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Thin polymeric coatings are commonly used for altering surface properties and modulating the interfacial performance of materials. Possible contributions from the substrate to the interfacial forces and effects are, however, usually ignored and are not well understood, nor is it established how the coating thickness modulates and eventually eliminates contributions from substrates to the van der Waals (vdW) interfacial force. In this study we quantified, by colloid-probe atomic force microscope (AFM) and by theoretical calculations, the interfacial vdW contributions from substrates acting through ethanol plasma polymer (EtOHpp) coatings of a range of thicknesses on Au and Si bulk materials. In approach force curves against EtOHpp-coated Au substrates the magnitude of the vdW force decreased as the EtOHpp coating thickness increased to 18 nm and then plateaued with further increases in coating thickness, providing direct evidence for a contribution to the total interfacial vdW force from the Au substrate acting through thin coatings. The experimental observations accord with theoretical calculations of the thickness dependence of Hamaker coefficients derived from rigorous simulation using the Lifshitz theory. In addition, the measured forces agree well with theoretical predictions including correction for finite roughness. Thus, our experimental and theoretical results establish how the thickness of polymer thin film coatings modulates the total interfacial vdW force and how this can be used to tune the net vdW force so as to either contain a large substrate contribution or arise predominantly from the polymeric overlayer. Our findings enable rational design of coating thickness to tailor interfacial interactions and material performance. Refereed/Peer-reviewed

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

In recent years, increasing evidence has been collated on the contributions of fungal species, particularly Candida, to medical device infections. Fungal species can form biofilms by themselves or by participating in polymicrobial biofilms with bacteria. Thus, there is a clear need for effective preventative measures, such as thin coatings that can be applied onto medical devices to stop the attachment, proliferation, and formation of device-associated biofilms. However, fungi being eukaryotes, the challenge is greater than for bacterial infections because antifungal agents are often toxic towards eukaryotic ho st cells. Whilst there is extensive literature on antibacterial coatings, a far lesser body of literature exists on surfaces or coatings that prevent attachment and biofilm formation on medical devices by fungal pathogens. Here we review strategies for the design and fabrication of medical devices with antifungal surfaces. We also survey the microbiology literature on fundamental mechanisms by which fungi attach and spread on natural and synthetic surfaces. Research in this field requires close collaboration between biomaterials scientists, microbiologists and clinicians; we consider progress in the molecular understanding of fungal recognition of, and attachment to, suitable surfaces, and of ensuing metabolic changes, to be essential for designing rational approaches towards effective antifungal coatings, rather than empirical trial of coatings. Refereed/Peer-reviewed

Ethnopharmacological relevance Australian Aboriginal people used crushed leaves of Geijera parviflora Lindl. both internally and externally for pain relief, including for toothache ( Cribb and Cribb, 1981 ). This study tested the hypothesis that this traditional use might be at least in part explained by the presence of compounds with anti-inflammatory activity. Materials and methods A crude extract (95% EtOH) was prepared from powdered dried leaves. From the CH 3 Cl fraction of this extract compounds were isolated by bioassay-guided fractionation and tested for: (1) cytotoxicity in RAW 264.7 murine leukemic monocyte–macrophages, (2) prostaglandin E 2 (PGE 2 ) inhibitory activity in 3T3 Swiss albino mouse embryonic fibroblast cells, as well as (3) nitric oxide (NO) and (4) tumour necrosis factor alpha (TNFα) inhibitory activity in lipopolysaccharide (LPS)-stimulated RAW 264.7 cells. Isolated compounds were also tested for (5) antibacterial activity against a panel of Gram-positive ( Staphylococcus aureus ATCC 29213 and ATCC 25923, Staphylococcu s epidermidis ATCC 35984, biofilm-forming) and Gram-negative ( Escherichia coli ATCC 25922, Pseudomonas aeruginosa ATCC 27853) strains by broth microdilution. Results Eleven compounds were isolated, including one new flavone and one new natural product, with a further four compounds reported from this species for the first time. Some of the compounds showed good anti-inflammatory activity in vitro . In particular, flindersine ( 1 ) and N-(acetoxymethyl) flindersine ( 3 ) inhibited PGE 2 release with IC 50 values of 5.0 μM and 4.9 μM, respectively, without any significant cytotoxicity. Several other compounds showed moderate inhibition of NO ( 5 , 6 , 7 ) and TNF-α ( 6) , with IC 50 in the low micromolar range; however much of this apparent activity could be accounted for by the cytotoxicity of these compounds. None of the compounds showed anti-bacterial activity. Conclusions The inhibition of PGE 2 , an important mediator of inflammation and pain, by flindersine and a derivative thereof, along with the moderate anti-inflammatory activity shown by several other compounds isolated from Geijera parviflora leaf extract, support the traditional use of this plant for pain relief by Australian Aboriginal people.

Infection disease after biomedical implant surgery is often caused by unintentional contamination of micro-organism. Novobiocin is one of the most attractive antibiotic due to its high activity against gram positive bacteria and its relatively compatible to fibroblast cell line. Based on the molecular structure of novobiocin, it may be conjugated or coated onto material surfaces. The coating steps were plasma polymerisation, polymer grafting, and novobiocin conjugation. XPS analysis showed that the elements and high resolution of C 1s confirmed that the surface chemical had changed. Novobiocin, after conjugation, became more dominant in covering the surface. Antibacterial Assay to Staphylococcus epidermidis by using dead and live kit indicated the reduction of bacteria reached up to 97.27% and only 0.07% of live bacteria left. This result led to a conclusion that immobilised novobiocin may be considered as novel antibacterial coating that can prevent nosocomial infection.

Microwave PECVD with vapours of tetramethyldisiloxane and oxygen was used to deposit transparent organosilicone coatings on PMMA. The ratio of tetramethyldisiloxane to oxygen within the plasma has a large influence on the chemical and physical properties of the deposited coatings. The oxygen flow rate was varied during deposition so as to deposit a chemically graded coating. Grading offers the ability to change the chemical and mechanical properties of a coating from the substrate to the surface. Coatings with constant oxygen flow rate were compared to those with oxygen varied in an exponential-like increase, a linear increase and a logarithmic-like increase during deposition. Additionally, a linear increase in power level during deposition was also explored. The coatings were characterised via their stress levels, refractive index and adhesion to PMMA. Abrasion and durability performance were also determined, via the steelwool test, salt water boil test and stress to craze test. It was found that the rate of grading significantly influenced the stress and performance of the coating. For enhanced coating performance, in all tests, an exponential-like increase of oxygen was shown to be best. Industrially, these coatings are relevant to the aviation and automotive industries as protective coatings on plastic windows or lenses Refereed/Peer-reviewed

Optical biosensors such as waveguides and surface-plasmon resonance (SPR) sensors have found numerous applications in biomolecular sciences. We provide an overview of these technologies in relation to the specific requirements of label-free and high-throughput cellular studies. We dedicate specific emphasis to SPR-based biosensors and recent developments particularly suitable for cellular studies, such as long-range SPR. We discuss the advantages and the disadvantages of the most successful optical-sensing technologies, and potential approaches in the next generation of optical technologies. Refereed/Peer-reviewed

We report the total synthesis of leubethanol (1), a serrulatane compound that has recently been reported as having considerable antibacterial activity against multidrug-resistant bacteria, such as Staphylococcus aureus, and is of interest for applications in the control of bacterial biofilms in human medicine. Our synthetic route begins with (−)-isopulegol (4) and key steps include substrate directed hydroboration to generate the C1' stereocentre and formation of the aromatic ring via the α-oxoketene-S,S-acetal intermediate 3. Overall the conversion of (−)-isopulegol (4) to leubethanol was achieved in 13 steps and an overall yield of 7%. Comparison of our spectroscopic data with those reported for leubethanol (1), isolated from Leucophyllum frutescens, verified the structure of the natural product. Refereed/Peer-reviewed

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

In this study, the abrasion resistance of a reflective thin film multilayer system consisting of Chromium Nitride (CrNx) layers deposited on specially prepared coated polymeric substrates is presented. The abrasion resistance is quantified by the Bayer abrasion test, and then correlated with the physical properties of the film. Their resistance to abrasion is identified as being defined partially by the microstructure of the layers within the multilayer system. Relative measures of the abrasion resistance are made by quantifying the surface roughness in the specific case where the substrate is the same (hardness and elastic moduli) and the elemental and phase composition of the coating is the same. Importantly, the optical measurement of the diffuse reflectance is used to assess the relative structure of the coatings prior to the abrasion test. By doing so, a useful, non-destructive technique is presented for characterising the relative abrasion resistance of sputtered thin film coatings. Refereed/Peer-reviewed

The chemical composition of the surface layers of synthetic biomaterials used for human medical devices and in biotechnology plays a key role in determining interfacial interactions between biological media (such as protein solutions, cells, tissue) and the synthetic material. Accordingly, considerable research efforts focus on improving the 'biocompatibility' of biomaterials by applying various surface modification and thin film coating approaches. Here we focus on the patterning of surface chemistries, often designed to exercise spatial control over events such as cell attachment and spreading. Secondly, we review recent developments in chemical characterisation of biomaterials surfaces, which is essential both for verifying the success of intended surface modification strategies and for reliable interpretation of observed biological responses. Biomaterials surface analysis by imaging ToF-SIMS and XPS and compositional depth profiling are discussed, as is the emerging complementary technique of Metastable Induced Electron Spectroscopy. Refereed/Peer-reviewed

Established methods for cleaning and sterilising biomedical devices may achieve removal of bioburden only at the macroscopic level while leaving behind molecular levels of contamination (mainly proteinaceous). This is of particular concern if the residue might contain prions. We investigated at the molecular level the removal of model and real-life proteinaceous contamination from model and practical surfaces by air plasma (ionised air) treatment. The surface-sensitive technique of X-ray photoelectron spectroscopy (XPS) was used to assess the removal of proteinaceous contamination, with the nitrogen (N1s) photoelectron signal as its marker. Model proteinaceous contamination (bovine serum albumin) adsorbed on to a model surface (silicon wafer) and the residual proteinaceous contamination resulting from incubating surgical stainless steel (a practical biomaterial) in whole human blood exhibited strong N1s signals [16.8 and 18.5 atomic percent (at.%), respectively] after thorough washing. After 5 min air plasma treatment, XPS detected no nitrogen on the sample surfaces, indicating complete removal of proteinaceous contamination, down to the estimated XPS detection limit 10 ng/cm2. Applying the same plasma treatment, the 7.7 at.% nitrogen observed on a clinically cleaned dental bur was reduced to a level reflective of new, as-received burs. Contact angle measurements and atomic force microscopy also indicated complete molecular-level removal of the proteinaceous contamination upon air plasma treatment. This study demonstrates the effectiveness of air plasma treatment for removing proteinaceous contamination from both model and practical surfaces and offers a method for ensuring that no molecular residual contamination such as prions is transferred upon re-use of surgical and dental instruments. Refereed/Peer-reviewed

Silicone hydrogel contact lenses, which have been a major advance in the field of vision correction, require surface modification or coatings for comfort and biocompatibility. While current coatings show adequate clinical performance, advanced coatings may improve the biocompatibility of contact lenses further by reducing biofouling and related adverse clinical events. Here, we have produced coatings on Lotrafilcon A contact lenses by deposition of a thin film of allylamine plasma polymer (ALAPP) as a reactive interlayer for the high density grafting of poly(ethylene oxide) dialdehyde (PEO(ALD) 2 ), which had previously shown complete resistance to protein adsorption in vitro . The performance of these contact lenses was evaluated in a controlled clinical study over 6 h using Focus ® Night and Day™ (also known as Air Optix ® Night & Day ® ) contact lenses as control lenses. Surface modified lenses were characterised by X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM) before and after wear. Clinical data showed a high level of biocompatibility of the PEO coated lenses equivalent to control lenses. Surface analysis of worn contact lenses demonstrated that the high density PEO coating is effective in reducing biofouling in vivo compared to control lenses, however small amounts of protein deposits were still detected on all worn contact lenses. This study highlights that elimination of biofouling in vivo can be much more demanding than in vitro and discusses issues that are important for the analysis of worn contact lenses as well as the design of improved contact lenses.

We report a search for antimicrobial compounds in the Australian plant Eremophila serrulata . Bioassay directed fractionation of a diethyl ether extract prepared from the leaves of E. serrulata led to the isolation of two compounds, an ο -naphthoquinone, 9-methyl-3-(4-methyl-3-pentenyl)-2,3-dihydronaphtho[1,8- bc ]pyran-7,8-dione ( 2 ), and a serrulatane diterpenoid, 20-acetoxy-8-hydroxyserrulat-14-en-19-oic acid ( 3 ). Two other known serrulatane-type diterpenoids, 8,20-dihydroxyserrulat-14-en-19-oic acid ( 4 ) and 8,20-diacetoxyserrulat-14-en-19-oic acid ( 5 ) were also isolated. None of these compounds had previously been tested for antimicrobial activity. Compounds 2 – 5 showed antimicrobial activity against Staphylococcus aureus (ATCC 29213) with minimum inhibitory concentrations (MICs) ranging from 15.6 to 250 μg/mL. Compound 2 was the most active with an MIC of 15.6 μg/mL and a minimum bactericidal concentration (MBC) of 125 μg/mL. This compound also showed antimicrobial activity against other Gram-positive bacteria including Streptococcus pyogenes , and Streptococcus pneumoniae . No activity was observed for this compound against all Gram-negative bacteria tested.

Control of the precise location and extent of cellular attachment and proliferation, and of tissue outgrowth is important in a number of biomedical applications, including biomaterials and tissue engineered medical devices. Here we describe a method to control and direct the location and define boundaries of tissue growth on surfaces in two dimensions. The method relies on the generation of a spatially defined surface chemistry comprising protein adsorbing and non-adsorbing areas that allow control over the adsorption of cell-adhesive glycoproteins. Surface modification was carried out by deposition of thin acetaldehyde and allylamine plasma polymer coatings on silicon wafer and FEP substrates, followed by grafting of a protein resistant layer of poly(ethylene oxide). Spatially controlled patterning of the surface chemistry was achieved by masking during plasma polymerization. XPS and AFM were used to provide evidence of successful surface modifications. Adsorption of the extracellular matrix protein collagen I followed by tissue outgrowth experiments with bovine corneal epithelial tissue for up to 21 days showed that two-dimensional control over tissue outgrowth is achievable with our patterning method over extended time frames. The method promises to be an effective tool for use in a number of in vitro and in vivo applications.

The highly sensitive surface analytical techniques X-ray photoelectron spectroscopy (XPS) and time-of-flight static secondary ion mass spectrometry (ToF-SIMS) were used to test the resistance of poly(ethylene glycol) (PEG) coatings towards adsorption of lysozyme (LYS) and fibronectin (FN). PEG coatings were prepared by grafting methoxy-terminated aldehyde-PEG (MW 5000 Da) onto two amino-functionalised surfaces with different amine group densities, generated by radio frequency glow discharge polymerisation of n-heptylamine and allylamine. Grafting was performed at the lower critical solution temperature to maximise the graft density of the PEG chains. XPS showed that the grafted density of PEG chains was slightly higher on the allylamine surface. XPS detected no adsorption of either protein on either PEG coating. ToF-SIMS analysis, on the other hand, found, in the positive ion spectra, minute but statistically significant signals assignable to amino acid fragment ions from both proteins adsorbed to the lower density PEG coating and from LYS but not FN on the higher density PEG coating. Negative ion spectra contained relatively more intense protein fragment ion signals for the lower density PEG coating but no changes assignable to adsorbed proteins on the higher density PEG coating. These results demonstrate the importance of utilising highly sensitive techniques to study protein adsorption on surfaces intended to be protein resistant, and that both positive and negative ion ToF-SIMS spectra should be acquired to probe for possible very low levels of protein adsorption.

Liposomes were immobilized onto the surface of perfluorinated polymer tape samples and tissue culture polystyrene well-plates using a multilayer immobilization strategy. In the first step, a thin interfacial bonding layer with surface aldehyde groups was deposited from a glow discharge struck in acetaldehyde vapour. Polyethylenimine was then covalently bound onto the aldehyde groups by reductive amination, followed by covalent binding of NHS-PEG-biotin molecules onto the surface amine groups by carbodiimide chemistry. Next, NeutrAvidin protein molecules were bound onto the PEG-biotin layer. Finally, liposomes containing PEG-biotinylated lipids were docked onto the remaining binding sites of the surface-immobilized NeutrAvidin molecules. AFM was used to image surface-bound liposomes and revealed a density well below close packing. The release characteristics of the surface-bound liposomes were measured by the fluorescence intensity changes of carboxyfluorescein upon release. Liposomes filled with sodium orthovanadate were surface immobilized and used in two in vitro angiogenesis assays. Marked differences compared to various control samples were observed, demonstrating the utility of drug-filled, surface-bound liposomes for evoking localized, controlled biological host responses proximal to an implanted biomedical device.

Coatings from carboxymethylated dextrans (CMDs) were fabricated, analyzed by XPS, and investigated for their ability to inhibit corneal epithelial tissue outgrowth and bovine corneal epithelial cell attachment and growth. CMDs with differing degrees of carboxymethyl substitution and various molecular weights were synthesized by the solution reaction of dextrans with bromoacetic acid under different reactant ratios. The CMD compounds thus obtained were attached onto aminated surfaces produced in two ways: by the plasma deposition of a coating from n-heptylamine vapour, and by the plasma deposition of an acetaldehyde coating onto whose surface aldehyde groups the polyamine compounds polylysine, polyethyleneimine and polyallylamine were immobilized to provide platforms for CMD immobilization. XPS spectra showed that the latter route produced thicker coatings than the former approach. CMD molecules attached directly onto the plasma-fabricated amine surface supported some tissue migration; the extent of carboxymethyl substitution and the molecular weight of the CMDs had little influence. For CMDs immobilized via polyamine spacers, on the other hand, tissue outgrowth was completely inhibited, and again there were no discernible effects from the extent of carboxymethyl substitution and the molecular weight of the CMDs. In assays involving cell attachment and growth, analogous observations were found. Thus, the mode of immobilization of these polysaccharide coatings is the dominant factor in their anti-fouling performance, suggesting that optimization of the architecture of polysaccharide coatings may be an important factor for maximizing their cell-repellent abilities.

Lysozyme, lactoferrin, trypsin and myoglobin were bound onto thin carboxymethyl-dextran coatings in two ways: by physisorption, and by an intended carbodiimide interfacial linking reaction. XPS analyses recorded substantial protein loadings on all the samples. In some cases, the protein coverages achieved by physisorption were larger than on covalent binding, indicating substantial affinity of the proteins for spontaneous adsorption onto the coatings. The observation of significant physisorption raised the question of to what extent physisorption competed with covalent binding when the intended covalent linking reaction was performed. The technique of Surface-MALDI mass spectrometry was found to be rapid, convenient, sensitive, and eminently suitable for probing for the presence of a physisorbed population among the covalently linked proteins. Control experiments with physisorbed samples showed that all the four proteins investigated gave rise to strong signals. On samples produced using carbodiimide linking, however, no protein signals were detected while photomatrix signals attested to successful evaporation of the matrix. Covalently linked proteins evidently were immune to desorption and detection by Surface-MALDI-MS. Using signal-to-noise ratios of spectra recorded on samples with approximate monolayer coverage of physisorbed proteins, it was estimated that a signal should have been detectable if, among the covalently coupled protein molecules, >1–2% of the total protein coverage present after intended covalent immobilization were physisorbed. Therefore, Surface-MALDI analyses suggest that within experimental accuracy, the carbodiimide chemistry used led to complete covalent interfacial immobilization of all four protein layers.

The irreversible accumulation of biological material on synthetic surfaces ("biofouling") adversely affects for instance contact lenses, implantable biomedical devices, biosensors, water purification, transport and storage systems, and marine structures. It is shown here that proteins adsorbed on contact lenses can be detected directly, rapidly, and conveniently, with high sensitivity, by matrix-assisted laser desorption ionization (MALDI)-mass spectrometry. This new approach allows detection of minor (and major) proteinaceous constituents of biofouled layers on samples retrieved from clinical usage and in vitro protein adsorption studies, at levels substantially below monolayer coverage. Identification of the detected biological molecules can be done by comparison of the detected mass peaks with known protein molecular masses or with spectra recorded of pure compounds or by separate biochemical assays. The MALDI mass spectra recorded on different contact lenses contain peaks assignable to lysozyme and a number of smaller proteins. Such sensitive characterization of the early stages of biofouling enhances the understanding of protein/materials interactions and assists in designing guided strategies toward control of biological adsorption processes.

The search for surfaces that resist bioadhesion has continued with the pursuit of a number of avenues. A large part of the studies has investigated PEG coatings. Nevertheless, there is still controversy about what exactly the properties and modes of action of an ‘ideal’ PEG coating should be. While some studies have reported no irreversible protein adsorption, other, very similar coatings appear less able to resist bioadhesion. Of great interest are results showing that PEG surfaces with very short chains are capable of rejecting proteins. As it is very difficult to obtain direct information about the microstructure of the coatings, studies typically employ plausible models to interpret observations. New analytical techniques and the direct measurement of interfacial forces between proteins and surfaces open up the possibility of improved, guided design and feedback in the optimization of surfaces intended to resist bioadhesion.

A range of carboxymethylated poly(hydroxyethyl methacrylate) (CM-PHEMA) hydrogels with varying degrees of carboxymethylation was synthesized for a systematic study of the effects of ionized groups (‘charge’) on the uptake by hydrogel matrices of the proteins, lysozyme and human serum albumin (HSA). Using a radiolabel-tracer technique, X-ray photoelectron spectroscopy, and laser scanning confocal microscopy, we attempted to differentiate between protein molecules that were irreversibly adsorbed onto the hydrogel surface and those that penetrated into the hydrogel matrix. The effective pore size of the CM-PHEMA hydrogels was modelled and compared with the known molecular dimensions of the two proteins. The effects of the presence of varying amounts of ionized groups in the hydrogel matrix differed for the two proteins. For lysozyme, increased uptake was observed at higher carboxymethylation; this is interpreted as resulting from a combination of electrostatic attraction and increasing ease of penetration of the protein into the more porous hydrogel matrix. For HSA, on the other hand, the uptake was primarily by surface adsorption, with little diffusive penetration into the matrix.

The initial attachment of cultured bovine corneal epithelial cells and stromal fibroblasts to two oxygen-containing synthetic polymers was studied. Cultured epithelial cells and stromal fibroblasts were seeded onto two oxygen-containing surfaces: 'tissue culture' polystyrene (TCPS) and a polymer film deposited by RF plasma deposition using a methylmethacrylate monomer (MMA/FEP). To establish the mechanism of cell attachment, the effect of the selective removal of the vitronectin and fibronectin from the serum used in the culture medium was tested. The attachment of cultured epithelial cells during the first 90 min of culture was reduced by 40% (TCPS)-80% (MMA/FEP) as a result of removing vitronectin from the medium. Attachment of these cells to TCPS was reduced by 85-95% when the serum was depleted of both fibronectin and vitronectin. However, depletion of fibronectin reduced cell attachment to TCPS by 20%, whilst on MMA/FEP cell attachment was equivalent, or higher, than that for intact serum. The attachment of cultured corneal stromal fibroblasts was similarly dependent on vitronectin but less dependent on fibronectin. Therefore, for the attachment of both cultured epithelial cells and fibroblasts to oxygen-containing surfaces in the presence of serum, there is a high requirement for serum vitronectin but a lesser requirement for fibronectin. The effects of the establishment of corneal epithelial cells in culture and the site of origin of the cells, were determined. Primary isolates of epithelial cells isolated from the limbal, central or peripheral regions of the cornea were less dependent on vitronectin for initial attachment to TCPS than were these cells after several passages in culture. Furthermore, the primary isolates were dramatically less responsive to vitronectin than the cultured cells. These results indicate that the mechanism of attachment of corneal epithelial cells to TCPS varies with the culture experience of the cells. Cells that are culture neophytes can employe endogenous mechanisms for the initial attachment to TCPS, whereas cells established in culture are dependent on exogenous vitronectin in order to attach.

Advancing and receding contact angles for various liquids placed on the surface of thin n -hexane plasma polymer films have confirmed that the surface is hydrophobic; comparable to polyethylene. A waveguide technique has been employed to determine the refractive indices of the plasma polymer films in the visible and near infrared regions of the dielectric spectrum. Along with ESCA data that provide polymer group functionality, this information has been used to estimate the n -hexane plasma polymer density and to construct a simple dielectric permeability function (ϵ(iξ), the dielectric constant at imaginary frequency iξ) for the polymer. The dielectric permeability function and Lifshitz theory have been used to calculate the Hamaker function (including non-retarded Hamaker constants) which should characterise the van der Waals interaction in systems that contain n -hexane plasma polymers. The atomic force microscope (AFM) has been employed to measure the force of interaction between n -hexane plasma polymer films deposited on muscovite mica flat plates and either uncoated silicon nitride AFM tips or n -hexane plasma polymer coated glass spheres. The force versus separation curves have been compared with DLVO theory. The homointeraction between n -hexane plasma polymer coatings in water initially displays a long-range attraction additional to van der Waals interaction. There is evidence that after prolonged immersion in water the thin n -hexane plasma polymer films swell.

Of significance in the routine use of BIAcore is the cost of the sensor chips. This is particularly evident during the phase of method development of an assay where it is not unusual to expend several chips in a day in attempts to optimize immobilization conditions for a novel peptide or protein. In addition, it is accepted practice to discard a chip once its ligand binding capacity has diminished to an unacceptable level. While the high cost of sensor chips has been addressed to some degree through the recent introduction of research-grade sensor chips, we were interested in assessing the possibility of regenerating or reconditioning sensor chips in order to allow them to be reused. In particular, we concerned ourselves with regenerating sensor chips onto which peptide or protein had been immobilized. Our aim was to develop a general procedure that would allow reuse of such chips but would not decrease ligand immobilization capacity or increase nonspecific ligand adsorption properties. We present a method which employs a combination of enzymatic (Pronase E) and chemical (bromoacetic acid) treatments of used sensor chips. Regeneration requires an overnight incubation of the sensor chip ex situ so that one can continue to perform BIAcore experiments. The data demonstrate that this simple two-step procedure substantially removes immobilized proteins such as IgG, Protein G, an HIV-1 envelope glycoprotein (gp120) and a neoglycoprotein based on bovine serum albumin, as determined by reflectance measurements and X-ray photoelectron spectroscopy. In addition, a high density of proteins can be immobilized onto the reconditioned surfaces, since reactive carboxylic acids are regenerated by the procedure.

The discovery, in 1988, that “iodine-doped” rubber can conduct electricity attracted a great deal of interest [1,2]. However, it also generated some fundamental questions [2]: First, what is the mechanism from which the conductivity of “I 2 -doped” rubbers arises? Second, why does cis-1,4-polybutadiene not become electrically conductive by “I 2 -doping”, but its trans-conterpart does? Third, what is the effect of “I 2 -doping” and conductivity in the rubber component on rubber-containing conducting composites and/or copolymers? We have previously demonstrated that “I 2 -doping” of cis-1,4-polyisoprene produces conjugated sequences of unsaturated double bonds in the polymer backbone, which confer conductivity. Recently, we have found that “I 2 -doping” of cis-1,4-polybutadiene, unlike the trans-isomer, does not lead to the formation of conjugated sequences at room temperature — a finding which leads to the formation of conducting patterns through patterned photoisomerization of cis-1,4-polybutadiene films followed by “I 2 -doping”. We have also observed, for the first time, the occurrence of “I 2 -doping” of the polyisoprene component in polyisoprene-polyacetylene copolymers.

Poly[1-(trimethylsilyl)-1-propyne] (PTMSP) membranes have a very high oxygen permeability but a low separation factor for oxygen and nitrogen. Hexafluorobutyl methacrylate (HFBM) was incorporated into PTMSP membranes in order to increase the selectivity of the membrane for oxygen. HFBM was imbibed into the cast PTMSP membrane and polymerized by UV irradiation. The resulting membranes were not fully symmetrical; the chemical modification took place to a larger extent in the membrane volume closer to the UV light. The activation energy for the permeation of oxygen and nitrogen through the modified PTMSP membranes was determined to be positive. For HFBM modified PTMSP membranes, the higher the flux was, the lower the separation efficiency. Values of the permeability coefficient P for oxygen at 20°C, and of the separation factor for the modified membranes were: P (O 2 )=1.39 × 10 −7 cm 3 (STP)-cm/cm 2 -sec-cmHg, and P (O 2 )/ P (N 2 ) = 5.4 for the sample with the highest separation efficiency, and P (O 2 )=5.56 × 10 −7 cm 3 (STP)-cm/cm 2 -sec-cmHg, and P (O 2 )/ P (N 2 ) = 2.0 for the sample with the highest permeability. Both the unmodififed and HFBM modified PTMSP membranes showed no decline in P (O 2 ) and P (O 2 )/ P (N 2 ) values over a period of six months.

Samples of 1:1 and 2:1 poly(styrene-co-maleic anhydride) films were exposed to radiation from a QUVB-313 light source under atmospheric oxygen and their photooxidative reactions studied using FTIR, UV-VIS and 13C NMR spectroscopy. A major finding was that the bulk of the photodegradation resulted in loss of low molecular weight volatile fragments from the polymer chains as demonstrated by the continuous decrease in intensity of anhydride (1780 cm−1) and aromatic (704 cm−1) bands in the infrared spectrum with only minor changes in the 13C NMR spectra of the residual polymers. The UV-VIS spectra showed very significant increases in absorbance up to approximately 450 nm. Combined with the formation of new hydroxyl (3500-3000 cm−1), carbonyl (1725 cm−1) and CO (1240 cm−1) bands in the FTIR spectra, the data have enabled a scheme of chemical changes to be proposed to account for the early degradative reactions which lead to the material loss. Changes in the FTIR and UV-VIS spectra occurred more rapidly for the 2:1 copolymer than for the 1:1 copolymer, indicating that an increase in the proportion of styrene units decreased the stability of poly(styrene-co-maleic anhydride) towards photooxidation on exposure to the QUVB-313 light source.

Polyurethanes are used in biomedical devices because they constitute one of the few classes of polymers that are highly elastomeric and show good biocompatibility. However, there is continuing debate in the literature regarding their long term stability in biomedical environments, and the validity of using polyurethanes for extended implant applications is still very much in question. While evidence of polymer degradation in explanted devices has been reported by a number of workers, other studies conclude that degradation is minimal. This review discusses possible pathways of biomedical degradation, such as enzymatic and oxidative attack, as well as observed effects such as cracking and calcification. Metal catalyzed degradation may also occur in devices such as pacemaker leads. While a number of model studies have assessed various modes of degradation, reliable accelerated tests for the prediction of the rates of biomedical ageing effects have apparently not been established. The role of additives and surface contaminants in biocompatibility and degradation is also discussed. Finally, as important interactions between a polyurethane polymer and the host body occur at the interface, the surface analysis of polyurethanes is discussed, and it is concluded that proper characterization of the implant surface before and after degradation studies is important for the understanding of degradation, in particular to exclude effects caused not by the polyurethane itself, but by surface contaminants which appear to have been present on the majority of materials subjected to detailed characterization so far.

Poly(tetrafluoroethylene) (PTFE) samples were surface modified in gas plasma atmospheres of air, oxygen, argon and water vapour in order to increase the surface energy. Its dispersive and polar components were determined by contact angle measurements after various treatment times. Plasma treatment times of only 15s were sufficient in all gases studied for substantial surface modification of PTFE. The chemical composition of the surfaces was studied by X-ray photoelectron spectroscopy (X.p.s.). The main results of all the plasma treatments were the abstraction of fluorine and the production of surface crosslinks, whereas only a low level of oxygen-containing groups was attached into the surface layer.

Using an appropriate mask, we have developed a versatile method for obtaining patterned conducting polymers by first depositing a thin, patterned plasma polymer layer onto a metal-sputtered electrode, and then performing electropolymerization of monomers such as pyrrole.

The relative chelating strengths and co-ordination numbers of a series of aromatic-substituted ethanedioic acid bis-hydrazides and N , N ′-di- α -phenoxypropionyl isophthalyl dihydrazide (Cunox AX®) complexed with Cu 2+ , Ni 2+ , Co 2+ and Zn 2+ have been investigated by UV absorption spectroscopy using N , N -dimethylformamide as solvent. The data indicate that there is 1:1 complexation between the cations and the various bishydrazides with equilibrium constants in the range 0·4−4·9 × 10 6 mol −1 , and 2:1 complexation for Cunox with equilibrium constants in the range 0·4−5·2 × 10 11 mol −2 . For two bis-hydrazides, fluorescence quenching experiments were also performed for independent verification of this strong complexation. The complexation data show that these compounds are not only useful as copper inhibitors, but also strongly deactivate other transition metal ions known to accelerate the degradation of polyolefins. A computer simulation of the extent of complexation with increasing ion concentration enabled comparisons to be made between the bis-hydrazides and Cunox. The importance of these results in assessing metal chelators as stabilizers of polyethylene insulated copper cables, and of polyolefins in contact with metals in general, is discussed.

The decay times of the S2 fluorescence of azulene and five derivatives were determined using the single-photon counting method. Whereas the lifetimes are only slightly altered by the nature of the solvent they are definitely temperature dependent. Furthermore, the variation in fluorescence lifetime with temperature is also strongly influenced by the positions of substituents. Our results show that the calculation of fluorescence lifetimes in azulene compounds using quantum yields and integrated absorption spectra is not very reliable; this is caused by the varying ratios between the allowed component and the vibronically induced component of the oscillator strength.

A simple, inexpensive and versatile custom built reactor for experimental plasma deposition and surface treatment is presented. The two outstanding features are a compact web conveyancing system with a web speed that is variable in the range 0.15–6 m min−1, and a defined gas flow path. The web transport accepts rolls containing of the order of 100 m of flexible thin substrate and is reversible in order to enable multistep plasma processing without breaking the vacuum. The reactor provides stable and uniform plasma conditions for extended coating of thin polymer films by plasma polymerization.

The emission spectra of the second excited singlet state of [18] annulene and of monofluoro [18] annulene (in a 3-methylpentane glass at 4 K) are reported. The large energy gap between the first and second excited singlet states inhibits fast internal conversion and favours the appearance of S 2 → S 0 emission. In addition, fluorescence from the S 1 state can be observed in monofluoro [13] annulene by exciting into the S 2 or directly into the S 1 absorption.

The energies and orbital natures of the lowest two triplet states of xanthone and the temperature dependence of the phosphorescence spectra have been investigated in six hosts. The energy separation between T 1 ≈ 3 ππ * and T 2 ≈ 3 Ππ * varies sensitively with the solvent and accounts for the dual phosphorescence.

The phosphorescence spectrum of xanthone in n -hexane is resolved into three components, one of which is due to thermally activated emission from a n π * origin. The other two emissions originate from extremely widely split sublevels of the lowest triplet state, which is of 3 ππ* origin. higher energy of T L x , and T 1 y , and thus below 4K there is thermal depletion of T 1 z which has the largest radiative strength. Th consequence of spin-orbit coupling between the T x and T y sublevels of the-two very close-lying, lowest triplet states. There are signif mixing of orbital character, a mixing which is governed by spin-orbit coupling rather than vibronic coupling.

Highly resolved phosphorescence and optical-microwave double-resonance spectra of thioxanthone are reported. In contrast to related molecules, not only the z sublevel, but also the y sublevel carries substantial oscillator strength, whereas intersystem crossing still is highly selective, reaching the z sublevel only. A new zero-field resonance assignment is given.

Optical and ODMR studies on the lowest triplet state of xanthone have revealed the presence of substantial spin-orbit and vibronic interactions between the two lowest triplet states, T 1 ≈ 3 ππ ∗ and T 2 ≈ 3 nπ ∗ . Their energy separation δE T depends strongly on the solvent and varies in the range 27 to 1000 cm -1 in the systems studied. This severely perturbs the zero-field splitting in T 1 , whereas the vibrational structure of the phosphorescence T 1 →S 0 is hardly affected. The relative importance of the competing coupling mechanisms is discussed with respect to the magnitude of δE T .

The three phosphorescence components of xanthone in n-pentane originate from three states of one solvated species: From the z sublevel of the second triplet state, of 3nπ* origin, and from two widely split sublevels of the lowest triplet state, of 3ππ* origin. Its z sublevel is thermally depleted across the spin-orbit mixing induced zero-field sublevel splitting of 15.1 cm−1.

The lifetimes of the fluorescences S1 → S0 and S2 → S0 of three carbonyl derivatives of azulene were investigated by means of a single-photon counting apparatus using laser excitation pulses of 250 ps duration. The S1 lifetimes are observed to correlate with the energy gap. The S2 lifetimes are smaller than 50 ps. in qualitative agreement with expectations based on the large decrease of the S2 → S1 energy gap relative to that azulene. No evidence was found for a significant participation of triplet states in the deactivation of both singlet states, Spectral data indicate that the carbonyl group interacts only very weakly with the azulene chromophore, the main effect being a shift of the S1 state towards higher energies.

High resolved phosphorescence spectra of xanthone have been recorded in four host matrices in order to study vibronic coupling between the lowest tripl origin in all hosts, and the energetically close-lying second triplet state T 2 , which is of nπ* orbital origin. In three hosts, there is thermall to phosphorescence from T 1 . Vibrational analyses of the two emissions are reported. The vibrational structure of both emissions depends little on t vibronic mixing between the lowest two triplet states is weak, in spite of the small energy separation in some hosts. The importance of the different i 1 and its sublevels is discussed, and it is concluded that across energy separations smaller than about 200 cm −1 spin—orbit mixing is more orbital mixing between the 3 ππ* and 3 nπ* configurations of xanthone.

The fluorescence decay time of pinacyanol (1,1′-diethyl-2,2′-carbocyanine) iodide has been measured in the temperature range 95–225 K. The results indicate that two separate internal-conversion processes are operative. One of these involves torsional relaxation and is viscosity dependent.

The decay processes of the first and second excited singlet ??? S 1 and S 2 , of azulene and some simple derivatives have been examined. The fluorescence S 2 → S 1 , observed for the first time in azulene derivatives, allows a precise measurement of the substituent-induced variation of the S 2 S 1 energy gap. The internal conversion (IC) rates are interpreted using the Englman-Jortner description of radiationless transitions in the weak coupling limit. The IC S 2 -S 1 is the most important decay mechanism. The very small deuterium effect on the S 2 lifetime indicates that most of the energy is accepted by the CC skeletal stretching modes rather than the high-frequency CH stretching modes. This interpretation leads to parameters in the rate constant expression which are of the same order of magnitude as those for other aromatic hydrocarbons. A similar energy gap dependence is observed in the S 1 lifetimes of three carbonyl derivatives of azulene. The experimental data, however, cannot be satisfactorily interpreted with the Englman-Jortner model, because the matrix element connecting S 1 and S 2 is too large for the weak coupling limit. It is suggested that this is due to the coupling strength approaching the intermediate region, a conclusion which is supported by the strong temperature dependence of the emission quantum yield and by the very short S 1 lifetime previously reported.