Parallel Plate Flow Cell Research Articles

Preparation, nano-mechanics and particle deposition behavior of thin, antifouling hydrogel coatings

Hydrogels based on hydrophilic, crosslinked polymer networks can reduce surface contamination in aqueous environments and continue attracting research interest due to their low adhesion, biocompatibility and tunable properties. In particular, sub-micron hydrogel films can potentially screen a surface from interaction with foulant colloids and microorganisms without compromising original functions, such as water permeation in membranes. This study focuses on the preparation of thin hydrogel films with the goal of understanding their adhesive and micromechanical properties, as well as factors affecting the dynamics of microparticle deposition on such films, mimicking the initial stages of surface fouling with colloids, microparticles and microorganisms. For this purpose, a simple procedure was developed to simultaneously crosslink and covalently anchor multi-arm-PEG precursors to a surface to form a submicron coating as a representative model. The effects of synthetic parameters and external conditions on adhesion and viscoelasticity were studied by force spectroscopy using polystyrene colloidal probes. The same particles were also employed in macroscopic deposition experiments in a parallel plate flow cell under identical solution conditions. Microscopic adhesion and elasticity were unaffected by the hydrogel crosslinking density and by salinity, but strongly affected by solution pH and dwell time, whereas macroscopic deposition was strongly affected both by salinity and by pH. These differences were ascribed to the effect of long-range double-layer forces, involved in deposition but absent in measurements of adhesion and elasticity. The results highlight the differences and similarities between the two types of measurements and underlying phenomena, as a step towards the understanding and rational design of soft antifouling coatings.

Electroreduction of Acetochlor at Silver Cathodes in Aqueous Media

We report electroreduction of acetochlor at silver cathodes in aqueous media to provide insight related to electroreduction as a practical application for remediation of haloorganic pollutants. Cyclic voltammetry was used to determine the electrochemical behavior of acetochlor in water as a function of pH. Electrolysis was employed as a means for bulk reduction, with both constant-potential (CPE) and constant-current electrolysis (CCE) considered. CPE offers high selectivity and is preferred for mechanistic analysis, however, long electrolysis times are required for complete reduction. In contrast, CCE was found to provide an alternative for fast electroreduction of acetochlor, with the caveat that current densities must be chosen carefully, to retain selectivity against competing reactions (e.g., proton reduction). In addition, the effect of cell configuration (divided vs undivided) was explored. Finally, an undivided parallel-plate flow cell, in single pass, was employed for flow CCE. The effect of applied current, flow rate, and interelectrode gap were considered for optimal results.

Control of Texture and Morphology of Zinc Films through Pulsed Methods from Additive‐Free Electrolytes

AbstractWe investigate the electrodeposition of zinc on steel substrates using pulsed methods from additive‐free electrolytes in an industrially scalable parallel plate flow cell. We demonstrate that variables such as peak current and duty cycle can be used to independently control the morphology and preferential texture of the crystalline structure, which is, in turn, desirable for a variety of applications. Specifically, we have observed a transition of the preferential (002) facets at low peak current density (or low duty cycle) to (101) preferring facets at higher peak current density (or high duty cycle) as determined by the analysis of texture coefficients. Further analysis using scanning electron microscopy reveals a transition from the conventional hexagonal‐shaped particles of zinc to needle‐shaped structures, accompanied by a change in average crystallite size from 33 to 19 nanometers, determined from X‐ray diffraction studies. The variation in morphology is also correlated to crystallographic textures through the analysis of texture coefficients and an understanding of crystallization mechanisms occurring during deposition. Collectively, these results demonstrate that the morphology and crystalline orientation of zinc can be easily manipulated through tuning of the pulse parameters without the use of complex and expensive additives that have been traditionally used to achieve similar effects.

Independent Variation of Reynolds Number, Wall Shear Stress and Flow Velocity for Cleaning Experiments: A Geometrically Flexible Parallel Plate Flow Cell

For a long time, determining the factors influencing the cleaning of technical surfaces in the food and beverage industry has been of significant interest. In this study, an innovative test setup with a newly designed parallel plate flow cell was implemented to assess the cleaning of soluble molecular fouling materials, which allows for the independent variation of flow parameters, such as the Reynolds number, velocity, and wall shear stress. The test setup used fluorescence spectroscopy; it was found to produce reliable measurements of cleaning, and the results were confirmed with the help of another fluorescent tracer. A comparison of cleaning times for both equipment revealed that the cleaning times tend to have a geometrically independent power-law relationship with the wall shear stress and velocity, and they were used to directly correlate the cleaning times of the used soluble fouling material. However, the Reynolds number showed a geometric dependence on cleaning times. Nevertheless, on dividing the Reynolds number with respective channel characteristic lengths, geometric independence was observed, and, therefore, a correlation was obtained. We also suggest that complex fouling materials should still be investigated to elucidate their cleaning mechanisms better and test for parameter influences on complex cleaning mechanisms.

Development and Assembly of a Flow Cell for Single‐Pass Continuous Electroorganic Synthesis Using Laser‐Cut Components

AbstractFlow electrolysis cells are essential for the scale up of synthetic organic electrochemistry. We have developed a simple and inexpensive parallel plate flow cell that can be easily assembled using a stack of laser‐cut Mylar foils, which act as gaskets, insulating material, interelectrode gap and flow channel. The ease with which the laser‐cutting pattern can be customized has enabled the development of interelectrode separators with mixing geometries, which improve the mass transfer and thus the current efficiency. The performance of the flow electrolysis cell has been evaluated using the anodic decarboxylative methoxylation of diphenylacetic acid as model transformation. Very high conversions and selectivities have been achieved with single‐pass processing, with nearly quantitative current efficiency in some cases.

Analysing the Initial Bacterial Adhesion to Evaluate the Performance of Antifouling Surfaces.

The aim of this work was to study the initial events of Escherichia coli adhesion to polydimethylsiloxane, which is critical for the development of antifouling surfaces. A parallel plate flow cell was used to perform the initial adhesion experiments under controlled hydrodynamic conditions (shear rates ranging between 8 and 100/s), mimicking biomedical scenarios. Initial adhesion studies capture more accurately the cell-surface interactions as in later stages, incoming cells may interact with the surface but also with already adhered cells. Adhesion rates were calculated and results shown that after some time (between 5 and 9 min), these rates decreased (by 55% on average), from the initial values for all tested conditions. The common explanation for this decrease is the occurrence of hydrodynamic blocking, where the area behind each adhered cell is screened from incoming cells. This was investigated using a pair correlation map from which two-dimensional histograms showing the density probability function were constructed. The results highlighted a lower density probability (below 4.0 × 10−4) of the presence of cells around a given cell under different shear rates irrespectively of the radial direction. A shadowing area behind the already adhered cells was not observed, indicating that hydrodynamic blocking was not occurring and therefore it could not be the cause for the decreases in cell adhesion rates. Afterward, cell transport rates from the bulk solution to the surface were estimated using the Smoluchowski-Levich approximation and values in the range of 80–170 cells/cm2.s were obtained. The drag forces that adhered cells have to withstand were also estimated and values in the range of 3–50 × 10−14 N were determined. Although mass transport increases with the flow rate, drag forces also increase and the relative importance of these factors may change in different conditions. This work demonstrates that adjustment of operational parameters in initial adhesion experiments may be required to avoid hydrodynamic blocking, in order to obtain reliable data about cell-surface interactions that can be used in the development of more efficient antifouling surfaces.

Simulations of fluid flow, mass transport and current distribution in a parallel plate flow cell during nickel electrodeposition

Abstract A laboratory filter-press flow cell with parallel plate electrodes is designed for nickel electrodeposition on mild steel from a diluted solution. Design features, such as electrolyte manifolds and turbulence promoters, produced by 3D printing, following computational fluid dynamics (CFD) simulations, are used to minimize jet flow and edge effects on current density. A hydrodynamic analysis is performed by solving the Reynolds averaged Navier-Stokes (RANS) equations with the k − e turbulence model. The averaged convective-diffusion equation is solved for mass transport simulations, while wall functions are used to simulate tertiary current distribution considering the side reaction of hydrogen evolution (HER). The flow cell design minimizes electrolyte flow and current density edge effects at the entrance to the cell by using an electrolyte manifold followed by polymer mesh turbulence promoter and a flow calming zone before the reaction region of the flow channel. The experimental validation of nickel electrodeposition agrees with the predicted tertiary current distribution profiles.

Escherichia coli O157:H7 and Salmonella Typhimurium adhesion to spinach leaf surfaces: Sensitivity to water chemistry and nutrient availability

This study investigated the effects of solution chemistry and growth conditions on bacterial deposition on spinach leaf surfaces using a parallel plate flow cell. Two food safety pathogens of concern and two non-pathogen bacterial surrogates (environmental E. coli isolates) were grown in ideal (LB media) and nutrient-restricted (M9 media) conditions. Bacterial attachment was quantified as mass transfer rate coefficients for cells suspended in 10 mM KCl, CaCl2 and artificial groundwater, and cell and leaf surfaces were extensively characterized (zeta potential, hydrophobicity, extracellular polymer (EPS) composition). Between the pathogens, E. coli O157:H7 attachment was greater than that of Salmonella Typhimurium, attributed to measurable variability in cell surface charge and hydrophobicity. When grown in M9 media, both pathogens were significantly more adhesive to spinach surfaces (p < 0.01) than when grown in LB media. Surrogates did not follow this trend and showed minimal changes in adhesion kinetics and surface properties between growth conditions. EPS sugar/protein ratios were reduced in some of the highest attachment scenarios, suggesting that changes in EPS composition in favor of proteins may play a role. These results show the importance of growth conditions and solution complexities in understanding mechanisms of aqueous bacterial adhesion to food surfaces.

Electron Transfer Reactions at Liquid-Liquid Interfaces

Liquid-liquid interfaces can be polarised to carry out charge transfer reactions, in particular electron transfer (ET) reactions between a hydrophilic and a lipophilic redox molecule. These reactions can be studied by classical electrochemical methods such as cyclic voltammetry. By combining spectroscopic time resolved techniques such Surface Second Harmonic Generation with electrochemical methods, we have studied photo-initiated electron transfer reactions between adsorbed porphyrins and redox quenchers located in one of the adjacent phases. By this approach, we can measure the ET kinetics of adsorbed species located mainly at the interface. We have shown that these interfacial ET reactions involving surface species are not sensitive to the interfacial polarisation. More generally, ET reactions at polarised liquid-liquid interfaces will be discussed to place the present results in perspective. In the second part of the talk, the concept of photo-ionic cells will be presented. Here, the photo-products of a photo-ET reactions occurring in the interfacial region are separated between the two adjacent immiscible phases, thereby resulting in energy storage. This electrochemical energy can then be recovered in a classical parallel plate flow cell. We shall discuss the pros and cons of this method of production of solar fuels.

Cyclohexanedione as the negative electrode reaction for aqueous organic redox flow batteries

The electrochemical reduction and oxidation of cyclohexanedione is evaluated for the first time as the negative electrode reaction in an organic redox flow battery. Electrochemical characterization indicates that the redox reaction of cyclohexanedione is a proton-coupled electron transfer process with quasi-reversible behavior in acidic media (pH<3). Among three isomeric compounds (1,2-, 1,3- and 1,4-cyclohexanedione), the reduction of 1,3-cyclohexanedione exhibits the most negative electrode potential (c.a. −0.6Vvs. Ag|AgCl (c.a. −0.4Vvs. NHE)) as well as the widest pH operating range (pH 1–5) for relatively reversible reactions. The resulting electrode potential is the most negative of those to have been reported in neutral/acidic electrolytes. 1,3-cyclohexanedione is subsequently used as the active species in the negative electrode of a parallel plate flow cell, which is charge-discharge cycled at 3.4mAcm−2 for 100 cycles, yielding half-cell coulombic efficiencies of c.a. 99%. The organic molecules derived from this group are observed to have high solubilities (>2M) and exhibit reduction process with up to 4 electrons transferred.

Electrochemical Oxidation of Phenol Using Boron-Doped Diamond Electrodes

IntroductionThe cleanup of liquids or slurries that contain >1% total organic carbon (TOC), defined as non-wastewater hazardous waste (1), offer particular difficulties for on-site remediation efforts. The electrolytic destruction of organic wastes shows real promise for remediation of a wide variety of organic materials in aqueous waste streams (2). However, the electrochemical oxidation of organic waste is limited with the traditional electrode materials, platinum, ruthenium dioxide, lead dioxide and tin dioxide. The specific limitations arise from low reaction rates and efficiencies, corrosion of the electrodes and fouling and poisoning of the active electrode surfaces. Using phenol as a test compound, the work reported here demonstrates that boron-doped diamond electrodes prepared by chemical vapor deposition (cvd) are not susceptible to these limitations and can oxidize phenol completely to CO2 (3).The oxidation of phenol was chosen as a test reaction because it is one of the most difficult organic molecules to oxidize electrochemically. It is well known for its rapid fouling of the electrode surface due to formation of a blocking polymer layer produced by the polymerization of the phenoxy radicals generated in the initial stages of the reaction (4,5). This results in termination of the reaction in minutes. This communication compares previous work using Ti mesh substrates with approximately 10 μm of boron doped diamond to results obtained using a parallel plate flow cell (3). ExperimentalThe working electrode is a Nb plate (8.5 cm x 9 cm) coated with approximately 1 μm of boron doped diamond via microwave plasma enhanced chemical vapor deposition. A two step deposition process was utilized to achieve uniform nucleation and good film adhesion. The films were characterized with SEM and Raman to establish the quality and stability of the cvd-carbon films.The oxidation of phenol was studied with cyclic voltammetry in a solution of 0.1M H2SO4 containing 0.16 mM phenol in a beaker cell with a Pt counter electrode and a reversible hydrogen reference electrode. Experiments were also run with a parallel flow cell in which 5 liters of 10 mM phenol in 0.1M H2SO4 was circulated through the cell at 100 ml/sec and the total organic carbon (TOC) was monitored as a function of time and cell current. Results and DiscussionIn our previous experiments phenol has been oxidized on boron-doped diamond electrodes without any reduction of the current arising from fouling or poisoning of the electrode even for concentrations of phenol which would put it in the category of non-wastewater hazardous waste. The total carbon in solution was reduced at high efficiency (80-90 %) from ~1% TOC to <0.1% TOC with no observable decrease in decomposition rate. This means that the reacted phenol was converted completely to CO2. These results are extraordinary in that they are preliminary experiments on small surface area electrodes and the experiment has not been optimized. In light of these results, it should also be possible to treat a 10 % TOC solution as readily as a 1 % TOC solution. We will report recent efforts that explore this possibility with more concentrated phenol solutions using a parallel plate flow cell and compare degradation rates to our previous work. AcknowledgementsSupport for this work from the Naval Research Laboratory is gratefully acknowledged.

Short-Term Inactivation Rates of Selected Gram-Positive and Gram-Negative Bacteria Attached to Metal Oxide Mineral Surfaces: Role of Solution and Surface Chemistry

Metal oxides such as ferric or aluminum oxides can play an important role in the retention of bacteria in granular aquatic environments; however, their role in bacterial inactivation is not well understood. Herein, we examined the role of water chemistry and surface chemistry on the short-term inactivation rates of three bacteria when adhered to surfaces. To evaluate the role of water chemistry on the inactivation of attached bacteria, the loss in membrane integrity of bacteria attached to an iron oxide (Fe2O3) surface was measured over a range of water ionic strengths of either monovalent or divalent salts in the absence of a growth substrate. The influence of surface chemistry on the inactivation of attached bacteria was examined by measuring the loss in membrane integrity of cells attached to three surfaces (SiO2, Fe2O3, and Al2O3) at a specific water chemistry (10 mM KCl). Bacteria were allowed to attach onto the SiO2 or metal oxide coated slides mounted in a parallel-plate flow cell, and their inactivation rate (loss in membrane integrity) was measured directly without removing the cells from the surface and without disturbing the system. X-ray photoelectron spectroscopy analysis revealed a high correlation between the amounts of C-metal or O-metal bonds and the corresponding bacterial inactivation rates for each surface. Finally, for all three surfaces, a consistent increase in inactivation rate was observed with the type of bacterium in the order: Enterococcus faecalis, Escherichia coli O157:H7, and Escherichia coli D21f2.

The influence of antiscalants on biofouling of RO membranes in seawater desalination

Antiscalants are surface active polyelectrolyte compounds commonly used in reverse osmosis (RO) desalination processes to avoid membrane scaling. In spite of the significant roles of antiscalants in preventing membrane scaling, they are prone to enhance biofilm growth on RO membranes by either altering membrane surface properties or by serving as nutritional source for microorganisms. In this study, the contribution of antiscalants to membrane biofouling in seawater desalination was investigated. The effects of two commonly used antiscalants, polyphosphonate- and polyacrylate-based, were tested. The effects of RO membrane (DOW-Filmtec SW30 HRLE-400) exposure to antiscalants on its physico-chemical properties were studied, including the consequent effects on initial deposition and growth of the sessile microorganisms on the RO membrane surface. The effects of antiscalants on membrane physico-chemical properties were investigated by filtration of seawater supplemented with the antiscalants through flat-sheet RO membrane and changes in surface zeta potential and hydrophobicity were delineated. Adsorption of antiscalants to polyamide surfaces simulating RO membrane's polyamide layer and their effects on the consequent bacterial adhesion was tested using a quartz crystal microbalance with dissipation monitoring technology (QCM-D) and direct fluorescent microscopy. A significant increase in biofilm formation rate on RO membranes surface was observed in the presence of both types of antiscalants. Polyacrylate-based antiscalant was shown to enhance initial cell attachment as observed with the QCM-D and a parallel plate flow cell, due to rendering the polyamide surface more hydrophobic. Polyphosphonate-based antiscalants also increased biofilm formation rate, most likely by serving as an additional source of phosphorous to the seawater microbial population. A thicker biofilm layer was formed on the RO membrane when the polyacrylate-based antiscalant was used. Following these results, a wise selection of antiscalants for scaling control should take into account their contribution to membrane biofouling propensity.

Vorticity Banding in Biphasic Polymer Blends

Pattern formation under the action of flow is a subject of considerable scientific interest with applications going from microfluidics to granular materials. Here, we present a systematic investigation of shear-induced banding in confined biphasic liquid-liquid systems, i.e., formation of alternating regions of high and low volume fraction of droplets in a continuous phase (shear bands). This phenomenon is investigated in immiscible polymer blends sheared in a sliding parallel plate flow cell. Starting from a spatially uniform distribution of droplets, the formation of bands aligned along the flow direction is observed, eventually leading to an almost complete separation between droplet-rich and continuous phase regions. The initial band size is related to the gap dimension; the merging of bands and consequent spacing reduction has also been observed for long times. Shear banding is only observed when the viscosity of the dispersed phase is lower as compared to the continuous phase and in a limited range of the applied shear rate. Rheological measurements show that band formation is associated with a viscosity decrease with respect to the homogeneous case, thus implying that system microstructure is somehow evolving toward reduced viscous dissipation under flow.

Nanoparticle deposition onto biofilms.

We develop a mathematical model of nanoparticles depositing onto and penetrating into a biofilm grown in a parallel-plate flow cell. We carry out deposition experiments in a flow cell to support the modeling. The modeling and the experiments are motivated by the potential use of polymer nanoparticles as part of a treatment strategy for killing biofilms infecting the deep passages in the lungs. In the experiments and model, a fluid carrying polymer nanoparticles is injected into a parallel-plate flow cell in which a biofilm has grown over the bottom plate. The model consists of a system of transport equations describing the deposition and diffusion of nanoparticles. Standard asymptotic techniques that exploit the aspect ratio of the flow cell are applied to reduce the model to two coupled partial differential equations. We perform numerical simulations using the reduced model. We compare the experimental observations with the simulation results to estimate the nanoparticle sticking coefficient and the diffusion coefficient of the nanoparticles in the biofilm. The distributions of nanoparticles through the thickness of the biofilm are consistent with diffusive transport, and uniform distributions through the thickness are achieved in about four hours. Nanoparticle deposition does not appear to be strongly influenced by the flow rate in the cell for the low flow rates considered.

Design of microdevices for long-term live cell imaging

Advances in fluorescent live cell imaging provide high-content information that relates a cell's life events to its ancestors. An important requirement to track clonal growth and development is the retention of motile cells derived from an ancestor within the same microscopic field of view for days to weeks, while recording fluorescence images and controlling the mechanical and biochemical microenvironments that regulate cell growth and differentiation. The aim of this study was to design a microwell device for long-term, time-lapse imaging of motile cells with the specific requirements of (a) inoculating devices with an average of one cell per well and (b) retaining progeny of cells within a single microscopic field of view for extended growth periods. A two-layer PDMS microwell culture device consisting of a parallel-plate flow cell bonded on top of a microwell array was developed for cell capture and clonal culture. Cell deposition statistics were related to microwell geometry (plate separation and well depth) and the Reynolds number. Computational fluid dynamics was used to simulate flow in the microdevices as well as cell–fluid interactions. Analysis of the forces acting upon a cell was used to predict cell docking zones, which were confirmed by experimental observations. Cell–fluid dynamic interactions are important considerations for design of microdevices for long-term, live cell imaging. The analysis of force and torque balance provides a reasonable approximation for cell displacement forces. It is computationally less intensive compared to simulation of cell trajectories, and can be applied to a wide range of microdevice geometries to predict the cell docking behavior.

Method for the Direct Observation and Quantification of Survival of Bacteria Attached to Negatively or Positively Charged Surfaces in an Aqueous Medium

The risk of groundwater contamination by microbial pathogens is linked to their survival in the subsurface. Although there is a large body of literature on the inactivation behavior of suspended (planktonic) microorganisms, little is known about the inactivation of bacteria when attached to sand grain surfaces in groundwater aquifers. The main goal of this study was to develop a fluorescence-based experimental technique for evaluating the extent of inactivation over time of bacteria adhered onto a surface in an aqueous environment. Key features of the developed technique are as follows: (i) attached cells do not need to be removed from the surface of interest for quantification, (ii) bacterial inactivation can be examined in real-time for prolonged time periods, and (iii) the system remains undisturbed (i.e., the aqueous environment is unchanged) during the assay. A negatively or positively charged substrate (i.e., bare or coated glass slide) was mounted in a parallel-plate flow cell, bacteria were allowed to attach onto the substrate, and the loss of bacterial membrane integrity and respiratory activity were investigated as a function of time by fluorescence microscopy using Live/Dead BacLight and BacLight RedoxSensor CTC (5-cyano-2,3-ditolyl tetrazolium chloride) viability assays. These two different measures of bacterial inactivation result in comparable trends in bacterial inactivation, confirming the validity of the experimental technique. The results of this work show that the developed technique is sensitive enough to distinguish between the inactivation kinetics of different representative bacteria attached to either a negatively charged (bare glass) surface or a positively charged (coated glass) surface. Hence, the technique can be used to characterize bacterial inactivation kinetics when attached to environmentally relevant surfaces over a broad range of groundwater chemistries.

The role of alginate in Pseudomonas aeruginosa EPS adherence, viscoelastic properties and cell attachment

Among various functions, extracellular polymeric substances (EPS) provide microbial biofilms with mechanical stability and affect initial cell attachment, the first stage in the biofilm formation process. The role of alginate, an abundant polysaccharide in Pseudomonas aeruginosa biofilms, in the viscoelastic properties and adhesion kinetics of EPS was analyzed using a quartz crystal microbalance with dissipation (QCM-D) monitoring technology. EPS was extracted from two P. aeruginosa biofilms, a wild type strain, PAO1, and a mucoid strain, PAOmucA22 that over-expresses alginate production. The higher alginate content in the EPS originating from the mucoid biofilms was clearly shown to increase both the rate and the extent of attachment of the EPS, as well as the layer's thickness. Also, the presence of calcium and elevated ionic strength increased the thickness of the EPS layer. Dynamic light scattering (DLS) showed that the presence of calcium and elevated ionic strength induced intermolecular attractive interactions in the mucoid EPS molecules. For the wild type EPS, in the presence of calcium, an elevated shift in the distribution of the diffusion coefficients was observed with DLS due to a more compacted conformation of the EPS molecules. Moreover, the alginate over-expression effect on EPS adherence was compared to the effect of alginate over-expression on P. aeruginosa cell attachment. In a parallel plate flow cell, under similar hydraulic and aquatic conditions as those applied for the EPS adsorption tests in the QCM-D flow cell, reduced adherence of the mucoid strain was clearly observed compared to the wild type isogenic bacteria. The results suggest that alginate contributes to steric hindrance and shielding of cell surface features and adhesins that are known to promote cell attachment.

Antibacterial fluorinated silica colloid superhydrophobic surfaces.

A superhydrophobic xerogel coating synthesized from a mixture of nanostructured fluorinated silica colloids, fluoroalkoxysilane, and a backbone silane is reported. The resulting fluorinated surface was characterized using contact angle goniometry, scanning electron microscopy (SEM), and atomic force microscopy (AFM). Quantitative bacterial adhesion studies performed using a parallel plate flow cell demonstrated that the adhesion of Staphylococcus aureus and Pseudomonas aeruginosa was reduced by 2.08 ± 0.25 and 1.76 ± 0.12 log over controls, respectively. This simple superhydrophobic coating synthesis may be applied to any surface, regardless of geometry, and does not require harsh synthesis or processing conditions, making it an ideal candidate as a biopassivation strategy.

Dynamics of Pseudomonas aeruginosa association with anionic hydrogel surfaces in the presence of aqueous divalent-cation salts

Binding of bacteria to solid surfaces is complex with many aspects incompletely understood. We investigate Pseudomonas aeruginosa uptake kinetics onto hydrogel surfaces representative of soft-contact lenses made of nonionic poly(2-hydroxyethylmethacrylate) (p-HEMA), anionic poly(methacrylic acid) (p-MAA), and anionic poly(acrylic acid) (p-AA). Using a parallel-plate flow cell under phase-contrast microscopy, we document a kinetic “burst” at the anionic hydrogel surface: dilute aqueous P. aeruginosa first rapidly accumulates and then rapidly depletes. Upon continuing flow, divalent cations in the suspending solution sorb into the hydrogel network causing the previously surface-accumulated bacteria to desorb. The number of bacteria eventually bound to the surface is low compared to the nonionic p-HEMA hydrogel. We propose that the kinetic burst is due to reversible divalent-cation bridging between the anionic bacteria and the negatively charged hydrogel surface. The number of surface bridging sites diminishes as divalent cations impregnate into and collapse the gel. P. aeruginosa association with the surface then falls. Low eventual binding of P. aeruginosa to the anionic hydrogel is ascribed to increased surface hydrophilicity compared to the counterpart nonionic p-HEMA hydrogel.