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Biomedical subjects

A W Neumann

Publications and source records attributed to A W Neumann.

At least 19 recordsLinked to original sources
PubMed1999

Effect of the compression ratio on properties of lung surfactant (bovine lipid extract surfactant) films.

Using axisymmetric drop shape analysis (ADSA) and a captive bubble technique, the properties of lung surfactant (BLES) films under different compression ratios (i.e. the ratio of maximum to minimum surface area of the bubble) were investigated. In particular, the effect of the compression ratio of the films on the shape of the volume area surface tension-time (VAST) graphs and on the shape of the surface tension relative area (gamma-A ) graphs was examined at the air-liquid interface. Under relatively low compression ratios of the films, the VAST and gamma-A graphs indicate that the cycling is reversible (i.e. the gamma-A graphs are identical for expansion and compression). When the compression ratio of the films increases, failure tends to occur when the surface film can not support the increasing surface pressure, causing a hysteresis loop in the gamma-A graph. It was also found that low surface tension (i.e. below 5 mJ/m2) at the interface could be attained with a 30% compression ratio and collapse of the films always occurs near or below 1 mJ/m2.

Adsorption↗
PubMed1999

Study of binding of 12(S)-hydroxy-5(Z),8(Z),10(E), 14(Z)-eicosatetraenoic acid to bovine serum albumin using dynamic surface tension measurements.

In a recent paper,(1) we demonstrated that molecular interactions between biopolymers and other smaller molecules can be detected by means of dynamic surface tension measurements. In the present paper, we demonstrate that the same methodology can be employed for investigating dose effects and specificity of molecular interactions. Three similar lipids were chosen for this study: 12(S)-hydroxy-5(Z), 8(Z),10(E),14(Z)-eicosatetraenoic acid (12(S)-HETE-free acid), methyl 12(S)-hydroxy-5(Z),8(Z),10(E),14(Z)-eicosatetraenoate (12(S)-HETE-methyl ester), and 5(Z),8(Z),11(Z), 14(Z)-eicosatetraenoic acid (arachidonic acid-free acid). These substances were added to a fatty acid free bovine serum albumin (BSA) aqueous solution at different lipid concentrations. The characteristic tension response indicates that molecular interactions between 12(S)-HETE-free acid and BSA exist. The detected interactions are concentration dependent: at a molecular ratio of lipid to protein of 1:1, the binding of 12(S)-HETE-free acid to BSA is hydrophobic in nature; at the molecular ratio of lipid to protein of 10:1, a secondary binding occurs and is hydrophilic in nature. Similar molecular interactions were not detected between 12(S)-HETE-methyl ester or arachidonic acid-free acid and BSA, indicating that the interactions between 12(S)-HETE-free acid and BSA are specific. As an independent means, surface elasticity is used to probe the molecular interactions at the interface. In the case of 12(S)-HETE-free acid but not its methyl ester or arachidonic acid, distinct higher surface elasticities were observed at lipid concentrations in excess of a molecular ratio of lipid to protein of 1:1. This finding reinforces the above stipulations.

12-Hydroxy-5,8,10,14-eicosatetraenoic Acid↗
PubMed1999

Surface hydrophobicity is increased in the ileum and proximal colon of cystic fibrosis mice.

Patients with cystic fibrosis (CF) have abnormal concentrations and composition of electrolytes and macromolecules in gastrointestinal secretions. Such alterations could change intestinal surface properties, such as surface hydrophobicity, and may influence the adhesion of macromolecules, bacteria, or microbial toxins to the intestinal surface. The objective of this study was to compare the surface hydrophobicity of the gastrointestinal tract in wild type and CF mice. We used axisymmetric drop shape analysis-contact diameter to determine surface hydrophobicity by measuring contact angles of sessile water droplets placed onto epithelial surfaces. In wild type mice, there were no differences in contact angles between the duodenum, upper jejunum, lower jejunum, and ileum. The contact angle of the gastric mucosa was lower than the rest of the gastrointestinal tract. Contact angles of the proximal colon and distal colon were both higher than that of the gastric mucosa and those of the small intestinal sections. In CF mice, contact angles along the gastrointestinal tract followed the same pattern as in wild type mice. However, contact angles in the ileum and proximal colon of CF mice were greater than those from wild type mice. This study of the murine intestine showed regional differences in surface hydrophobicity comparable to those observed in other mammalian species. In addition, we showed that the ileum and proximal colon of CF mice were more hydrophobic than the corresponding segments in wild type mice. These observations are of potential clinical relevance because patients with CF exhibit clinical manifestations of gastrointestinal disease primarily in the ileum and proximal colon.

Animals↗
PubMed1996

Surface properties of Helicobacter mustelae and ferret gastrointestinal mucosa.

Helicobacter mustelae is a gastric pathogen in ferrets that adheres to epithelial cells both in vitro and in vivo. In this study, the authors examine the role of surface hydrophobic properties in the adhesion of these organisms to eukaryotic cell surfaces. The surface properties of six H. mustelae strains were characterized by hydrophobic interaction chromatography (HIC), salt aggregation testing (SAT) and contact-angle measurement by axisymmetric drop-shape analysis (ADSA). Contact angles in multiple regions of the gastrointestinal tract, obtained from infected and uninfected ferrets, were also measured. The cell surface of H. mustelae was found to be hydrophilic by SAT but relatively hydrophobic by HIC. Contact-angle measurements for H.mustelae (mean 22.5 degrees, 95% confidence interval [CI] 9.3 degrees to 35.7 degrees) were higher than values previously reported for Helicobacter pylori (mean 12.1 degrees, 95% CI 2.0 degrees to 22.2 degrees, p < 0.05). The body of the stomach was more hydrophilic in infected ferrets (mean contact angle 59.9 degrees, 95% CI 52.5 degrees to 67.3 degrees) than in uninfected animals (mean contact angle 94.2 degrees, 95% CI 84.4 degrees to 104.0 degrees, p < 0.05). Reductions in the surface hydrophobicity of the ferrets' stomachs were correlated with the degree of mucosal inflammation (p < 0.01). These findings demonstrate that H. mustelae has surface properties comparable to those of H. pylori strains. Like the human stomach infected by H. pylori, there is a reduction in surface hydrophobicity of the ferret antrum associated with H. mustelae infection and the resulting mucosal inflammatory cell response.

Ammonium Sulfate↗
PubMed1994

Surface hydrophobicity properties of rabbit stomach in vitro.

To quantitate surface hydrophobicity of the stomach, we measured contact angles formed with water droplets in different regions of rabbit stomach at varying ages (suckling, weanling, and adult). Contact angles were measured using novel methods: axisymmetric drop-shape analysis-contact diameter for contact angles < 90 degrees and axisymmetric drop-shape analysis-maximum diameter for contact angles > 90 degrees. To determine whether gastric mucus was responsible for the physical properties of the surface mucosa, the surface tension of mucus derived from the body of stomach was measured by axisymmetric drop-shape analysis on pendant drops. Contact angles of adult antrum 82.9 degrees +/- 5.5 degrees (mean +/- SEM) were greater than in the body of stomach (36.1 degrees +/- 2.6 degrees, p = 0.0001). Contact angles on mucosa obtained from the body of the stomach of both suckling rabbits (76.4 degrees +/- 2.7 degrees) and weanling rabbits (84.2 degrees +/- 2.9 degrees) were greater than in adult animals (ANOVA, p < 0.05). Pendant drop analysis of mucus derived from the body of stomach showed a high surface tension (57.72 +/- 0.06 mJ/m2, mean +/- SD). We conclude that there are maturational changes and regional differences in the surface hydrophobicity of the lapine stomach. These changes are likely caused by changes in the overlying mucus layer.

Animals↗
PubMed1992

Surface hydrophobicity of the intestinal tract.

To quantitate surface hydrophobicity of the intestine, we measured contact angles formed with water droplets in multiple regions of rabbit intestine at varying ages (suckling, weanling, and adult) and after dinitrochlorobenzene-induced colitis. Contact angles were measured using novel methods: axisymmetric drop-shape analysis-contact diameter for contact angles less than 90 degrees and axisymmetric dropshape analysis-maximum diameter for contact angles greater than 90 degrees. To determine whether mucus was present on the surface of intestine used, indirect immunofluorescence was performed using antibody specific to goblet cell mucin. To confirm that intestinal mucus could be responsible for the physical properties of surface mucosa, surface tensions of mucus prepared from distal ileum, distal colon, and inflamed distal colon of adult rabbits were measured by axisymmetric drop-shape analysis on pendant drops. Contact angles of adult small intestine [duodenum, 38.0 +/- 11.2 degrees (SD); jejunum, 44.0 +/- 22.9 degrees; ileum, 56.4 +/- 23.3 degrees] were less than proximal colon (93.2 +/- 6.7 degrees; P less than 0.05) and distal colon (86.4 +/- 24.2 degrees; P less than 0.05). Contact angles on proximal colon from suckling rabbits (53.2 +/- 8.4 degrees) were less than both weanling (93.2 +/- 23.3 degrees; P less than 0.05) and adult rabbits (93.2 +/- 6.7 degrees; P less than 0.05). Contact angles on inflamed adult distal colon (54.7 +/- 20.6 degrees) were decreased from values on normal distal colons (86.4 +/- 24.2 degrees). Indirect immunofluorescence demonstrated that mucin was present in both vacuoles of goblet cells and on the colonic surface.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1990

In vitro surface properties of the newly recognized gastric pathogen Helicobacter pylori.

There appears to be a particular association between Helicobacter pylori and the gastric antrum, but the mechanisms by which the organism adheres to and colonizes the gastric mucosa are unclear. Surface hydrophobicity and surface charge mediate the adherence of other bacterial pathogens to mucosal epithelial cell surfaces. Therefore, in this study we characterized both the surface hydrophobicity and the surface charge of 10 H. pylori strains grown in broth culture. Four complementary methods were used to determine hydrophobicity: hydrophobic interaction chromatography, the salt aggregation test, comparison of bacterial adherence to polystyrene with adherence to sulfonated polystyrene, and measurement of contact angle with droplets of water. Three of the methods (salt aggregation test, adherence to polystyrene, and contact angles) indicated that each of the 10 strains expressed a relatively hydrophilic cell surface. In contrast, hydrophobic interaction chromatography determinations with both phenyl- and octyl-Sepharose suggested that the H. pylori strains were relatively hydrophobic. However, tetramethyl urea (0.4 M) did not reduce the binding of H. pylori to phenyl-Sepharose columns. DEAE-cellulose ion-exchange chromatography showed that each of the 10 strains of H. pylori had a surface which, overall, was highly negatively charged. We conclude that H. pylori expresses an overall relatively hydrophilic and negatively charged surface in vitro.

Bacterial Adhesion↗
PubMed1989

Human erythrocyte adhesion and spreading on protein-coated polymer surfaces.

Protein adsorption is the first event which occurs when polymer surfaces are exposed to blood. The adsorption of proteins modifies the surface properties of the substrates and therefore influences subsequent cell-surface interactions. In an attempt to elucidate the fundamental mechanisms governing cell-proteinated-surface interactions, the extent of fresh human erythrocyte adhesion and spreading on protein-coated surfaces was examined. Five human serum proteins (albumin, fibrinogen, immunoglobulin G, fibronectin, and transferrin) were used at bulk concentrations ranging from 0.01 mg/mL to 50 mg/mL. Polymer substrates covering a wide range of wettability were employed. Protein adsorption significantly reduces erythrocyte adhesion and spreading on all test surfaces with minimum adhesion observed on fibrinogen: IgG greater than albumin greater than fibronectin greater than transferrin greater than fibrinogen. The extent of these effects is dependent on the nature of the adsorbed protein, the protein bulk concentration, and the surface properties of the underlying polymer substrates.

Biopolymers↗
PubMed1989

Adhesion of suspension-cultured Catharanthus roseus cells to surfaces: effect of pH, ionic strength, and cation valency.

The correlation between the effects of pH, ionic strength and cation valency on the electrophoretic mobility and the extent of adhesion of suspension-cultured Catharanthus roseus cells to various polymer substrates is presented. The electrophoretic mobility of cells was unaltered in the pH range of 6-8, but decreased from approximately -2.2 x 10(-8) m V-1 s-1 and approached zero as the pH of the suspending liquid was decreased from 6 to 2. Similarly, the value of electrophoretic mobility decreased continuously as the ionic strength was increased from 0 to 1.0 M when cells were suspended in salt solutions of sodium chloride, calcium chloride, and aluminum chloride. However, using equimolar concentrations, the slope of the decrease in electrophoretic mobility increased following the sequence sodium chloride less than calcium chloride less than aluminium chloride. The electrophoretic mobility was near zero for suspensions containing 1.0 M calcium chloride or 0.1 M aluminium chloride. The extent of adhesion of the cells to the polymers sulphonated polystyrene less than polyethylene terephthalate less than polystyrene less than fluorinated ethylene-propylene followed this sequence. These results agree with a thermodynamic model of plant cell adhesion that implicates the importance of interfacial tensions in the adhesion process. However, higher levels of adhesion were generally observed when the electrophoretic mobility for the cells in the corresponding test liquid was at a minimum absolute value. These results can be explained by considering the effects of the electrolytic properties of the suspending liquid on the electrostatic repulsive interactions between the cells and the polymer surface in terms of a double-layer phenomenon and the DLVO theory.(ABSTRACT TRUNCATED AT 250 WORDS)

Biocompatible Materials↗
PubMed1989

Bacterial cell surface hydrophobicity properties in the mediation of in vitro adhesion by the rabbit enteric pathogen Escherichia coli strain RDEC-1.

The role of hydrophobicity in the attachment of enteropathogens to gastrointestinal mucosa is controversial. In vitro binding of Escherichia coli RDEC-1 to rabbit intestine is dependent on the expression of pili. We examined in vitro adherence of piliated RDEC-1 after altering either the hydrophobicity of the organisms, the hydrophobicity of the substrate for attachment, or the surface tension of the suspending liquid. Hydrophobicity of RDEC-1 was determined using four complementary methods. In each assay piliated RDEC-1 demonstrated relatively more hydrophobic properties compared with both organisms grown to suppress pilus expression and a mutant that cannot express mannose-resistant pili. When piliated RDEC-1 were pretreated with tetramethyl urea to disrupt hydrophobic bonds surface hydrophobicity decreased. Concurrently, bacterial adherence to rabbit ileal microvillus membranes, mucus and mucin was reduced. Binding of piliated organisms to hydrophobic surfaces was significantly higher compared to both nonpiliated bacteria and the adherence of piliated RDEC-1 to relatively hydrophilic surfaces. Addition of propanol reduced the surface tension of the suspending liquid, and decreased adhesion of piliated RDEC-1 to polystyrene by 80%. Conversely, adherence of piliated organisms to a hydrophilic surface increased 12-fold after lowering the surface tension of the suspending liquid. We conclude that hydrophobic properties have a role in mediating in vitro adherence of this E. coli enteric pathogen.

Animals↗
PubMed1988

Kinetics of cell adhesion to polymer surfaces.

Results of the kinetics of adhesion of granulocytes as well as fresh and glutaraldehyde-fixed erythrocytes, suspended in Hanks Balanced Salt Solution (HBSS; pH 7.2, ionic strength of 0.15) to various polymeric substrates are presented. Cell adhesion increases rapidly initially and reaches a plateau value after approximately 30 minutes. There is no evidence for a lag-time in the onset of cell adhesion, suggesting that electrostatic double-layer forces are negligible under these experimental conditions. For the experiments in which the cells are suspended in HBSS, which has a surface tension larger than that of the cells, the level of cell adhesion increases with decreasing surface tension of the polymeric substrates. An additional experiment with fresh human granulocytes suspended in HBSS containing 10% dimethyl sulfoxide was also performed. The surface tension of the resulting liquid medium is below that of the cells and the pattern of adhesion is reversed, in agreement with the predictions of a thermodynamic model for cell adhesion. The slightly different behavior of siliconized glass as a substrate is discussed in terms of "screening."

Biocompatible Materials↗
PubMed1987

Protein adsorption to polymer particles: role of surface properties.

Adsorption isotherms of four plasma proteins (fibrinogen, IgG, human serum albumin, and bovine serum albumin) using four different types of small particles as substrates (siliconized glass, Teflon, polyvinylchloride, and Nylon-6,6) are reported. The suspending liquid medium was phosphate-buffered saline, with a surface tension higher than that of any of the proteins. In keeping with the thermodynamic expectations for these systems, protein adsorption decreases for all solids in sequence from fibrinogen (the most hydrophobic) to IgG, human serum albumin, and bovine serum albumin (the most hydrophilic). Furthermore, the extent of protein adsorption also decreases from the low surface tension (hydrophobic) to the higher surface tension solids, again as expected on thermodynamic grounds. There is one minor yet interesting exception to the thermodynamic pattern: In spite of the slightly lower surface tension of siliconized glass, the extent of protein adsorption is slightly higher to Teflon than to siliconized glass. This result is attributed to the theoretically well known phenomenon of "screening."

Adsorption↗
PubMed1985

Determination of the surface tension of various species of erythrocytes by means of the solidification front technique.

The solidification front technique is employed to determine the surface tension of fixed erythrocytes of dog, horse, human, chicken, and turkey. The results range from 65.5 erg/cm2 for dog erythrocytes to 67.6 erg/cm2 for turkey erythrocytes. A detailed error analysis shows that the differences obtained are statistically significant. Since cellular interactions are governed to a considerable extent by surface tension effects, it is concluded that caution needs to be exercised when results obtained for one species are used to predict the behavior of cells of another species.

Animals↗
PubMed1983

Surface tension of animal cartilage as it relates to friction in joints.

Measurement of the surface tension of articular cartilage and friction experiments were carried out to provide further evidence in support of a new theory regarding the mechanism of friction in joints. To determine the surface tension of cartilage, contact angle measurements were used in conjunction with the equation of state for interfacial tensions. The advancing contact angle between saline drops and articular cartilage was found to be 100 degrees +/- 5 degrees, indicating a highly hydrophobic surface. The corresponding surface tension value was calculated to be 22.5 ergs/cm2. Friction of cartilage against hydrophobic surfaces is shown to be lower than the friction of cartilage against hydrophilic surfaces. All these results further support the theory that lubrication by nonwetting drops occurs in joints and may be responsible for the exceptional friction characteristics of the joints.

Animals↗
PubMed1983

Interaction of phagocytes with other blood cells and with pathogenic and nonpathogenic microbes.

Owing to the high surface tension of blood cells and to the equally high surface tension of their liquid habitat, the Hamaker coefficients A131 of blood cells (subscript 1) in blood (subscript 3), are unusually small; they are of the order of 0.25 to 2.5 X 10(-16) ergs. The very small van der Waals attractions such low Hamaker coefficients give rise to, coupled to the medium low but still sizable negative xi-potentials (-11 to -18 mV) of the cells, which cause an appreciable mutual electrostatic repulsion between blood cells, have been used to elaborate potential energy vs. distance diagrams, which closely reflect the unusual stability of blood cells in blood. When bacteria find their way into the bloodstream, they initially form an almost equally stable suspension. However, relatively hydrophobic nonpathogenic bacteria quickly aspecifically adsorb immunoglobulin G (IgG) molecules from blood serum, whilst hydrophilic pathogenic bacteria sooner or later also become coated with specific antibody molecules of the IgG-class. Through receptor sites on the surface of phagocytic blood cells, which can specifically bind to the Fc tails of IgG molecules, bacteria are first bound and then removed from the blood circulation and surrounding tissues. These Fc-receptor bonds presumably also are of a combined van der Waals and electrostatic nature. Thus in the normal course of events and by purely physicochemical mechanisms, phagocytic leukocytes will neither interfere with other leukocytes nor with any other blood cells, whilst they specifically interact with microorganisms and other unwanted foreign particles via IgG-IgG-receptor interactions. Also discussed, in the light of the principles elaborated above, are: some of the antiphagocytic mechanisms developed by certain pathogenic bacteria; the phagocytic disposal of aged, weak, or abnormal blood cells; and the role played by immunoglobulins other than IgG, and by complement, in the removal of bacteria and viruses.

Adhesiveness↗