Home About us Contact
|
Home About us Contact | ||
|
|
||
Adhesion Forces (adhesion + force)
Selected AbstractsOral bacterial adhesion forces to biomaterial surfaces constituting the bracket,adhesive,enamel junction in orthodontic treatmentEUROPEAN JOURNAL OF ORAL SCIENCES, Issue 4 2009Li Mei Bacterial adhesion to biomaterial surfaces constituting the bracket,adhesive,enamel junction represents a growing problem in orthodontics, because bacteria can adversely affect treatment by causing demineralization of the enamel surface around the brackets. It is important to know the forces with which bacteria adhere to the surfaces of these junction materials, as the strength of these forces will determine how easy it will be to remove the bacteria. We compared the adhesion forces of five initially colonizing and four cariogenic strains of bacteria to an orthodontic adhesive, stainless steel, and enamel, with and without a salivary conditioning film. Adhesion forces were determined using atomic force microscopy and a bacterial probe. In the absence of a salivary conditioning film, the strongest bacterial adhesion forces occurred to the adhesive surface (,2.9 to ,6.9 nN), while adhesion forces to the enamel surfaces were lowest (,0.8 to ,2.7 nN). In the presence of a salivary conditioning film, adhesion forces were reduced strongly, to less than 1 nN, and the differences between the various materials were reduced. Generally, however, initial colonizers of dental hard surfaces presented stronger adhesion forces to the different materials (,4.7 and ,0.6 nN in the absence and presence of a salivary conditioning film, respectively) than cariogenic strains (,1.8 and ,0.5 nN). [source] Polymeric Nanohairs: Stooped Nanohairs: Geometry-Controllable, Unidirectional, Reversible, and Robust Gecko-like Dry Adhesive (Adv. Mater.ADVANCED MATERIALS, Issue 22 200922/2009) Kahp Suh, Hong Lee, and co-workers present on p. 2276 a simple, yet robust method for fabricating an array of stooped "nanohairs" by applying a proper choice of materials and post e-beam exposure, even for an aspect ratio of 10. The stooped nanohairs possess the unidirectional feature of frictional adhesion with a remarkably high adhesion force (,11 N cm,2). [source] Stooped Nanohairs: Geometry-Controllable, Unidirectional, Reversible, and Robust Gecko-like Dry AdhesiveADVANCED MATERIALS, Issue 22 2009Tae-il Kim A simple yet robust method to fabricate an array of stooped nanohairs is presented, with a proper choice of material and post e-beam exposure even for an aspect ratio of 10. The stooped nanohairs have the unidirectional feature of frictional adhesion with a remarkably high adhesion force (,11,N cm,2). [source] Influence of Binding-Site Density in Wet BioadhesionADVANCED MATERIALS, Issue 20 2008Jijun Wang The biomimetic adhesion polymer poly[(dopamine acrylamide)- co -(butylamine acrylamide)] shows strong adhesion even in aqueous environments. With single-molecule atomic force microscopy experiments, we show that the adhesion force does not depend on the density of the functional dopamine groups. [source] Understanding weathering of oil sands ores by atomic force microscopyAICHE JOURNAL, Issue 12 2009Sili Ren Abstract Effect of weathering on colloidal interactions between bitumen and oil sands solids was studied by atomic force microscopy (AFM). The change in bitumen chemistry due to weathering was found to have a negligible effect on the interactions of bitumen with solid particles. However, the increase in solid surface hydrophobicity due to ore weathering reversed the long-range interaction forces between bitumen and solids from repulsive to attractive with a corresponding increase in adhesion force. The measured force profiles between bitumen and various solids can be well fitted with the extended DLVO theory by considering an additional attractive force. The attractive long-range force and increased adhesion force make the separation of bitumen from solids more difficult and the attachment of fine solids on liberated bitumen easier, thereby leading to poor bitumen liberation and lower aeration efficiency. Such changes account for the observed poor processability of the weathered ores. © 2009 American Institute of Chemical Engineers AIChE J, 2009 [source] Atomic force microscopy study of the role of LPS O-antigen on adhesion of E. coliJOURNAL OF MOLECULAR RECOGNITION, Issue 5 2009Joshua Strauss Abstract The O-antigen is a highly variable component of the lipopolysaccharide (LPS) among Escherichia coli strains and is useful for strain identification and assessing virulence. While the O-antigen has been chemically well characterized in terms of sugar composition, physical properties such as O-antigen length of E. coli LPS have not been well studied, even though LPS length is important for determining binding of bacteria to biomolecules and epithelial cells. Atomic force microscopy (AFM) was used to characterize the physicochemical properties of the LPS of eight E. coli strains. Steric repulsion between the AFM tip (silicon nitride) and the E. coli cells was measured and modeled, to determine LPS lengths for three O157 and two O113 E. coli strains, and three control (K12) strains that do not express the O-antigen. For strains with an O-antigen, the LPS lengths ranged from 17,±,10 to 37,±,9,nm, and LPS length was positively correlated with the force of adhesion (Fadh). Longer lengths of LPS may have allowed for more hydrogen bonding between the O-antigen and silanol groups of the AFM silicon nitride tip, which controlled the magnitude of Fadh. For control strains, LPS lengths ranged from 3,±,2 to 5,±,3,nm, and there was no relationship between LPS length and adhesion force between the bacterium and the silicon nitride tip. In the absence of the O-antigen, we attributed Fadh to electrostatic interactions with lipids in the bacterial membrane. Copyright © 2009 John Wiley & Sons, Ltd. [source] Intrinsic adhesion force of lubricants to steel surfaceJOURNAL OF PHARMACEUTICAL SCIENCES, Issue 9 2004Jonghwi Lee Abstract The intrinsic adhesion forces of lubricants and other pharmaceutical materials to a steel surface were quantitatively compared using Atomic Force Microscopy (AFM). A steel sphere was attached to the tip of an AFM cantilever, and its adhesion forces to the substrate surfaces of magnesium stearate, sodium stearyl fumarate, lactose, 4-acetamidophenol, and naproxen were measured. Surface roughness varied by an order of magnitude among the materials. However, the results clearly showed that the two lubricants had about half the intrinsic adhesion force as lactose, 4-acetamidophenol, and naproxen. Differences in the intrinsic adhesion forces of the two lubricants were insignificant. The lubricant molecules were unable to cover the steel surface during AFM measurements. Intrinsic adhesion force can slightly be modified by surface treatment and compaction, and its tip-to-tip variation was not greater than its difference between lubricants and other pharmaceutical particles. This study provides a quantitative fundamental basis for understanding adhesion related issues. © 2004 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 93:2310,2318, 2004 [source] Stress Development Due to Capillary Condensation in Powder Compacts: A Two-Dimensional Model StudyJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 6 2000Stefan Lampenscherf A model experiment is presented to investigate the relationship between the humidity-dependent liquid distribution and the macroscopic stress in a partially wet powder compact. Therefore, films of monosized spherical particles were cast on silicon substrates. Using environmental SEM the geometry of the liquid necks trapped between particles was imaged as a function of relative humidity. Simultaneously the macroscopic stress in the substrate adhered particle film was measured by capacitive deflection measurement. The experimentally found humidity dependence of the liquid neck size and the macroscopic film stress are compared with model predictions. The circle,circle approximation is used to predict the size of the liquid necks between touching particles as a function of the capillary pressure. Using the modified Kelvin relation between capillary pressure and relative humidity, we consider the effect of an additional solute which may be present in the capillary liquid. The results of the stress measurement are compared with the model predictions for a film of touching particles in hexagonal symmetry. The contribution of the capillary interaction to the adhesion force between neighboring particles is calculated using the integrated Laplace equation. The resulting film stress can be approximated relating this capillary force to an effective cross section per particle. The experimentally found humidity dependence of the liquid neck size is in good agreement with the model predictions for finite solute concentration. The film stress corresponds to the model predictions only for large relative humidities and shows an unexpected increase at small values. As is shown with an atomic force microscope, the real structure of the particle,particle contact area changes during the wet/dry cycle. A solution/reprecipitation process causes surface heterogeneities and solid bridging between the particles. It is claimed that the existence of a finite contact zone between the particles gives rise to the unexpected increase of the stress at small relative humidities. [source] Continuous peripheral nerve block catheter tip adhesion in a rat modelACTA ANAESTHESIOLOGICA SCANDINAVICA, Issue 6 2006C. C. Buckenmaier III Background:, Continuous peripheral nerve block (CPNB) has been used effectively in combat casualties from Iraq and Afghanistan to provide surgical anesthesia and extended duration analgesia during evacuation and convalescence. Little information is available concerning catheter tip tissue reaction with prolonged use. Methods:, Forty-eight male Sprague-Dawley rats were assigned (12 per group) to one of four catheter tip designs provided by Arrow International: group A, 20-gauge catheter with three side-holes and a bullet-shaped tip; group B, 19-gauge StimuCathÔ catheter with coiled omni-port end with hemispherical distal tip; group C, 19-gauge catheter with single end-hole in conducting tip; group D, 19-gauge catheter with closed conducting tip with four side-holes. Following laparotomy, a randomly assigned catheter tip was sutured to the parietal peritoneal wall with the tip extending between experimental injuries created on the abdominal wall and cecum. After 7 days in situ, the catheter tips were removed from the adhesion mass using a force gauge, and the grams of force needed for removal were recorded. Results:, The mean force ± standard deviation values were 1.09 ± 1.21 g for group A, 21.20 ± 30.15 g for group B, 0.88 ± 1.47 g for group C and 1.60 ± 2.50 g for group D. The variation of each catheter group mean force compared with that of group B was significant (P < 0.05). There was no significant difference in adhesion force between groups A, C and D. Conclusions:, These results suggest that the manufactured design of a CPNB catheter tip can contribute to the adhesion of the tip in an intense inflammatory environment. This finding may have important clinical implications for CPNB catheters left in place for extended periods of time. [source] Atom force microscopic characterisation of the interaction forces between bovine serum albumin and cross-linked alkylated chitosan membranes in media of different pHPOLYMER INTERNATIONAL, Issue 12 2002Wen Guang Liu Abstract Butyl, octyl and hexadecyl moieties were introduced into chitosan. The adhesion of bovine serum albumin (BSA) onto glucose aldehyde-crosslinked alkylated chitosan membranes in pH media was investigated by probing the force-displacement curves with BSA-coated Atom force microscope (AFM) tips. The results indicated that, at the isoelectric point (IP), the sample membranes exhibited higher adhesion forces; and deviating from IP ie at pH 2, pH 6, the adhesion forces decreased. The adhesion forces at pH 2 are less than those at pH 6 due to the presence of electrostatic repulsive and attractive interactions, respectively. Measurements of the adhesion force confirmed quantitatively that the introduction of hydrophobic side-chains to chitosan can facilitate protein adsorption; however, longer flexible side-chains can depress protein adsorption to a certain degree. From an analyses of the adhesion forces, it is proposed that protein adsorption can be tuned by adjusting the lengths of the introduced side-alkyl moieties. © 2002 Society of Chemical Industry [source] Simulation of Thrombus Formation in Shear Flows Using Lattice Boltzmann MethodARTIFICIAL ORGANS, Issue 8 2009Masaaki Tamagawa Abstract This article describes the prediction of index of thrombus formation in shear blood flow by computational fluid dynamics with the Lattice Boltzmann Method (LBM), applying to backward-facing step flow, which is a simple model of shear flow in the rotary blood pumps and complicated geometry of medical fluid devices. Assuming that the blood flow is a multiphase flow composed of blood plasma and activated fibrinogen, the effects of surface tension and adhesion force to the wall were added to the LBM computational model. It was found that the thrombus formation in the backward-facing step flow occurred just after the reattachment point and behind the step. These results corresponded to our observation results of thrombus formation. For the thrombus formation in every case of blood flow to be predicted, effects of threshold level of physical parameters such as shear rate and adhesion force (effective distance from the wall) were estimated. Moreover, it was also found that the predicted adhesion point on the wall agrees with the visualization of thrombus formation by predicting proper thresholds. [source] Effects of defrosting period on mold adhesion force of epoxy molding compoundASIA-PACIFIC JOURNAL OF CHEMICAL ENGINEERING, Issue 2 2009Hwe-Zhong Chen Abstract In integrated circuit (IC) packaging, when epoxy-molding compound (EMC) is filled in the mold cavity and cured in the mold, adhesion occurs in the interface between EMC and the mold surface. Too large an adhesion force can cause many problems. For example, too large an adhesion force may damage an IC during ejection and cause the package to fail and thus lower the yield rate. To resolve mold adhesion problems, improving the mold design and applying suitable surface treatments, such as mold surface coating, are the common approaches. Applying suitable surface coating is a more popular and practical approach. Defrosting is a process to increase the frozen EMC temperature to room temperature, and to retain it at room temperature for some period before molding. It is a common practice to put EMC under required atmospheric environment during defrosting. It has been found by molding engineers that increased defrosting period will increase the frequency of mold cleaning. But there is no quantitative description on how much the adhesion force increases during the defrosting process. This paper describes the use of a semiautomatic EMC adhesion force test instrument to measure the normal adhesion force between the mold surface and EMC. By measuring the adhesion force, one can quantify how much adhesion force exists between EMC and the mold surface under different defrosting periods. The results show that it is best to use the EMC with 24,32 h of defrosting, to prevent excessive amount of mold adhesion force and it has been found that the adhesion force of the 24 h defrosting period will be 24% less than that of the 48 h defrosting period. Decreasing moisture absorption will decrease the increase in adhesion force for prolonged defrosting period cases. Copyright © 2008 Curtin University of Technology and John Wiley & Sons, Ltd. [source] Functional Adhesive Surfaces with "Gecko" Effect: The Concept of Contact Splitting,ADVANCED ENGINEERING MATERIALS, Issue 5 2010Marleen Kamperman Abstract Nature has developed reversibly adhesive surfaces whose stickiness has attracted much research attention over the last decade. The central lesson from nature is that "patterned" or "fibrillar" surfaces can produce higher adhesion forces to flat and rough substrates than smooth surfaces. This paper critically examines the principles behind fibrillar adhesion from a contact mechanics perspective, where much progress has been made in recent years. The benefits derived from "contact splitting" into fibrils are separated into extrinsic/intrinsic contributions from fibril deformation, adaptability to rough surfaces, size effects due to surface-to-volume ratio, uniformity of stress distribution, and defect-controlled adhesion. Another section covers essential considerations for reliable and reproducible adhesion testing, where better standardization is still required. It is argued that, in view of the large number of parameters, a thorough understanding of adhesion effects is required to enable the fabrication of reliable adhesive surfaces based on biological examples. [source] Oral bacterial adhesion forces to biomaterial surfaces constituting the bracket,adhesive,enamel junction in orthodontic treatmentEUROPEAN JOURNAL OF ORAL SCIENCES, Issue 4 2009Li Mei Bacterial adhesion to biomaterial surfaces constituting the bracket,adhesive,enamel junction represents a growing problem in orthodontics, because bacteria can adversely affect treatment by causing demineralization of the enamel surface around the brackets. It is important to know the forces with which bacteria adhere to the surfaces of these junction materials, as the strength of these forces will determine how easy it will be to remove the bacteria. We compared the adhesion forces of five initially colonizing and four cariogenic strains of bacteria to an orthodontic adhesive, stainless steel, and enamel, with and without a salivary conditioning film. Adhesion forces were determined using atomic force microscopy and a bacterial probe. In the absence of a salivary conditioning film, the strongest bacterial adhesion forces occurred to the adhesive surface (,2.9 to ,6.9 nN), while adhesion forces to the enamel surfaces were lowest (,0.8 to ,2.7 nN). In the presence of a salivary conditioning film, adhesion forces were reduced strongly, to less than 1 nN, and the differences between the various materials were reduced. Generally, however, initial colonizers of dental hard surfaces presented stronger adhesion forces to the different materials (,4.7 and ,0.6 nN in the absence and presence of a salivary conditioning film, respectively) than cariogenic strains (,1.8 and ,0.5 nN). [source] Temperature-Responsive Substrates: Adhesion and Mechanical Properties of PNIPAM Microgel Films and Their Potential Use as Switchable Cell Culture Substrates (Adv. Funct.ADVANCED FUNCTIONAL MATERIALS, Issue 19 2010Mater. Abstract Thermoresponsive poly(N -isopropylacrylamide) (PNIPAM) microgel films are shown to allow controlled detachment of adsorbed cells via temperature stimuli. Cell response occurs on the timescale of several minutes, is reversible, and allows for harvesting of cells in a mild fashion. The fact that microgels are attached non-covalently allows using them on a broad variety of (charged) surfaces and is a major advantage as compared to approaches relying on covalent attachment of active films. In the following, the microgels' physico-chemical parameters in the adsorbed state and their changes upon temperature variation are studied in order to gain a deeper understanding of the involved phenomena. By means of atomic force microscopy (AFM), the water content, mechanical properties, and adhesion forces of the microgel films are studied as a function of temperature. The analysis shows that these properties change drastically when crossing the critical temperature of the polymer film, which is the basis of the fast cell response upon temperature changes. Furthermore, nanoscale mechanical analysis shows that the films posses a nanoscopic gradient in mechanical properties. [source] Adhesion and Mechanical Properties of PNIPAM Microgel Films and Their Potential Use as Switchable Cell Culture SubstratesADVANCED FUNCTIONAL MATERIALS, Issue 19 2010Stephan Schmidt Abstract Thermoresponsive poly(N -isopropylacrylamide) (PNIPAM) microgel films are shown to allow controlled detachment of adsorbed cells via temperature stimuli. Cell response occurs on the timescale of several minutes, is reversible, and allows for harvesting of cells in a mild fashion. The fact that microgels are attached non-covalently allows using them on a broad variety of (charged) surfaces and is a major advantage as compared to approaches relying on covalent attachment of active films. In the following, the microgels' physico-chemical parameters in the adsorbed state and their changes upon temperature variation are studied in order to gain a deeper understanding of the involved phenomena. By means of atomic force microscopy (AFM), the water content, mechanical properties, and adhesion forces of the microgel films are studied as a function of temperature. The analysis shows that these properties change drastically when crossing the critical temperature of the polymer film, which is the basis of the fast cell response upon temperature changes. Furthermore, nanoscale mechanical analysis shows that the films posses a nanoscopic gradient in mechanical properties. [source] Detachment Lithography of Photosensitive Polymers: A Route to Fabricating Three-Dimensional StructuresADVANCED FUNCTIONAL MATERIALS, Issue 2 2010Junghoon Yeom Abstract A technique to create arrays of micrometer-sized patterns of photosensitive polymers on the surface of elastomeric stamps and to transfer these patterns to planar and nonplanar substrates is presented. The photosensitive polymers are initially patterned through detachment lithography (DL), which utilizes the difference in adhesion forces to induce the mechanical failure in the film along the edges of the protruded parts of the mold. A polydimethylsiloxane (PDMS) stamp with a kinetically and thermally adjustable adhesion and conformal contact can transfer the detached patterns to etched or curved substrates, as well as planar ones. These printed patterns remain photochemically active for further modification via photolithography, and/or can serve as resists for subsequent etching or deposition, such that photolithography can be used on highly nonconformal and nonplanar surfaces. Various 3D structures fabricated using the process have potential applications in MEMS (micro-electromechanical systems) sensors/actuators, optical devices, and microfluidics. [source] Designing Superhydrophobic Porous Nanostructures with Tunable Water AdhesionADVANCED MATERIALS, Issue 37 2009Yuekun Lai Basic principles of capillary-induced adhesion and roughness-enhanced hydrophobicity are utilized to design three superhydrophobic porous-nanostructure models whose adhesion forces ranged from strong to weak. The design idea is well-supported by experimental results, which indicated that adhesive forces may be tailored by modifying structural morphologies to manipulate solid,liquid contact behavior and air-pocket composition in open or sealed systems. [source] Intrinsic adhesion force of lubricants to steel surfaceJOURNAL OF PHARMACEUTICAL SCIENCES, Issue 9 2004Jonghwi Lee Abstract The intrinsic adhesion forces of lubricants and other pharmaceutical materials to a steel surface were quantitatively compared using Atomic Force Microscopy (AFM). A steel sphere was attached to the tip of an AFM cantilever, and its adhesion forces to the substrate surfaces of magnesium stearate, sodium stearyl fumarate, lactose, 4-acetamidophenol, and naproxen were measured. Surface roughness varied by an order of magnitude among the materials. However, the results clearly showed that the two lubricants had about half the intrinsic adhesion force as lactose, 4-acetamidophenol, and naproxen. Differences in the intrinsic adhesion forces of the two lubricants were insignificant. The lubricant molecules were unable to cover the steel surface during AFM measurements. Intrinsic adhesion force can slightly be modified by surface treatment and compaction, and its tip-to-tip variation was not greater than its difference between lubricants and other pharmaceutical particles. This study provides a quantitative fundamental basis for understanding adhesion related issues. © 2004 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 93:2310,2318, 2004 [source] KAI1 gene suppresses invasion and metastasis of hepatocellular carcinoma MHCC97-H cells in vitro and in animal modelsLIVER INTERNATIONAL, Issue 1 2008Jian-min Yang Abstract Background: Downregulation of KAI1 gene expression has been found in many types of cancer cells and is closely related to cancer invasion and metastasis. This study was aimed at investigating the effects and possible underlying mechanisms of KAI1 gene on invasion and metastasis of human hepatocellular carcinoma (HCC). Methods: The invasive ability, visco-elastic properties and cell adhesion forces were analysed in different HCC cells originating from the MHCC97-H cell line transfected with either the sense or the antisense KAI1 expression plasmid. Tumuorigenicity, metastatic abilities, extracellular matrix (ECM) and intercellular adhesion molecule-1 (ICAM-1) expression were also evaluated in the nude mouse models of the xenografted and orthotopic liver cancer cells. Results: Compared with their parental cells, in the HCC cells transfected with the sense KAI1 gene, the invasive ability in vitro was significantly decreased (P<0.01); the cellular elastic coefficients K1, K2 and , were significantly higher (P<0.05); the cells adhesion forces to fibronectin were significantly lower (P<0.01). The sense KAI1 gene transfection into the cancer cells also inhibited their invasion and lung metastasis in the orthotopic liver cancer nude mice. However, the opposite changes were observed in the HCC cells transfected with the antisense KAI1 gene. KAI1 gene transfection also affected ECM and ICAM-1 expression in the transplanted liver cancer. Conclusion: The KAI1 gene plays an important role in the invasion and metastasis of human HCC and its upregulation in HCC cells suppresses their invasive and metastatic abilities. KAI1 gene functioned as a metastasis inhibitor by regulating the HCC cell biophysical behaviours including aggregation, adhesion, motility and visco-elastic properties. [source] Optical, morphological and spectro- scopic characterization of graphene on SiO2PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 3-4 2010F. Giannazzo Abstract This work addresses the issue of determining the number of layers in few layers of graphene (FLG) flakes by cross-comparison of several techniques: optical microscopy (OM), atomic force microscopy (AFM) and micro-Raman (,R) spectroscopy. SL were preliminarily identified by ,R spectroscopy, which allows an unambiguous distinction between monolayers, bilayers and multilayers from the shape and relative intensity of the G and 2D peaks. It is demonstrated that the thickness of a SL measured by tapping mode AFM with respect to the SiO2 substrate is affected by an "offset" ,0.3 nm. This offset is explained in terms of the different adhesion forces between tip and SiO2 and tip and graphene measured by force spectroscopy curves. A calibration curve relating the height of a flake measured by AFM with the number of graphene layer was obtained. Finally, the optical contrast (OC) variations with FLG thickness was measured for different wavelengths in the visible range and for different oxide thicknesses (from 100 to 300 nm). OC was correlated with the number of layers (independently measured by AFM). (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Physicochemical Properties of Functional Surfaces in Pitchers of the Carnivorous Plant Nepenthes alata Blanco (Nepenthaceae)PLANT BIOLOGY, Issue 6 2006E. V. Gorb Abstract: Pitchers of the carnivorous plant Nepenthes alata are highly specialized organs adapted to attract, capture, and digest animals, mostly insects. They consist of several well distinguishable zones, differing in macro-morphology, surface microstructure, and functions. Since physicochemical properties of these surfaces may influence insect adhesion, we measured contact angles of non-polar (diiodomethane) and polar liquids (water and ethylene glycol) and estimated the free surface energy of 1) the lid, 2) the peristome, 3) the waxy surface of the slippery zone, and 4) the glandular surface of the digestive zone in N. alata pitchers. As a control, the external surface of the pitcher, as well as abaxial and adaxial surfaces of the leaf blade, was measured. Both leaf surfaces, both lid surfaces, and the external pitcher surface showed similar contact angles and had rather high values of surface free energy with relatively high dispersion component. These surfaces are considered to support strong adhesion forces based on the capillary interaction, and by this, to promote successful attachment of insects. The waxy surface is almost unwettable, has extremely low surface energy, and therefore, must essentially decrease insect adhesion. Both the peristome and glandular surfaces are wetted readily with both non-polar and polar liquids and have very high surface energy with a predominating polar component. These properties result in the preclusion of insect adhesion due to the hydrophilic lubricating film covering the surfaces. The obtained results support field observations and laboratory experiments of previous authors that demonstrated the possible role of different pitcher surfaces in insect trapping and retention. [source] Atom force microscopic characterisation of the interaction forces between bovine serum albumin and cross-linked alkylated chitosan membranes in media of different pHPOLYMER INTERNATIONAL, Issue 12 2002Wen Guang Liu Abstract Butyl, octyl and hexadecyl moieties were introduced into chitosan. The adhesion of bovine serum albumin (BSA) onto glucose aldehyde-crosslinked alkylated chitosan membranes in pH media was investigated by probing the force-displacement curves with BSA-coated Atom force microscope (AFM) tips. The results indicated that, at the isoelectric point (IP), the sample membranes exhibited higher adhesion forces; and deviating from IP ie at pH 2, pH 6, the adhesion forces decreased. The adhesion forces at pH 2 are less than those at pH 6 due to the presence of electrostatic repulsive and attractive interactions, respectively. Measurements of the adhesion force confirmed quantitatively that the introduction of hydrophobic side-chains to chitosan can facilitate protein adsorption; however, longer flexible side-chains can depress protein adsorption to a certain degree. From an analyses of the adhesion forces, it is proposed that protein adsorption can be tuned by adjusting the lengths of the introduced side-alkyl moieties. © 2002 Society of Chemical Industry [source] On the Thermodynamic Stability of Liquid Capillary BridgesTHE CANADIAN JOURNAL OF CHEMICAL ENGINEERING, Issue 5 2007Janet Aw Elliott Abstract Capillary condensation is important in the behaviour of various materials encountered in nature and in industrial processes. The behaviour of liquid capillary bridges has mostly been investigated from a mechanical perspective, with an emphasis on computing the relevant adhesion forces. In the present paper, a thermodynamic approach is used, computing the free energy of such systems (based on numerically constructed shapes of liquid bridges) in order to determine the nature and properties of their equilibrium states. The dependence of the thermodynamic equilibrium configurations on the geometry of the system is investigated, and comparisons are made with experimental findings reported in the literature. La condensation capillaire est importante dans le comportement de divers matériaux rencontrés dans la nature et dans les procédés industriels. Le comportement des ponts capillaires liquides a surtout été étudié d'un point de vue mécanique, l'accent étant mis sur le calcul par ordinateur des forces d'adhésion pertinentes. Dans le présent article, on utilise une approche thermodynamique utilisant le calcul par ordinateur de l'énergie libre de tels systèmes (d'après les formes numériquement construites des ponts liquides), dans le but de déterminer la nature et les propriétés de leurs états d'équilibre. La dépendance des configurations d'équilibre thermodynamique sur la géométrie du système est étudiée, et des comparaisons sont faites avec les résultats expérimentaux présentés dans la littérature scientifique. [source] Expression of Functional Recombinant Mussel Adhesive Protein Type 3A in Escherichia coliBIOTECHNOLOGY PROGRESS, Issue 3 2005Dong Soo Hwang Mussel adhesive proteins, including the 20-plus variants of foot protein type 3 (fp-3), have been suggested as potential environmentally friendly adhesives for use in aqueous conditions and in medicine. Here we report the novel production of a recombinant Mytilus galloprovincialis foot protein type 3 variant A (Mgfp-3A) fused with a hexahistidine affinity ligand in Escherichia coli and its ,99% purification with affinity chromatography. Recombinant Mgfp-3A showed a superior purification yield and better apparent solubility in 5% acetic acid (prerequisites for large-scale production and practical use) compared to those of the previously reported recombinant M. galloprovincialis foot protein type 5 (Mgfp-5). The adsorption abilities and adhesion forces of purified recombinant Mgfp-3A were compared with those of Cell-Tak (a commercial mussel extract adhesive) and recombinant Mgfp-5 using quartz crystal microbalance analysis and modified atomic force microscopy, respectively. These assays showed that the adhesive ability of recombinant Mgfp-3A was comparable to that of Cell-Tak but lower than that of recombinant Mgfp-5. Collectively, these results indicate that recombinant Mgfp-3A may be useful as a commercial bioadhesive or an adhesive ingredient in medical or underwater environments. [source] | |||||||||||||||||||