Sameer A. Al-Bataineh

Furanone at Subinhibitory Concentrations Enhances Staphylococcal Biofilm Formation by luxS Repression

ABSTRACT Brominated furanones from marine algae inhibit multicellular behaviors of gram-negative bacteria such as biofilm formation and quorum sensing (QS) without affecting their growth. The interaction of furanone with QS in gram-positive bacteria is unknown. Staphylococci have two QS systems, agr and luxS, which lower biofilm formation by two different pathways, RNAIII upregulation and bacterial detachment, and polysaccharide intercellular adhesin (PIA) reduction, respectively. We synthesized natural furanone compound 2 [(5Z)-4-bromo-5-(bromomethylene)-3-butyl-2(5H)-furanone] from Delisea pulchra and three analogues to investigate their effect on biofilm formation in gram-positive bacteria. Compound 2, but not the analogues, enhanced the biofilms of Staphylococcus epidermidis 1457 and 047 and of S. aureus Newman at concentrations between 1.25 and 20 μM. We show the growth inhibition of S. epidermidis and S. aureus by free furanone and demonstrate bactericidal activity. An induction of biofilm occurred at concentrations of 10 to 20% of the MIC and correlated with an increase in PIA. The biofilm effect was agr independent. It was due to interference with luxS, as shown by reduced luxS expression in the presence of compound 2 and independence of the strong biofilm formation in a luxS mutant upon furanone addition. Poly(l-lysine)-grafted/poly(ethylene glycol)-grafted furanone was ineffective on biofilm and not bactericidal, indicating the necessity for free furanone. Free furanone was similarly toxic for murine fibroblasts as for staphylococci, excluding a therapeutic application of this compound. In summary, we observed a biofilm enhancement by furanone in staphylococci at subinhibitory concentrations, which was manifested by an increase in PIA and dependent on luxS.

Combination of iCVD and porous silicon for the development of a controlled drug delivery system.

We describe a pH responsive drug delivery system which was fabricated using a novel approach to functionalize biodegradeable porous silicon (pSi) by initiated chemical vapor deposition (iCVD). The assembly involved first loading a model drug (camptothecin, CPT) into the pores of the pSi matrix followed by capping the pores with a thin pH responsive copolymer film of poly(methacrylic acid-co-ethylene dimethacrylate) (p(MAA-co-EDMA)) via iCVD. Release of CPT from uncoated pSi was identical in two buffers at pH 1.8 and pH 7.4. In contrast, the linear release rate of CPT from the pSi matrix with the p(MAA-co-EDMA) coating was dependent on the pH; release of CPT was more than four times faster at pH 7.4 (13.1 nmol/(cm(2) h)) than at pH 1.8 (3.0 nmol/(cm(2) h)). The key advantage of this drug delivery approach over existing ones based on pSi is that the iCVD coating can be applied to the pSi matrix after drug loading without degradation of the drug because the process does not expose the drug to harmful solvents or high temperatures and is independent of the surface chemistry and pore size of the nanoporous matrix.

On the effect of monomer chemistry on growth mechanisms of nonfouling PEG-like plasma polymers.

It has been shown that both ions and neutral species may contribute to plasma polymer growth. However, the relative contribution from these mechanisms remains unclear. We present data elucidating the importance of considering monomer structure with respect to which the growth mechanism dominates for nonfouling PEG-like plasma polymers. The deposition rate for saturated monomers is directly linked with ion flux to the substrate. For unsaturated monomers, the neutral flux also plays a role, particularly at low power. Increased fragmentation of the monomer at high power reduces the ability of unsaturated monomers to grow via neutral grafting. Chemical characterization by X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectrometry (ToF-SIMS) confirm the role that plasma phase fragmentation plays in determining the deposition rate and surface chemistry of the deposited film. The simple experimental method used here may also be used to determine which mechanisms dominate plasma deposition for other monomers. This knowledge may enable significant improvement in future reactor design and process control.

Covalent immobilization of antibacterial furanones via photochemical activation of perfluorophenylazide

N-(3-trimethoxysilylpropyl)-4-azido-2,3,5,6-tetrafluorobenzamide (PFPA-silane) was used as a photoactive cross-linker to immobilize antibacterial furanone molecules on silicon oxide surfaces. This immobilization strategy is useful, especially for substrates and molecules that lack reactive functional groups. To this end, cleaned wafers were initially incubated in solutions of different concentrations of PFPA-silane to form a monolayer presenting azido groups on the surface. The functionalized surfaces were then treated with a furanone solution followed by illumination with UV light and extensive rinsing with ethanol to remove noncovalently adhered molecules. In the presented study, we demonstrate the ability to control the surface density of the immobilized furanone molecules by adjusting the concentration of PFPA-silane solution used for surface functionalization using complementary surface analytical techniques. The fluorine in PFPA-silane and the bromine in furanone molecules were convenient markers for the XPS study. The ellipsometric layer thickness of the immobilized furanone molecules on the surface decreased with decreasing PFPA-silane concentration, which correlated with a decline of water contact angle as a sign of film collapse. The intensity of characteristic azide vibration in the MTR IR spectra was monitored as a function of PFPA-silane concentration, and the peak disappeared completely after furanone application followed by UV irradiation. As a complementary technique to XPS, TOF-SIMS provided valuable information on the chemical and molecular structure of the modified surfaces and spatial distribution of the immobilized furanone molecules. Finally, this report presents a convenient, reproducible, and robust strategy to design antibacterial coating based on furanone compounds for applications in human health care.

Fabrication and Characterization of a Porous Silicon Drug Delivery System with an Initiated Chemical Vapor Deposition Temperature-Responsive Coating

This paper reports on the fabrication of a pSi-based drug delivery system, functionalized with an initiated chemical vapor deposition (iCVD) polymer film, for the sustainable and temperature-dependent delivery of drugs. The devices were prepared by loading biodegradable porous silicon (pSi) with a fluorescent anticancer drug camptothecin (CPT) and coating the surface with temperature-responsive poly(N-isopropylacrylamide-co-diethylene glycol divinyl ether) (pNIPAM-co-DEGDVE) or non-stimulus-responsive poly(aminostyrene) (pAS) via iCVD. CPT released from the uncoated oxidized pSi control with a burst release fashion (∼21 nmol/(cm(2) h)), and this was almost identical at temperatures both above (37 °C) and below (25 °C) the lower critical solution temperature (LCST) of the switchable polymer used, pNIPAM-co-DEGDVE (28.5 °C). In comparison, the burst release rate from the pSi-pNIPAM-co-DEGDVE sample was substantially slower at 6.12 and 9.19 nmol/(cm(2) h) at 25 and 37 °C, respectively. The final amount of CPT released over 16 h was 10% higher at 37 °C compared to 25 °C for pSi coated with pNIPAM-co-DEGDVE (46.29% vs 35.67%), indicating that this material can be used to deliver drugs on-demand at elevated temperatures. pSi coated with pAS also displayed sustainable drug delivery profiles, but these were independent of the release temperature. These data show that sustainable and temperature-responsive delivery systems can be produced by functionalization of pSi with iCVD polymer films. Benefits of the iCVD approach include the application of the iCVD coating after drug loading without causing degradation of the drug commonly caused by exposure to factors such as solvents or high temperatures. Importantly, the iCVD process is applicable to a wide array of surfaces as the process is independent of the surface chemistry and pore size of the nanoporous matrix being coated.

Surface engineering of porous silicon to optimise therapeutic antibody loading and release

The proinflammatory cytokine, tumor necrosis factor-α (TNF-α), is elevated in several diseases such as uveitis, rheumatoid arthritis and non-healing chronic wounds. Adding Infliximab, a chimeric IgG1 monoclonal antibody raised against TNF-α, to chronic wound fluid can neutralise human TNF-α, thereby providing a potential therapeutic option for chronic wound healing. However, to avoid the need for repeated application in a clinical setting, and to protect the therapeutic antibody from the hostile environment of the wound, suitable delivery vehicles are required. Porous silicon (pSi) is a biodegradable high surface area material commonly employed for drug delivery applications. In this study, the use of pSi microparticles (pSi MPs) for the controlled release of Infliximab to disease environments, such as chronic wounds, is demonstrated. Surface chemistry and pore parameters for Infliximab loading are first optimised in pSi films and loading conditions are transferred to pSi MPs. Loading regimens exceeding 60 μg of Infliximab per mg of pSi are achieved. Infliximab is released with zero-order release kinetics over the course of 8 days. Critically, the released antibody remains functional and is able to sequester TNF-α over a weeklong timeframe; suitable for a clinical application in chronic wound therapy.

Microplasma arrays: a new approach for maskless and localized patterning of materials surfaces

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

Surface protein gradients generated in sealed microchannels using spatially varying helium microplasma

Spatially varied surface treatment of a fluorescently labeled Bovine Serum Albumin (BSA) protein, on the walls of a closed (sealed) microchannel is achieved via a well-defined gradient in plasma intensity. The microchips comprised a microchannel positioned in-between two microelectrodes (embedded in the chip) with a variable electrode separation along the length of the channel. The channel and electrodes were 50 μm and 100 μm wide, respectively, 50 μm deep, and adjacent to the channel for a length of 18 mm. The electrode separation distance was varied linearly from 50 μm at one end of the channel to a maximum distance of 150, 300, 500, or 1000 μm to generate a gradient in helium plasma intensity. Plasma ignition was achieved at a helium flow rate of 2.5 ml/min, 8.5 kVpk-pk, and 10 kHz. It is shown that the plasma intensity decreases with increasing electrode separation and is directly related to the residual amount of BSA left after the treatment. The plasma intensity and surface protein gradient, for the different electrode gradients studied, collapse onto master curves when plotted against electrode separation. This precise spatial control is expected to enable the surface protein gradient to be tuned for a range of applications, including high-throughput screening and cell-biomolecule-biomaterial interactions.

Attachment of Poly(l-lactide) Nanoparticles to Plasma-Treated Non-Woven Polymer Fabrics Using Inkjet Printing.

Active dressings that based on fabric materials are an area of interest for the treatment of wounds. Poly(l-lactide) nanoparticles containing the antimicrobial agent octenidine can be controllably lysed by toxins released by pathogenic bacteria thus releasing antimicrobial material in response to the presence of the bacterial toxins and so counteracting the infection. We developed an integrated engineering solution that allows for the stable immobilisation of nanoparticles on non-woven fabrics. The process involves coating nanoparticles on non-woven polymer surfaces by using an inkjet printing process. In order to improve the adhesion and retention of the nanoparticles on the fabric, surface pretreatment of the non-woven fabric using plasma jet treatment can be applied to increase its surface energy.

ToF-SIMS analysis of poly(l-lysine)-graft-poly(2-methyl-2-oxazoline) ultrathin adlayers

AbstractUnderstanding of the interfacial chemistry of ultrathin polymeric adlayers is fundamentally important in the context of establishing quantitative design rules for the fabrication of nonfouling surfaces in various applications such as biomaterials and medical devices. In this study, seven poly(l-lysine)-graft-poly(2-methyl-2-oxazoline) (PLL–PMOXA) copolymers with grafting density (number of PMOXA chains per lysine residue) 0.09, 0.14, 0.19, 0.33, 0.43, 0.56, and 0.77, respectively, were synthesized and characterized by means of nuclear magnetic resonance spectroscopy (NMR). The copolymers were then adsorbed on Nb2O5 surfaces. Optical waveguide lightmode spectroscopy method was used to monitor the surface adsorption in situ of these copolymers and provide information on adlayer masses that were then converted into PLL and PMOXA surface densities. To investigate the relationship between copolymer bulk architecture (as shown by NMR data) and surface coverage as well as surface architecture, time-of-flight secondary ion mass spectrometry (ToF-SIMS) analysis was performed. Furthermore, ToF-SIMS method combined with principal component analysis (PCA) was used to verify the protein resistant properties of PLL–PMOXA adlayers, by thorough characterization before and after adlayer exposure to human serum. ToF-SIMS analysis revealed that the chemical composition as well as the architecture of the different PLL–PMOXA adlayers indeed reflects the copolymer bulk composition. ToF-SIMS results also indicated a heterogeneous surface coverage of PLL–PMOXA adlayers with high grafting densities higher than 0.33. In the case of protein resistant surface, PCA results showed clear differences between protein resistant and nonprotein-resistant surfaces. Therefore, ToF-SIMS results combined with PCA confirmed that the PLL–PMOXA adlayer with brush architecture resists protein adsorption. However, low increases of some amino acid signals in ToF-SIMS spectra were detected after the adlayer has been exposed to human serum. Figureᅟ