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Biomedical subjects

A W Neumann

Publications and source records attributed to A W Neumann.

At least 55 records · Page 3Linked to original sources
PubMed1982

Surface thermodynamics of phagocytic ingestion of non-opsonized bacteria by granulocytes in liquids of different surface tensions.

The free energy of engulfment of four bacterial species by human granulocytes is calculated from contact angle data as a function of the surface tension gamma LV of the suspending liquid. The resulting curves predict that at low liquid surface tensions gamma LV, the phagocytic ingestion increases with decreasing hydrophobicity of the bacteria while at high surface tensions gamma LV, it increases with increasing hydrophobicity. Furthermore, these curves reach a minimum at values of gamma LV equal to the surface tension gamma LV of the bacteria. The experimental results support these predictions. Thus, the determination of the surface tension of the suspending medium at which phagocytic ingestion becomes minimum represents a novel technique to establish the surface tension of ingested particles, such as bacteria. The results obtained in this fashion for the four bacterial species are in good agreement with those obtained from contact angles, as well as those derived from bacterial adhesion experiments.

Bacterial Physiological Phenomena↗
PubMed1982

Effect of surface roughness on platelet adhesion under static and under flow conditions.

Normal blood clots when exposed to surfaces other than endothelial. Various unsuccessful attempts have been made to find a synthetic material that is compatible with blood. Both platelets and clotting factors are involved in thrombosis at foreign surfaces. The authors are concerned with platelet adhesion as a first step in thrombus formation. The determination of the number of platelets adhering per unit area, therefore, appears to be a useful criterion for the choice of appropriate biomaterials contacting blood. However, laboratory tests are often carried out with specially prepared, well-defined biomaterials with a smooth surface, whereas biomaterials in clinical use may have a variable degree of roughness. In this paper the authors present data on platelet adherence to a hydrophilic (glass) and to a hydrophobic (silane) material, with smooth and rough surfaces. Additional data are presented that document the extent of platelet adhesion to a wide range of smooth polymer materials having a large variation in surface hydrophobic quality. There was no difference in platelet adherence between the smooth and rough surfaces when tested under static conditions. When the surfaces were tested in a laminar flow cell, the addition of roughness caused a decrease in platelet adhesion on the hydrophilic surface and an increase in platelet adhesion on the hydrophobic surface.

Animals↗
PubMed1981

Determination of the Surface tension of proteins. I. Surface tension of native serum proteins in aqueous media.

The desorption patterns of serum proteins in hydrophobic chromatography suggest that serum proteins that remain immersed in an aqueous medium and do not become in a protein-air interface are very hydrophilic. Contact angle measurements on fairly thick layers of hydrated serum proteins, formed on ultrafiltration membranes, yield surface tensions that correlate well with the degree of hydrophilicity derived from desorption data obtained by hydrophobic chromatography. For further confirmation the absorptivity of four human serum proteins was measured with respect to surfaces of different polymers of various surface tensions, for solution in aqueous solvents of different surface tensions. The surface tension of the solvent from which a dissolved protein adsorbs to precisely the same extent onto all solid substrates (regardless of their surface tensions) is equal to the surface tension of that protein. The surface tensions found by the contact angle (first value given) and by the protein adsorption methods (second value given) were. in erg/cm2; alpha 2-macroglobulin, 71.0, 71.0; serum albumin, 70.5, 70.2; immunoglobulin M, 69.5, 69.4; immunoglobulin G, 67.4, 67.7.

Adsorption↗
PubMed1981

Determination of surface tensions of proteins. II. Surface tension of serum albumin, altered at the protein-air interface.

Serum albumin, which itself has a surface tension of congruent to 70.3 erg/cm2, when dissolved in water lowers the surface tension of water from 72.5 to congruent to 50 erg/cm2, as measured by a variety of means, including the pendant drop, the Wilhelmy plate and the platinum ring methods. Equally low and even lower surface tensions are found with the contact angle method, on a thin layer of albumin that had been adsorbed onto a low energy surface and subsequently exposed to air. Surface tensions of drops of albumin solutions varying in concentration from 0.01 to 5.5% (w/v) yielded, with a contact angle method, values that only varied between 67 and 61 erg/cm2. With the pendant drop, the Wilhelmy plate and the platinum ring methods, one essentially measures the surface tension at the air-liquid interface, at which proteins tend to adsorb, and where reversible or irreversible reorientation can be expected. The same holds for a thin layer of protein adsorbed onto a low energy surface, exposed to air. Thus, when through the very act of surface tension measurement, or after adsorbing protein onto a substrate, protein is exposed at the air-liquid interface, it apparently loses the pronounced hydrophilicity characteristic of its native hydrated state and manifests through reorientation a much more hydrophobic tertiary configuration.

Air↗
PubMed1981

Elution of blood group antibodies from red cells.

By slowly lowering the surface tension of the aqueous medium through the admixture of 47.5% dimethyl sulfoxide (DMSO) and 0.1% bovine serum albumin (BSA) and by raising the pH to 9, complete elution of A, D, and K antibodies from sensitized erythrocytes (RBC) could be achieved. The eluates comprising the antibodies were subjected to dialysis to remove the DMSO and to neutralize the pH, and to ultrafiltration to remove the excess water. Recovery of a sizeable proportion of the eluted RBC (of blood groups A and K) proved possible by slow and careful removal of the DMSO with phosphate-buffered saline containing 2% BSA.

Antibodies↗
PubMed1980

Kinetic and thermodynamic aspects of platelet adhesion from suspension to various substrates.

Kinetics of platelet adhesion from suspension to various substrates leads to Langmuir isotherm types of curves, both for suspensions in which the platelets were isolated by means of gel filtration as well as by centrifuging and washing. The level of platelet adhesion increases with increasing surface tension of the substrate. These results cannot be explained on the basis of the theoretical transport model of Ruckenstein et al. The plot of the platelet adhesion at equilibrium vs. gamma SV brings the observations in yet closer agreement with thermodynamic predictions based on free energy calculations than was found previously for the adhesion of platelets after short contact times between platelet suspension and substrate.

Animals↗
PubMed1980

Surface thermodynamics of normal and pathological human granulocytes.

Surface tensions of normal and pathological granulocytes were determined by (1) adhesion to solid substrates of different surface tensions while suspended in liquid media of different surface tensions, and by (2) measurement of cell-liquid-vapor contact angles obtained with sessile drops of saline water on cell monolayers. The results obtained by the two different methods were in close conformation with one another. With the cell adhesion method some residual leukocyte adhesion still persists even under conditions where there no longer is a van der Waals attraction between cells and solid substrate. At low ionic strength and by the abolishment of all multivalent cations through the admixture of EDTA, that residual cell adhesion virtually disappears (with normal as well as with pathological granulocytes), indicating that the earlier residual cell adhesion did indeed arise from electrostatic interactions mediated by multivalent cations (probably Ca2+). Comparison of the capacities for engulfment and the surface thermodynamics data of normal and pathological granulocytes obtained in this study leads to the novel observation that the phagocytic episode from half to complete engulfment of bacterial particles by granulocytes appears to be the crucial step from the thermodynamic point of view.

Cell Adhesion↗
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↗