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Query: UMLS:C0001511 (Adhesion)
 5,955 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Adhesion of restorative and protective materials to dentin is an important requirement for operative and preventive dentistry. Wettability and roughness are dentin substrate conditions that are critical to establishing good adhesion. This study examined superficial and deep dentin for variations in water contact angle measurements and roughness for polished, etched, dehydrated, and rehydrated states. Superficial and deep dentin disks from 6 non-carious third molars were prepared for AFM (Atomic Force Microscope) observation, roughness measurement, and contact angle measurements following specific treatments: hydrated and polished, etched (10% H3PO4), dehydrated (desiccator for 24 hrs); and rehydrated (in water for 24 hrs). Contact angles were measured by means of the ADSA (Axisymmetric Drop Shape Analysis) technique with filtered and purified water of surface tension 72.79 ergs/cm2. The AFM was used to quantify the intertubular roughness. Mean and SD of roughness and contact angle were calculated for each dentin state, and two-way Repeated Measures ANOVA with Tukey's HSD multiple comparisons were performed at p < 0.05. Wetting and roughness both increased after etching, with roughness tending to increase further while wettability dramatically decreased after desiccation. After rehydration, water contact angle values were equivalent to those of the etched condition. Although intertubular roughness did not depend on depth, lower water contact angles were found for deep dentin. Depth and dehydration resulted in altered dentin substrates with exposed hydrophobic moieties that could interfere with bonding to hydrophilic primer coats.
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PMID:Acid-etching and hydration influence on dentin roughness and wettability. 1051 90

An atomic force microscope has been used to quantify directly the adhesion between single Aspergillus niger spores and freshly cleaved mica surfaces. The measurements used "spore probes" constructed by immobilizing a single spore at the apex of a tipless AFM cantilever. Adhesion was quantified from force-distance data for the retraction of the spore from the surface. Studies in NaCl solutions over a range of pH and electrolyte concentration showed that the decrease of long-range electrostatic repulsion with decreasing pH provided a contribution in increasing the overall adhesion, but the variation of such repulsion with ionic strength did not correlate with changes in the magnitude of adhesion. Specific interactions between appendages and protusions on the spore surface must play an important role in adhesion. The AFM spore probe technique provides a useful new method for evaluating the interactions of spores and surfaces. It has the potential to become a powerful asset for both fundamental studies and the assessment of new materials with low adhesion properties. Copyright 2000 Academic Press.
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PMID:Direct Quantification of Aspergillus niger Spore Adhesion in Liquid Using an Atomic Force Microscope. 1092 84

The aim of this paper was to determine the adhesion of two physico-chemically characterized bacterial strains to a surface hydrophilic (CL A, water contact angle 57 degrees) and hydrophobic (CL B, water contact angle 106 degrees) hydrogel contact lens (CL) with and without an adsorbed tear film in a parallel plate flow chamber. Hydrophobicity (by water contact angles), charge (by particulate microelectrophoresis) and elemental composition (by XPS) of the surfaces of seven bacterial strains were characterized, after which two strains were selected for further studies. On CL surfaces, hydrophobicity, elemental composition, and mean surface roughness (by AFM) were determined, as well as the protein composition of tear films adsorbed on these lenses (by sodium dodecylsulphate-polyacrylamide gel electrophoresis (SDS-PAGE)). Bacterial cell surfaces were relatively uncharged and water contact angles on lawns of different strains ranged from hydrophobic to hydrophilic. After adsorption of tear film components, N/C elemental surface concentrations increased on CL A and CL B and differences in water contact angles between both lenses reduced to range from 57 degrees (CL A) to 69 degrees (CL B). However, different protein compositions were inferred. The surface roughness of CL A increased from 4 to 13 nm. while it remained 16 nm for CL B. Adhesion of hydrophobic Pseudomonas aeruginosa #3 was more extensive than of hydrophilic Staphylococcus aureus 799, with no differences between both lenses. The hydrophobicity of P. aeruginosa #3 after cell surface damage decreased and its adhesion was reduced on CL A and strongly on CL B. In addition, passage of an air-liquid interface yielded more detachment of S. aureus 799 than of P. aeruginosa #3 from the CL surfaces. In conclusion, the hydrophobicity of CL surfaces dictates the composition of the adsorbed tear film and therewith plays an important role in bacterial adhesion to lenses. Adhesion of hydrophobic P. aeruginosa #3 was more tenacious than of hydrophilic S. aureus 799.
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PMID:Bacterial adhesion to surface hydrophilic and hydrophobic contact lenses. 1170 Jul 93

Mucins have been ascribed both pro- and anti-adhesive functions. To clarify how both functions can be embodied in the same molecule we studied the interaction of human ocular mucins with mica and with mucins deposited on mica. Adhesion energy and forces of interaction were evaluated as a function of speed of approach, dwell time at maximum extension, and presence of divalent cations in the imaging buffer. Mucins were tethered to an AFM gold-coated tip. Repeated cycles of approach and retract to mica revealed a large number of adhesions in each cycle. Adhesion energy (0.2-48 aJ) and detachment forces (0.1-4 nN) increased with the addition of Ni(II) ions, and with lengthening dwell time. Speed of approach made little difference to the interactions. Most detachments occurred less than 40 nm from the surface. Inter-detachment distances reflected the major periodicities of the mica basal plane. Short distances of interaction, magnitude of detachment forces, and imaging of mucins on SAM all suggest deformable compact mucin aggregates on the AFM tip. Inter-detachment distances suggest a large degree of interpenetration between neighboring molecules. Tip-tethered mucins did not adhere to mucins deposited on mica. This phenomenon is analogous with the nonadherence of the mucin gels on lids and on cornea during blinking.
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PMID:Exploring the molecular adhesion of ocular mucins. 1174 12

Polyethylene (PE) foils were modified by irradiation with Ar+ and Xe+ ions to different fluences and different physico-chemical properties of the irradiated PE were studied in relation to adhesion and proliferation of keratinocytes on the modified surface. Changes in the PE surface roughness were examined using the AFM technique, the production of conjugated double bonds and oxidized structures by UV-VIS and FTIR techniques respectively. The surface polarity was determined by measuring surface contact angle and two-point technique was used for the determination of PE sheet resistance. Adhesion and proliferation of keratinocytes was characterized using the MTT-test. The ion irradiation leads to creation of conjugated double bonds which, together with progressive carbonization, contribute to the observed decrease of sheet resistance. Oxidation of the irradiated PE surface layer during the ion implantation is observed. Besides oxidation, the PE surface polarity is affected by other factors. The observed increase of the PE surface roughness due to the ion irradiation is inversely proportional to the ion size. The adhesion and proliferation of keratinocytes on the ion irradiated PE is significantly higher than on the pristine PE. Distribution of results in keratinocyte cultivation and the number of cells is related to the ion fluence applied and to ion species as well.
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PMID:Adhesion and proliferation of keratinocytes on ion beam modified polyethylene. 1534 90

Molecular recognition imaging by AFM was extended to dual component protein films adsorbed on mica. AFM probes were functionalized by covalently linking polyclonal antibodies against fibrinogen. Adhesion mapping mode of AFM was used to generate both topographic images and adhesion images. The efficacy of the functionalized probes was first established by performing adhesion mapping on patterned dual component protein films formed by microcontact printing bovine serum albumin on a mica surface and then backfilling with fibrinogen. Next, adhesion mapping was done on randomly distributed two-component protein monolayers generated by sequential adsorption of submonolayer amounts of fibrinogen followed by backfilling with bovine serum albumin. The adhesion maps were used to generate binary recognition images where the specific and non-specific interactions were differentiated based on a statistically derived cut-off value. The surface coverage of fibrinogen obtained from the recognition image over the complete dual protein monolayer was similar to that obtained prior to backfilling with bovine serum albumin. The number of recognition events that were observed decreased by >80% after blocking the surface with anti-fibrinogen antibodies. This result demonstrated that the positive events in the recognition image were indeed specific antibody-fibrinogen interactions.
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PMID:Adhesion mode atomic force microscopy study of dual component protein films. 1569 72

The molecular interaction force of the intermonolayer hydrogen bonding between phenylurea groups on a probe tip and carboxyl groups in self-assembled monolayers was measured directly by means of atomic force microscopy in ethanol. Gold-coated AFM probe tips were modified chemically with 2-(N'-phenylureido)ethanethiol possessing a terminal urea moiety, which is a well-known powerful functionality for forming stable hydrogen bondings with neutral and anionic species. Adhesion force measurements were carried out on gold substrates coated with a COOH-terminated SAM composed of 6-mercaptohexanoic acid in ethanol using the phenylurea-functionalized probe tip. The adhesion force observed was decreased in the presence of H2PO4(-) in the measurement bath, indicating that the intermonolayer hydrogen bonding between the phenylurea moieties and carboxyl groups attached covalently to the probe tip and substrate, respectively, is suppressed by the anion added to the measurement solution. The specific hydrogen-bonding force was measured on binary mixed SAMs prepared by mixing 6-mercaptohexanoic acid with 1-hexanethiol. The individual hydrogen-bonding force between the phenylurea-modified tip and the binary mixed SAMs with various fractions of MHA was evaluated by repetitive force measurements and their statistical analyses by an autocorrelation method. We discuss the effect of diluting the COOH-terminated component in the mixed SAM on the adhesion force and the single force between the phenylurea and carboxyl groups in terms of competition between intermonolayer and intramonolayer hydrogen bonding.
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PMID:Effect of intramonolayer hydrogen bonding of carboxyl groups in self-assembled monolayers on a single force with phenylurea on an AFM probe tip. 1676 May 91

Scanning force microscopy has been used to probe the surface of the emerging pathogenic yeast Candida parapsilosis, in order to get insight into its surface structure and properties at submicrometer scales. AFM friction images eventually show patches with a very strong contrast, showing high lateral interaction with the tip. Adhesion force measurement also reveals a high normal interaction with the tip, and patches show extraordinarily high pull off values. The tip eventually sticks completely at the center of the patches. While an extraordinarily high interaction is measured by the tip at those zones, topographic images show extraordinarily flat topography over those zones, both of which characteristics are consistent with a liquid-like area. High resolution friction images show those zones to be surrounded by microfibrillar structures, concentrically oriented, of a mean width of about 25 nm, structures that become progressively less defined as we move away from the center of the patches. No structure can be appreciated inside the zones of maximum contrast. Also some helical or ribbon-like structure can be resolved from friction images. There is not only an ordered disposition of the microfibrillar structures, but also the adhesion force increases radially in the direction towards the center of the patches. These structures responsible for the high adhesion are thought to be incipient-emerging budding zones. Microfibrillar structures are thought to represent the first steps of chitin biosynthesis and cell wall digestion, with chitin polymers being biosynthesized, associated with other macromolecules of the yeast cell wall. They can be also beta glucan helical structures, made visible in the zone of yeast division due to the action of autolysins. The observed gradient in surface adhesion and elastic properties correlates well with that expected from a biochemical point of view. The higher adhesion force measured could be either due to the different macromolecular nature of the patches, or to a mechanical adhesion effect due to the different plasticity of that zone. This work reveals the importance of taking into account the dynamic nature of the cell wall physico-chemical properties. Processes related to the normal cell-cycle, as division, can strongly alter the surface morphology and physico-chemical properties and cause important heterogeneities that might have a profound impact on the adhesion behavior of a single cell, which could not be detected by more macroscopic methods.
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PMID:Ultrastructural and physico-chemical heterogeneities of yeast surfaces revealed by mapping lateral-friction and normal-adhesion forces using an atomic force microscope. 1677 41

Colloid probe atomic force microscopy (CP-AFM) was used to investigate two strains of Burkholderia cepacia in order to determine what molecular scale characteristics of strain Env435 make it less adhesive to surfaces than the parent strain, G4. CP-AFM approach curves analyzed using a gradient force method showed that in a high ionic strength solution (IS=100 mM, Debye length=1 nm), the colloid probe was attracted to the surface of strain G4 at a distance of approximately 30 nm, but it was repelled over a distance of 25 nm when approaching strain Env435. Adhesion forces measured under the same solution conditions during colloid retraction showed that 1.38 nN of force was required to remove the colloid placed in contact with the surface of strain G4, whereas only 0.58 nN was required using strain Env435. At IS=1mM (Debye length=10nm), the attractive force observed with G4 was no longer present, and the repulsive force seen with Env435 was extended to approximately 250 nm. The adhesion of the bacteria to the probe was much less at low IS solution (1 mM) than at high IS (100 mM). The greater adhesion characteristics of strain G4 compared to Env435 were confirmed in column tests. Strain G4 had a collision efficiency of alpha=0.68, while strain Env435 had a much lower collision efficiency of alpha=0.01 (IS=100 mM). These results suggest that the reduced adhesion of strain Env435 measured in column tests is due to the presence of high molecular weight extracellular polymeric substances that extend out from the cell surface, creating long-range steric repulsion between the cell and a surface. Adhesion is reduced as these polymers do not appear to be "sticky" when placed in contact with a surface in AFM tests.
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PMID:Adhesion characteristics of two Burkholderia cepacia strains examined using colloid probe microscopy and gradient force analysis. 1754 7

Understanding solvation in hydrofluoroalkane (HFA) propellants is of great importance for the development of novel pressurized metered-dose inhaler (pMDI) formulations. HFA-based pMDIs are not only the most widely used inhalation therapy devices for treating lung diseases, but they also hold promise as vehicles for the systemic delivery of biomolecules to and through the lungs. In this work we propose a combined microscopic experimental and computational approach to quantitatively relate the chemistry of moieties to their HFA-philicity. Binding energy calculations are used to determine the degree of interaction between a propellant HFA and candidate fragments. We define a new quantity, the enhancement factor E, which also takes into account fragment-fragment interactions. This quantity is expected to correlate well with the solubility and the ability of the moieties of interest to impart stability to colloidal dispersions in HFAs. We use a methyl-based (CH) segment and its fluorinated analog (CF) to test our approach. CH is an important baseline case since it represents the tails of surfactants in FDA-approved pMDIs. CF was chosen due to the improved solubility and ability of this chemistry to stabilize aqueous dispersions in HFAs. Adhesion force from Chemical Force Microscopy (CFM) is used as an experimental analog to the binding energy calculations. The force of interaction between a chemically modified AFM tip and substrate is measured in a model HFA, which is a liquid at ambient conditions. Silanes with the same chemistry as the fragments used in the ab initio calculations allow for direct comparison between the two techniques. The CFM results provide an absolute scale for HFA-philicity. Single molecule (pair) forces calculated from the CFM experiments are shown to be in very good agreement to the E determined from the ab initio calculations. The ab initio calculations and CFM are corroborated by previous experimental studies where propellants HFAs are seen to better solvate the CF functionality.
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PMID:Understanding solvation in hydrofluoroalkanes: ab initio calculations and chemical force microscopy. 1758 Aug 55


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