Orientation of irreversible adhesion of spherical particles on prolate spheroidal collectors

When one sphere adheres to a second sphere, the location or orientation of the adhesion on the second sphere is seldom considered. However, when a sphere adheres to a prolate spheroid, the orientation of the adhesion is sometimes critical. We have performed Brownian dynamics simulations to predict the orientation of adhesion of a sphere on a prolate spheroid. When the spheroid has a high rotational diffusion coefficient, simulations show that the spherical particle adheres near the end of the spheroid. We tested our model experimentally for two systems: (1) oppositely-charged spherical and spheroidal colloids and (2) like-charged colloidal spheres and E. coli K-12 D21 bacteria. For the latter case, the spheres have previously been shown to adhere only to one end of the bacterium. Experiments in case (1) support the results of the simulations, while data from case (2) do not agree with predictions. Case (2) data reveal that the end-on adhesion of the spheres on the bacteria is not a purely Brownian phenomenon.     

Force variation of chlorinated butyl-rubber peeling from steel in the process of vulcanization

Vulcanization of an adhered layer with the use of low-temperature vulcanizing agents with different adhesion activities was carried out to increase the heat resistance and resistance to displacement of the adhesive tapes with different adhesive activity. It is shown that the force variation of the vulcanized adherent layer based on the chlorobutyl rubber and polymeric petroleum resin for peeling from steel depends on the measurement temperature: at 25°C, the peeling force decreases, while at 80°C it increases as compared with nonvulcanized adhesive. The observed changes are conditioned both by the increase of the cohesion strength of the adhered layer and by decrease of the elastic component in the layer peeling energy.     

Interaction forces between waterborne bacteria and activated carbon particles

Activated carbons remove waterborne bacteria from potable water systems through attractive Lifshitz-van der Waals forces despite electrostatic repulsion between negatively charged cells and carbon surfaces. In this paper we quantify the interaction forces between bacteria with negatively and positively charged, mesoporous wood-based carbons, as well as with a microporous coconut carbon. To this end, we glued carbon particles to the cantilever of an atomic force microscope and measured the interaction forces upon approach and retraction of thus made tips. Waterborne Raoultella terrigena and Escherichia coli adhered weakly (1-2 nN) to different activated carbon particles, and the main difference between the activated carbons was the percentage of curves with attractive sites revealed upon traversing of a carbon particle through the bacterial EPS layer. The percentage of curves showing adhesion forces upon retraction varied between 21% and 69%, and was highest for R. terrigena with positively charged carbon (66%) and a coconut carbon (69%). Macroscopic bacterial removal by the mesoporous carbon particles increased with increasing percentages of attractive sites revealed upon traversing a carbon particle through the outer bacterial surface layer.     

Dynamic single cell culture array

It is important to quantify the distribution of behavior amongst a population of individual cells to reach a more complete quantitative understanding of cellular processes. Improved high-throughput analysis of single cell behavior requires uniform conditions for individual cells with controllable cell-cell interactions, including diffusible and contact elements. Uniform cell arrays for static culture of adherent cells have previously been constructed using protein micropatterning techniques but lack the ability to control diffusible secretions. Here we present a microfluidic-based dynamic single cell culture array that allows both arrayed culture of individual adherent cells and dynamic control of fluid perfusion with uniform environments for individual cells. In our device no surface modification is required and cell loading is done in less than 30 seconds. The device consists of arrays of physical U-shaped hydrodynamic trapping structures with geometries that are biased to trap only single cells. HeLa cells were shown to adhere at a similar rate in the trapping array as on a control glass substrate. Additionally, rates of cell death and division were comparable to the control experiment. Approximately 100 individual isolated cells were observed growing and adhering in a field of view spanning approximately 1 mm(2) with greater than 85% of cells maintained within the primary trapping site after 24 hours. Also, greater than 90% of cells were adherent and only 5% had undergone apoptosis after 24 hours of perfusion culture within the trapping array. We anticipate uses in single cell analysis of drug toxicity with physiologically relevant perfused dosages as well as investigation of cell signaling pathways and systems biology.     

An image analysis strategy to study cell adhesion

A semi-automated in situ technique has been developed for the study of the extent and kinetics of cell adhesion at the individual cell level. Our investigation involves the static sedimentation of glutaraldehyde-fixed human erythrocytes suspended in 10 mM NaCl or 10 mM NaCl containing 2% (v/v) 1-propanol onto flat, horizontal, and transparent surfaces. The surfaces used are glass, poly(ethylene terephthalate), polystyrene, and fluorinated ethylene propylene. An inverted microscope is utilized for observations. Brownian motion is used as the distinguishing criterion between adherent and non-adherent cells. The extent of adhesion is expressed as the percentage of adherent cells. Two digital image processing techniques, image averaging and image subtraction, are presented for automation of the methodology. Although all non-adherent cells undergo Brownian motion, they exhibit this behavior to varying degrees. Factors under consideration are the liquid medium's surface tension (γ_LV) and the solid substrate surface tension (γ_SV). Preliminary results reveal that, in general, variations of γ_SV and γ_LV have a statistically significant effect on the extent of adhesion at the 99% and 96% confidence levels, respectively. A time depepdence for the adhesion of populations of cells is observed. However, individual cells either instantly or gradually adhere. Image subtraction generally overestimates the number of adherent cells due to the difficulty in detection of minute oscillations. The deviation between the adhesion percentage obtained from visual observations of the monitor and image subtraction is less than 10%.     

Interaction of hepatocytes with polyelectrolyte complex(I): the effect of nonspecific interaction on adhesion of the cell

The adhesion of hepatocytes to polyelectrolyte complex (PEC), prepared by mixing of aqueous solutions of polycation and polyanion, is discussed. Four PECs, poly((dimethyliminio)ethylene(dimethyliminio)methylene‐1,4‐phenylenemethylene dichloride)–poly(acrylic acid)2X–(PAA), 2X‐poly(acrylic acid–co‐2‐ethylhexylacrylate(COA), 2X‐poly(acrylicacid–co‐butylacrylate) (CBA) and 2X‐poly(acrylic acid–co‐laurylacrylate)(CLA) were prepared. Hydrophobic properties of these PECs increased in the order of 2X–PAA < 2X–COA < 2X–CLA ≤ 2X–CBA. About all the hepatocytes adhered rapidly to various PECs even in the absence of serum, while fewer cells adhered to polystrene (tissue culture grade) dishes. At 37 °C (biological condition) about 70–80% of cells adhered to a collagen‐coated dish, but at 4 °C (nonbiological condition), no cell adhered to it. Nonactive cells (prepared by a single cycle of freezing and thawing) did not adhere to collagen, either. On the contrary about 40% of cells adhered to PEC‐coated dishes even at 4 °C, and nonactive cells also adhered to them. Cytocharosine B and colchicine, which are known as inhibitors of the polymerization of intracellular matrix, did not prevent cell adhesion to PECs. From these results it was suggested that hepatocytes adhered to PEC‐coated dishes mainly through a nonbiological interaction. Copyright © 1999 John Wiley & Sons, Ltd.     

Dendrimer-based Hydrogels with Controlled Drug Delivery Property for Tissue Adhesion

In recent years,the hydrogel-based tissue adhesives have been extensively investigated for their excellent biocompatibility and the ability to be administered directly within the adherent tissue.To meet the requirement for more controllable release in various physiological settings,the components of hydrogel adhesive should be more precisely tailored.In this work,the POSS-ace-PEG hydrogel adhesive was fabricated with the polyacetal dendrimer G1'-[NH3Cl]16 and poly(ethylene glycol) succinimidyl carbonate (PEG-SC) due to the regular peripheral amino structure of G1'-[NH3Cl]16.Rheological and adhesion tests demonstrated that the hydrogel adhesive had good mechanical and adhesive properties,which could effectively adhere to the pigskin and severed nerves.Moreover,the tissue adhesive exhibited good stability under neutral conditions and the rapid degradation under acidic conditions,allowing for the release of doxycycline hydrochloride (DOX) drug in response to pH.Together,these results suggested that the POSS-ace-PEG adhesive had the potential to provide an alternative to tissue adhesives for applications in pathological environments (inflammation,tumors,etc.).     

Quantitative changes in the elasticity and adhesive properties of Escherichia coli ZK1056 prey cells during predation by bdellovibrio bacteriovorus 109J

Atomic force microscopy (AFM) was used to explore the changes that occur in Escherichia coli ZK1056 prey cells while they are being consumed by the bacterial predator Bdellovibrio bacteriovorus 109J. Invaded prey cells, called bdelloplasts, undergo substantial chemical and physical changes that can be directly probed by AFM. In this work, we probe the elasticity and adhesive properties of uninvaded prey cells and bdelloplasts in a completely native state in dilute aqueous buffer without chemical fixation. Under these conditions, the rounded bdelloplasts were shown to be shorter than uninvaded prey cells. More interestingly, the extension portions of force curves taken on both kinds of cells clearly demonstrate that bdelloplasts are softer than uninvaded prey cells, reflecting a decrease in bdelloplast elasticity after invasion by Bdellovibrio predators. On average, the spring constant of uninvaded E. coli cells (0.23 +/- 0.02 N/m) was 3 times stiffer than that of the bdelloplast (0.064 +/- 0.001 N/m) when measured in a HEPES-metals buffer. The retraction portions of the force curves indicate that compared to uninvaded E. coli cells bdelloplasts adhere to the AFM tip with much larger pull-off forces but over comparable retraction distances. The strength of these adhesion forces decreases with increasing ionic strength, indicating that there is an electrostatic component to the adhesion events.     

E. coli adhesion to silica in the presence of humic acid

The influence of humic acid on the adhesion of Escherichia coli to silica particles or glass surfaces was investigated. After adsorbing various amounts of humic acid to the particles or surfaces, bacteria were added to the sample and allowed to adhere. For the silica particles the number of bacteria-particle couplets formed were counted from video microscopy images. For the glass surfaces, a differential electrophoresis force was applied, and the force required to detach the bacteria was quantified. These experiments showed a slight increase in the number of couplets formed in the presence of humic acid, and also showed a slight increase in the force required for detachment of the bacteria. Although an increase in adhesion number and strength was measured, the magnitude of the increase was small, indicating that humic acid plays a small role in bacterial adhesion to silica or glass surfaces.     

Quantitative and morphological analysis of biofilm formation on self-assembled monolayers

In spite of intensive studies over the past two decades, the influence of surface properties on bacterial adhesion and biofilm formation remains unclear, particularly on late steps. In order to contribute to the elucidation of this point, we compared the impact of two different substrates on the formation of bacterial biofilm, by analysing bacterial amount and biofilm structure on hydrophilic and hydrophobic surfaces. The surfaces were constituted by NH₂- and CH₃-terminated self-assembled monolayers (SAMs) on silicon wafers, allowing to consider only the surface chemistry influence because wafers low roughness. A strain of Escherichia coli K12, able to produce biofilm on abiotic surfaces, was grown with culture durations varying from 4 h to 336 h on both types of substrates. The amount of adhered bacteria was determined after detachment by both photometry at 630 nm and direct counting under light microscope, while the spatial distribution of adhered bacteria was observed by fluorescence microscopy. A general view of our results suggests a little influence of the surface chemistry on adherent bacteria amount, but a clear impact on dynamics of biofilm growth as well as on biofilm structure. This work points out how surface chemistry of substrates can influence the bacterial adhesion and the biofilm formation.     

Structural Features of the Algal Cell Determine Adhesion Behavior at a Charged Interface

We aimed to examine the effects of algal structural features on adhesion at a charged interface. Results showed that algae with a glycocalyx, and with a cellulose amphiesma adhered at a charged interface at species-specific potential ranges. Algae, encased with a calcite-encrusted theca, and with an organosilicate cell wall, did not adhere to the interface. These differences in the amperometrically determined adhesion behavior of algal cells are in agreement with reported cell mechanical properties. Critical interfacial tensions of adhesion show differences between the studied soft algal cells as a consequence of their distinct cell barrier structure, composition, and properties.     

Cranberry derived proanthocyanidins reduce bacterial adhesion to selected biomaterials

Catheter associated urinary tract infections (CAUTI) linked with the uropathogens Escherichia coli (E. coli) and Enterococcus faecalis (E. faecalis) account for the majority of nosocomial infections acquired in the clinical environment. Because these infections develop following initial adhesion of the bacterial pathogens to the catheter surface, there is increased interest in developing effective methods to inhibit attachment of cells to biomaterials used in the manufacture of indwelling devices. High molecular weight proanthocyanidins (PAC) extracted from the North American cranberry (Vaccinium macrocarpon) were examined for their potential to reduce the initial adhesion of uropathogenic bacteria (E. coli CFT073 and E. faecalis 29212) to two model biomaterials, poly(vinyl chloride) (PVC) and polytetrafluoroethylene (PTFE). Well-controlled experiments conducted in a parallel-plate flow chamber (PPFC) demonstrated decreased attachment of both bacteria to PVC and PTFE when either the bacteria, biomaterial or both surfaces were treated with PAC. Most significant inhibition of bacterial adhesion was observed for the condition where both the bacteria and biomaterial surfaces were coated with PAC. Additional experiments conducted with nonbiological model particles demonstrate comparable extents of adhesion inhibition, supporting a nonbiospecific mechanism of PAC action. The results of this study are promising for the implementation of PAC in the clinical milieu for prevention of device associated infection as the proposed functional modification is independent of antibacterial mechanisms that may give rise to resistant strains.     

Molded polyethylene glycol microstructures for capturing cells within microfluidic channels

The ability to control the deposition and location of adherent and non-adherent cells within microfluidic devices is beneficial for the development of micro-scale bioanalytical tools and high-throughput screening systems. Here, we introduce a simple technique to fabricate poly(ethylene glycol)(PEG) microstructures within microfluidic channels that can be used to dock cells within pre-defined locations. Microstructures of various shapes were used to capture and shear-protect cells despite medium flow in the channel. Using this approach, PEG microwells were fabricated either with exposed or non-exposed substrates. Proteins and cells adhered within microwells with exposed substrates, while non-exposed substrates prevented protein and cell adhesion (although the cells were captured inside the features). Furthermore, immobilized cells remained viable and were stained for cell surface receptors by sequential flow of antibodies and secondary fluorescent probes. With its unique strengths in utility and control, this approach is potentially beneficial for the development of cell-based analytical devices and microreactors that enable the capture and real-time analysis of cells within microchannels, irrespective of cell anchorage properties.     

Effect of interfacial proteins on osteoblast-like cell adhesion to hydroxyapatite nanocrystals

A quartz crystal microbalance with dissipation (QCM-D) technique was employed to detecting the protein adsorption and subsequent osteoblast-like cell adhesion to hydroxyapatite (HAp) nanocrystals. The interfacial phenomena with the preadsorption of three proteins (albumin (BSA), fibronectin (Fn), and collagen (Col)), the subsequent adsorption of fetal bovine serum (FBS), and the adhesion of the cells were investigated. The QCM-D measured the frequency shift (Δf) and dissipation energy shift (ΔD), and the viscoelastic properties of the adlayers were evaluated using ΔD-Δf plot and Voigt-based viscoelastic model. The Col adsorption significantly showed higher Δf, ΔD, elasticity, and viscosity values as compared to the BSA and Fn adsorption, and the subsequent FBS adsorption depended on the preadsorbed proteins. The ΔD-Δf plot of the cell adhesion also showed a different behavior depending on the surfaces, and the Fn- and Col-modified surfaces showed the rapid mass and ΔD changes by forming the viscous interfacial layers with cell adhesion, indicating that the processes were affected by the cellular reaction through the extracellular matrix (ECM) proteins. The confocal laser scanning microscope images of adherent cells showed a different morphology and pseudopod on the surfaces. The cells adhered to the surfaces modified with the Fn and Col had significantly uniaxially expanded shapes and fibrous pseudopods, and those modified with the BSA had a round shape. Therefore, the different cell-protein interactions would cause the arrangement of the ECM and the cytoskeleton changes at the interfaces, and these phenomena were successfully detected by the QCM-D and Voigt-based model.     

Adhesion of Candida albicans and Candida dubliniensis to acrylic and hydroxyapatite

The aim of this work was to compare the ability of strains of Candida albicans and Candida dubliniensis to adhere to acrylic and hydroxyapatite (HAP). In order to interpret the adhesion results, the surface properties of cells and materials were determined. Surface tension components (polar and apolar) and hydrophobicity were calculated through contact angle measurement and the elemental composition was determined by X-ray photoelectron spectroscopy (XPS). The results showed no significant differences in the number of adhered cells of both species to acrylic and hydroxyapatite. This was corroborated by the similarities in their surface properties and elemental composition. For both species, the adhesion to acrylic increased in the presence of artificial saliva due to the increase in the electron-donor capacity of this material. In the absence of artificial saliva, the number of adhered cells to HAP was greater than to acrylic, on account of the higher number of electron-donor groups of HAP. Hydrophobicity played a minor role in the adhesion process of both candidal species. Conversely, Lewis acid–base interactions seamed to govern this phenomenon.     

Physicochemical aspects of microbial adhesion — Influence of antibody adsorption on the deposition ofStreptococcus sobrinus in a parallel-plate flow chamber

Deposition of the oral bacteriumStreptococcus sobrinus HG977 onto glass (water contact angle 0°) and onto FEP-Teflon (fluoroethylenepropylene; water contact angle 110°) was studied in a parallel-plate flow chamber in the presence and absence of polyclonal antibodies (pAb) and monoclonal antibodies (mAbs) adsorbed onto the cells. The zeta potentials of the bacteria ranged from −7.1 to −8.5 mV at pH 6.8 and were not affected by the presence of pAb or mAbs. Hydrophobicity (by water contact angles) increased from 30° (no antibodies) to 88° in the presence of pAb adsorbed onto the bacterial cell surface. The untreatedS. sobrinus had a greater tendency to adhere to glass (44.5 × 10⁶ cm⁻²) than to FEP-Teflon (18.3 × 10⁶ cm⁻²), in accordance with thermodynamic modelling. After preincubation ofS. sobrinus with pAb, its clear preference for adhesion to glass disappeared as expected from its increased hydrophobicity. Although forS. sobrinus preincubated with OMVU10 no difference was found in hydrophobicity in comparison to the untreated bacteria, the number of bacteria adhering to glass decreased to 10.2 ¢ 10⁶ cm⁻². Formation of bacterial aggregates was found whenS. sobrinus, preincubated with pAb or OMVU10, adhered to glass and FEP. This was also observed when untreated bacteria adhered to glass coated with OMVU10, or to FEP coaled with OMVU10 or pAb. Adhesion in these experiments is therefore thought to occur via near-neighbour collection induced by the presence of pAb or mAbs. Low numbers of bacteria were removed from glass after draining the flow cell, whereas high numbers of untreated bacteria and bacteria preincubated with OMVU10 were removed from FEP.S. sobrinus cells preincubated with pAb were not removed but piled up. It was concluded that the adhesion of untreatedS. sobrinus andS. sobrinus preincubated with pAb is in accordance with thermodynamic modelling, based on the overall wettability of the cell surfaces, whereas the adhesion ofS. sobrinus preincubated with OMVU10 may be through localized interactions, not expressed in overall surface properties.     

Surface characterization of three marine bacterial strains by Fourier transform IR, X-ray photoelectron spectroscopy, and time-of-flight secondary-ion mass spectrometry, correlation with adhesion on stainless steel surfaces

Adhesion of bacterial strains on solid substrates is likely related to the properties of the outer shell of the micro-organisms. Aiming at a better understanding and control of the biofilm formation in seawater, the surface chemical composition of three marine bacterial strains was investigated by combining Fourier transform IR spectroscopy, X-ray photoelectron spectroscopy (XPS), and time-of-flight secondary-ion mass spectrometry (ToF-SIMS). The D41 strain surface showed evidence of proteins, as deduced from the NH2 and NCO XPS and ToF-SIMS fingerprints; this strain was found to adhere to stainless steel, glass, or Teflon surfaces in a much higher quantity (2 orders of magnitude) than the two other ones, DA and D01. The latter are either enriched in COOH or sulfates, and this makes them more hydrophilic and less adherent to all substrates. Correlations with physicochemical properties and adhesion seem to demonstrate the role of the external layer composition, in particular the role of proteins more than that of hydrophobicity, on their adhesion abilities.     

The quartz crystal microbalance: a new tool for the investigation of the bioadhesion of diatoms to surfaces of differing surface energies

Diatoms are a major component of the biofoul layer found on modern low-surface-energy, 'foul release' coatings. While diatoms adhere more strongly to hydrophobic, as opposed to hydrophilic, surfaces, surprisingly little is known of the chemical composition of their adhesives. Even less is known about the underlying processes that characterize the interaction between the adhesive and a given surface, including those of differing wettability. Using the quartz crystal microbalance with dissipation monitoring (QCM-D), we examined differences in the viscoelastic properties of the extracellular adhesives produced by the marine diatoms Amphora coffeaeformis Cleve and Craspedostauros australis Cox interacting with surfaces of differing wettability; 11-mercaptoundecanoic acid (MUA) that is hydrophilic and 1-undecanethiol (UDT) that is hydrophobic. While the overall delta f/delta D ratios were slightly different, the trends were the same for both diatom species, with the layer secreted upon UDT to be more viscoelastic and far more consistent over several experiments, compared to that on MUA which was less viscoelastic and demonstrated far more variability between experiments. While the nature of the parameter shifts for C. australis were the same for both surfaces, A. coffeaeformis cells settling upon UDT illustrated significant positive f and D shifts during the initial stages of cell settlement and adhesion to the surface. Further experiments revealed the parameter shifts to occur only during the initial adhesion of cells upon the pristine virgin UDT surface. The mechanism behind these parameter responses was isolated to the actin-myosin/adhesion complex (AC), using the myosin inhibitor 2,3-butanedione 2-monoxime (BDM) to remove the cells ability to 'pull' on adhesive strands emanating from the cell raphe. The observations made herein have revealed that adhesives secreted by fouling diatoms differ significantly in their interaction with surfaces depending on their wettability, as well as illustrating the unique mechanics behind the adhesion of A. coffeaeformis upon hydrophobic surfaces, a mechanism that may contribute significantly to the cells success in colonizing hydrophobic surfaces.     

Oligonucleotide nanostructured surfaces: effect on Escherichia coli curli expression

Oligonucleotide model surfaces allowing independent variation of topography and chemical composition were designed to study the adhesion and biofilm growth of E.coli. Surfaces were produced by covalent binding of oligonucleotides and immobilization of nucleotide-based vesicles. Their properties were confirmed through a combination of fluorescence microscopy, XPS, ellipsometry, AFM and wettability studies at each step of the process. These surfaces were then used to study the response of three different strains of E.coli quantified in a static biofilm growth mode. This study led to convincing evidence that oligonucleotide-modified surfaces, independent of the topographical feature used in this study, enhanced curli expression without an increase in the number of adherent bacteria.     

Quantification of E. coli adhesion to polyamides and polystyrene with atomic force microscopy

Atomic force microscopy (AFM) was used to measure adhesion forces between E. coli bacteria and surfaces consisting of a series of polyamides and polystyrene, materials that are prominent in carpeting, upholstery, and other indoor surfaces. Bioparticle adhesion to such surfaces in air is poorly understood, yet these interactions are thought to play a key role in their accumulation and release as indoor air pollutants. The polymers employed were polyamide 6 (PA6), polyamide 6,6 (PA66), polyamide 12 (PA12) and polystyrene (PS). We report the interaction forces between immobilized E. coli and AFM tips coated with each polymer. The adhesion forces for the tip-bacterial interactions were in the range between 2.9 and 6.7 nN, which is of the same magnitude as the polymer-polymer interactions for the same series of polymers. Polystyrene had stronger adhesion with E. coli than any of the three polyamides, by an average factor of 1.4. The work of adhesion and Hamaker constants of the probe-surface interactions were calculated using a square-pyramid flat-surface model developed previously. A drag-force analysis suggests that model spheres with the same adhesion force as E. coli-poly(amide) (F approximately 4 nN) will remain adherent under normal foot traffic (F approximately 0.2 nN), but will release during vacuum cleaning (F>or=30 nN).