stability of the plasma-polymerized amine-coating was demonstrated by X-ray photoelectron spectroscopy analysis and imaging time-of-flight secondary ion mass spectrometry revealed that a uniform plasma amine-coating was deposited throughout the scaffold. Based upon comparison with controls, it was evident that the combination scaffold aided cell ingress and the formation of distinct fibroblast and keratinocyte layers.

Amine containing plasma polymer films are of interest due to their ability to bind biomolecules either covalently or electrostatically. One issue with generating such plasma polymers is the need to generate sufficient amine density on the surface to enable binding, while simultaneously maintaining the chemical, physical stability of the surface in aqueous media. Here we investigate the relationship between plasma parameters, film stability for two commonly used monomers, allylamine AA, ethylenediamine EDA. Plasma polymer films from AA, EDA were produced at radio frequency RF powers between 2 and 20 W at a constant monomer flowrate. Deposition rate, ion flux, ion energy, plasma phase mass spectrometry were used to investigate the plasma-surface interactions. Film stability was assessed by comparing X-ray photoelectron spectroscopy XPS, atomic force microscopy AFM measurements before, after washing in phosphate buffered saline PBS. The results show that films generated from EDA plasmas are generally unstable in aqueous media, while films generated from AA plasmas exhibit higher stability, particularly those deposited at high RF power. The chemical, physical stability of the films is then related to the mechanisms of deposition, the energy density provided to the surface during film growth.

The influence of the electrical and optical properties of a spatially varying He microplasma on the gradient surface modification of an adsorbed protein layer inside a microfluidic chip was investigated. Microplasma was generated inside a native polydimethylsiloxane (PDMS) microchannel. Excited and metastable states of He and N2 (from air) potentially played a major role in the removal/modification of protein during the discharge period. In-between discharge events, N2(A) metastables can also induce bond breaking and surface modification. The purge time of the feed gas was shown to be important in the use of small scale microplasma sources for surface processing or protein modification. Refereed/Peer-reviewed

This paper reports a method for producing protein arrays on antifouling PEO-like coatings using a “non-contact” atmospheric pressure helium microplasma array. ToF-SIMS characterization of PEO-like coatings after short plasma treatment revealed the antifouling plasma polymer was largely modified/removed within the microplasma-exposed regions. Incubation of microplasma-patterned PEO-like coatings with a fluorescently labeled streptavidin resulted in selective and uniform protein adsorption within the modified regions. A protein sensing application was demonstrated where a target red fluorescent protein (RFP) was only captured on the anti-RFP functionalized regions. This indicates the adsorbed antibody protein on the microplasma-treated PEO-like regions retained its bioactivity.

This multi-centre investigation explores the variability that results from using the power/flow rate ratio (W/F) to describe plasma treatment and plasma polymerization processes. Results from fourteen reactors of different design and spread across ten laboratories, showed that the chemistry of the treated and deposited polymer/plasma polymer films is highly variable between reactor systems, and that there was no clear pattern linking these variations to other properties of the reactor systems (e.g. pressure, volume, electrode configuration). Although W/FM provides a useful rule-of-thumb for process optimization within a single system, it does not provide sufficient information to enable the same plasma polymer to be produced on a different system.

We investigate an approach for the patterning of reactive oxygen and nitrogen species (RONS) onto polystyrene using atmospheric-pressure microplasma arrays. The spectrally integrated and time-resolved optical emission from the array is characterized with respect to the applied voltage, applied-voltage frequency and pressure; and the array is used to achieve spatially resolved modification of polystyrene at three pressures: 500, 760, and 1000 Torr. As determined by time-of-flight secondary ion mass spectrometry (ToF-SIMS), regions over which surface modification occurs are clearly restricted to areas that are exposed to individual microplasma cavities. Analysis of the negative-ion ToF-SIMS mass spectra from the center of the modified microspots shows that the level of oxidation is dependent on the operating pressure, and closely correlated with the spatial distribution of the optical emission. The functional groups that are generated by the microplasma array on the polystyrene surface are shown to readily participate in an oxidative reaction in phosphate buffered saline solution (pH 7.4). Patterns of oxidized and chemically reactive functionalities could potentially be applied to the future development of biomaterial surfaces, where spatial control over biomolecule or cell function is needed. Refereed/Peer-reviewed

Culture surfaces that substantially reduce the degree of cell manipulation in the delivery of cell sheets to patients are described. These surfaces support the attachment, culture, and delivery of multipotent adult progenitor cells (MAPC). It was essential that the processes of attachment/detachment to the surface did not affect cell phenotype nor the function of the cultured cells. Both acid-based and aminebased surface coatings were generated from acrylic acid, propanoic acid, diaminopropane, and heptylamine precursors, respectively. While both functional groups supported cell attachment/detachment, amine coated surfaces gave optimal performance. X-ray photoelectron spectroscopy (XPS) showed that at a primary amine to carbon surface ratio of between 0.01 and 0.02, greater than 90% of attached cells were effectively transferred to a model wound bed. A dependence on primary amine concentration has not previously been reported. After 48 h of culture on the optimized amine surface, PCR, functional, and viability assays showed that MAPC retained their stem cell phenotype, full metabolic activity, and biological function. Consequently, in a proof of concept experiment, it was shown that this amine surface when coated onto a surgical dressing provides an effective and simple technology for the delivery of MAPC to murine dorsal excisional wounds, with MAPC delivery verified histologically. By optimizing for cell delivery using a combination of in vitro and in vivo techniques, we developed an effective surface for the delivery of MAPC in a clinically relevant format. Refereed/Peer-reviewed

The reduced pressure synthesis of poly(3,4-ethylenedioxythiophene) (PEDOT) with sheet-like morphology has been achieved with the introduction of an amphiphilic triblock copolymer into the oxidant thin film. Addition of the copolymer not only results in an oxidant thin film which remains liquid-like under reduced pressure but also induces structured growth during film formation. PEDOT films were polymerized using the vacuum vapor phase polymerization (VPP) technique, in which we show that maintaining a liquid-like state for the oxidant is essential. The resulting conductivity is equivalent to commercially available indium tin oxide (ITO) with concomitant optical transmission values. PEDOT films can be produced with a variety of thicknesses across a range of substrate materials from plastics to metals to ceramics, with sheet resistances down to 45 Ω/□ (ca. 3400 S·cm−1), and transparency in the visible spectrum of >80% at 65 nm thickness. This compares favorably to ITO and its currently touted replacements. Refereed/Peer-reviewed

Subretinal transplantation of functioning retinal pigment epithelial (RPE) cells grown on a synthetic substrate is a potential treatment for age-related macular degeneration (AMD), a common cause of irreversible vision loss in developed countries. Plasma polymers give the opportunity to tailor the surface chemistry of the artificial substrate whilst maintaining the bulk properties. In this study, plasma polymers with different functionalities were investigated in terms of their effect on RPE attachment and growth. Plasma polymers of acrylic acid (AC), allyl amine (AM) and allyl alcohol (AL) were fabricated and characterised using X-ray photoelectron spectroscopy (XPS) and water contact angle measurements. Octadiene (OD) hydrocarbon films and tissue culture polystyrene were used as controls. Wettability varied from hydrophobic OD to relatively hydrophilic AC. XPS demonstrated four very different surfaces with the expected functionalities. Attachment, proliferation and morphological examination of an RPE cell line and primary RPE cells were investigated. Both cell types grew on all surfaces, with the exception of OD, although the proliferation rate of primary cells was low. Good epithelial morphology was also demonstrated. Plasma polymerised films show potential as cell carrier surfaces for RPE cells in the treatment of AMD. Refereed/Peer-reviewed

Dr. S. A. Al-Bataineh, E. J. Szili, P. J. Gruner, R. D. Short, D. A. Steele Mawson Institute, University of South Australia, Mawson Lakes, SA 5095, Australia Fax: þ61 (0)8 8302 5689; E-mail: sameer.al-bataineh@unisa.edu.au C. Priest, H. J. Griesser Ian Wark Research Institute, University of South Australia, Mawson Lakes, SA 5095, Australia N. H. Voelcker Flinders University, School of Chemical and Physical Sciences, Bedford Park, SA 5042, Australia Current address: Mawson Institute, University of South Australia, Mawson Lakes, SA 5095, Australia Surface modification of materials with microscale features through plasma treatment or deposition is of high value, and is considered one of the great challenges in plasma-based materials processing. This article reports a versatile method for the fabrication of microcavity plasma array devices. A 7 7 microcavity plasma array device (each cavity was 250mm in diameter and separated by 500mm) was used in this study to demonstrate the capability of these devices for localised, non-contact surface treatment/polymer deposition. The device can be reused multiple times for plasma treatment and polymerisation. X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectrometry (ToF-SIMS) imaging and region of interest (ROI) analysis, in addition to surface hydration, were employed to characterise the micropatterns on microplasma-treated PS. The results showed that microplasma treatment/ deposition could be spatially confined to regions exposed to the individual ignited microcavities. However, the results also demonstrated that the size of the treated spots tended to increase with increasing treatment time until they eventually overlapped resulting in a homogeneous surface treatment confined to the size of the array. Similarly, the concentration of oxygen quantified on the treated spots reached saturation after 75 s of treatment. The versatility of the device was demonstrated by depositing an array of octadiene plasma polymer (ODpp) onto a silicon substrate as confirmed by XPS imaging and ROI analysis. A key advantage of these microcavity array devices is that they can be easily integrated into manufacturing and do not require contact with the substrate surface to impart well-defined chemical modifications on materials surfaces.

Single-walled carbon nanotubes (SWCNTs) and polyaniline (PANI) composites with different proportions of SWCNTs were synthesized by in situ polymerization. The resultant composites were characterized by Fourier TransformInfrared (FTIR) spectroscopy and theirmorphology was studied by transmission electronmicroscopy (TEM). Their specific surface areas were determined by N2 adsorption/desorption tests and the mesoporous structure of the composites was analyzed using the Barrett-Joyner-Halenda (BJH) method. A band shift in the FTIR spectrum indicates a strong interaction between PANI and SWCNTs. The mesopore volume was increased by introducing PANI into the SWCNTs. Cyclic voltammetry (CV) was carried out to study their electrochemical properties. The SWCNT/PANI composites obtained exhibited reversible electrochemical and faster ion transport properties, even in a neutral aqueous environment. This is probably due to /pi - /pi interaction between the PANI backbone and the graphite-like structure of carbon nanotubes. Finally, a capacitive deionization (CDI) test was conducted in a batch mode bench-scale cell. The electrodes made from SWCNT/PANI composites showed a higher ion electrosorption capacity than those made from SWCNTs alone and the composite electrodes can be easily regenerated, indicating excellent recyclability. Refereed/Peer-reviewed

There is considerable interest in the spatial control of plasma polymerisation such as to produce sub-millimetre features with high fidelity, versatility and reproducibility, for example, for arrays or writable specific patterns. This study reports the design of a microcavity plasma device and a method for its fabrication, with the device comprising a single cavity of � 400 mm diameter. The device can be fabricated within a short time and at low cost in a standard laboratory, with no need for a clean room facility. The device is capable of multiple operations in plasma polymerisation mode. XPS imaging combined with small-spot ROI analysis showed localised thin film deposition of an acrylic acid plasma polymer with good retention of carboxylate groups from the monomer. The device can be configured with flexibility and addressedforplasma polymer writing of complex patterns.

Vacuum vapour phase polymerisation (V-VPP) was used to synthesis high conductivity poly(3,4-ethylenedioxythiophene) (PEDOT) on glycol/oxidant coated substrates. Thermo gravimetric analysis (TGA) indicated that up to 15 wt.-% glycol was able to complex with the Fe(Tos)3 oxidant solution and that this loading produced PEDOT with the highest conductivity, namely 1487 S cm-1. Further addition beyond 15 wt.-% resulted in an unbounded excess of glycol which appeared to inhibit the polymerisation process, resulting in reduced doping levels and conductivity. XPS data showed that glycol was incorporated within the PEDOT matrix after polymer synthesis, and that this may contribute to the high conductivity achieved using the V-VPP technique. XPS data also confirmed that the highest conductivity coincided with the highest recorded doping level, d = 28.4%. Refereed/Peer-reviewed

We report a novel, versatile method for generating number density gradients of individual gold (Au) and silver (Ag) nanoparticles by a two-step method. First, a chemical gradient of amine surface functional groups is deposited by plasma copolymerization. Second, a density gradient of nanoparticles is formed by the immersion of the chemical gradient in solutions of nanoparticles. Chemical characterization by X-ray photoelectron spectroscopy and morphological analysis by atomic force microscopy shows that nanoparticle density closely follows the change in nitrogen surface concentration across the gradients. We also demonstrate that it is possible to control the slope of the gradients by using nanoparticle solutions of different concentrations. Important for technological and research applications, this method can be used with nanoparticles of various sizes and different materials. In addition, the use of plasma deposition allows such gradients to be generated on any type of substrate. Refereed/Peer-reviewed

A micro-cavity discharge array (2500 cavities of 50 µm2 size) was operated in neon at atmospheric pressure to modify polystyrene (PS), fluorinated ethylene–propylene co-polymer (FEP) and polytetrafluoroethylene(PTFE) polymer surfaces and, with the injection of a polymerisable monomer (acrylic acid), to deposit patterned, thin polymeric coatings. The aim of this study was to investigate the utility of these micro-discharge sources in the surface treatment of polymers and for the patterned deposition of polymeric material. The influence of the driving frequency, treatment time and sample-array distance on polymer surface treatment was investigated. X-ray photoelectron spectroscopy (XPS) was used to explore the surface chemistry of the treated polymer surfaces and of the polymer deposits. It was found that increasing themicro-cavity discharge source driving frequency and/or treatment time and decreasing the sample-arraydistance all led to a significant decrease in surface energy as determined by water contact angle measurements. For a period of time, post treatment surface hydrophilicity degraded due to the well known“ageing effect” but stabilized after two days. Finally, it was demonstrated that the device could be used forthe localized, array sized, deposition of acrylic acid. High resolution XPS analysis of the deposit registered a C1s spectra typical of poly(acrylic acid) with a prominent peak centred at approximately 289.3 eV indicating a relatively high level retention of the original monomer functionality. These results demonstrate that microcavity discharges, operated at or near atmospheric pressure, can be used to both modify and locally depositpolymeric material. Refereed/Peer-reviewed

A parallel plate dielectric barrier glow discharge operating at around atmospheric pressure was used to deposit functional coatings onto thin ( 130°) were produced using lower power and higher flow rate of octamethylcyclotetrasiloxane whereas relatively more hydrophilic coatings (contact angles 50 to 100°) resulted when a lower flow rate of octamethylcyclotetrasiloxane was used.

This paper reports on the fabrication of a pSi-based drug delivery system, functionalized with an initiated chemical vapor deposition (iCVD) polymer film, for the sustainable and temperature-dependent delivery of drugs. The devices were prepared by loading biodegradable porous silicon (pSi) with a fluorescent anticancer drug camptothecin (CPT) and coating the surface with temperature-responsive poly(N-isopropylacrylamide-co-diethylene glycol divinyl ether) (pNIPAM-co-DEGDVE) or non-stimulus-responsive poly(aminostyrene) (pAS) via iCVD. CPT released from the uncoated oxidized pSi control with a burst release fashion (∼21 nmol/(cm2 h)), and this was almost identical at temperatures both above (37 °C) and below (25 °C) the lower critical solution temperature (LCST) of the switchable polymer used, pNIPAM-co-DEGDVE (28.5 °C). In comparison, the burst release rate from the pSi-pNIPAM-co-DEGDVE sample was substantially slower at 6.12 and 9.19 nmol/(cm2 h) at 25 and 37 °C, respectively. The final amount of CPT released over 16 h was 10% higher at 37 °C compared to 25 °C for pSi coated with pNIPAM-co-DEGDVE (46.29% vs 35.67%), indicating that this material can be used to deliver drugs on-demand at elevated temperatures. pSi coated with pAS also displayed sustainable drug delivery profiles, but these were independent of the release temperature. These data show that sustainable and temperature-responsive delivery systems can be produced by functionalization of pSi with iCVD polymer films. Benefits of the iCVD approach include the application of the iCVD coating after drug loading without causing degradation of the drug commonly caused by exposure to factors such as solvents or high temperatures. Importantly, the iCVD process is applicable to a wide array of surfaces as the process is independent of the surface chemistry and pore size of the nanoporous matrix being coated. Refereed/Peer-reviewed

This contribution chronicles the research history over the past ten years behind a cell therapy product for the treatment of chronic wounds. The product is a plasma coated bandage, which delivers autologous cells (keratinoctyes) to non-healing wound beds. The account given is chronological, starting with the initial investigations of cell (keratinocyte) attachment to a range of plasma polymer surfaces. It details the subsequent selection of acrylic acid plasma polymer surfaces, on which the growth, proliferation and transfer of keratinoctyes to an in vitro wound model are studied. It concludes with the translation of this technology from the laboratory to the clinic, describing the first "proof of concept" study undertaken with non-healing diabetic foot ulcers.

A systematic study has been made to characterise a pulsed RF discharge used for the plasma treatment of polymers. Using a time-resolved Langmuir probe and a time-resolved retarding field energy analyser (RFA) the electron temperature and density, plasma potential, ion energy distribution function (IEDF) and electron energy distribution function (EEDF) has been measured. The source was pulsed for a range of frequencies from 100 Hz to 1 KHz at various duty cycles from 20 to 80%. A base pressure less than 10 −5 Torr was achieved to decrease the level of impurities in the chamber. The electron temperature ( T e ) decreases from 5 eV to less than 0.5 eV in afterglow. The cooling rate of T e depends on the pressure, power and duty cycle. By pulsing a biased grid synchronously with the pulsed RF, ions are selected from different time of the plasma and allowed to impinge on a polymer surface. Modified oxygen to carbon (O/C) ratio in the upper layer of polystyrene has been measured by X-ray photon emission spectroscopy (XPS) for different energy and flux of plasma ions. These results show that the treatment is either insensitive to ion energy or dominated by the UV in the discharge.

We describe the development and diagnosis of a two-stage plasma discharge in which a source plasma is separated from a secondary process plasma by a fine mesh. Through the application of a DC bias potential to the mesh the electron temperature T e and mean ion bombarding energy E i to an electrically isolating substrate can be well controlled in the secondary discharge. Electrical probe and retarding field analyser measurements have shown that T e and E i can be varied in the range 0.2–4 and 1–26 eV, respectively, and are found to be spatially uniform. Using this system, the bombarding ion flux can also be varied in the range from 10 17 to 10 19 m −2 s −1 , independently of the ion energy through the combined variation of the primary discharge power, and pressure and substrate location. These types of plasmas may find applications in the controlled plasma modification of materials through tailoring of the ion energy and flux.

Objective: The bond of a silane-coupling agent to a ceramic surface is expected to be influenced by the composition and chemical state of the ceramic surface. The purpose of this study was to determine the variation in the composition and the chemical states of the surfaces of a range of leucite-reinforced feldspathic (LRF) ceramics using X-ray photoelectron spectroscopy (XPS). Methods: Five LRF ceramic discs (IPS Empress,Optec HSP,VMK 68, Mirage, and a modified Mirage) were produced and polished to a 1 μm finish. A further nine discs of the modified Mirage were produced. The discs were stored for 48 h in a vacuum oven at 110°C to remove absorbed water. The surfaces of these discs were analysed by XPS. Survey scans at 30° take-off angle were taken and surface composition (in at%) was calculated from the narrow scans for Si 2p, O 1s, Al 2p, Mg 2s, K 2p, Na 1s, Ca 2p and N 1s. Results: Atomic concentration of elements (after exclusion of C) for the five LRF ceramics were in the range: O, 45.0–51.6%; Si, 26.7–35.6%; Al, 6.3–9.7%; Mg, 4.9–8.8%; K, 0.5–2.2%; N, 0.9–2.9% and less than 1% of Na and Ca. The shapes of the O 1s and Si 2p narrow scan core lines of the five LRF ceramics were virtually identical. Significance: All five LRF ceramics were found to have a silica-rich surface layer due to a reduction in K and Na relative to the bulk composition. Both the composition and chemical states of the surfaces for the five LRF ceramics were very similar.

Using an RF-driven collecting surface, mounted on the front end of a high-resolution energy-resolved mass spectrometer, the ion energy distribution functions (IEDFs) within a 13.56 MHz argon discharge have been measured and controlled. A technique of RF signal feedback has been developed, in which the RF amplitude and phase (fundamental and first two harmonics) in the sheath are varied, so manipulating the mean bombarding ion energies and widths of the IEDFs. For high RF sheath potentials, the IEDFs are broad and bi-modal. However as the sheath potential drop is reduced (with imposed matched RF signal) the IEDFs narrow, eventually becoming single peaked when no RF potential drop is present in the sheath. The observed widths in the IEDFs broadly agree with simple modelling predictions for the `high frequency' RF sheath regime; however we calculate, from the ion spectral data, marginally thinner sheaths than given by the Child-Langmuir law (derived using the mean DC sheath potential).

By use of Langmuir probes and energy-resolved mass spectrometry, the properties of a cold plasma suitable for the surface treatment of polymers are investigated. The 13.56 MHz radio frequency (rf) ...

The purpose of this study was: (a) to examine the effect of plasma-gas composition on plasma polymer oxygen/carbon (O/C) ratio, functional group composition and stability in water, and then (b) to examine cell attachment to surfaces containing different concentrations of O/C and functional groups. Oxygen-functionalised surfaces were deposited by means of the plasma copolymerisation of acrylic acid/1,7-octadiene. The use of a diluent hydrocarbon allowed the deposition of surfaces with a range of O/C concentrations. Plasma copolymer surfaces were characterised by X-ray photoelectron spectroscopy (XPS). Changes in functional group composition with % acrylic acid monomer and the non-dispersive and dispersive parts of the surface energy of these plasma copolymers were measured. The solubility of the plasma copolymers was assessed by means of XPS. The degree of attachment of ROS 17/2.8 osteoblast-like cells to plasma copolymer surfaces deemed to be 'stable' in aqueous medium was measured. Tissue culture polystyrene (TCPS) was included as a control. Attachment was found to be greatest to the plasma copolymer surface with an O/C of 0.11. This surface had a carboxylic acid concentration of ca. 3%. Attachment did not correlate with increased surface wettability (i.e. the non-dispersive component of the surface energy).

A simultaneous improvement of both the fracture toughness and strength of composite materials is very hard to realise. In this study, plasma polymerised HMDSO/O2 coatings have been deposited onto carbon fibres to provide a distinct interphase and a means of achieving this aim. Utilising a microwave energy source, coatings of various thickness were examined. By carefully controlling the flow rate of oxygen into the plasma, the resultant coating modulus could be selected within the range 0.7–2.0 of the resin modulus. Thus, the technique can be used to achieve interfacial interlayers with a range of stiffness. The micromechanics of interfacial failure were evaluated by the fragmentation test. Various fibre pretreatments (with O2, N2, Ar) and coating post-treatments (with O2 and acrylic acid) were also employed. Oxygen plasma pretreatment was found to significantly improve the adhesion of the coating to the fibre.

A composite of activated carbon particles (AC) and the conducting polymer polyaniline (PANI) was synthesised by in-situ polymerisation. The resultant composite was used as electrodes in the capacitive deionisation. The PANI presence was confirmed by Fourier transform infrared spectroscopy (FTIR). The morphology and porous structure were investigated by scanning electron microscopy (SEM) and N2 adsorption-desorption measurement. Electrochemical behaviour was studied by a cyclic voltammetry (CV) test. The results showed that the electrodes made of the composite had an ion removal capacity of 3.15 mg/g, which was much higher than that of AC only electrodes (1.98 mg/g) at the initial concentration of around 250 mg/L.Moreover, a faster ion removal rate was found for the composite electrodes with an absorption rate constant of 0.67, more than twice as high as the original activated carbon electrodes (0.23). The combination of two materials reduced the number of micropores and increased conductivity. It was believed that PANI formed conducting chains that connected micro-AC particles together and blocked most of the micropores. Weak acid functional groups at the surface of AC acted as dopant for PANI to increase its conductivity. It was found that the ion electrosorption by AC/PANI composite follows the Langmuir adsorption model. Refereed/Peer-reviewed

Capacitive deionization (CDI) is a novel ion removal technology that uses static electrical force to drive ions to the charged electrode and stores the ions into porous structure of the electrode. Graphene and graphene nanocomposites are considered promising materials for electrodes because of its good conductivity and extraordinarily high specific surface area. Graphene/Polyaniline nanocomposite was chosen that aims to increase the ion-electrosorption capacitance of graphene. In this work, graphene nanosheets were obtained by reducing oxidized graphite flasks. Graphene/Polyaniline (G/PANI) nanocomposites were synthesized by chemical polymerization of aniline in the presence of dispersed graphene sheets. The morphology and electrochemical property of the composite were characterized. The ion removal performance of the composite was determined by using a membrane capacitive deionization (CDI) bench-scale system. Refereed/Peer-reviewed

Age related macular degeneration of the eye is brought about by damage to the retinal pigment epithelium (RPE) and is a major cause of adult blindness. One potential treatment method is transplantation of RPE cells grown in vitro. Maintaining RPE cell viability and physiological function in vitro is a challenge, and this must also be achieved using materials that can be subsequently used to deliver an intact cell sheet into the eye. In this paper, plasma polymerisation has been used to develop a chemically modified surface for maintaining RPE cells in vitro. Multiwell plates modified with a plasma copolymer of allylamine and octadiene maintained RPE cell growth at a level similar to that of TCPS. However, the addition of bound glycosaminoglycans (GAGs) to the plasma polymerised surface significantly enhanced RPE proliferation. Simply adding GAG to the culture media had no positive effect. It is shown that a combination of plasma polymer and GAG is a promising method for developing suitable surfaces for cell growth and delivery, that can be applied to any substrate material.

Sol-gel has been used to prepare thin titania films. We have investigated the effects of dip rate, sintering temperature and time on the chemical composition of the films, their physical structure and thickness, and adherence to a silica substrate. Our aim has been to produce films that mimic as closely as possible the natural oxide layer that is found on titanium. These films are to be used as substrates in an in vitro model of osseointegration.

External parameters (RF power and precursor flow rate) are typically quoted to define plasma polymerization experiments. Utilizing a parallel-plate electrode reactor with variable geometry, it is shown that these parameters cannot be transferred to reactors with different geometries in order to reproduce plasma polymer films using four precursors. Measurements of ion flux and power coupling efficiency confirm that intrinsic plasma properties vary greatly with reactor geometry at constant applied RF power. It is further demonstrated that controlling intrinsic parameters, in this case the ion flux, offers a more widely applicable method of defining plasma polymerization processes, particularly for saturated and allylic precursors. Refereed/Peer-reviewed

Film thickness and functional group retention are routinely measured parameters for plasma polymers. It is known that other parameters such as density, solubility and mechanical properties can affect the performance of the plasma polymer film, however such parameters are not often measured; nor is there any understanding of the link between the mechanisms of film growth and these properties. In this investigation we produced thin films from three classes of commonly used plasma polymers (hydrocarbons, glymes and carboxylic acids). By choosing the monomer structure and applied RF power, the dominant mechanism of film growth was varied between ionic deposition and neutral grafting. The density, solubility and modulus of the resulting films were then measured by atomic force microscopy. Films grown from saturated monomers had higher moduli, were less soluble, and surprisingly had lower density compared to their unsaturated analogues. The results demonstrate that cognizance of the mechanism of film growth allows the physical properties of the film to be tailored for specific applications. Refereed/Peer-reviewed

“Maskless” microplasma treatment of passivated surfaces has been developed for the micropatterning of materials surfaces. The micropatterned surfaces are used in the fabrication of arrays for protein and cell-based assays. The advantage of this micropatterning approach is that it can be easily integrated into current manufacturing practices and the resultant micropatterned surfaces used with existing life sciences techniques and instrumentation. Refereed/Peer-reviewed

Recently, surface gradients have attracted significant interest for various research and technological applications. In this paper, we report a facile and versatile method for generating surface gradients of immobilized nanoparticles, nanotopography and ligands that is independent from the substrate material. The method consists of first depositing a functional polymer layer on a substrate and subsequent time controlled immersion of this functionalized substrate in solution gold nanoparticles (AuNPs), silver nanoparticles (AgNPs) or poly (styrenesulfonate) (PSS). Chemical characterization by X-ray Photoelectron Spectroscopy (XPS) and morphological analysis by Atomic Force Microscopy (AFM) show that the density of nanoparticles and the concentration of PSS across the surface increases in a gradient manner. As expected, time of immersion determines the concentration of surface bound species. We also demonstrate the generation of surface gradients of pure nanotopography. This is achieved by depositing a 5 nm thick plasma polymer layer on top of the number density gradient of nanoparticles to achieve a homogeneous surface chemistry. The surface independent approach for generation of surface gradients presented in this paper may open opportunities for a wider use of surface gradient in research and in various technologies. Refereed/Peer-reviewed

The deposition of a thin film layer by plasma polymerization enables the surface functionalization of a wide range of substrate materials for biointerfacial interactions. Plasma polymers can surface-bind proteins specifically via covalent linkages or nonspecifically through other irreversible adsorption mechanisms; key questions are whether covalent chemisorption has indeed occurred, and whether the protein retains functionality. Here the mode of surface binding of streptavidin and the biotin binding functionality of the bound streptavidin layer are studied on plasma polymer (pp) surfaces deposited using propionaldehyde and ethanol that were plasma polymerized at different powers (P) to investigate possible mechanisms for protein binding to a range of different surface chemistries. As expected, with pp surfaces composed principally of aldehyde groups, protein conjugation appears to be specific (chemisorption) allowing the immobilization of streptavidin (SAV) molecules retaining the ability to bind biotinylated probes. To contrast with this, we present the first study of protein adsorption to ethanol pp surfaces prepared at different P. This provides an investigation into retention of the hydroxyl functionality in the pp at low P and its effect on protein adsorption. Adsorption of human serum albumin (HSA) to ethanol pp was similar to that on propionaldehyde pp except at low P (5 W) where hydroxyl group retention and hydration presumably has a role in reducing protein adsorption. Although we observed SAV adsorption to ethanol pp surfaces at all P, interestingly, the protein lost its ability to bind biotinylated probes. Thus we suggest that irreversible, nonspecific adsorption of protein on ethanol pp surfaces results in apparent protein denaturation despite the hydrophilic nature of the ethanol pp surface. We conclude by making inferences between the pp structure as measured by X-ray photoelectron spectroscopy (XPS) and the related protein adsorption mechanisms. Refereed/Peer-reviewed

This paper presents a method for chemical and biomolecule patterning on planar (2D) surfaces using atmospheric pressure microplasmas. Spatially controlled surface modification is important for the development of emerging technologies such as microfluidic lab-on-a-chip devices, biosensors and other diagnostics tools. A non-fouling layer of poly(N-isopropylacrylamide) aldehyde (pNIPAM-ald) polymer, grafted onto heptylamine plasma polymer (HApp) modified silicon substrates, was used to achieve this goal. The non-fouling behaviour of the pNIPAM-ald coating was investigated at a temperature below its lower critical solution temperature (LCST) using human serum albumin (HSA). XPS and ToF-SIMS were used to characterise the plasma polymer coating and its subsequent modification with pNIPAM-ald before and after HSA adsorption. A 7 x 7 microcavity plasma array device (each cavity had a 250 µm diameter and was separated by 500 µm) was used for microplasma patterning. In a non-contact mode, helium microplasma treatment of the pNIPAM-ald coating was carried out for 60 s. The polymer coating was removed from regions directly exposed to microplasma cavities, as shown by ToF-SIMS. Microplasma treated regions were able to support the adsorption of fluorescently-labelled streptavidin whereas the rest of the coating was still non-fouling. This approach therefore resulted in spatially separated areas of immobilised protein. Refereed/Peer-reviewed

Glycosaminoglycans play an important role in tissue organisation through interactions with a diverse range of proteins, growth factors and other chemokines. In this report, we demonstrate the GAG-binding ‘fingerprint’ of two important GAG-binding proteins – osteoprotogerin and TIMP-3. The technique uses a straightforward method for attaching GAGs to assay surfaces in a non-covalent manner using plasma polymerization that leaves the adsorbed GAG able to participate in subsequent ligand binding. We show that OPG and TIMP-3 bind preferentially to different GAGs in a simple ELISA and that this binding does not correlate directly with simple GAG properties such as degree of sulfation. The methods outlined in this report can be easily applied to tissue engineering scaffolds in order to exploit the potential of surface-bound GAGs in influencing the structure of engineered tissues. Refereed/Peer-reviewed

A rapid, high-precision method for localised plasma-treatment of bonded PDMS microchannels is demonstrated. Patterned electrodes were prepared by injection of molten gallium into preformed microchannel guides. The electrode guides were prepared without any additional fabrication steps compared to conventional microchannel fabrication. Alignment of the “injected” electrodes is precisely controlled by the photomask design, rather than positioning accuracy of alignment tools. Surface modification is detected using a fluorescent dye (Rhodamine B), revealing a well-defined micropattern with regions less than 100 µm along the length of the microchannel. Refereed/Peer-reviewed

In this paper we describe the spatial surface chemical modification of bonded microchannels through the integration of microplasmas into a microfluidic chip (MMC). The composite MMC comprises an array of precisely aligned electrodes surrounding the gas/fluid microchannel. Pairs of electrodes are used to locally ignite microplasmas inside the microchannel. Microplasmas, comprising geometrically confined microscopic electrically-driven gas discharges, are used to spatially functionalise the walls of the microchannels with proteins and enzymes down to scale lengths of 300 μm inside 50 μm-wide microchannels. Microchannels in poly(dimethylsiloxane) (PDMS) or glass were used in this study. Protein specifically adsorbed on to the regions inside the PDMS microchannel that were directly exposed to the microplasma. Glass microchannels required pre-functionalisation to enable the spatial patterning of protein. Firstly, the microchannel wall was functionalised with a protein adhesion layer, 3-aminopropyl-triethoxysilane (APTES), and secondly, a protein blocking agent (bovine serum albumin, BSA) was adsorbed onto APTES. The functionalised microchannel wall was then treated with an array of spatially localised microplasmas that reduced the blocking capability of the BSA in the region that had been exposed to the plasma. This enabled the functionalisation of the microchannel with an array of spatially separated protein. As an alternative we demonstrated the feasibility of depositing functional thin films inside the MMC by spatially plasma depositing acrylic acid and 1,7-octadiene within the microchannel. This new MMC technology enables the surface chemistry of microchannels to be engineered with precision, which is expected to broaden the scope of lab-on-a-chip type applications. Refereed/Peer-reviewed

The use of low pressure, low power plasma established in an atmosphere of precursor monomer(s) affords the deposition of functionalized films. Such films can retain the functional group and molecular structure of the starting compound(s) in an ultrathin ‘plasma polymer’ deposit. A basic introduction to plasma and the modulation of some of the important physical and chemical properties will identify some of the key relationships between the plasma physics and the chemistry of the resultant plasma polymer films. There then follows an examination of where plasma polymerized films have found application in the area of biomaterial preparation and, in summary, identification of the likely direction of future developments.

Gaining a deeper understanding of the growth of poly(3,4-ethylenedioxythiophene) (PEDOT) films by vapour phase polymerisation (VPP) is essential for the rational design and optimization of such films. The VPP process was used to synthesise films of PEDOT on oxidant-coated substrates. Atomic force microscopy images showed that the morphology of the films changed considerably with time. Utilising a quartz crystal microbalance with dissipation measurement (QCM-D), we found that the kinetics of polymerisation and the viscoelastic properties of the films varied. The data reveal four distinct stages in film growth. Each stage produces a layer having different conductivity values, from a low of 276 S cm-1 to a high of 1196 S cm-1. Conductivity and electrochromic optical contrast, Δ%Tx, can thus be maximized by appropriate termination of the polymerisation reaction. Factors determining the polymerisation rate and changes in conductivity and optical performance are discussed. Refereed/Peer-reviewed

The purpose of this review is to explore the development, applications and outcomes of using plasmadeposited (polymeric) surfaces as culture and delivery vehicles for cells in the replacement, repair and regeneration of damaged tissues. After a brief introduction to biomaterials and cell therapy, examples of the use of plasma polymerization in surface engineering are presented. The use of these surfaces for both in vitro cell culture and ex vivo delivery is reviewed with a particular emphasis on the epithelium. The review concludes with a look at some of the emerging and potential future directions for this technology in mediating cell-surface interactions. Refereed/Peer-reviewed

Many fundamental biological processes, including early embryo development, immune responses and the progression of pathogens, are mediated by gradients of biological molecules. Understanding these vital physiological processes requires the development of biomaterial platforms that can mimic them in-vitro. Such platforms include laboratory generated surface gradients of biological molecules. In this work, we report a method for the generation of surface gradients of two proteins. We used a surface grafting density gradient of polyethylene glycol (PEG) to control protein adsorption. In addition, we used protein size as a tool to control the position and the adsorbed amount of both proteins. To demonstrate our concept, we used fibrinogen as an example of a large protein and lysozyme as an example of a small protein. However, we speculate that the same strategy could be extended to any other pair of large and small proteins. We used X-ray photoelectron spectroscopy and sessile drop contact angle measurements to determine the chemical composition and wettability of the gradients. Protein adsorption was studied by surface plasmon resonance imaging.