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At least 1,099 records · Page 61Linked to original sources
PubMed1999

Liquid morphologies on structured surfaces: from microchannels to microchips

Liquid microchannels on structured surfaces are built up using a wettability pattern consisting of hydrophilic stripes on a hydrophobic substrate. These channels undergo a shape instability at a certain amount of adsorbed volume, from a homogeneous state with a spatially constant cross section to a state with a single bulge. This instability is quite different from the classical Rayleigh Plateau instability and represents a bifurcation between two different morphologies of constant mean curvature. The bulge state can be used to construct channel networks that could be used as fluid microchips or microreactors.

Journal Article↗
PubMed2001

Fast drop movements resulting from the phase change on a gradient surface.

The movement of liquid drops on a surface with a radial surface tension gradient is described here. When saturated steam passes over a colder hydrophobic substrate, numerous water droplets nucleate and grow by coalescence with the surrounding drops. The merging droplets exhibit two-dimensional random motion somewhat like the Brownian movements of colloidal particles. When a surface tension gradient is designed into the substrate surface, the random movements of droplets are biased toward the more wettable side of the surface. Powered by the energies of coalescence and collimated by the forces of the chemical gradient, small drops (0.1 to 0.3 millimeter) display speeds that are hundreds to thousands of times faster than those of typical Marangoni flows. This effect has implications for passively enhancing heat transfer in heat exchangers and heat pipes.

Journal Article↗
PubMed1983

Detection of microbial proteolytic activity by a cultivation plate assay in which different proteins adsorbed to a hydrophobic surface are used as substrates.

A screening technique for microbial proteases, the thin-layer enzyme assay cultivation technique, was developed. The inner surface of a polystyrene petri dish was coated with protein and then covered with a culture agar medium. The enzymes, produced during growth of the microorganisms, reach the protein-coated surface by diffusion in the agar. Degradation of the protein was visualized by condensation of water vapor on the surface after removal of the agar medium. The wettability of the enzyme-affected protein-coated polystyrene surface was decreased compared with the unaffected protein surface. Enzyme substrates used were fibrinogen, immunoglobulin G, egg albumin, human serum albumin, bovine serum albumin, hemoglobin, mucin, and gelatin. It was possible to use a variety of culture agar media, nonselective as well as selective, in the assay. The technique provides a sensitive, convenient, and inexpensive method for screening various microbial proteases. In addition, the technique can be used for screening proteolytic enzyme activity of specific microbial species in a mixed microbial sample as well as for studies of factors that influence the cultivation conditions for protease production and activity.

Bacteria↗
PubMed1983

Amino Acid assimilation and electron transport system activity in attached and free-living marine bacteria.

Amino acid assimilation and electron transport system activity of a marine Pseudomonas sp. was evaluated to determine whether the activity of bacteria attached to solid surfaces differed from that of free-living bacteria or bacteria which had been attached but subsequently desorbed from the substratum (detached bacteria). Bacteria were allowed to attach to glass and to a range of plastic surfaces (Thermanox, polyvinylidene fluoride, polyethylene, polytetrafluoroethylene). Microautoradiography and staining with a tetrazolium salt to demonstrate electron transport system activity were used to compare the activity of these organisms with that of free-living or detached cells. The water-wettability of the surfaces was evaluated by measuring the advancing contact angle (theta(A)) of water on each surface, to determine whether there was a relationship between activity and substratum hydrophilicity. There was an increase in the proportion of leucine-assimilating attached bacteria and in the proportion of attached cells demonstrating electron transport system activity with an increase in substratum theta(A), but the relationship between activity of attached and free-living cells depended on the substratum. Activity appeared to promote firm attachment, and detached bacteria assimilated fewer amino acids than did attached cells. There was no general effect of surfaces on attached bacterial activity, and attached cells may be more, or less, active than free-living cells, depending on the amino acid, its concentration, and substratum properties.

Journal Article↗
PubMed1994

Evaluation of some essential oils for their toxicity against fungi causing deterioration of stored food commodities.

During screening of essential oils for their antifungal activities against Aspergillus flavus, the essential oil of Cymbopogon citratus was found to exhibit fungitoxicity. The MIC of the oil was found to be 1,000 ppm, at which it showed its fungistatic nature, wide fungitoxic spectrum, nonphytotoxic nature, and superiority over synthetic fungicides, i.e., Agrosan G. N., Thiride, Ceresan, Dithane M-45, Agrozim, Bavistin, Emison, Thiovit, wettable sulfur, and copper oxychloride. The fungitoxic potency of the oil remained unaltered for 7 months of storage and upon introduction of high doses of inoculum of the test fungus. It was thermostable in nature with treatment at 5 to 100 degrees C. These findings thus indicate the possibility of exploitation of the essential oil of C. citratus as an effective inhibitor of storage fungi.

Aspergillus flavus↗
PubMed2000

Role of leaf surface sugars in colonization of plants by bacterial epiphytes.

The relationship between nutrients leached onto the leaf surface and the colonization of plants by bacteria was studied by measuring both the abundance of simple sugars and the growth of Pseudomonas fluorescens on individual bean leaves. Data obtained in this study indicate that the population size of epiphytic bacteria on plants under environmentally favorable conditions is limited by the abundance of carbon sources on the leaf surface. Sugars were depleted during the course of bacterial colonization of the leaf surface. However, about 20% of readily utilizable sugar, such as glucose, present initially remained on fully colonized leaves. The amounts of sugars on a population of apparently identical individual bean leaves before and after microbial colonization exhibited a similar right-hand-skewed distribution and varied by about 25-fold from leaf to leaf. Total bacterial population sizes on inoculated leaves under conditions favorable for bacterial growth also varied by about 29-fold and exhibited a right-hand-skewed distribution. The amounts of sugars on leaves of different plant species were directly correlated with the maximum bacterial population sizes that could be attained on those species. The capacity of bacteria to deplete leaf surface sugars varied greatly among plant species. Plants capable of supporting high bacterial population sizes were proportionally more depleted of leaf surface nutrients than plants with low epiphytic populations. Even in species with a high epiphytic bacterial population, a substantial amount of sugar remained after bacterial colonization. It is hypothesized that residual sugars on colonized leaves may not be physically accessible to the bacteria due to limitations in wettability and/or diffusion of nutrients across the leaf surface.

Carbohydrates↗
PubMed2002

Surface modifications created by using engineered hydrophobins.

Hydrophobins are small (ca. 100 amino acids) secreted fungal proteins that are characterized by the presence of eight conserved cysteine residues and by a typical hydropathy pattern. Class I hydrophobins self-assemble at hydrophilic-hydrophobic interfaces into highly insoluble amphipathic membranes, thereby changing the nature of surfaces. Hydrophobic surfaces become hydrophilic, while hydrophilic surfaces become hydrophobic. To see whether surface properties of assembled hydrophobins can be changed, 25 N-terminal residues of the mature SC3 hydrophobin were deleted (TrSC3). In addition, the cell-binding domain of fibronectin (RGD) was fused to the N terminus of mature SC3 (RGD-SC3) and TrSC3 (RGD-TrSC3). Self-assembly and surface activity were not affected by these modifications. However, physiochemical properties at the hydrophilic side of the assembled hydrophobin did change. This was demonstrated by a change in wettability and by enhanced growth of fibroblasts on Teflon-coated with RGD-SC3, TrSC3, or RGD-TrSC3 compared to bare Teflon or Teflon coated with SC3. Thus, engineered hydrophobins can be used to functionalize surfaces.

Amino Acid Sequence↗
PubMed2005

Use of a quartz crystal microbalance to investigate the antiadhesive potential of N-acetyl-L-cysteine.

The reduction of bacterial biofilm formation on stainless steel surfaces by N-acetyl-L-cysteine (NAC) is attributed to effects on bacterial growth and polysaccharide production, as well as an increase in the wettability of steel surfaces. In this report, we show that NAC-coated stainless steel and polystyrene surfaces affect both the initial adhesion of Bacillus cereus and Bacillus subtilis and the viscoelastic properties of the interaction between the adhered bacteria and the surface. A quartz crystal microbalance with dissipation was shown to be a powerful and sensitive technique for investigating changes in the applied NAC coating for initial cell surface interactions of bacteria. The kinetics of frequency and dissipation shifts were dependent on the bacteria, the life cycle stage of the bacteria, and the surface. We found that exponentially grown cells gave rise to a positive frequency shift as long as their cell surface hydrophobicity was zero. Furthermore, when the characteristics of binding between the cell and the surface for different growth phases were compared, the rigidity increased from exponentially grown cells to starved cells. There was a trend in which an increase in the viscoelastic properties of the interaction, caused by the NAC coating on stainless steel, resulted in a reduction in irreversibly adhered cells. Interestingly, for B. cereus that adhered to polystyrene, the viscoelastic properties decreased, while there was a reduction in adhered cells, regardless of the life cycle stage. Altogether, NAC coating on surfaces was often effective and could both decrease the initial adhesion and increase the detachment of adhered cells and spores. The most effective reduction was found for B. cereus spores, for which the decrease was caused by a combination of these two parameters.

Acetylcysteine↗
PubMed2005

A Hydrophobin of the chestnut blight fungus, Cryphonectria parasitica, is required for stromal pustule eruption.

Hydrophobins are abundant small hydrophobic proteins that are present on the surfaces of many filamentous fungi. The chestnut blight pathogen Cryphonectria parasitica was shown to produce a class II hydrophobin, cryparin. Cryparin is the most abundant protein produced by this fungus when grown in liquid culture. When the fungus is growing on chestnut trees, cryparin is found only in the fungal fruiting body walls. Deletion of the gene encoding cryparin resulted in a culture phenotype typical of hydrophobin deletion mutants of other fungi, i.e., easily wettable (nonhydrophobic) hyphae. When grown on the natural substrate of the fungus, however, cryparin-null mutation strains were unable to normally produce its fungal fruiting bodies. Although the stromal pustules showed normal development initially, they were unable to erupt through the bark of the tree. The hydrophobin cryparin thus plays an essential role in the fitness of this important plant pathogen by facilitating the eruption of the fungal fruiting bodies through the bark of its host tree.

Ascomycota↗
PubMed2000

Genetics of swarming motility in Salmonella enterica serovar typhimurium: critical role for lipopolysaccharide.

Salmonella enterica serovar Typhimurium can differentiate into hyperflagellated swarmer cells on agar of an appropriate consistency (0.5 to 0.8%), allowing efficient colonization of the growth surface. Flagella are essential for this form of motility. In order to identify genes involved in swarming, we carried out extensive transposon mutagenesis of serovar Typhimurium, screening for those that had functional flagella yet were unable to swarm. A majority of these mutants were defective in lipopolysaccharide (LPS) synthesis, a large number were defective in chemotaxis, and some had defects in putative two-component signaling components. While the latter two classes were defective in swarmer cell differentiation, representative LPS mutants were not and could be rescued for swarming by external addition of a biosurfactant. A mutation in waaG (LPS core modification) secreted copious amounts of slime and showed a precocious swarming phenotype. We suggest that the O antigen improves surface "wettability" required for swarm colony expansion, that the LPS core could play a role in slime generation, and that multiple two-component systems cooperate to promote swarmer cell differentiation. The failure to identify specific swarming signals such as amino acids, pH changes, oxygen, iron starvation, increased viscosity, flagellar rotation, or autoinducers leads us to consider a model in which the external slime is itself both the signal and the milieu for swarming motility. The model explains the cell density dependence of the swarming phenomenon.

Agar↗
PubMed2005

Self-propelled running droplets on solid substrates driven by chemical reactions.

We study chemically driven running droplets on a partially wetting solid substrate by means of coupled evolution equations for the thickness profile of the droplets and the density profile of an adsorbate layer. Two models are introduced corresponding to two qualitatively different types of experiments described in the literature. In both cases an adsorption or desorption reaction underneath the droplets induces a wettability gradient on the substrate and provides the driving force for droplet motion. The difference lies in the behavior of the substrate behind the droplet. In case I the substrate is irreversibly changed whereas in case II it recovers allowing for a periodic droplet movement (as long as the overall system stays far away from equilibrium). Both models allow for a non-saturated and a saturated regime of droplet movement depending on the ratio of the viscous and reactive time scales. In contrast to model I, model II allows for sitting drops at high reaction rate and zero diffusion along the substrate. The transition from running to sitting drops in model II occurs via a super- or subcritical drift-pitchfork bifurcation and may be strongly hysteretic implying a coexistence region of running and sitting drops.

Journal Article↗
PubMed2006

Slip vs. viscoelasticity in dewetting thin films.

Ultrathin polymer films on non-wettable substrates display dynamic features which have been attributed to either viscoelastic or slip effects. Here we show that in the weak- and strong-slip regime, effects of viscoelastic relaxation are either absent or essentially indistinguishable from slip effects. Strong slip modifies the fastest unstable mode in a rupturing thin film, which questions the standard approach to reconstruct the effective interface potential from dewetting experiments.

Journal Article↗
PubMed1987

Does aspirin damage canine gastric mucosa by reducing its surface hydrophobicity?

Intraluminally administered aspirin disrupts the gastric mucosal barrier in a pH-dependent manner and may do so by compromising the hydrophobic or nonwettable lining to the stomach. We examined the pH dependence and time-course of aspirin's effects on barrier integrity by measuring the aspirin-induced changes in surface wettability, potential difference (PD), and electrical resistance (R) of canine gastric mucosa mounted in Ussing chambers. Luminal surface hydrophobicity, as determined by contact angle (CA) measurements, and PD were reduced by acidic aspirin solutions but were not reduced by acidic solutions without aspirin (pH 2.6) or by aspirin solutions that were neutral or only mildly acidic (pH greater than 4.0). Significant reductions in CA were correlated well with the proportion of aspirin in its lipid-soluble undissociated form (r = 0.93, P less than 0.001). Acidified-aspirin solutions significantly reduced CA and PD after a 2.5-min incubation period. Significant reductions in R occurred 25 min after exposure to acidified aspirin. Morphological damage to the gastric epithelium was not apparent after a 5-min exposure to acidified aspirin but was conspicuous 30 min after aspirin treatment. Aspirin-induced reductions in CA were highly associated with decreases in mucosal PD in both the pH and time-dependent studies (r = 0.93 and r = 0.99, respectively, P less than 0.001). These data support the hypothesis that the undissociated form of aspirin compromises the protective nonwettable lining of the stomach and in doing so, disrupts the gastric mucosal barrier.

Animals↗
PubMed1979

Newborn northern fur seals (Callorhinus ursinus)--do they suffer from cold?

Several hundred thousand northern fur seals (C. ursinus) are born each summer during July at St. Paul Island in the Bering Sea. The weather in the area is usually cold, wet, and windy during the breeding season. At birth the pups are small (5--6 kg) and insulated only by a partly wettable pelt and a 2- to 4-mm layer of blubber. In air, the pups' lower critical temperature appears to be below the 6 degrees C 50-yr record low July temperature for the islands. During rainy weather much of the insulative value of the pelt is lost, and the pups, which already have a high resting metabolic rate of 3.5 W.kg-1, must increase heat production by shivering and/or nonshivering thermogenesis to maintain deep body temperature. The high level of metabolism (up to 18 W.kg-1) is supported by a very rich milk. The pups will, nevertheless, become hypothermic if their insulation is not improved through peripheral vasoconstriction and shedding of water from the pelt by periodic shudder. Even with these protections the newborn and very young pups are brought close to their limit of tolerance during rainy and windy days. Unfit pups are likely to succumb under such circumstances.

Adipose Tissue↗
PubMed1983

Contact-angle hysteresis induced by pulmonary surfactants.

Hydrophilic surfaces in the form of glass slides have been coated with monolayers of three of the major components of pulmonary surfactant, and the wettabilities of the resulting surfaces have been studied by applying a single drop of saline. As fluid was added and removed over successive cycles, there was much hysteresis between the contact angle measured by a goniometer and the location of the triple point. All three surfactants, especially dipalmitoyl lecithin, were found to impart antiwetting properties, with maximum (advancing) contact angles sometimes exceeding 90 degrees and minimum (receding) contact angles seldom less than 28 degrees. In all cases (216 cycles on 36 films) fluid receded to expose the dry subphase. The hysteresis loops agree well with a similar loop calculated from published data for a cat lung in which the pressure-volume cycle has been established for both liquid and air inflation. Contact-angle hysteresis is offered as a possible alternative to surface tension as the surface parameter primarily responsible for the interfacial contribution to compliance hysteresis in the excised lung.

Animals↗
PubMed2003

Enhanced biocompatibility for SAOS-2 osteosarcoma cells by surface coating with hydrophobic epoxy resins.

BACKGROUND AND AIMS: Implants for surgical needs are produced from different materials including metals, alloys, ceramics or polymers. Metal implants are preferred in those disciplines where sufficient mechanical strength is needed, including traumatology, orthopedic or dental surgery. Further, modern tissue engineering techniques require scaffold materials to generate shape and stability for in vitro generated transplants. However, the biocompatibility and surface contact of most implants or scaffold materials to vital bone or other tissues are not optimal. Therefore we investigated the biocompatibility of different polymer surfaces to an osteoblastic cell line as a function of wettability or hydrophobicity to describe some of the surface parameters influencing the cell to implant or cell to scaffold contact. METHODS: Glass slides were coated with different polymers and in some cases physically or chemically modified. SAOS-2 osteosarcoma cells were used for the biocompatibility tests on 16 different polymers and modifications thereof. The viability of the adherent cells was investigated by MTT assay. Commercially available tissue culture vessels served as controls. RESULTS: We report that excellent biocompatibility to SAOS-2 osteoblastic cells can be obtained with hydrophobic surfaces generated for instance by epoxy resins. Chemical modification of epoxy resin surfaces yielded even a further increased viability index surpassing the viability index obtained with cell culture vessels. CONCLUSION: We conclude that modified hydrophobic surfaces represent an interesting group of compounds for coating endoprosthetic implants or scaffolds for the purposes of tissue engineering.

Alloys↗
PubMed1986

Development of ocular mucin: scanning EM analysis.

Ocular mucin (mucus) development in the mouse was examined using several different fixatives and scanning electron microscopy. One of the fixatives, a picric acid--paraformaldehyde-glutaraldehyde (PA-P-G) preparation which fixes mucin at the adult mouse corneal surface, first demonstrated mucin at the surface of the pup cornea and conjunctiva at postnatal day 10. The mucus was scant, strand-like as well as granular in morphology and did not form smooth patches as in the adult. Thus, mucin is present at the ocular surface well before the mouse eye opens (day 14-15). Its presence is essential to ensure tear film stability, corneal wettability and possibly to protect the eye from bacterial and viral insult.

Animals↗
PubMed1996

Assessment of variability in some lysosomal and soluble enzyme activities in corneal epithelium from slaughterhouse bovine eyes.

The corneal epithelium was scraped from bovine eyes (Hereford or Holstein) within 3 h post mortem. The mitochondriallysosomal fraction of the cells was assayed for hexosaminidase (HEX) and acid phosphatase (AP), and the membrane-soluble fraction for lactate dehydrogenase (LDH) and leucine arylamidase (LAA) activity. Pairs of eyes with clear corneas showed variances (+/-1 SD, n = 10 pairs) of +/-62, +/-57, +/-72 and +/-31% in the four enzyme activities (HEX, AP, LDH, LAA). Selection based on age (corneal diameter) reduced the variance to +/-41, +/-37, +/-39 and +/-30%. Additional selection for corneal surface wettability reduced variances to +/-26, +/-21, +/-22 and +/-26% in the activities. The latency of the lysosomal enzymes (HEX, AP) increased substantially with eye selection.

Abattoirs↗