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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

In the future, stem-cell-based therapies could offer new approaches to treat kidney disease and reduce the incidence of ESRD (end-stage renal disease), but, as yet, research in this area is only being conducted in rodents and it is not clear whether or when it could be applied to human patients. Drug therapies, on the other hand, have been very effective at delaying the progression of kidney disease, but, for various reasons, current drug regimes are not suitable for all patients. A greater understanding of the molecular mechanisms that underlie disease progression in chronic kidney disease could help to identify novel drug targets. However, progress in this area is currently hindered due to the lack of appropriate in vitro culture systems for important renal cell types, such as proximal tubule cells and podocytes. This problem could be overcome if it were possible to direct the differentiation of kidney stem cells to renal cell types in vitro. In the present review, we highlight the potential of surface gradients of small chemical functional groups to direct the differentiation of kidney stem cells.

Time-of-flight secondary ion mass spectrometry (ToF-SIMS) has been employed to monitor the chemical changes occurring with continuous UV irradiation in the surface region of neat films of polystyrene and the copolymer of styrene and 2-(2-hydroxy-3-vinyl-5-methylphenyl)benzotriazole (HVB, 2% w/w). Previous conclusions concerning the relative rates of oxygen uptake of these systems have been confirmed. New data are presented that enable delineation of two different surface reactions and demonstrate activation of the polymer surface by HVB with respect to polymer degradation as well as oxygen uptake. Some conclusions are drawn concerning the mechanism by which this activation is achieved.

ToF-SIMS has been employed to monitor the changes in molecular weight which occur on UV irradiation in a polystyrene standard (MW 1700) as a thin film on silver. The ToF-SIMS spectrum of unirradiated polystyrene is also described. Polysiloxane contamination was present in some of the polystyrene samples studied; no effort was made to remove this contamination as it was considered to be part of the system under analysis and proved useful in confirming the role of the phenyl substituent in the photodegradation of polystyrene. Implications of this study, the possible development of the technique described and its application to real polymer surfaces are discussed.

Time-of-flight secondary ion mass spectroscopy (ToF-SIMS) and x-ray photoelectron spectroscopy (XPS) have been employed to study the plasma surface oxidation of poly(ether etherketone) (PEEK). The positive and negative ion ToF-SIM spectra obtained from a cleaned PEEK surface were easily interpreted using conventional mass spectrometry rules. Plasma oxidation of PEEK was found to prodoce complex positive and negative ion spectra. In these spectra, ions diagnostic of the PEEK repeat unit were much reduced in intensity, and new ions diagnostic of plasma treatment were introduced

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.

We describe a method to produce antibody-captured ligand gradients over biologically relevant distances (hundreds of micrometers) whereby the ligand density and gradient shape may be tailored. Separation of the ligand from the solid-phase surface ensures that the biological activity of the ligand remains unaffected by immobilization. Our method involves the use of a plasma-masking method to generate a surface chemical gradient on a glass substrate to which the 9E10 antibody is covalently coupled. This antibody captures myc-tagged biomolecules. In our example, the antibody is then used to immobilize a gradient of the intercellular signaling molecule delta-like-1 (Dll1). To visualize the gradient of Dll1, we have used the multistep approach of binding with rabbit anti-Dll1 primary antibody and then adding colloidal-gold-conjugated secondary antibody. Refereed/Peer-reviewed

Rats received diets containing average daily doses of 0, 50, 150, and 500 mg/kg/day of hexamethylenediamine over two generations. Although no treatment-related mortality was observed in any of the groups, the weight gain of adults and pups was slightly reduced in the high dose group. While the litter size was also slightly reduced at birth in the high dose group, there was no adverse effect on survival during lactation in any of the treated groups. Thus, the dietary administration of up to 150 mg/kg/day of hexamethylenediamine over two generations did not adversely affect reproduction or fertility in rats.

Some surface aspects of the argon plasma induced degradation reactions of cellulose nitrate have been investigated by X-ray Photoelectron Spectroscopy (XPS). It is shown that plasma treatment results in an initial decrease in the surface nitrogen and oxygen concentrations, the creation of highly oxidized carbon environments (as observed by a broadening in the C1s spectra of the treated materials) and the creation of new ‘reduced’ nitrogen functionalities (which appear at lower binding energies [398–402 eV]). Whilst little change is noted in the surface nitrogen and oxygen concentrations after the first minute of treatment, plasma irradiation continues to produce changes in the C1s and N1s core level spectra. In the N1s core level there is a slow but continued conversion of nitrate esters to the new nitrogen functionalities. However, the rate of this conversion is much faster in the first minute of irradiation than afterwards and consequently even after 40-min plasma treatment there is still a significant concentration of nitrate esters remaining in the top 50 A of the treated materials. The observed changes in surface chemistry of cellulose nitrate with plasma treatment are correlated with the depth to which direct and indirect energy transfer processes are known to induce degradation in polymers.

The surface photo-oxidation of styrene/2-(2-hydroxy-5-vinylphenyl)-2H-benzotriazole (HVB) copolymers in the presence of two different antioxidants has been studied by ESCA. The results indicate that in order to protect the surface of such materials properly, it is necessary to combine the copolymer with a small percentage of antioxidant. Bis-(2,2,6,6-tetramethyl-4-piperidyl)-sebacate has been found to be very effective.

Thumbnail image of graphical abstract A gradient of functional heparin is fabricated onto a surface chemical gradient of plasma-polymerized allyl amine (see figure). While heparin functionality changes across the gradient, increased adsorption of heparin onto the surface is not accompanied with a continued, corresponding rise in heparin function. Refereed/Peer-reviewed

This study reports on the use of static secondary ion mass spectroscopy (SSIMS) to chemically characterize complex methacrylate copolymers used in the pharmaceutical industry for controlled drug delivery. Ions diagnostic of the component monomer residues were detected, which could be interpreted using a fragmentation model for alkylmethacrylate homopolymers proposed previously. This model is extended to include the SSIMS analysis of nitrogen-containing methacrylate copolymer residues.

Background, Chronic wounds are a growing clinical burden on healthcare systems and with increasing incidences of obesity, diabetes and an aging population this problem is set to snowball. Chronic wounds present a hostile environment and unique challenges. Cell therapies may offer a solution with a range of cell based approaches beginning to cross the rift from bench-to-bedside. Supporting data suggests that the appropriate administration of stem cells can accelerate wound healing. The effectiveness of a therapy will depend not only on what we deliver but how we deliver it. Aims or Objectives, Our aim was to generate a method of delivering cells to wounds where injection may not be ideal. We achieved this by manufacturing a cell-laden bandage. This bandage was capable of supporting cell attachment without affecting phenotype. When placed onto a wound, the cells then leave this surface in preference for the wound Materials and Methods, Plasma polymerisation was used to generate a range of functional surfaces on candidate dressings. Coating conditions were varied and these surfaces were then tested with multipotent adult progenitor cells (MAPC). An in vitro transfer assay was used to determine the migration of viable cells from the patch onto a wound model. Results & Discussion, By varying surface treatments we were able to optimise a range of surfaces that supported the attachment of MAPC and subsequently allow these cells to leave in preference for a model wound bed. Conclusions, There is mounting evidence showing that cell therapies are effective in the treatment of chronic wounds. In order to promote clinical uptake of these new approaches, we need to make the use and delivery of cell therapies simple and effective. Our approach aims to create a simple bandage that is non-traumatic and easily applied at the bedside Refereed/Peer-reviewed

After osteogenic induction CD271-MSC samples showed higher levels of mineral deposition compared to the PA-MSCs. RNA analysis showed CD271MSCs expressed significantly higher (p 0.05) levels of alkaline phosphatase compared to the PA-MSCs in passage 2 and 3, supporting the observation that CD271-MSCs produce higher levels of mineralisation. These findings showed that even partial CD271 enrichment could enhance the osteogenic potency of MSCs. Furthermore, enhanced osteogenic potency of CD271-MSC appeared to be limited to the early stage of MSC expansion.

Background: Glycosaminoglycans (GAGs) are be found in the extracellular matrix of many tissues, and play an important role in cell binding, growth and organization processes leading to the establishment and maintenance of tissue structure. In particular, GAGs preserve growth factors in vivo, and enable the release and presentation of these molecules. We have developed a straight-forward surface modification platform for binding GAGs from simple buffer solutions (without chemical modification) which enables their use as a cell culture substrate. The presence of GAGs on a material surface allows the binding and presentation of growth factors, such as FGF-2 and FGF-7 to be enhanced. Methods: Plasma co-polymerization is a technique capable of producing thin polymeric films with controllable concentrations of chemical functional groups on cell culture surfaces. Using radio-labelling and high-resolution surface analysis techniques, we can show the binding of heparin and other GAGs to the surfaces, and their subsequent capture of growth factors FGF-2 and FGF-7. We culture human primary fibroblasts and keratinocytes on the surfaces with growth factors pre-adsorbed to the matrix, or added separately to the cell culture.Results and Conclusion: The results show significant improvement in the cell viability from much lower concentrations of growth factor for both FGF-2 and FGF-7 - by as much as two orders of magnitude. This approach has the potential to reduce the amounts of expensive growth factors used for culturing therapeutic cells by the use of novel surface engineering approaches.

We report a simple experimental approach to follow the transport of helium (He) plasma generated reactive oxygen and nitrogen species (RONS) through millimetre thick agarose targets. These RONS may be either primary RONS, generated directly by the plasma jet,or secondary RONS generated for example at the surface of, or within, the material. Our experiment involves placing an agarose film over a quartz cuvette filled with deionized water.The agarose film is exposed to a He plasma jet and the UV absorption profile (of the deionized water) is recorded in real-time. Plasma exposure time, source-target distance and agarose film thickness and composition are varied to explore their effects on the depth of RONS delivery by the plasma jet. We conclude that plasma UV plays a minor role in the transport of RONS; whereas direct plasma contact and the He gas flow promote the transport of RONS into tissue.Our data indicate an accumulation of RONS within the agarose film (during plasma exposure)and a subsequent (time-lagged) release into the deionized water. Our approach can be readily adapted to other plasma sources; it can accommodate more complex biological materials, and has the potential to provide new insights into plasma-induced phenomena within real tissues. Refereed/Peer-reviewed

Using a novel RF biasing technique, the energy of positive ions at a depositing substrate is controlled, independently of other parameters. Under bias conditions which gave the maximum and minimum ion energies, plasmas of propionic and acrylic acid were investigated using mass spectrometry, an ion flux probe, quartz crystal microbalance, and X-ray photoelectron spectroscopy (XPS). For both compounds investigated, the ion energy affects the deposition rate but leaves the neutral gas-phase chemistry and positive ion fluxes unchanged. The chemistry of the polymer deposit for acrylic acid is unaffected by the change in ion energy, but the chemistry of the propionic acid plasma polymer changes markedly. We argue that the results presented are consistent with the hypothesis that, under the plasma conditions explored, the carbon-carbon double bond present in acrylic acid plays a significant role in the formation of the polymer. Conversely, the absence of this bond in propionic acid leads us to conclude that positive ions contribute significantly to film formation for this compound.

“Living bandages” containing patients’ own skin cells can help treat previously non-healing chronic wounds such as diabetic foot ulcers, venous leg ulcers and burns. These chronic wounds affect some 6 million people in Europe and the US, and are a huge drain on the resources of healthcare providers. There is a strong clinical need for an effective delivery system that enables cells to be introduced into a wound bed to kick start the healing process. Early patient trials using a plasma polymer material have been highly encouraging, with healing demonstrated in diabetic foot ulcers and other non-healing wounds.

Plasma polymerisation of N -isopropyl acrylamide (NIPAAm) presents an exciting route for the production of thermally responsive coatings on a wide variety of substrates for applications in tissue culture and microfluidics. One issue associated with the polymerisation of NIPAAm via plasma polymerisation is the limited volatility of the monomer and the subsequent requirement for monomer and reactor heating to create and maintain the vapour. It is already well established that power is critical in the balance between polymer functionality and coating stability in plasma polymers. However, little is known of how reactor and substrate temperatures may be used to influence the physico-chemical characteristics of polymers produced from such low-volatility monomers. In this paper, we examine the effects of a range of plasma deposition parameters on the functionality and stability of plasma-polymerised NIPAAm surfaces. X-ray photoelectron spectroscopy (XPS), near-edge X-ray absorption fine structure spectroscopy (NEXAFS), ellipsometry and contact angle goniometry have been used to examine coating chemistry, stability in aqueous environments, deposition rates and thermo-responsive behaviour. Our results indicate that plasma polymerisation at low powers and low temperatures enhances the ability of plasma-polymerised NIPAAm to display a wettability phase transition, but also contributes to instability of the coating to dissolution or delamination in water. Our spectroscopic measurements confirm that retention of the monomer structure is facilitated by low power and temperature deposition and reveal that conversion of the amide groups to amine and nitrile groups occurs during the polymerisation process, particularly at high discharge powers.

Time-of-flight secondary ion mass spectrometry (ToF-SIMS) studies, utilizing both laterial imaging and shallow depth profiling, of a 50 :50 poly(vinyl chloride)/poly(methyl methacrylate) (PVC :PMMA) blend have confirmed the presence of a thin overlayer of PMMA on the phase-separated bulk morphology.

tert-Octylcalix(8)arene and derivatives in which the lower rim hydroxy groups have been converted into OCH2CO2Et and OCH2COCH3 groups have been shown to form Langmuir−Blodgett films readily. These films adsorb a range of anions and cations from solution. XPS determinations on the films identify both the nucleus and the extent of adsorption into the films. For anions the order of selection is I > F > Br > Cl and for cations is Cs > Rb > Na ≫ K. Such films clearly have potential applications in ion sensing.

We have recently reported that irradiated human fibroblasts can be used as a feeder layer, to expand keratinocytes under serum-free conditions, on a chemically defined plasma polymer surface developed for the culture and transfer of keratinocytes for clinical use. While this is a significant advance in developing a serum-free keratinocyte culture approach, the need to irradiate fibroblasts to growth-arrest them and prevent them from overgrowing the keratinocytes introduces another small, but potential, risk for the patient. The aim of the present study was to develop conditions for the coculture of normal human keratinocytes with nonirradiated normal human fibroblasts under serum-free conditions. We examined the fibroblast/keratinocyte relationship on three separate surfaces: tissue culture plastic, non-tissue culture plastic, and a plasma polymer surface designed for clinical use. We report that it is possible to achieve rapid and successful expansion of human keratinocytes under serum-free conditions on all three surfaces providing one uses a keratinocyte-friendly media, a minimum seeding density of keratinocytes, and a ratio of fibroblasts to keratinocytes that does not exceed 1 : 1. These results provide us with a rapid laboratory expansion of proliferative human keratinocytes, under completely defined culture conditions, without any xenobiotic cells (mouse fibroblasts) or material (bovine serum), for the treatment of patients with extensive skin loss.

Independent control over the electron temperature and ion bombarding flux has been achieved in weakly ionised discharge through the use of two electrically biased meshes. The meshes divide the discharge into two parts; a main RF plasma and dc processing plasma, the latter is sustained through controlled diffusion of particles from the main plasma. By varying the bias to each of the grids separately, and at typical pressures of 2.6 Pa in the processing chamber, the electron temperatures can be varied in the range 0.2–5.6 eV. To an electrically isolated surface, the ion bombarding fluxes can be controlled between 0.2 and 5.4×10 18 m 2 s −1 . This method of electron temperature control, which gives more flexibility than the single grid separation technique, allows ion energies to be varied from 1 to 27 eV, independently of the ion flux. This is useful, both for the fundamental study of plasma-surface interactions and for developing discharges with controlled parameters to tailor the properties of materials such as polymeric surfaces.

The purpose of this study was to develop a convenient methodology for the coculture of autologous melanocytes and keratinocytes for grafting of patients with vitiligo. While grafting of pure melanocytes may achieve repigmentation, the inclusion of keratinocytes ensures rapid reepithelialization. Previously we have used confluent sheets of keratinocytes (with melanocytes present) to transfer cells. However, we found that as the keratinocyte density increased, melanocyte number and function were downregulated. Accordingly in this study we explored combinations of three culture surfaces and three media, seeking to achieve subconfluent culture of primary keratinocytes with a reasonable density of melanocytes, using cells immediately after isolation from skin. For this in vitro study, the surfaces studied were uncoated glass coverslips, and glass coverslips coated with collagen I or a nitrogen-containing plasma polymer. The results show that both the substrate surface and the medium composition influence the proliferation and survival of melanocytes. Keratinocytes and melanocytes could be successfully cocultured on a chemically defined plasma polymer substrate using a serum-free medium.

Functionalised thin films of copolymers of acrylic acid and 1,7-octadiene have been deposited by plasma-co-polymerisation to create a range of surfaces of well-defined chemistry, containing carboxyl functional groups. X-Ray photoelectron spectroscopy (XPS) has been used to characterise the deposits. Adsorption of immunoglobulin G from single solution has been studied by indirect, antibody detection (ELISA), and by direct, radio-labelling and fluorescent detection methods. In addition, XPS analysis of the surface adsorbed protein was also performed. Direct measurement techniques showed an apparent decrease in protein binding on carboxylic acid functionalised surfaces, whilst antibody detection showed an increase in binding with increased carboxylic acid content of the surface. This difference has been ascribed to orientational/conformational and/or packing differences of the proteins on the different surfaces, leading to an increased biological (“functional”) activity on the carboxylic acid functionalised surfaces. Adsorption of IgG from serum has also been probed by ELISA. An increase in IgG binding with surface carboxylic acid content was measured, indicating a similar effect when IgG is adsorbed from a complex protein mixture.

Polymeric functional thin films have been deposited from plasmas of allyl alcohol, acrylic acid, allylamine and octa-1,7-diene onto polystyrene microwells and aluminium foil, and analysed by X-ray photoelectron spectroscopy (XPS) and water contact angle measurement. The films were found to be conformal and pin-hole free. Advancing and receding water contact angles measured in air showed that the surfaces had a range of hydrophilicities. The adsorption of human vitronectin, human immunoglobulin G (IgG) and heat-denatured bovine type II collagen to the different plasma polymer surfaces from single solutions was compared by enzyme linked immunosorbent assay (ELISA). Results demonstrate that the adsorption of proteins depends not only on the chemistry of the surface, but also on the nature of the protein. Vitronectin adsorbed most extensively to the acrylic acid-deposited surface, while immunoglobulin G adsorbed more readily to the allylamine deposited surface. The functionalised surfaces performed poorly in terms of collagen binding, with much higher levels of adsorption to the hydrocarbon (octa-1,7-diene) plasma polymer, and the uncoated polystyrene control wells. The amount of adsorbed protein detected on a surface is often explained in terms of surface hydrophilicity/hydrophobicity. The results of this study show that adsorption of these proteins is not simply a matter of wettability, but relates more to the chemical functionality of the surface, which in turn affects a number of surface properties, including wettability, surface charge and pKa.

The pre-treatment of aluminium alloys prior to painting or adhesive bonding is an essential technology in many industrial sectors (e.g. aerospace industry). However, the pre-treatments used on the substrates, which are vital to ensure reliable long-term performance, often comprise a range of environmentally objectionable chemicals, such as solvents and chromates, some of which are carcinogenic. The plasma deposition of thin coatings on aluminium, which exhibit strong interfacial bonding, could be an alternative to the traditional chromate-based treatments. It is envisaged that in a single plasma reactor, plasma cleaning, etching and deposition could provide a complete preparation cycle before painting, avoiding the use, handling and disposal of hazardous materials. In the present work, the corrosion behaviour and adhesive joint performance of plasma-coated Alclad AA2024-T3 alloy were investigated. The coatings were deposited from hexamethyldisiloxane monomer (HMDSO) in a capacitively coupled RF plasma reactor. The same evaluations were carried out on specimens painted with an epoxy primer after coating deposition. The coatings conferred protection against corrosion and provided a good interface for strong, durable adhesive bonds.

A coating consisting of an aqueous emulsion of epoxy resin and a polyamidoamine hardener has been developed which effectively strengthens glass containing large flaws. By substituting a silane coupling agent for some of the resin the deleterious effects of ageing can be prevented; the strength of samples aged for two months at 52°C and 96% relative humidity was not reduced, maintaining a 197% improvement in strength with respect to uncoated samples. X-ray photoelectron spectroscopy showed that the accelerated ageing treatment led to an increase in the concentration of hydroxyl groups in the resin resulting from the scission of amine crosslinking groups. The migration of sodium from the substrate to the surface was also demonstrated. It is concluded that the coupling agent does not render the coating immune to hydrolytic ageing or protect the substrate from hydrolytic attack. It only provides a hydrolytically-stable linkage between the two.

Thin polymer films have been grown from hyperthermal [m/z 147, Si2OMe5+] ions, using ion energies of 15, 25, 50, and 100 eV. X-ray photoelectron spectroscopy (XPS) and secondary ion mass spectrometry (SIMS) analyses were undertaken of the air-aged polymer films. The SIMS and XPS of samples deposited from ion beams of 15 and 25 eV energies (15 and 25 eV polymers) are remarkably similar, but different in a number of respects to those of the 50 and 100 eV polymers. The positive SIMS of the lower energy polymers resemble closely that of the linear polymer polydimethyl siloxane (PDMS). However, the XPS of these polymers reveal a range of silicon binding environments [Si–C/H, Si(–O1) Si(–O2) (Si–O3) and Si(–O4)], whilst the ‘monomer ion’ (m/z 147) has only one, Si(–O1). Although the positive ion SIMS of the 50 and 100 eV polymers contain ‘PDMS-like’ fragments (m/z 147, 207, 221, 281), these ions are much reduced in intensity (cf. 15 and 25 eV), and we postulate that the extent of cross-linking is much higher in these polymers. In fitting the XPS of these polymers it was necessary to include an additional component peak for Si(–Si3). These polymers are compared with a low power plasma polymer of HMDSO. The polymers grown from the 15 and 25 eV ions are remarkably similar to the plasma polymer in terms of their molecular structure and their surface chemistry.

Both XPS and time-of-flight secondary ion mass spectrometry (ToF-SIMS) imaging have been used to characterize chemically micropatterned surfaces formed by plasma polymerization, using a copper transmission electron microscope grid as a mask. Micropatterns of spatially distinct regions of fluorine, carboxylic acid and hydrocarbon functionalities have been imaged by ToF-SIMS, whereas imaging XPS has demonstrated the ability to produce patterns of nitrogen-containing functionalities. Features as small as 50μm bars and 75μm ‘islands’ have been imaged. The utility of these chemically defined patterns has been demonstrated by the spatial binding of protein and by the attachment of cerebellar granule neurons. Copyright © 2001 John Wiley & Sons, Ltd.

The radio-frequency-induced plasma polymerization of allylamine has been investigated in the plasma-gas phase by mass spectrometry and at the plasma−solid interface by means of an ion flux probe and a quartz mass balance. The surface chemistry of the deposits has been determined by X-ray photoelectron spectroscopy. The objective of this study was to unravel the mechanism(s) by which allylamine plasma polymers form. The results are compared with those obtained in an earlier investigation of the plasma polymerization of acrylic acid. In the plasma-gas phase, evidence is provided for reactions between cations and intact neutral monomers (allylamine). These oligomerization reactions were found to be relatively power-insensitive compared with those seen in plasmas of acrylic acid, as was the gas-phase concentration of the intact neutral monomer. At the polymer surface, ion fluxes were found to increase with plasma input power (P) from 6.6 × 1016 ions m-2 s-1 at 1 W to 1.4 × 1018 ions m-2 s-1 at 14 W. The ionic mass transport to the polymer surface (ion mass flux) was calculated by multiplying the measured ion flux by the average ion mass (determined by mass spectrometry). At P = 1 W, the ion mass flux was 11.7 μm m-2 s-1, and at 14 W, the ion mass flux was 226.6 μm m-2 s-1. These values differed from the total mass deposition rates measured by the quartz mass balance, which were 18.7 and 127.1 μm m-2 s-1, respectively. However, the relationship found between the ion mass flux, the mass deposition rate, and P was complex, and it is shown that, at very low P (

New insight is given into the complex molecular structure and composition of thin-film deposits of acrylic acid (AA) and 1,7-octadiene (OD) by variable-temperature ellipsometry. An AA plasma polyme...

Sol–gel derived titania coatings are being developed for use as biomedical coatings. In this study, bone marrow stromal (BMS) cells and ROS osteoblast-like cells have been cultured on sol–gel derived titania coatings and are compared with cultures on glass and tissue culture plastic (TCPS) surfaces. Over 24 h both the BMS and ROS cells attach well to all three substrates. On the titania coatings both cell types spread well, displaying morphologies that conform with those expected of these cells. The ROS cells did not spread well on the glass or TCPS surfaces. The titania coatings were deposited onto glass by means of an alkoxide sol–gel route and characterised using a number of analytical techniques, including X-ray photoelectron spectroscopy (XPS). The effects of withdrawal rate (in the dipping process) and firing temperature on coating integrity and adherence (to the glass substrate) have been investigated. From this study, parameters have been identified that yield thin, smooth, crack-free titania coatings of homogeneous surface chemistry.

Absolutely calibrated vacuum ultraviolet (VUV) spectroscopy has been used to determine the energy fluxes of VUV photons at an electrically floating substrate in a low-pressure 13.56-MHz radiofrequency plasma reactor used for polymer surface treatments. These fluxes have been compared with the positive ion flux that was reported in an earlier study. At the typical operating parameters of 10-mTorr pressure and 10-W power, the total VUV energy flux is 2.2 mW cm-2, compared with a value of 3.3 mW cm-2 from the ions. With increasing power (from 0.5 to 12 W), both the ion and VUV energy fluxes increase monotonically. However, as the pressure increases, (1−100 mTorr), the ion energy flux declines, while the VUV component increases. At discharge powers of 10 W, and pressures greater than 25 mTorr, the greater part of the energy flux to the surface is from the VUV photons. These measurements are used to determine which of the plasma components, VUV or ions, will be most effective in the treatment of polystyrene surfaces in a pure Ar plasma. Because of the low VUV absorption coefficient of polystyrene most of the photon flux penetrates through the outermost 2 nm of the polymer surface without attenuation. Consequently, we calculate that under typical plasma operating parameters, the ions play the major role in the modification of polystyrene surfaces because of their shorter stopping distances.

A quantitative X-ray Photoelectron Spectroscopy (XPS) analysis of deposits formed from a microwave sustained hexamethyl disiloxane (HMDSO) plasma is undertaken. Curve fitting of the Si 2p core level has been achieved using component peak binding energies determined from standard compounds. The pure HMDSO plasma deposit was dominated by Si(–O)2 (44%) environments indicating a large proportion of siloxane bond formation in the plasma environment. The introduction of 200 sccm (standard cubic centimetres per minute) of oxygen to the plasma produced a deposit in which half the silicon atoms were co-ordinated with four oxygen atoms while the majority of the remaining silicon was co-ordinated to three.

Ion flux, mass spectral and mass deposition rate measurements have been made in radiofrequency-induced continuous-wave plasmas of acrylic acid. At 1 W input power, an ion flux of 0.05±0.1×1018 ions m-2 s-1 was measured for acrylic acid. At this power, ions corresponding to (2M+H)+ and (3M+H)+ were prominent in the positive-ion mass spectrum. When this spectrum was corrected for the transmission function of the quadrupole mass spectrometer (conservatively taken as intensity∝m-1), it was evident that the cationic portion of plasma contained many ions of high m/z, as opposed to small fragments of acrylic acid. The m/z of the ‘average’ ion was calculated as 115. The mass of ions arriving at a solid surface in the centre of the plasma was then calculated by multiplying the flux by the average mass to give 9.6 µg m-2 s-1. This value represents a significant fraction of the total mass deposited, determined by means of a quartz crystal mass balance (45.5 µg m-2 s-1). Repeating the calculation for a 5 W plasma yields an ion mass flux of 39.6 µg m-2 s-1 (measured mass deposition of 57.3 µg m-2 s-1). At 15 W, the calculated mass deposited (based on ion flux) exceeds that measured by the quartz mass balance. The ‘average’ ion mass decreased as plasma input power increased. Based on these data, and XPS measurements of the solid-phase deposit we make a first attempt at describing semi-quantitatively the possible role of ions in deposit formation.

The first comparative study of cell attachment to self-assembled monolayers (SAMs) and plasma-deposited films is reported. Osteoblast-like cells attached extensively to acid-terminated alkyl thiol SAMs and to a plasma co-polymer of acrylic acid and octa-1,7-diene (acid-PCP). However, they attached poorly to methyl-terminated SAMs and a plasma polymer of octa-1,7-diene (OD-PP).

Inductively coupled, radiofrequency-induced plasmas of allyl amine, operated at low values of electrical power P/ monomer flow rate Φ (ΦP/Φ), have been investigated using mass spectrometry (MS) and deposition rate measurements. The solid, plasma deposit products were obtained as films and analyzed by X-ray photoelectron spectroscopy (XPS) and grazing angle infra-red (IR). The positiveion MS data indicate that species of the general types (nM − H)+, (nM+H)+, and nM+, where M represents a unit of the starting material (monomer), are present in the plasma. The relative abundance of these was monitored as a function of the electrical power supplied to the plasma. Mass spectrometry of the plasma neutrals revealed that only M and its fragments are present in the plasma: no neutral oligomeric species were detected. XPS analysis revealed that the plasma deposits contain at least three different nitrogen functional groups. The relative proportions of these were only marginally affected by plasma power. The deposition rate increased with P/Φ. The observation of three classes of species in the plasma-phase sets allyl amine apart from other compounds previously studied. We believe that the plasma-phase chemistry accounts for the low retention of amine in the solid-phase plasma product and for the weak dependence of deposit chemistry on P/Φ. Plasmas and Polymers Plasmas and Polymers Look Inside 7 Citations Other actions Export citation Register for Journal Updates About This Journal Reprints and Permissions Add to Papers Share Share this content on Facebook Share this content on Twitter Share this content on LinkedIn

The specificity of plasma gas-phase reactions, in low-power plasmas, has been investigated. Quadrupole mass spectrometry has been used to detect the gas-phase species in the inductively coupled, radiofrequency-induced 1–10 W plasmas of propenoic acid and styrene. The mass spectra have been compared with those for plasmas of the individual compounds. Both ionic and neutral species, present in the plasma, can be sampled through a 50 µm aperture which provides an interface between the plasma reactor (10-2 mbar) and the spectrometer (10-7 mbar). In styrene plasmas, oligomeric species in the form of radical cations, nM+, were observed in the positive ion mass spectrum. Oligomers were also observed in the positive ion spectrum of the propenoic acid plasmas, but in this case they were in a protonated form (nM+H)+. Oligomers were not observed as neutral species in the plasmas of either compound. The mass spectra of plasmas containing the vapour of both monomers showed no significant new peaks. It is argued that the two monomers do not react with each other in the plasma to produce stable new species. This implies a hitherto unexpected specificity in the plasma gas-phase reactions.

Films of a series of monodisperse, moderately syndiotactic poly(methyl methacrylate) (PMMA) standards, with Mw ranging from 2,900–428,000, were solution-cast and spun-cast from chloroform onto clean aluminium substrates. The polymers were thoroughly characterized by conventional spectroscopic and chromatographic techniques. The films were studied using x-ray photoelectron spectroscopy (XPS) and time-of-flight secondary-ion mass spectrometry (ToF SIMS). The effects of molecular weight and film thickness on SIMS spectra were investigated thoroughly by unit-mass and high-resolution ToF SIMS. Film thickness had a pronounced effect on the negative SIMS spectra, particularly in films a few monolayers thick. This was seen in both the total negative ion counts (m/z 31–200) and the key negative ion intensity ratios. A parallel effect was observed with respect to the effect of molecular weight. These differences are attributed to (i) the original end-group concentration in the surface which decreases with increasing molecular weight and (ii) the original end-group concentration in the surface which increases as film thickness decreases.

Argon plasma treatment followed by exposure to atmospheric oxygen has been used to introduce new carbon–oxygen functionalities to polymer surfaces. We report on the treatment of poly(styrene) (PS), low density poly(ethylene) (LDPE), poly(propylene) (PP) and poly(ethylene terephthalate) (PET). Argon plasma-treated polymer surfaces exhibit a ‘saturation’ level and a ‘stable’ level of oxygen incorporation. The former is the maximum amount of oxygen which can be introduced into the surface. The latter is the maximum level of oxygen incorporation at which the surface is stable to both washing with a polymer non-solvent, and ageing with time. PS exhibits the greatest level of stable oxygen incorporation followed by LDPE and PP. PET displays very little stable oxygen incorporation. ‘Stable’ surfaces are characterised by a high selectivity towards C–O functionalities (>70% for PS at O/C ratio=0.2). At least 40% of these functionalities have been shown to be hydroxy groups through chemical derivatisation. The O 1s/O 2s ratio has been used to highlight differences in modification depths between the hydrocarbon polymers. We think that the inert gas plasma treatment imparts reactivity to a surface through an energy transfer process. Our results are rationalised on the basis of the accepted mechanisms of cross-linking vs. chain scission for the polymers.

This paper explores the relationship between fibre surface chemistry and interfacial bond formation in carbon-fibre/epoxy composites. Plasma copolymerisation of acrylic-acid/hexane, allyl-alcohol/hexane and allylamine/octadiene gas mixtures is used to obtain molecularly thin, conformai coatings on Type A carbon-fibre surfaces. Since the microporosity and chemical functionality of the untreated fibre surface can be concealed, any functionality incorporated into the film can be considered to provide the principal adhesion mechanism. The single-filament fragmentation test has been employed to estimate the adhesion of these modified fibres to an epoxy resin. Coatings of a hydrocarbon nature inhibit chemical interaction between the fibre and matrix. Improvements in the level of adhesion may be attributed to the introduction of oxygen- and nitrogen-containing functionalities which have known reactivity to epoxy groups. Thus, carboxylic acid and amine groups are shown to be more effective than hydroxyl groups.

The effect of oxygen addition to microwave-sustained plasmas of hexamethyldisiloxane (HMDSO) has been investigated. Attention was directed to the solid products formed on aluminium substrates (plasma deposits). To enable a quantitative analysis of these, X-ray photoelectron spectroscopy (XPS) of standard silicon-containing materials was carried out. When suitable charge correction is applied to the XP spectra of HMDSO/O2 plasma deposits, a number of very clear trends emerge. From changes in elemental composition, core line binding energies (Si2p, C 1s, and O 1s) and widths, we show how oxygen addition to the plasma affects the chemical nature of the plasma deposit. The data reported also provide (some limited) information on the reactions taking place in the plasma.

The plasma copolymerization of allyl amine with 1,7-octadiene and of acrylic acid with hexane has been investigated. Plasma copolymerization is shown to be a promising route to the fabrication of new surfaces with controlled concentrations of specific surface functionalities; in this case, amine and carboxylic acid.

Rigorous and exhaustive procedures are employed when titanium (Ti) is surgically implanted, whether for orthopaedic or dental applications. Many of these are adopted because it is thought that surface cleanliness is paramount for clinical success. This paper critically examines the necessity for some of these procedures, concentrating on the surface chemistry of Ti plates. Radio frequency plasma treatments are used to remove contamination from “as received” Ti plates; XPS and ToF-SIMS were used to monitor the effects of surface chemistry. Ti plates are contaminated by immersing them in BSA or by deliberate contamination with the endospores of Bacillus stearothermophilus ATCC 7953. The effectiveness of simple cleaning procedures to remove BSA/Bacillus stearothermophilus are investigated. Attention is given to both the surface cleanliness and sterility after cleaning.