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Biomedical subjects

D R Absolom

Publications and source records attributed to D R Absolom.

At least 37 records · Page 2Linked to original sources
PubMed1983

Zeta potentials, van der Waals forces and hemagglutination.

It has recently become possible to determine the van der Waals (Hamaker) coefficient of erythrocytes, whilst their zeta-potential has been known for some time. With these two data the net potential energy of interaction versus distance diagrams could be elaborated for unsensitized human erythrocytes suspended in saline water, as well as for erythrocytes monogamously sensitized with anti-D (Rh0) antibodies of the IgG class. Unsensitized erythrocytes can approach each other, to within approximately equal to 79 A of their sialoglycoprotein surfaces, leaving a distance between their actual cell membranes of approximately equal to 180 A, which is considerably more than the maximum distance between the two valencies of an IgG molecule (approximately equal to 120 A). This explains why unaided anti-D (Rh0) antibodies of the IgG class cannot cross-link two D (Rh0)-positive erythrocytes, although cross-linking can easily be achieved with IgM class antibodies. D (Rh0)-positive erythrocytes, monogamously sensitized with antibodies of the IgG class, can approach each other to within approximately equal to 60 A (between the Fc ends of the protruding antibodies), which makes cross-linking by means of anti-IgG antibodies of the IgG class feasible.

Cell Communication↗
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↗
PubMed1983

Surface thermodynamics of bacterial adhesion.

The adhesion of five strains of bacteria, i.e., Staphylococcus aureus (strain 049), Staphylococcus epidermidis (strain 047), Escherichia coli (strains 055 and 2627), and Listeria monocytogenes, to various polymeric surfaces was studied. The design of the experimental protocol was dictated by thermodynamic considerations. From the thermodynamic model for the adhesion of small particles from a suspension onto a solid substratum, it follows that the extent of adhesion is determined by the surface properties of all three phases involved, i.e., the surface tensions of the adhering particles, of the substrate, and of the suspending liquid medium. In essence, adhesion is more extensive to hydrophilic substrata (i.e., substrata of relatively high surface tension) than to hydrophobic substrata, when the surface tension of the bacteria is larger than that of the suspending medium. When the surface tension of the suspending liquid is larger than that of the bacteria, the opposite pattern of behavior prevails. Suspensions of bacteria at a concentration of 10(8) microorganisms per ml were brought into contact with several polymeric surfaces (Teflon, polyethylene, polystyrene, and acetal and sulfonated polystyrene) for 30 min at 20 degrees C. After rinsing, the number of bacteria adhering per unit surface area was determined by image analysis. The surface tension of the suspending medium. Hanks balanced salt solution, was modified through the addition of various amounts of dimethyl sulfoxide. It was found that the number of bacteria adhering per unit surface area correlates well with the thermodynamic predictions and that these data may be used to determine the surface tension of the different bacterial species. The surface tensions of the bacteria obtained in this fashion are in excellent agreement with those obtained by other methods.

Acetals↗
PubMed1983

Determination of the surface tension of protein coated materials by means of the advancing solidification front technique.

We investigated whether substrates with different surface tensions would induce a different degree of conformational change in adsorbed protein molecules, which would be reflected by differences in the surface tension of the adsorbed layers. The solidification front technique allowed this study without requiring to expose the protein coated-particle to an air interface which would induce conformational changes in the adsorbed protein layer. With a low bulk albumin concentration (0.1%) decreasing surface tension of the adsorbed protein layer with increasing hydrophobicity of the substrate, suggested more extensive conformational changes on the more hydrophobic surfaces. At high bulk concentrations (0.5% and above) the surface tension of the adsorbed albumin layer was independent of the substrate material and increased to a value of approximately 70.2 ergs/cm2. This was consistent with the surface tension of albumin derived from other independent techniques such as contact angle measurements on thick layers of the protein material or from adsorption data. Freezing front measurements with albumin (BSA or HSA), immunoglobulin G (IgG), and fibrinogen adsorbed onto one and the same substrate material, octyl-sepharose beads, indicate that the hydrophobicity of the protein coated sepharose increased in the following order: BSA less than HSA less than IgG less than Fibrinogen. This was in good agreement with the relative hydrophobicity of these proteins determined by other independent methods.

Animals↗
PubMed1983

The effect of temperature on the extent of platelet adhesion to foreign surfaces.

For a given temperature the extent of platelet adhesion increased with increasing substrate surface tension, in agreement with earlier findings. For a given substrate platelet adhesion decreases linearly with decreasing temperature. Morphometric evaluation of the adhering platelets indicated that the extent of platelet spreading as a function of temperature follows the same pattern as the extent of platelet adhesion. Smaller quantities of ADP were required to induce aggregation at the reduced temperatures. Substrate roughness did not appear to influence the extent of platelet adhesion to any of the surfaces for any of the temperatures examined.

Biocompatible Materials↗
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

Affinity diffusion. I. Method for measuring dissociation constants of precipitating antibodies.

Dissociation constant (Kd) of antigen-antibody reactions can be obtained from the rates (measured by the progression of the precipitate vs. time) with which antigens diffuse into antibody-containing gels, as a function of antibody-concentration. A bovine serum albumin vs. rabbit anti-bovine serum albumin system was studied with whole antiserum and with its purified IgG fraction. A value was found for Kd of approximately 1.0 x 10-5 moles per liter. It is note- worthy that in monodimensional single diffusion gel precipitation systems of this type, the rate of progression of the precipitate front is significantly faster than the molecular diffusion coefficient of the antigen.

Antibody Affinity↗
PubMed1982

Affinity diffusion II. Comparison between thermodynamic data obtained by affinity diffusion and precipitation in tubes.

Association constants (Ka) of the precipitating system bovine serum albumin (BSA) goat anti-BSA were obtained at different temperatures via affinity diffusion (taking l/Kd - Ka) as well as via precipitation in tubes at optimal ratios. With affinity diffusion values of Ka of 0.6 to 1.1 x 10(5) l/M were found, whilst with precipitation in tubes Ka was from 3.3 to 11.2 X 10(7) l/M, using the same BSA and anti-BSA preparations. Via affinity diffusion binding energies delta F of approximately -6 to -7 kcal/M were found, with values of delta H close to zero, and a delta S of +23 entropy units. With precipitation in tubes these values were delta F -10.2 to -10.7 kcal/M, delta H -4.6 to -7.6 kcal/M and delta S +10 to +20 entropy units. The differences found with the two different methods must be ascribed to the fact that with affinity diffusion of precipitating antigen-antibody systems one just measures the interaction between the precipitating components with the highest dissociation constants, whilst with precipitation in tubes one measures the total energy of association of the system. With affinity diffusion and with precipitation in tubes, the same degree of positive entropy is observed. The system measured with affinity diffusion is approximately isothermic, whilst the total system, measured by precipitation in tubes, is strongly exothermic. Affinity diffusion still takes place at pH 9.5, at which pH no precipitation in the liquid phase takes place at optimal ratio; one may conclude from this that affinity diffusion mainly involves van der Waals interactions, as electrostatic bonding between BSA and anti-BSA is virtually abolished at that pH. This agrees well with the observation that the affinity diffusion reaction is isothermic.

Antibody Affinity↗
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↗