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

Adhesion problems during tablet manufacturing have been observed to be dependent on many formulation and process factors including the run time on the tablet press. Consequently, problems due to sticking may only become apparent towards the end of the development process when a prolonged run on the tablet press is attempted for the first time. It would be beneficial to predict in a relative sense if a formulation or new chemical entity has the potential for adhesion problems early in the development process. It was hypothesized that favorable intermolecular interaction between the drug molecules and the punch face is the first step or criterion in the adhesion process. Therefore, the rank order of adhesion during tablet compression should follow the rank order of these energies of interaction. The adhesion phenomenon was investigated using molecular simulations and contact mode atomic force microscopy (AFM). Three model compounds were chosen from a family of "profen" compounds. Silicon nitride AFM tips were modified by coating a 20-nm iron layer on the surfaces by sputter coating. Profen flat surfaces were made by melting and recrystallization. The modified AFM probe and each profen surface were immersed in the corresponding profen saturated water during force measurements using AFM. The work of adhesion between iron and ibuprofen, ketoprofen, and flurbiprofen in vacuum were determined to be -184.1, -2469.3, -17.3 mJ. m(-2), respectively. The rank order of the work of adhesion between iron and profen compounds decreased in the order: ketoprofen > ibuprofen > flurbiprofen. The rank order of interaction between the drug molecules and the iron superlattice as predicted by molecular simulation using Cerius(2) is in agreement with the AFM measurements. It has been demonstrated that Atomic Force Microscopy is a powerful tool in studying the adhesion phenomena between organic drug compounds and metal surface. The study has provided insight into the adhesion problems occurring during tablet compression and a direction for continued study.
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PMID:Modeling of adhesion in tablet compression--I. Atomic force microscopy and molecular simulation. 1266 Oct 65

The role of lipopolysaccharides (LPS) in bacterial adhesion was investigated via atomic force microscopy (AFM). Adhesion between a silicon nitride tip and Escherichia coli JM109 was measured in water and 0.01 M phosphate-buffered saline (PBS) on untreated cells and on a sample of E. coli treated with 100 mM ethylenediaminetetraacetic acid (EDTA), which removes approximately 80% of the LPS molecules. LPS removal decreased the adhesion affinity between the bacterial cells and the AFM tip from -2.1 +/- 1.8 to -0.40 +/- 0.36 nN in water and from -0.74 +/- 0.44 to -0.46 +/- 0.23 nN in 0.01 M PBS (statistically different, Mann-Whitney rank sum test, P < 0.01). The distributions of adhesion affinities between E. coli LPS macromolecules and the AFM tip could be described by gamma distribution functions. Direct measurements of the adhesive force between E. coil and a surface were compared with adhesion in batch and column experiments, and agreement was observed between the influences of LPS on adhesion in each system. Bacterial batch retention to glass or in packed beds to quartz sand decreased after LPS removal. When interaction forces were measured during the approach of the AFM tip to a bacterium, steric repulsive forces were seen for both treated and untreated cells, but the repulsion was greater when the LPS was intact A model for steric repulsion predicted a reduction of the equilibrium length of the surface polymers from 242 to 64 nm in water and from 175 to 81 nm in buffer, after removal of a portion of the LPS. DLVO calculations based on conventional and soft-particle DLVO theories predicted higher energy barriers to adhesion for all surfaces after LPS removal, consistent with experimental findings. Adhesion forces between the AFM tip and bacterial polymers were correlated with bacterial attachment and retention, while measurements of interaction forces during the approach of the AFM tip to the bacterium did not correlate with subsequent adhesion behavior to glass or quartz sand.
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PMID:Role of lipopolysaccharides in the adhesion, retention, and transport of Escherichia coli JM109. 1278 23

Implantation of stents into stenosed arteries helps to restore normal blood flow in ischemic organs. However, limited biocompatibility of the applied medical steel can cause acute thrombosis and long-term restenosis. Adhesion of monocytes to stent metal may participate in those acute and long-term complications of stent placement. Based on described prominent electrochemical properties of the interaction between the monocyte integrin receptor Mac-1 and its various ligands, we hypothesized, that this receptor is a central mediator of monocyte adhesion to stent metal and that semiconductor coating of medical steel reduces monocyte adhesion. Adhesion of monocytes on L-316 stainless steel was directly evaluated by light microscopy. Mac-1 could be identified as mediator of monocyte adhesion, since cell adhesion could be blocked by anti-Mac-1-antibodies, including the cross-reacting anti-GPIIb/IIIa antibody fragment abciximab. To further prove the central role of Mac-1, two CHO cell lines were generated expressing recombinant Mac-1 either as wild type, resulting in a low affinity receptor, or mutant with a GFFKR deletion of the alpha(M) subunit, resulting in a high affinity receptor. Indeed, adhesion was specific for Mac-1 and dependent on the affinity state of this integrin. Finally, we could demonstrate that Mac-1-mediated adhesion of monocytes to stents can be significantly inhibited by silicon carbide coating of the stent metal. In conclusion, the integrin Mac-1 and its affinity state could be identified as major mediators of monocyte adhesion on medical steel. As therapeutic strategies, the blockade of Mac-1 by antibodies or silicon carbide coating of steel inhibits monocyte adhesion on stents.
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PMID:Adhesion of monocytes to medical steel as used for vascular stents is mediated by the integrin receptor Mac-1 (CD11b/CD18; alphaM beta2) and can be inhibited by semiconductor coating. 1288 Oct 37

This work has dealt with the in vitro physicochemical, elastic, and microbiological properties of polymer lining materials used in dental prosthetics. Representatives of two soft polymer groups were analyzed: Vertex Soft NF, a plastified acrylic polymer, and Molloplast B, a silicon elastomer. Vertex Rapid Simplified and Triplex--two acrylic polymers routinely used at the Department of Prosthetic Dentistry were chosen as representatives of rigid acrylic material. The laminar plates of the denture are lined with elastic material to reduce wear discomfort and eliminate symptoms associated with compression of the oral mucosa by the denture. Wear-dependent deterioration in physicochemical, elastic, and microbiological properties presents as prosthetic stomatopathies due to the combined action of mechanical lesions, fungal growth, and toxicity of components of the denture, necessitating replacement of the denture. Samples used in this study were prepared at the Department of Dental Prosthetics, Pomeranian Academy of Medicine. The process of polymerization was carried out strictly as recommended by the manufacturers. The in vitro analyses were done at the Polymer Institute, Technical University of Szczecin, and the Department of Microbiology and Immunology, Pomeranian Academy of Medicine. A special system was used to reproduce conditions in the oral cavity and study their effects on the elastic liners. Samples were placed in the chamber for varying periods, depending on the type of test and material. Thermodynamic analysis was done to confirm proper polymerization and hardening. Time-dependent loss of contact between the elastic liner and rigid denture under tangential (shear) and normal (tear) stress applied to the liner-denture interface was examined. Resistance was studied using INSTRON model 4206-006 universal testing machine. Compressive changes in elastic properties of the soft materials were examined by calculating Young's modulus. Changes in viscoelastic properties of the materials depending on temperature and frequency were followed using dynamic mechanical thermal analysis (DMTA). A precision microbalance from Sartorius (+/- 0.00001 g) was used to measure time-dependent changes in weight and sorption of water. Adhesion of Candida albicans to the rigid and soft acrylic materials was determined after incubation for 3, 6 or 24 h at 37 degrees C. The study has shown that adhesive strength is much greater for acryl-acryl than acryl-silicon interface. Elastic properties of Molloplast B are very stable and superior to those of Vertex Soft NF. Time-dependent sorption of water and changes in weight have confirmed the stable nature of Molloplast B. Adhesion of Candida albicans to Vertex Soft NF was less noticeable.
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PMID:[Comparative analysis of elastic materials for lining of removable dental prosthesis in vitro]. 1460 76

In order to achieve defined adhesion and neurite outgrowth, the growth substrate must be patterned in an appropriate way. We utilised ink-jet printing by means of a piezo-based microdispenser to create defined line patterns of a polymer with typical dimensions of 100 microm width on glass, silicon, gold and carbon substrates. Vinnapas, a co-polymer of vinyl acetate and ethylene, was mixed with the extracellular matrix protein laminin to achieve neuronal adhesion on the surface of the patterns. It could be demonstrated that the laminin entrapped in the polymer lines can be recognised by a specific antibody. Adhesion of embryonic chicken forebrain neurones is following the prepared lines, and identity of adhering cells could be shown by neurofilament staining. These findings open the route for the generation of complex small neuronal arrays and for the electrochemical investigation of the obtained neuronal matrix.
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PMID:Ink-jet printing for micropattern generation of laminin for neuronal adhesion. 1465 34

Leukocyte beta2 integrins Mac-1 and p150,95 are promiscuous cell-surface receptors that recognise and mediate cell adhesion to a variety of adsorbed and denatured proteins. We used albumin as a model protein to study whether leukocyte adhesion and activation depended on the nm-scale topography of a protein adlayer. Albumin adsorbed from the native conformation gave rise to different adlayer topographies and different amounts of adsorbed protein on hydrophobic and relatively hydrophilic polystyrene and silanised silicon-wafer surfaces, whereas adsorption of pre-denatured Alb resulted in similar adlayer topographies and similar amounts of adsorbed protein on these surfaces. All three distinct protein-adlayer topographies supported adhesion of in vitro differentiated, macrophage-like U937 and THP-1 cells, but did not support adhesion of their promonocytic precursors. Human monocytes freshly isolated from peripheral blood did not adhere to adsorbed albumin, not even in the presence of monocyte chemoattractant protein-1 and macrophage inflammatory protein-1alpha chemokines. Adhesion of the macrophage-like cells to albumin in any of the three topographies was inhibited by antibodies against beta2 integrins, but not by antibodies against beta1 integrins, and did not induce secretion of the proinflammatory cytokine tumour necrosis factor-alpha.
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PMID:The recognition of adsorbed and denatured proteins of different topographies by beta2 integrins and effects on leukocyte adhesion and activation. 1560 99

Aureobasidium pullulans is a potentially pathogenic microfungus that produces and secretes the polysaccharide pullulan and other biomacromolecules, depending on the microbe's physiological state. The role of these macromolecules in mediating adhesion and attachment were examined. Interfacial forces and adhesion affinities of A. pullulans were probed for early-exponential phase (EEP) and late-exponential phase (LEP) cells, using atomic force microscopy (AFM). Biochemical assays showed that A. pullulans produces both pullulan and a uronic acid based polymer. The pullulan is not produced until the LEP, and it can be removed by treatment with pullulanase. Both adhesion forces between the microbe and the AFM tip (silicon nitride) and attachment of the cells to quartz sand grains were controlled by the density of the uronic acid polymer. Uronic acid polymers doubled in density between the EEP and the LEP and were unaffected by the enzyme pullulanase. Retention to quartz in a packed column was quantified using the collision efficiency (alpha), the fraction of collisions between the microbes, and the sand grains, that result in attachment. Adhesion forces and retention on glass were well correlated, with these values being higher for EEP cells (F(adh) = 7.65 +/-4.67 nN; alpha = 1.15) than LEP (F(adh) = 2.94 +/- 0.75; alpha = 0.49) and LEP + pullulanase cells (F(adh) = 2.33 +/-2.01 nN; alpha = 0.43). Steric interactions alone do not describe the adhesion behavior of this fungus, but they do provide information regarding the length and density of the macromolecules studied.
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PMID:Adhesion of Aureobasidium pullulans is controlled by uronic acid based polymers and pullulan. 1576 85

An alternative method for fabricating functionalized, atomic force microscopy (AFM) tips is presented. This technique is simple and requires only minimal preparation and tip modification to generate chemically sensitive probes that have a robust organic monolayer of flexible terminal chemistry attached to the surface. Specifically, commercially microfabricated Si3N4 AFM tips were modified with self-assembled monolayers (SAMs) of octadecyltrichlorosilane and (11-bromoundecyl)trichlorosilane after removing the native silicon oxide surface layer with concentrated hydrofluoric acid. The structure of these SAM films on solid silicon nitride surfaces was studied using contact angle goniometry and Fourier transform infrared spectroscopy. Pull-off force measurements on various bare (mica, graphite, and silicon) and SAM-functionalized substrates confirm that mechanically robust, long-chain organic silane SAMs can be formed on HF-treated Si3N4 tips without the presence of an intervening oxide layer. Adhesion experiments show that the integrity of the organic film on the chemically modified tips is maintained over repeated measurements and that the functionalized tips can be used for chemical sensing experiments since strong discrimination between different surface chemistries is possible.
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PMID:Alternative method for fabricating chemically functionalized AFM tips: silane modification of HF-treated Si3N4 probes. 1596 6

Poly(vinyl pyrrolidone) (PVP) is widely used for bioengineering and pharmaceutical applications, and its adhesion characteristics are critical. When used as a binder in pharmaceutical granulation, it covers the resultant granules and governs their surface properties. The intrinsic adhesion forces of PVP toward common hydrophobic (magnesium stearate) and hydrophilic (lactose) pharmaceutical materials have been studied as a function of relative humidity (RH). The effect of RH on adhesion force was more significant for the PVP/hydrophilic material than the PVP/hydrophobic material. Adhesion was lowest between 20 and 40% RH, and it increased at RH above 40% and below 20%. This is likely to be due to the development of capillary and triboelectrification forces, respectively. In a nano-indentation experiment using a silicon tip at room temperature, the PVP surface underwent a glass transition at 70% RH. This result suggests that surface softening contributes to the increased PVP adhesion at RH above 70%. To adjust the adhesion properties of PVP, humidity control should be an essential part of research and development. Effect of humidity on the adhesion forces between PVP and lactose (LT) or magnesium stearate (MS).
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PMID:Intrinsic adhesion properties of poly(vinyl pyrrolidone) to pharmaceutical materials: humidity effect. 1624 67

In this study we measured the adhesion forces between atomic force microscope (AFM) tips or particles attached to AFM cantilevers and different solid samples. Smooth and homogeneous surfaces such as mica, silicon wafers, or highly oriented pyrolytic graphite, and more rough and heterogeneous surfaces such as iron particles or patterns of TiO2 nanoparticles on silicon were used. In the first part, we addressed the well-known issue that AFM adhesion experiments show wide distributions of adhesion forces rather than a single value. Our experiments show that variations in adhesion forces comprise fast (i.e., from one force curve to the next) random fluctuations and slower fluctuations, which occur over tens or hundreds of consecutive measurements. Slow fluctuations are not likely to be the result of variations in external factors such as lateral position, temperature, humidity, and so forth because those were kept constant. Even if two solid bodies are brought into contact under precisely the same conditions (same place, load, direction, etc.) the result of such a measurement will often not be the same as that of the previous contact. The measurement itself will induce structural changes in the contact region, which can change the value for the next adhesion force measurement. In the second part, we studied the influence of humidity on the adhesion of nanocontacts. Humidity was adjusted relatively fast to minimize tip wear during one experiment. For hydrophobic surfaces, no signification change in adhesion force with humidity was observed. Adhesion force versus humidity curves recorded with hydrophilic surfaces either showed a maximum or continuously increased. We demonstrate that the results can be interpreted with simple continuum theory of the meniscus force. The meniscus force is calculated based on a model that includes surface roughness and takes into account different AFM tip (or particle) shapes by a two-sphere model. Experimental and theoretical results show that the precise contact geometry has a critical influence on the humidity dependence of the adhesion force. Changes in tip geometry on the sub-10-nm length scale can completely change adhesion force versus humidity curves. Our model can also explain the differences between earlier AFM studies, where different dependencies of the adhesion force on humidity were observed.
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PMID:On the adhesion between fine particles and nanocontacts: an atomic force microscope study. 1648 4


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