Effect of Microscale Contact State of Polyurethane Surface on Adhesion and Friction

The effect of microscale contact of rough surfaces on the adhesion and friction under negative normal forces was experimentally investigated. The adhesive force of single point contact - sapphire ball to flat polyurethane did not vary with the normal force. With rough surface contact, which was assumed to be a great number of point contacts, the adhesive force increased logarithmically with the normal force. Under negative normal force adhesive state, the tangential force （more than hundred mN） were much larger than the negative normal force （several mN） and increased with the linear decrease of negative normal force. The results reveal why the gecko＇s toe must slide slightly on the target surface when it makes contact on a surface and suggest how a biomimetic gecko foot might be designed.     

The Effects of Leaf Roughness,Surface Free Energy and Work of Adhesion on Leaf Water Drop Adhesion

The adhesion of water droplets to leaves is important in controlling rainfall interception, and affects a variety of hydrological processes. Leaf water drop adhesion (hereinafter, adhesion) depends not only on droplet formulation and parameters but also on the physical (leaf roughness) and physico-chemical (surface free energy, its components, and work-of-adhesion) properties of the leaf surface. We selected 60 plant species from Shaanxi Province, NW China, as experimental materials with the goal of gaining insight into leaf physical and physico-chemical properties in relation to the adhesion of water droplets on leaves. Adhesion covered a wide range of area, from 4.09 to 88.87 g/m² on adaxial surfaces and 0.72 to 93.35 g/m² on abaxial surfaces. Distinct patterns of adhesion were observed among species, between adaxial and abaxial surfaces, and between leaves with wax films and wax crystals. Adhesion decreased as leaf roughness increased (r =  −0.615, p = 0.000), but there were some outliers, such as Salix psammophila and Populus simonii with low roughness and low adhesion, and the abaxial surface of Hyoscyamus pusillus and the adaxial surface of Vitex negundo with high roughness and high adhesion. Meanwhile, adhesion was positively correlated with surface free energy (r = 0.535, p = 0.000), its dispersive component (r = 0.526, p = 0.000), and work of adhesion for water (r = 0.698, p = 0.000). However, a significant power correlation was observed between adhesion and the polar component of surface free energy (p = 0.000). These results indicated that leaf roughness, surface free energy, its components, and work-of-adhesion for water played important roles in hydrological characteristics, especially work-of-adhesion for water.     

Adhesion of Macroconidia to the Plant Surface and Virulence of Nectria haematococca

To study spore attachment of the cucurbit pathogen Nectria haematococca (anamorph, Fusarium solani f. sp. cucurbitae), mutants with adhesion-deficient macroconidia were isolated. The adhesion-deficient mutants were selected after treatment with N-methyl-N′ -nitro-N-nitrosoguanidine followed by repeated enrichment for macroconidia which did not attach to polystyrene. Two independently derived mutants produced macroconidia with an approximately 50% reduction in attachment to polystyrene and to zucchini fruits. When macroconidia were inoculated into wounded zucchini fruits, the adhesion-deficient mutants were as virulent as the wild-type strain. However, in disease assays in which macroconidia were deposited onto the surface of unwounded zucchini, the mutants were less virulent than the wild type. Thus, adhesion of N. haematococca macroconidia to its host surface appears to be a virulence factor.     

A Role for the Disintegrin Domain of Cyritestin, a Sperm Surface Protein Belonging to the ADAM Family, in Mouse Sperm–Egg Plasma Membrane Adhesion and Fusion

Sperm–egg plasma membrane fusion is preceded by sperm adhesion to the egg plasma membrane. Cell–cell adhesion frequently involves multiple adhesion molecules on the adhering cells. One sperm surface protein with a role in sperm–egg plasma membrane adhesion is fertilin, a transmembrane heterodimer (α and β subunits). Fertilin α and β are the first identified members of a new family of membrane proteins that each has the following domains: pro-, metalloprotease, disintegrin, cysteine-rich, EGF-like, transmembrane, and cytoplasmic domain. This protein family has been named ADAM because all members contain a disintegrin and metalloprotease domain. Previous studies indicate that the disintegrin domain of fertilin β functions in sperm–egg adhesion leading to fusion. Full length cDNA clones have been isolated for five ADAMs expressed in mouse testis: fertilin α, fertilin β, cyritestin, ADAM 4, and ADAM 5. The presence of the disintegrin domain, a known integrin ligand, suggests that like fertilin β, other testis ADAMs could be involved in sperm adhesion to the egg membrane. We tested peptide mimetics from the predicted binding sites in the disintegrin domains of the five testis-expressed ADAMs in a sperm–egg plasma membrane adhesion and fusion assay. The active site peptide from cyritestin strongly inhibited (80–90%) sperm adhesion and fusion and was a more potent inhibitor than the fertilin β active site peptide. Antibodies generated against the active site region of either cyritestin or fertilin β also strongly inhibited (80–90%) both sperm–egg adhesion and fusion. Characterization of these two ADAM family members showed that they are both processed during sperm maturation and present on mature sperm. Indirect immunofluorescence on live, acrosome-reacted sperm using antibodies against either cyritestin or fertilin β showed staining of the equatorial region, a region of the sperm membrane that participates in the early steps of membrane fusion. Collectively, these data indicate that a second ADAM family member, cyritestin, functions with fertilin β in sperm–egg plasma membrane adhesion leading to fusion.     

Effect of Temperature on Adhesion of Vibrio Strain AK-1 to Oculina patagonica and on Coral Bleaching

Laboratory aquarium experiments demonstrated that Vibrio strain AK-1 caused rapid and extensive bleaching of the coral Oculina patagonica at 29 degrees C, slower and less-complete bleaching at 23 degrees C, and no bleaching at 16 degrees C. At 29 degrees C, the application of approximately 100 Vibrio strain AK-1 cells directly onto the coral caused 50 and 83% bleaching after 10 and 20 days, respectively. At 16 degrees C, there was no bleaching, even with an initial inoculum of 1.2 x 10 bacteria. To begin to understand the effect of seawater temperature on bleaching of O. patagonica by Vibrio strain AK-1, adhesion of the bacteria to the coral as a function of temperature was studied. Inoculation of 10Vibrio strain AK-1 organisms into flasks containing 20 ml of seawater at 25 degrees C and a fragment of O. patagonica resulted in net levels of bacterial adhesion to the coral of 45, 78, and 84% after 2, 6, and 8 h, respectively. The adhesion was inhibited 65% by 0.001% d-galactose and 94% by 0.001% methyl-beta-d-galactopyranoside (beta-M-Gal). After the incubation of Vibrio strain AK-1 with the coral for 6 h, 42% of the input bacteria were released from the coral with 0.01% beta-M-Gal, compared to less than 0.2% when beta-M-Gal was present during the adhesion step. Adhesion did not occur when Vibrio strain AK-1 was grown at 16 degrees C, regardless of whether the corals were maintained at 16 or 25 degrees C, whereas bacteria grown at 25 degrees C adhered to corals maintained at 16 or 25 degrees C. Bacteria grown at 25 degrees C adhered avidly to Sepharose beads containing covalently bound beta-d-galactopyranoside but failed to bind if grown at 16 degrees C. These data suggest that elevated seawater temperatures may cause coral bleaching by allowing for the expression of adhesin genes of Vibrio strain AK-1.     

Particle Assemblies in the Plasma Membrane of Tetrahymena: Relationship to Cell Surface Topography and Cellular Morphogenesis1

During a freeze-fracture electron microscopical study of the plasma membrane of Tetrahymena, several different types of organized particle assemblies were observed. Three of these were found only on the protoplasmic face and were localized in the anterior-ventral region of the cell. These consisted of plate-like arrays composed of 4–25 triplet rows of small 3–4 nm particles; long, paired linear arrays localized at the tops of cortical ridges and composed of 7–8 nm particles; and elongated tetragonal arrays located in the grooves between ridges and composed of approximately 10 nm particles. The distribution of these arrays is consistent with roles in cellular morphogenesis, chemoreception, or cell-cell pairing during conjugation. In addition, a unique particle track associated with the cytoproct (anal pore) was observed in the external face of the plasma membrane. Furthermore, the protoplasmic face of the plasma membrane is characterized by a high density of particles organized into localized microarrays, consisting of small paracrystals or strings, which exhibit a loose higher-order patterning most evident toward the anterior end of the cell. Particle distributions on the protoplasmic face do not appear to be significantly altered by conditions that cause clumping of alveolar membrane particles. Taken together, these observations are consistent with the idea that the proteins of the plasma membrane are highly ordered and relatively immobile and that the structure of the plasma membrane is regionally differentiated.     

During the Long Way to Mars: Effects of 520 Days of Confinement (Mars500) on the Assessment of Affective Stimuli and Stage Alteration in Mood and Plasma Hormone Levels

For future interplanetary manned spaceflight, mental issues, as well as physiological problems, must inevitably be considered and solved. Mars500 is a high-fidelity ground simulation experiment that involved 520 days of confined isolation for six multinational crewmembers. This experiment provided a good opportunity to perform psycho-physiological and psycho-social researches on such missions. To investigate emotional responses and psychological adaptation over long-term confinement, the International Affective Pictures System (IAPS) was selected as the visual emotional stimuli in this study. Additional data collected and analyzed included the Profile of Mood States (POMS) questionnaire and the levels of four types of plasma hormones: cortisol, 5-hydroxy tryptamine, dopamine, and norepinephrine. The results demonstrated an obvious bias on valence rating for unpleasant stimuli with time (p<0.05), and the correlation between psychological and biochemical data was identified (p<0.05). Overall, we concluded that the confined crew tended to assign positive ratings to negative pictures with time, which might be driven by a defensive system. There was a stage-changing pattern of psychological adaptation of the Mars500 crew, which is similar to the third-quarter phenomenon.     

Effect of the Erosion of Collector Surface on the Operation of a Pulse-Periodic Plasma Relativistic Microwave Generator

Plasma Physics Reports - The pulse-periodic operation regime of a plasma relativistic microwave generator is considered. The reasons for the increase of average frequency of the output microwave...     

Activin,a Grape Seed-derived Proanthocyanidin Extract,Reduces Plasma Levels of Oxidative Stress and Adhesion Molecules (ICAM-1, VCAM-1 and E-selectin) in Systemic Sclerosis

This study evaluated whether a new generation antioxidant Activin derived from the grape seed proanthocyanidins, could reduce the induction of the adhesion molecules as a result of inflammatory response in the plasma of systemic sclerosis (SSc) patients. SSc patients were divided into two groups: one group was treated with Activin, a grape seed‐derived proanthocyanidins, while the other group served as control. Patients were given Activin 100 mg/day orally for one month after which the blood samples were withdrawn from both groups of the patients. Blood was also taken from normal human volunteers. Plasma was obtained in fasting state between 8 to 9 A.M. from two groups of SSc patients and controls. Soluble adhesion molecules including ICAM‐1, VCAM‐1, E‐selectin and P‐selectin as well as malonaldehyde, a marker for oxidative stress, were measured. The results of our study demonstrated up‐regulation of these soluble adhesion molecules except for P‐selectin, in the plasma of the SSc patients compared to those obtained from human volunteers. Activin significantly attenuated the increased expression of these adhesion molecules. In addition, there was a significant increase in the amount of malondialdehyde formation in the plasma of the SSc patients, which was also attenuated by Activin. The results of this study demonstrated that Activin could reduce the inflammatory response and the oxidative stress developed in SSc patients.     

Effect of Colchicine,Vinblastine, and Cytochalasin B on Cell Surface Anionic Sites of Tritrichomonas foetus1

ABSTRACT. Drugs that interact with microtubules (colchicine and vinblastine) and microfilaments (cytochalasin B) partially inhibited cell growth and motility of Tritrichomonas foetus. Parasites incubated with these substances became rounded and cell division was blocked. Neither colchicine nor vinblastine disrupted the microtubules that form the peltar-axostylar system. Any one of these drugs interfered with the net negative surface charge of T. foetus as evaluated by determination of the cellular electrophoretic mobility (EPM). The decrease in the EPM of cytochalasin B-treated cells was caused by dimethylsulfoxide, which was used as solvent. Untreated cells as well as cytochalasin B-treated cells showed a uniform distribution of anionic sites on the plasma membrane as seen with cationized ferritin particles. In cells treated with colchicine or vinblastine the anionic sites were distributed in patches. These results are discussed in terms of participation of labile cytoplasmic microtubules and microfilaments in the control of the distribution of anionic sitecontaining macromolecules located on the cell surface of T. foetus.     

Effect of Hydrofluoric Acid Etching Time on Titanium Topography,Chemistry, Wettability,and Cell Adhesion

Titanium implant surface etching has proven an effective method to enhance cell attachment. Despite the frequent use of hydrofluoric (HF) acid, many questions remain unresolved, including the optimal etching time and its effect on surface and biological properties. The objective of this study was to investigate the effect of HF acid etching time on Ti topography, surface chemistry, wettability, and cell adhesion. These data are useful to design improved acid treatment and obtain an improved cell response. The surface topography, chemistry, dynamic wetting, and cell adhesiveness of polished Ti surfaces were evaluated after treatment with HF acid solution for 0, 2; 3, 5, 7, or 10 min, revealing a time-dependent effect of HF acid on their topography, chemistry, and wetting. Roughness and wetting increased with longer etching time except at 10 min, when roughness increased but wetness decreased. Skewness became negative after etching and kurtosis tended to 3 with longer etching time. Highest cell adhesion was achieved after 5–7 min of etching time. Wetting and cell adhesion were reduced on the highly rough surfaces obtained after 10-min etching time.     

ABCA1, ABCG1, and ABCG4 Are Distributed to Distinct Membrane Meso-Domains and Disturb Detergent-Resistant Domains on the Plasma Membrane

ATP-binding cassette A1 (ABCA1), ABCG1, and ABCG4 are lipid transporters that mediate the efflux of cholesterol from cells. To analyze the characteristics of these lipid transporters, we examined and compared their distributions and lipid efflux activity on the plasma membrane. The efflux of cholesterol mediated by ABCA1 and ABCG1, but not ABCG4, was affected by a reduction of cellular sphingomyelin levels. Detergent solubility and gradient density ultracentrifugation assays indicated that ABCA1, ABCG1, and ABCG4 were distributed to domains that were solubilized by Triton X-100 and Brij 96, resistant to Triton X-100 and Brij 96, and solubilized by Triton X-100 but resistant to Brij 96, respectively. Furthermore, ABCG1, but not ABCG4, was colocalized with flotillin-1 on the plasma membrane. The amounts of cholesterol extracted by methyl-β-cyclodextrin were increased by ABCA1, ABCG1, or ABCG4, suggesting that cholesterol in non-raft domains was increased. Furthermore, ABCG1 and ABCG4 disturbed the localization of caveolin-1 to the detergent-resistant domains and the binding of cholera toxin subunit B to the plasma membrane. These results suggest that ABCA1, ABCG1, and ABCG4 are localized to distinct membrane meso-domains and disturb the meso-domain structures by reorganizing lipids on the plasma membrane; collectively, these observations may explain the different substrate profiles and lipid efflux roles of these transporters.     

The Tetraspanin CD9 Influences the Adhesion, Spreading, and Pericellular Fibronectin Matrix Assembly of Chinese Hamster Ovary Cells on Human Plasma Fibronectin

The role of CD9 in cell adhesion and spreading on adhesive proteins was investigated using a transfected Chinese hamster ovary (CHO) cell system. CD9 cell surface expression resulted in reduced adhesion and increased spreading on fibronectin (Fn). Whereas mock-transfected (mock CHO) and na?ve CHO cells assumed a typical fibroblast spindle shape morphology, CD9-transfected (CD9-CHO) cells were polygonal with many filipodial projections and exhibited a twofold greater surface area. The spread morphology of CD9-CHO cells, but not mock CHO cells, was inhibited by PB1 mAb blockade of alpha(5)beta(1), suggesting that the coexpression of alpha(5)beta(1) and CD9 influenced cell activity on Fn. The second extracellular loop of CD9 was implicated in regulation of adhesion since reduced CD9-CHO cell adhesion on Fn was reversed by either anti-CD9 antibody ligation to the second extracellular loop or with cells expressing a CD9 mutant lacking the second extracellular loop domain. Using cell adhesion assays and ELISA, we demonstrated CD9 binding to the HEP2/IIICS region of Fn. Finally, CD9 expression resulted in a twofold reduction in Fn-rich pericellular matrix assembly. Our observations show that CD9 dramatically influences CHO cell interactions with Fn and suggest that CD9 has an important role in modulating cell-extracellular matrix interactions.     

Borrelia Burgdorferi Upregulates the Adhesion Molecules E-selectin, P-selectin, ICAM-1 and VCAM-1 on Mouse Endothelioma Cells in vitro

In order to obtain more information on processes leading to Borrelia burgdorferi-induced inflammation in the host, we have developed an in vitro model to study the upregulation of cell surface expression of adhesion molecules on endothelial cells by spirochetes. A mouse endothelioma cell line, derived from brain capillaries, bEnd3, was used as indicator population. bEnd3 cells were incubated with preparations of viable, inactivated or sonicated spirochetes and the expression of E-selectin, P-selectin, ICAM-1 and VCAM-1 was monitored by immunocytochemistry and quantified by cell surface ELISA. We show that all three spirochetal preparations are able to upregulate cell surface expression of E-selectin, P-selectin, ICAM-1 and VCAM-1 on bEnd3 cells in a dose-dependent manner. The kinetics of cell surface expression of the individual adhesion molecules in the presence of Borrelia burgdorferi showed maxima at about 50 h of incubation or later; this was distinct from results obtained with sonicated-preparations of Escherichia coli bacteria or with enterobacterial LPS where peak expression was observed between 4 h and 16 h. The fact that Borrelia burgdorferi does not contain conventional LPS suggests that the mode of induction of adhesion molecules on endothelial cells is influenced by the phenotype of bacteria. At the peak of spirochete-induced cell surface expression of adhesion molecules (≈50 h), bEnd3 cells were found to bind cells of a VLA-4⁺ B lymphoma line (L1-2) much more efficiently than untreated control cells. The binding of L1-2 cells to presensitized bEnd3 cells was significantly inhibited (more than 75%) in the presence of monoclonal antibodies to both VLA-4 and its endothelial counterreceptor VCAM-1. These findings demonstrate that Borrelia burgdorferi organisms are able to induce functionally active adhesion molecules on endothelial cells in vitro and suggest that E-selectin, P-selectin, ICAM-1 and VCAM-1 play an important role in the pathogenesis of spirochetal infection.     

The Effect of Tunicamycin on the Glucose Uptake,Growth, and Cellular Adhesion in the Protozoan Parasite Crithidia fasciculata

Crithidia fasciculata represents a very interesting model organism to study biochemical, cellular, and genetic processes unique to members of the family of the Trypanosomatidae. Thus, C. fasciculata parasitizes several species of insects and has been widely used to test new therapeutic strategies against parasitic infections. By using tunicamycin, a potent inhibitor of glycosylation in asparaginyl residues of glycoproteins (N-glycosylation), we demonstrate that N-glycosylation in C. fasciculata cells is involved in modulating glucose uptake, dramatically impacting growth, and cell adhesion. C. fasciculata treated with tunicamycin was severely affected in their ability to replicate and to adhere to polystyrene substrates and losing their ability to aggregate into small and large groups. Moreover, under tunicamycin treatment, the parasites were considerably shorter and rounder and displayed alterations in cytoplasmic vesicles formation. Furthermore, glucose uptake was significantly impaired in a tunicamycin dose-dependent manner; however, no cytotoxic effect was observed. Interestingly, this effect was reversible. Thus, when tunicamycin was removed from the culture media, the parasites recovered its growth rate, cell adhesion properties, and glucose uptake. Collectively, these results suggest that changes in the tunicamycin-dependent glycosylation levels can influence glucose uptake, cell growth, and adhesion in the protozoan parasite C. fasciculata.     

Borrelia Burgdorferi Upregulates the Adhesion Molecules E-selectin,P-selectin,ICAM-1 and VCAM-1 on Mouse Endothelioma Cells in vitro

In order to obtain more information on processes leading to Borrelia burgdorferi-induced inflammation in the host, we have developed an in vitro model to study the upregulation of cell surface expression of adhesion molecules on endothelial cells by spirochetes. A mouse endothelioma cell line, derived from brain capillaries, bEnd3, was used as indicator population. bEnd3 cells were incubated with preparations of viable, inactivated or sonicated spirochetes and the expression of E-selectin, P-selectin, ICAM-1 and VCAM-1 was monitored by immunocytochemistry and quantified by cell surface ELISA. We show that all three spirochetal preparations are able to upregulate cell surface expression of E-selectin, P-selectin, ICAM-1 and VCAM-1 on bEnd3 cells in a dose-dependent manner. The kinetics of cell surface expression of the individual adhesion molecules in the presence of Borrelia burgdorferi showed maxima at about 50 h of incubation or later; this was distinct from results obtained with sonicated-preparations of Escherichia coli bacteria or with enterobacterial LPS where peak expression was observed between 4 h and 16 h. The fact that Borrelia burgdorferi does not contain conventional LPS suggests that the mode of induction of adhesion molecules on endothelial cells is influenced by the phenotype of bacteria. At the peak of spirochete-induced cell surface expression of adhesion molecules (≈50 h), bEnd3 cells were found to bind cells of a VLA-4⁺ B lymphoma line (L1-2) much more efficiently than untreated control cells. The binding of L1-2 cells to presensitized bEnd3 cells was significantly inhibited (more than 75%) in the presence of monoclonal antibodies to both VLA-4 and its endothelial counterreceptor VCAM-1. These findings demonstrate that Borrelia burgdorferi organisms are able to induce functionally active adhesion molecules on endothelial cells in vitro and suggest that E-selectin, P-selectin, ICAM-1 and VCAM-1 play an important role in the pathogenesis of spirochetal infection.