Coagulation contact system

At present, the activation of the extrinsic coagulation system is considered to be of more importance in the initiation of DIC than the activation of the contact system (LI2, Cl 3). The activation of the extrinsic system starts with the release of tissue factor (TF) from endothelial cells. TF is a macromolecule, composed of a protein and a lipid fraction, that is synthesized by endothelial cells and monocytes. TF... 

H7. Hack, C. E., Wagstaff, J., Strack Van Schijndel, R Eerenberg, A., Pinedo, H Thijs, L., and Nuijens, J., Studies on the contact system of coagulation during therapy with high doses of recombinant IL-2 Implications for septic shock. Thromb. Haemost. 65,497-503 (1991). 

Pixley FLA, De La Cadena R, Rage J D, et al. The contact system contributes to hypotension but not disseminated intravascular coagulation in lethal bacteremia in vivo use of a monoclonal anti-factor XII antibody to block contact activation in baboons. J Clin Invest 1993 92 61-68. 

As a result of the contact of blood with none-ndothelial surfaces, several humoral and cellular systems can be activated. Exposure of blood proteins and cells to blood contacting medical devices can activate plasma proteolytic systems (coagulation (blood clotting system), fibrinolysis (process by which clot is broken down), complement cascade (a system of soluble proteins involved in microbiocidal activity and the release of inflammatory components), Kallekrein-kinin and contact systems) and at least three cellular elements (leukocytes, endothelial cells, and platelets). Contrary to the normal situations whereby these mechanisms are localized and intended to promote wound healing, activation of these systems by medical devices can result in nonlocalized systemic reactions. The preclinical and clinical assessments of hemocompatibility are designed to minimize modification of these systems. 

In structured disperse systems with coagulation contacts between particles the viscosity undergoes a much more abrupt change. In this case one may outline a broad spectrum of different states that fall in between the two extreme cases fully structured systems and systems with totally destroyed structure. Depending on the magnitude of applied shear stress (flow rate), the rheological properties of structured disperse systems may change from those... 

As the shear stress reaches some value, xSchW(, the region of slow viscoplastic flow, known as Schwedov s region (Fig. IX-24, region II ), is observed in the system with almost undestroyed structure. In this region the shear strain is caused by fluctuational process of fracture and subsequent restoration of coagulation contacts. Due to the action of external pressures this process becomes directed in a certain way. Such mechanism of creep may be described analogously to the mechanisms of fluid flow, the description of which was developed by Ya.B. Frenkel and G. Eiring. 

Yaminskii, V.V., Pchelin, V.A., Amelina, E.A., Shchukin, E.D., Coagulation contacts in Disperse Systems, Khimiya, Moscow, 1982... 

Taking the above said in consideration, below we scrutinize cases of clay system deformations occurring on coagulation contacts under the impact of compressive, shearing, and three-axial (total) stresses. 

Yamlinskii, VV, Pchelin VA., Amelina E.A., Shchukin E.D. 1982. Coagulational contacts in disperse systems. Moscow Khimiya, p. 185. (in Russian)... 

The characteristic feature of coagulation contacts is the presence between particles of a thermodynamically stable thin hydrate film preventing the particles from coming into direct contact with each other. The thickness of that film corresponds to the free energy minimum of the system and may... 

For typical lyophobic colloidal systems with a complex Hamaker constant 10" J and a particle-particle separation of 0.2-1 nm, the adhesive energy in the contact is significantly larger than kT, which indicates that thermodynamics favors the formation of coagulation contacts. The primary potential energy minimum is even deeper in systems conposed of coarser particles. At the same time, for the case of low values of the complex Hamaker constant, 10 -10 J, the adhesion between the particles in systems that are not too coarse (particles with a diameter up to a micron) is overcome by the Brownian motion, and the formation of structures with coagulation contacts is impossible. 

When the shear stress reaches a particular value, T chw. the system reveals a viscoplastic flow with an essentially preserved structure and enters the so-called Schwedow creep region (region II in Figures 3.20 and 3.21). In this region, shear is caused by the fluctuation process of the destruction and subsequent restoration of the coagulation contacts. Due to external stresses, this process becomes directional. This mechanism of creep may be considered by the analogy with the mechanism of flow of liquids developed by Frenkel [19]. 

Sodium alumiaate is used ia the treatment of iadustrial and municipal water suppHes and the use of sodium alumiaate is approved ia the clarification of drinking water. The FDA approves the use of sodium alumiaate ia steam generation systems where the steam contacts food. One early use of sodium alumiaate was ia lime softening processes, where it iacreases the precipitation of ions contributing to hardness and improves suspended soHds removal from the treated water (17). Sodium alumiaate reacts with siHca to leave very low residual concentrations of siHca ia hot process water softeners. Sodium alumiaate is often used with other chemicals such as alum, ferric salts, clays, and polyelectrolytes, as a coagulant aid (18,19). 

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