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Biomedical subjects

A W Neumann

Publications and source records attributed to A W Neumann.

16 recordsLinked to original sources
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

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↗
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↗
PubMed1979

Surface thermodynamics of leukocyte and platelet adhesion to polymer surfaces.

Adhesion of leukocytes and platelets to solid substrates of different surface tensions and hence different wettability is studied from a thermodynamic point of view. A simple thermodynamic model predicts that a cellular adhesion should increase with increasing surface tension of the solid substrate if the surface tension of the medium in which the cells are suspended is lower than the surface tension of the cells. If the surface tension of the suspending medium is higher than that of the cells, the opposite behavior is predicted. These predictions are borne out completely by neutrophil adhesion tests, where the surface tension of the aqueous suspending medium is varied by addition of dimethyl sulfoxide (DMSO). Platelet adhesion experiments also confirm these predictions, the only difference being that surface tensions of the suspending medium above that of the platelets cannot be realized, owing to exudation of surface active solutes from the platelets. Utilization of the thermodynamic prediction that cellular adhesion should become independent of the surface tension of the substrate when the surface tensions of the cells and that of the suspending medium are equal leads to a value of the surface tension of neutrophils of 69.0 erg/cm(2), in excellent agreement with the value obtained from contact angles measured on layers of cells.

Cell Adhesion↗
PubMed1979

Thermodynamic studies of cellular adhesion.

Cellular adhesion of granulocytes and of platelets to solid substrates of different surface tensions has been studied from a thermodynamic aspect. A simple thermodynamic model predicts that cellular adhesion should increase as the surface tension of the solid substrate increases provided that the surface tension of the liquid medium in which the cells are suspended is lower than the surface tension of the cells themselves. If, however, the surface tension of the liquid medium is higher than the surface tension of the cells, then a decrease in cell adhesion with increasing substrate surface tension can be predicted. These predictions are completely substantiated by granulocyte adhesion tests in which the surface tension of the suspending liquid medium is varied through the addition of different volumes of dimethyl sulfoxide (DMSO). Platelet adhesion experiments also confirmed these predictions, the only difference being that it is not possible to obtain a suspending liquid medium with a surface tension higher than that of platelets themselves, as a consequence of the exudation of surface active substances by the platelets.

Blood Platelets↗
PubMed1978

The temperature dependence of the surface tension of aqueous solutions of plasma proteins.

The surface behavior of aqueous solutions of fibrinogen, transferrin, gamma-globulin and albumin at the liquid-gas interface has been investigated by a modified Wilhelmy technique. The temperature dependence of the surface tension was studied over a temperature range of 20--80 degrees C and a pH range of 2--12. Most pronounced conformational changes of fibrinogen with this technique were found in physiological conditions: 35--45 degrees C and pH 7--8. A conformational change was found for gamma-globulin and transferrin solutions, but at a higher temperature and less pronounced than fibrinogen. Albumin did not undergo conformational transitions to a significant extent.

Fibrinogen↗
PubMed1977

Platelet adhesion to solid surfaces. The effects of plasma proteins and substrate wettability.

Platelet adhesion tests were performed using protein-free washed pig platelet suspensions in conjunction with a simple open-static method on smooth, well-defined protein-coated glass and polymer surfaces and bare glass and polymer surfaces. A normalization technique was introduced in an attempt to correct day-to-day variations in platelet reactivity. Protein coatings reduced platelet adhesion (to glass as well as polymer surfaces) to such a low level that the platelet density on one protein/substrate combination could not be distinguished from that on any other protein/substrate combination. Specifically, albumin and fibrinogen behaved identically regardless of the substrate on which they were coated. The addition of albumin and gamma-globulin to the platelet-suspension also significantly reduced platelet adhesion to glass surfaces. Whereas the extent of platelet adhesion from protein-free suspensions to bare glass and polymer surfaces depended on their wettability, the presence of specific chemical groups in the proteins, such as (-CONH-), may have an overriding effect on platelet adhesion to solid surfaces.

Blood Proteins↗
PubMed1977

Comparison between antigen-antibody binding energies and interfacial free energies.

Antigen-antibody binding energies derived from equilibrium data are compared with the binding energies resulting from the interfacial free energies obtained from contact angle measurements of antigens and antibodies. From these interfacial free energies two sorts of theoretical antigen-antibody binding energies can be derived, as well as the Hamaker constants for most antigen-antibody systems. For interaction in vacuo the Hamaker constants obtained are between 4 and 6 X 10(-13) ergs, while these constants for hydrated antigen antibody interactions are less than 10(-14) ergs. For interactions in vacuo, interfacial free energies yield binding energies (delta Fa) that lie between -120 and -140 ergs/cm2. For interactions in the aqueous phase (with interstitial water still present), much lower binding energies (delta Fb) are derived, of the order of -.01 and -1 ergs/cm2. In comparison, dextran-anti-dextran interactions show a binding energy derived from equilibrium data (delta Feq) of the order of -10 ergs/cm2. In general the equilibrium binding energies delta Feq of most antigen-antibody systems would vary between -1 and -20 ergs/cm2. The implications of this comparison are discussed in the light of the influence of residual water between antigenic determinant and antibody-active site, as well as in the light of the degree of perfection of fit between these sites.

Antibodies↗
PubMed1976

Detection of lipid phase transitions by surface tensiometry.

A technique for the detection of lipid phase transitions is described, which involves measurement of the surface tension as a function of temperature. In the case of insoluble lipids, such as dipalmitoylphosphatidylcholine (DPPC) the lipid is spread as a multibilayer film on an aqueous substrate, while in the case of water-soluble lipids such as lysophosphatidylcholine (LPC) the surface tension of aqueous sols is measured. Surface tension at the interface, is monitored using a Wilhelmy plate while the temperature is continuously varied. Discontinuities or changes in slope in the surface tension-temperature (gamma-T) curve reflect phase transitions in the lipid. In the case of DPPC, the technique has been used to demonstrate the well-known gel-liquid crystalline thermal transition. This occurs at 36-38 degrees C in the multibilayer films; in bulk DPPC-water dispersions the transition is at 41 degrees. Cholesterol has the effect of lowering the thermal transition and broadening the temperature range. In films containing DPPC-cholesterol at a molar ratio of 2:1 or less, the transition is not present. These results are in agreement with a large number of previous studies of this system. In the case of LPC sols, a phase transition at about 70 degrees was detected when the concentration of SPC was close to the critical micelle concentration (CMC) at 70 degrees. This transition appears to reflect an increase in the equilibrium constant for micelle formation at this temperature. At higher concentrations of LPC a transition at 30 degrees, corresponding to a gel-liquid crystalline transition, was also detected. A complete description of gamma as a function of concentration and temperature in the range 10(-7) to 10(-3) g cm-3 and 20 degrees to 80 degrees has been obtained for LPC sols. The CMC varies from 6 X 10(-6) g cm-3 at 20 degrees to 10(-5) g cm-3 at 80 degrees.

Binding Sites↗
PubMed1975

[Thermodynamic aspects of phagocytosis and thrombosis (author's transl)].

In this paper, thermodynamic considerations are applied to two biological processes, phagocytosis and platelet adhesion, the latter being an important step in thrombosis formation. Simple thermodynamic models in terms of changes of the Helmholtz free energy are presented for the engulfment of bacteria by phagocystic cells, as well as for the attachment of platelets to biomaterial surfaces. The interfacial tensions contained in the expressions for the Helmholtz free energy may be obtained from contact angles, by means of an equation of state approach. The in vitro phagocytosis tests show that hydrophobic bacteria are more readily phagocytized than hydrophilic ones, and the thermodynamic model elucidates the reason for this pattern of behaviour. Preliminary results for two types of platelet adhesion tests are presented. Although there is, in terms of simple thermodynamic considerations, a strong similarity between platelet adhesion and the early stages of phagocytosis, we anticipate that specific interactions will play a larger role in platelet adhesion than in phagocytosis.

Bacteria↗
PubMed1975

The role of surface thermodynamics in thromboresistance of biomaterials.

A thermodynamic approach to the problem of platelet adsorption out of a suspension on to a smooth and homogeneous solid surface is developed. The interfacial tension values required may be estimated from contact angle data by means of an equation of state relation. According to the thermodynamic approach the functional dependence of platelet adsorption on surface tension of the solid differs according to whether the surface tension of the platelets is smaller or larger than the surface tension of the liquid in which they are suspended. The implications of this thermodynamic approach in situations where plasma proteins are present and the biomaterials surfaces may be heterogeneous and rough are discussed. Previous analyses using the critical surface tension of wetting and other surface-related parameters are compared with the thermodynamic analysis given here.

Biocompatible Materials↗
PubMedDate not supplied

The force of detachment of endothelial cells from different solid surfaces.

With the use of a technique based on the detachment of single cells by suctioning of the cells with a glass micropipette, the authors studied human endothelial cell adhesion on 4 different surfaces (Fluorocarbon FC 721, polyester, nylon, glass) versus time of contact in phosphate buffered solution and a complete culture medium. It was observed that the force of detachment from solid surfaces of endothelial cells increases significantly with time and with increasing substrate surface tension in PBS and decreasing substrate surface tension in complete culture medium. This dependence of cell-fiber interactions with surface tension of the fibers demonstrates that cell adhesion in the authors' experimental conditions in primarily controlled by surface tension.

Biomechanical Phenomena↗