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Date of Award

11-1991

Degree Type

Thesis

Degree Name

Doctor of Philosophy (PhD)

Department

Chemical Engineering

Supervisor

J.L. Brash

Abstract

Blood coagulation and protein adsorption were studied on a series of model surfaces. Silanes were used to covalently attach chemical groups (including sulfonate. amine, polyethylene oxide (PEO), lysine methyl, and octadecyl) to pure silica substrates. Surface chemical analysis by x-ray photoelectron spectroscopy (XPS) was used to quantify the elemental composition of these surfaces. All silane layers were estimated to be monolayers or less with thickness in the range 0.2 nm (for methyl groups) to 2.0 nm (for PEO). Contact angles were measured to help quantify the interaction between the model surfaces and pure solvents (water, glycerol, dimethyl sulfoxide (DMSO)). The data were fit to established interfacial tension (interfacial free energy) models but none was found to be adequate. A new empirical model, not related to surface energetics, was developed and demonstrated to be capable of fitting the data more precisely. Small deviations from the empirical model (± 2° to 8°) for DMSO and water contact angles were attributed to the possible influence of surface charge. Protein adsorption kinetics on the model surfaces was measured using ¹²⁵I-labeled fibrinogen and albumin as single proteins under static conditions. A simulation of transport and reaction in this experimental system was written and used to fit data to proposed models for protein adsorption. A simple bilayer mechanism was found to fit the kinetic data better than a number of multistate monolayer models for adsorption. The adsorption of fibrinogen from plasma was also measured in order to investigate a possible relationship between the Vroman effect and surface activated blood coagulation. A surface activated blood coagulation assay based on the partial thromboplastin time test was used to characterize the blood compatibility of model surfaces prepared on glass test tubes. The kinetics of cleavage of a fluorogenic substrate for thrombin was measured in real time on surfaces which were assumed to be closely comparable to those prepared on pure silica. Clotting times ranging between 2 and 11 minutes were measured. A correlation analysis was performed using surface chemistry, contact angle, protein adsorption, and blood coagulation data. Clotting times were found to be empirically related to surface chemistry, but not to fibrinogen adsorption or the Vroman effect. The Vroman effect for fibrinogen was found to be predictable in most cases given only single component fibrinogen adsorption data. Fibrinogen adsorption from buffer was found to increase with sulfur (sulfonate) content and decrease with nitrogen (amino) content, but contrary to suggestions in the literature was not a strong function of wettability. A multivariate approach to studying the interactions between blood, proteins and model surfaces proved to be a practical approach to a complex problem. It was demonstrated that univariate relationships are often inadequate in their ability to explain the interfacial behavior of blood and its elements, and in fact may lead to erroneous conclusions

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