Leanne Britcher

Solvent-induced porosity in ultrathin amine plasma polymer coatings.

Plasma polymers deposited from n-heptylamine onto silicon wafers have been found to form a porous microstructure when immersed in water and other solvents, with pores of dimensions and densities that vary considerably between coatings deposited under different plasma conditions. This solvent-induced pore formation was found to correlate with the observed percentage of extractable material. With low radio frequency (rf) power inputs, the resultant softer coatings possess considerably more extractable material than coatings deposited at higher applied power levels. The porosity is thus proposed to result from the formation of voids created by the extraction of soluble low-molecular-weight polymeric material, which produces shrinkage stress that the coating, firmly attached to the substrate, cannot relieve by macroscopic contraction. The microscopic contraction of plasma polymer volume creates voids that appear to span the entire film thickness. The effect of aging plasma polymers in air was also investigated. For films deposited at low power it led to reduced extraction of soluble material and different pore morphology, whereas for films deposited at higher rf power levels, the extracted amounts and pore formation were the same for aged coatings. It was also found that the density of surface amine groups was lower for films deposited under the two lowest power settings, in contrast to the commonly held belief that the use of minimal applied rf power aids retention of functional groups. These porous plasma polymer coatings with surface groups suitable for further interfacial chemical immobilization reactions may be useful for various membrane and biotechnology applications.

Fimbrolide-coated antimicrobial lenses: their in vitro and in vivo effects.

Purpose. To examine the ability of contact lenses coated with fimbrolides, inhibitors of bacterial quorum sensing, to prevent microbial adhesion and their safety during short-term clinical assessment. Methods. A fimbrolide was covalently attached to commercially available high Dk contact lenses. Subsequently Pseudomonas aeruginosa, Staphylococcus aureus, Serratia marcescens, or Acanthamoeba sp. were added to the lenses and control uncoated contact lenses. Lenses plus microbes were incubated for 24 h, then washed thoroughly to remove non-adherent microbes. Lenses were macerated and resulting slurry plated onto agar plates. After appropriate incubation, the numbers of colony forming units of bacteria (or numbers of Acanthamoeba trophozoites measured using a hemocytometer) from fimbrolide-coated and uncoated lenses were examined. A Guinea Pig model of lens wear was used to assess the safety of lenses worn on a continuous basis for 1 month. In a separate study, 10 subjects wore fimbrolide-coated lenses for 24 h. The responses of the Guinea Pigs and human volunteers to the lenses were assessed by slit lamp examination. Results. The fimbrolides-coated lenses reduced the adhesion of all bacterial strains tested, with reductions occurring of between 67 and 92%. For Acanthamoeba a reduction of 70% was seen. There were no significant differences in ocular responses to fimbrolide-coated lenses compared with controls in either the 1 month animal model or overnight human trial. Conclusions. Fimbrolide-coated lenses show promise as an antibacterial and anti-acanthamoebal coating on contact lenses and appear to be safe when worn on the eye in an animal model.

PEGylation of Porous Silicon Using Click Chemistry

Porous silicon has received considerable interest in recent years in a range of biomedical applications, with its performance determined by surface chemistry. In this work, we investigate the PEGylation of porous silicon wafers using click chemistry. The porous silicon wafer surface chemistry was monitored at each stage of the reaction via photoacoustic Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy, whereas sessile drop contact angle and model protein adsorption measurements were used to characterize the final PEGylated surface. This work highlights the simplicity of click-chemistry-based functionalization in tailoring the porous silicon surface chemistry and controlling protein-porous silicon interactions.

Characterization of sulfate and phosphate containing plasma polymer surfaces

This paper describes three methods for producing sulfated and phosphated surfaces using plasma-based technologies, namely plasma treatment, plasma polymerization, and plasma activation followed by chemical grafting. Plasma treatment using sulfur dioxide (SO2) produced sulfur-containing groups while plasma polymerization using triisopropyl phosphite (TIP) as the monomer created phosphated surfaces. The plasma-plus-grafting technique involved deposition of an amine plasma polymer followed by grafting with vinyl sulfonate or vinyl phosphonic acid via Michael addition. The various oxidation states and surface charges of chemical groups present on the surfaces were assessed by the surface analytical techniques X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared (FTIR). The stability and ageing mechanism of these plasma surfaces were also characterized.

QCM-D and XPS study of protein adsorption on plasma polymers with sulfonate and phosphonate surface groups

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

The effect of silane concentration on the adsorption of poly(vinyl acetate-co-maleate) and γ -methacryloxypropyl- trimethoxysilane onto E-glass fibers

The adsorption of a poly(vinyl acetate-co-maleate) (PVAM) emulsion onto E-glass fibers was investigated along with sizing formulations prepared by mixing the PVAM with varying concentrations of γ -methacryloxypropyltrimethoxysilane (MPS). The sized E-glass fibers were then characterized using Diffuse Reflectance Infrared Fourier Transform (DRIFT) spectroscopy, X-ray Photoelectron Spectroscopy (XPS) and Scanning Electron Microscopy (SEM). Loss on Ignition (LOI) along with the DRIFT spectra indicated that the addition of silane to the PVAM emulsion caused a decrease in the amount of size on the fiber. The decrease in amount of size on the E-glass fibers did not coincide with a decrease in surface coverage, instead the XPS results indicated surface coverage had increased with silane addition. These results showed that small increases in the silane concentration appear to affect the amount of size adsorbed to the E-glass fibers