Robert D. Short

A study of HMDSO/O2 plasma deposits using a high-sensitivity and -energy resolution XPS instrument: curve fitting of the Si 2p core level

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.

PLASMA TREATMENT OF POLYMERS : EFFECTS OF ENERGY TRANSFER FROM AN ARGON PLASMA ON THE SURFACE CHEMISTRY OF POLY(STYRENE), LOW DENSITY POLY(ETHYLENE), POLY(PROPYLENE) AND POLY(ETHYLENE TEREPHTHALATE)

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.

Attachment of human keratinocytes to plasma co-polymers of acrylic acid/octa-1,7-diene and allyl amine/octa-1,7-diene

Plasma co-polymers (PCPs) of acrylic acid/octa-1,7-diene and allyl amine/octa-1,7-diene have been prepared and characterised using X-ray photoelectron spectroscopy (XPS). The use of a hydrocarbon diluent in the monomer feed allowed the deposition of films with controlled concentrations of carboxylic acid and nitrogen-containing functional groups. Human keratinocytes were cultured on these PCP surfaces, tissue culture poly(styrene) (TCPS) and collagen I. The level of keratinocyte attachment over 24 h was measured. PCP surfaces containing low concentrations of carboxylic acid groups (2.3%) were found to promote keratinocyte attachment. The performance of these PCPs was similar to collagen I, a well established substratum for attachment. Nitrogen-containing PCP surfaces were found to promote attachment at higher functional group concentrations, although the attachment did not attain the level achieved on the acid functionalised PCP surfaces.

Plasma polymerisation for molecular engineering of carbon-fibre surfaces for optimised composites

Abstract 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.

Substrate influence on the initial growth phase of plasma-deposited polymer films

In this communication we demonstrate that in the initial stages of deposition of ultrathin plasma polymer films, both the growth rate and the chemical composition of the films are affected by the nature of the substrate which is an important question surprisingly neglected until now.

A new autologous keratinocyte dressing treatment for non‐healing diabetic neuropathic foot ulcers

Aims   To evaluate the use of a new cell‐tailored carrier surface (TranCell) for delivery of autologous keratinocytes to promote wound healing in patients with chronic neuropathic foot ulcers.

Clinical experience using cultured epithelial autografts leads to an alternative methodology for transferring skin cells from the laboratory to the patient

We report a 10-year audit using cultured epithelial autografts (CEAs) for patients with extensive burns. Clinical take using CEAs averaged only 45% (as has been reported by others) but over half of all cells cultured for these patients had to be discarded owing to difficulties of timing the production of CEA sheets to the needs of the patients. CEAs could not be used until they had reached confluence and formed an integrated sheet, which took, on average, 12 days. However, once formed, they needed to be used within 2-3 days or they lost the ability to attach to wound beds. In response to this we developed a simpler carrier dressing methodology for transferring cultured subconfluent keratinocytes from the laboratory to the wound bed. This methodology offers an increase in speed of delivery but its major contribution is the greater flexibility in timing the transfer of cells from the laboratory to the changing needs of the patients.

Antibacterial surfaces by adsorptive binding of polyvinyl-sulphonate-stabilized silver nanoparticles.

This paper presents a novel and facile method for the generation of efficient antibacterial coatings which can be applied to practically any type of substrate. Silver nanoparticles were stabilized with an adsorbed surface layer of polyvinyl sulphonate (PVS). This steric layer provided excellent colloidal stability, preventing aggregation over periods of months. PVS-coated silver nanoparticles were bound onto amine-containing surfaces, here produced by deposition of an allylamine plasma polymer thin film onto various substrates. SEM imaging showed no aggregation upon surface binding of the nanoparticles; they were well dispersed on amine surfaces. Such nanoparticle-coated surfaces were found to be effective in preventing attachment of Staphylococcus epidermidis bacteria and also in preventing biofilm formation. Combined with the ability of plasma polymerization to apply the thin polymeric binding layer onto a wide range of materials, this method appears promising for the fabrication of a wide range of infection-resistant biomedical devices.

Plasma copolymerization as a route to the fabrication of new surfaces with controlled amounts of specific chemical functionality

Abstract 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.

An X-ray photoelectron spectroscopic investigation into the chemical structure of deposits formed from hexamethyldisiloxane/oxygen plasmas

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.