Adhesion Maps Research Articles

Adhesion mode atomic force microscopy study of dual component protein films

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.

Pain Mapping of Adhesions

Study Objective To determine the nature and location of adhesions and their relationship to abdominal pain in patients undergoing awake microlaparoscopy. Design Retrospective analysis (Canadian Task Force classification II-1). Setting University teaching hospital. Patients Thirty women ages 26–49 years with chronic pelvic pain were studied over a 9-month period. Intervention Patients were kept awake during their laparoscopy to determine the site and degree of pain when the adhesions were palpated. Measurements and Main Results Patients with abdominal pain and a history suggestive that the pain was due to adhesions underwent an awake laparoscopy. Visual analog scores were used to evaluate the pain on palpation of the adhesion as it related to the nature of the adhesion as well as the location of the adhesion. Filmy adhesions that allowed for movement between two structures had the highest association with pain. Fixed adhesions that did not allow movement had the lowest pain scores. Adhesions that had a relationship to the peritoneum had a high association with pain. Conclusion Filmy adhesions between a movable structure, such as an ovary, and the peritoneum had the highest pain scores. Fixed or dense adhesions, no matter where they were located, had the lowest pain scores.

Patterned collagen layers on polystyrene: direct probing using AFM in the adhesion mapping mode

Patterned collagen layers, showing a net-like structure with nanometer-scale dimensions, were obtained by collagen adsorption onto polystyrene (PS) followed by drying at low rate. These obtained surfaces were characterized and compared, on the one hand, to the PS substratum and, on the other hand, to uniform collagen layers obtained by adsorption onto PS and drying at high rate. In a first approach, atomic force microscope (AFM) images, X-ray photoelectron spectroscopy data and wetting measurements were compared. The results indicated that PS was present at the extreme surface in the holes of the collagen net. A second approach, allowing a direct and spatially-resolved probing of the surface chemistry, was based on the adhesion mapping mode of the AFM. The net-like structure observed on the AFM topographic images was also found in the adhesion map obtained in water: no or very low adhesion was found on collagen threads as observed on a uniform collagen layer; a higher adhesion was recorded in the holes of the net as observed on pure PS. This shows, in a direct manner, that the patterned surface is chemically heterogeneous, with PS domains present at the outermost surface in the holes of the collagen pattern, and that this is preserved under water.

Imaging of lactic acid bacteria with AFM—elasticity and adhesion maps and their relationship to biological and structural data

The adhesion of lactic acid bacteria to the intestinal epithelium is one of the most important factors determining probiotic ability of a bacterial strain. Studying bacterial adhesion requires knowledge of the structure and properties of the bacterial surface, which can be studied by atomic force microscopy under native conditions. The observation of the surface topography of bacteria from the species Lactobacillus crispatus, L. helveticus and L. johnsonii shows major differences between bacteria having a crystalline-like protein layer as part of the cell wall and those without such layers. Force volume images calculated into elasticity and adhesion force maps of different bacterial strains show that L. crispatus and L. helveticus have a surface with a homogeneous stiffness with no adhesion events. This is most likely caused by the S-layer, which completely covers the surface of the bacteria. We infer that the absence of adhesion peaks is caused by the semi-crystalline character of such protein layers, in agreement with the results obtained from electron microscopy. Analysis of a number of L. johnsonii strains shows that these bacteria have surface properties which strongly differ from the L. crispatus and L. helveticus strains. For L. johnsonii DMS20533 and L. johnsonii ATCC33200 high adhesion forces are observed, which can be related to a surface rich in polysaccharides. L. johnsonii ATCC332 has lower adhesion forces compared to the other two and, furthermore, the surface topography shows depressions. We suppose that this strain has a surface pattern consisting of crystalline-like proteins alternating with polysaccharide-rich domains. The wide variety in surface properties of lactobacilli could well have wide-ranging implications for food processing and for health benefits.

Jumping mode scanning force microscopy: a suitable technique for imaging DNA in liquids

In this work, we introduce jumping mode (JM) scanning force microscopy (SFM) as a suitable technique for imaging soft samples in liquid environment like DNA adsorbed on mica. JM reveals as a non-intrusive technique where shear forces are minimized by performing the scanning motion without tip–sample contact. We find no visible damage on DNA samples and the nominal height of 2 nm of the molecules is achieved when imaging applying a maximum normal force of ∼150 pN. In addition to topographic images, adhesion maps of DNA are simultaneously recorded showing that the minimum adhesion force occurs on top of the DNA molecules.

Mapping of adhesion forces on soil minerals in air and water by atomic force spectroscopy (AFS)

The adhesion force between an atomic force microscope (AFM) tip and sample surfaces, mica and quartz substrates, was measured in air and water. The force curves show that the adhesion has a strong dependence on both the surface roughness and the environmental conditions surrounding the sample. The variability of the adhesion force was examined in a series of measurements taken at the same point, as well as at different places on the sample surface. The adhesion maps obtained from the distribution of the measured forces indicated regions contaminated by either organic compounds or adsorbed water. Using simple mathematical expressions we could quantitatively predict the adhesion force behavior in both air and water. The experimental results are in good agreement with theoretical calculations, where the adhesion forces in air and water were mostly associated with capillary and van der Waals forces, respectively. A small long-range repulsive force is also observed in water due to the overlapping electrical double-layers formed on both the tip and sample surfaces.

Pain mapping of adhesions

Pain mapping of adhesions

Structural Evolution of Octyltriethoxysilane Films on Glass Surfaces during Annealing at Elevated Temperature

Glass samples treated by octyltriethoxysilane were annealed for times ranging from 0 to 16 h, and their topography, adhesion, and stiffness properties were examined using pulsed-force mode (PFM) atomic force microscopy. While the surfaces of samples dried at room temperature were structurally featureless, those annealed at 145°C showed formation of islands, increasing in size and number with heating time. PFM adhesion and stiffness maps suggested that the glass substrate remained at least partially covered by silanes even after island formation.

Experimental analysis of the influence of surface topography on the adhesion force as measured by an AFM

Force curves have been acquired using an atomic force microscope (AFM) on homogeneous microspheres of three different materials (latex, glass and yttria), in order to study the possible influence of the surface topography/geometry on the adhesion force as measured by an AFM. Forces were measured in regions at the top of the spheres ( ≈ 90°), at half-heights ( ≈ 0°) and in an intermediate region between these two ( ≈ 45°), where the angle is measured from the equatorial plane of the sphere to its polar axis. A very irregular and non-reproducible behaviour was found at ≈ 0°, so only the other two regions were quantitatively analysed. For all the three materials, a much smaller adhesion force was obtained in the region corresponding to ≈ 45° as compared to ≈ 90°. Moreover, a quite similar adhesion decrease ratio of about 1.60 ± 0.5 was obtained for all the three materials, which may suggest that the observed behavior might be due to geometrical factors. This observed influence could, in part, explain the observed heterogeneity in adhesion maps of microbial cells reported in the literature. The influence of the surface roughness is also discussed and it seems to result in a poor reproducibility of force curves.

Adhesion of pharmaceutical particles to gelatin capsules having variable surface physicochemical properties: evaluation using a combination of scanning probe microscopy techniques

The adhesion of particles to solid surfaces is an important factor in the performance of a number of technologically significant systems. A combination of scanning probe microscopy (SPM) techniques, including adhesion mapping and force integration to equal limits imaging, is used to correlate the adhesion of particles with areas of distinct surface physicochemical properties. The utility of this approach is demonstrated using lactose particles and a gelatin capsule from a pharmaceutical dry powder inhalant drug delivery system. The particle adhesion forces were found to be higher on specific domains of the gelatin capsule identified as extraneous surface contamination. Furthermore, the dynamic nature of these contaminant domains on the capsule surface was found to result in a variance in the particle adhesion over time.

Thermal maps of gold micro-stripes obtained using scanningforce microscopy

In this paper two ways of measuring current maps ongold micro-stripes on a nanometric scale are shown. In the firstone, an alternating current is applied to the stripe and the thermal expansionof the tip-sample system is registered by the cantilever. Inthe second one, maps of adhesion of the surface are acquiredsimultaneously with the topography. The adhesion force mapvaries with the temperature because it depends mainly on thewater meniscus between tip and sample, and the size of themeniscus depends on the temperature.

Atomic Force Microscope Techniques for Adhesion Measurements

The Atomic Force Microscope (AFM) has become a powerful apparatus for performing real-time, quantitative force measurements between materials. Recently the AFM has been used to measure adhesive interactions between probes placed on the AFM cantilever and sample surfaces. This article reviews progress in this area of adhesion measurement, and describes a new technique (Jump Mode) for obtaining adhesion maps of surfaces. Jump mode has the advantage of producing fast, quantitative adhesion maps with minimal memory usage.

Detection and mapping of intraabdominal adhesions by using functional cine MR imaging: preliminary results.

To identify and map intraabdominal adhesions by using functional cine magnetic resonance (MR) Imaging. Twenty-seven patients suspected of having intraabdominal adhesions were examined. Section-by-section dynamic depiction of induced visceral slide throughout the whole abdomen was achieved by using a transverse or sagittal true fast imaging with steady-state precession sequence. Location and type of diagnosed adhesions were documented by using the nine segments of the abdominal map. These criteria and intraoperative results were compared in 13 patients. MR images depicted a total of 42 intraabdominal adhesions; 21 (50%) were in the lower abdomen. The most common types of adhesions were located between the ventral abdominal wall and small-bowel loops (n = 10 [24%]) and between adjacent small-bowel loops (n = 9 [21%]). Comparison with the intraoperative results showed a sensitivity of 87.5% and a specificity of 92.5%. MR imaging was most accurate in depicting adhesions to the abdominal wall (15 [94%] of 16) and subperitoneal space (eight [100%] of eight). The presence of adhesions between bowel loops was overestimated. Detection of visceral slide at functional cine MR imaging is easy to perform and represents a well-tolerated and accurate procedure for use in the identification of intraabdominal adhesions in patients with chronic pain and equivocal clinical findings.

Design of a digitally controlled adhesion imaging mode using a scanning force microscope

The design of a combined topography-adhesion-stiffness imaging mode in a scanning force microscope (SFM) based on a digital control system is presented. The digital control system provides for the flexibility in designing the shape of the loading-unloading force waveform and enables a fast rate (up to 1 kHz) of applying the loading-unloading waveform with a pre-defined maximum loading force. Furthermore, flexibility in optimizing the imaging conditions and analyzing the resulting force-displacement data is achieved. The limiting factor for the data acquisition speed appears to be the viscous drag of the working medium exerted onto the SFM cantilever. It is shown that subtracting a no-contact, zero-deflection baseline can compensate for the effects of the viscous drag. The performance of the digital adhesion mapping control system is illustrated by analyzing several different samples: a rigid silicon grid; a molecularly thin block copolymer film; and a thin, heterogeneous polymer film. The remaining problems are related to the cross-talk between the topography and stiffness-related slope.

Adhesion Maps Using Scanning Force Microscopy Techniques

A technique has been developed that allows a real-time measurement of the lift-off force required to remove a scanning force microscope tip from a substrate. Both topography and adhesion maps are obtained simultaneously, allowing the correlation between topography and adhesion properties to be studied. Quantitative values of important adhesion parameters can be extracted from these data. A number of examples are given which illustrate the utility of this technique.

Atomic Force Microscopy and Wettability Study of Oxidized Patterns at the Surface of Polystyrene

The surface properties of patterned surfaces made by a combination of photolithography and oxygen plasma treatment of polystyrene (PS) were investigated. PS and plasma-treated PS (PSox) were first characterized using X-ray photoelectron spectroscopy and the study of wetting dynamics (Wilhelmy plate method) in water and in solutions of different pH. The results indicated that the PSox surface may be viewed as covered with a polyelectrolyte-like gel, which swells depending on pH. It was then shown, using atomic force microscopy (AFM), that the adhesion force measured on PS with a silicon tip in water was higher compared with that measured on PSox. This feature allowed imaging of the oxidation patterns using the adhesion mapping mode. The origin of the pulloff force contrast, which could not be explained by combining Johnson–Kendall–Roberts theory and thermodynamic considerations, was attributed to repulsion between the tip and hydrated polymer chains present on the oxidized surface. Imaging was also performed in the lateral force mode, a higher friction being recorded on PS than on PSox.

Pain mapping of adhesions

Pain mapping of adhesions

Adhesion mapping of chemically modified and poly(ethylene oxide)-grafted glass surfaces

Two-dimensional mapping of the adhesion pull-off forces was used to study the origin of surface heterogeneity in the grafted poly(ethylene oxide) (PEO) layer. The variance of the pull-off forces measured over the μm-sized regions after each chemical step of modifying glass surfaces was taken to be a measure of the surface chemical heterogeneity. The attachment of γ-glycidoxypropyltrimethoxy silane (GPS) to glass decreased the pull-off forces relative to the clean glass and made the surface more uniform. The subsequent hydrolysis of the terminal epoxide groups resulted in a larger surface heterogeneity which was modeled by two populations of the terminal hydroxyl groups, each with its own distribution of adhesion forces and force variance. The activation of the hydroxyls with carbonyldiimmidazole (CDI) healed the surface and lowered its adhesion, however, the force variance remained rather large. Finally, the grafting of the α,ω-diamino poly(ethyleneoxide) chains to the CDI-activated glass largely eliminated adhesion except at a few discrete regions. The adhesion on the PEO grafted layer followed the Poisson distribution of the pull-off forces. With the exception of the glass surface, a correlation between the water contact angles and the mean pull-off forces measured with the Si 3N 4 tip surfaces was found for all modified glass surfaces.

Study of aged Langmuir-Blodgett monolayers by AFM and ToF-SIMS mapping

Langmuir-Blodgett (LB) monolayer samples of stearic acid transferred on hydrophilic plasma-oxidized silicon surfaces in the presence of barium chloride have been studied by combined atomic force microscopy (AFM) and time-of-flight secondary ion mass spectrometry (ToF-SIMS) mapping. By ageing, these samples develop holes of increasing size, and after some weeks these boles are large enough to be mapped by ToF-SIMS (lateral resolution ∼200 nm) but still in the domain of AFM imaging. High mass resolution ToF-SIMS spectra from such surfaces display Ba, CI, and stearate-related peaks, as well as substrate-related peaks, Chemical imaging by ToF-SIMS shows that barium, chlorine and stearate maps are correlated with each other and complementary to the signals from the substrate. Height image and interaction force (adhesion and friction) maps have been obtained by AFM on this chemically well-characterized system and show that it is possible to discriminate the organic film regions from the uncovered substrate on the basis of different interaction forces. In addition, the measurements allow us to state that film and substrate have good homogeneity. Furthermore, the interaction force images can be used to follow the early stages of the evolution of these systems, which are not accessible with other chemical mapping techniques.

Barium stearate Langmuir–Blodgett films investigated by mapping adhesion forces with atomic force microscopy

Barium stearate (BS) Langmuir–Blodgett monolayers have been deposited onto plasma oxidised silicon substrates. The films, aged in air at room temperature for several days, show relatively large holes. Height, friction and adhesion maps have been obtained in air by atomic force microscopy (AFM) on these aged films. The height and friction maps are in agreement with a picture in which BS molecules are assembled on the surface almost orthogonally. A point-by-point correspondence between morphological, friction and adhesion maps was found. Time-of-flight secondary ion mass spectrometry chemical maps have been obtained in order to confirm the AFM results.