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Biomedical subjects

A W Neumann

Publications and source records attributed to A W Neumann.

66 records · Page 4Linked to original sources
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

Determination of the surface tension of biological cells using the freezing front technique.

The freezing front technique for solid surface tension measurements was used to obtain the surface tensions of glutaraldehyde-fixed human erythrocytes, and fresh human lymphocytes and granulocytes in aqueous media. The results agree well with the values obtained by other methods and indicate that the freezing front technique is sufficiently sensitive to detect small differences (of the order of 0.1 ergs/cm2) in surface tension. This property, along with a number of applications for which it is uniquely suited, makes the freezing front technique an important new approach to the measurement of the surface tensions of biological cells and of small particles in general.

Cell Membrane↗
PubMedDate not supplied

Elution of human granulocytes from nylon fibers by means of repulsive van der Waals forces.

A novel method for the isolation of granulocytes from nylon fibers is described. It is modification of filtration leukapheresis based on cellular surface thermodynamics. The system takes into account both electrical and van der Waals forces. The elution buffer contains a chelating agent and a surface active agent which lowers the surface tension of the liquid to a value intermediate between that of the surface tensions of the nylon fibers and of the granulocytes. Thus, the attractive van der Waals interaction between the fibers and the granulocytes becomes a repulsion. This results in a two- to threefold increase in cell yield. Phagocytosis, candicidal activity, and oxygen consumption did not appear to be affected through the isolation procedure. By both light and transmission electron microscopy the isolated granulocytes appeared to be morphologically intact.

Animals↗
PubMedDate not supplied

Protein and platelet interactions with polymer surfaces.

An attempt is made to develop an understanding of the basic mechanism governing the interaction of the major blood proteins and cells with polymer surfaces with a focus on thermodynamic approach. It is believed that such investigations may be helpful to provide a rational for the design of suitable cardiovascular prosthetic materials and to choose materials in such a way that adsorption of certain proteins eg. 'fibrinogen' is thermodynamically unfavourable compared to adsorption of other proteins eg. 'albumin'.

Adsorption↗
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↗