Human Fibrinogen Adsorption on Positively ChargedLatex Particles.

Fibrinogen (Fb) adsorption on positivelycharged latex particles(average diameter of 800 nm) was studied using the microelectrophoreticand the concentration depletion methods based on AFM imaging. Monolayerson latex were adsorbed from diluted bulk solutions at pH 7.4 and anionic strength in the range of 10–3to 0.15 M wherefibrinogen molecules exhibited an average negative charge. The electrophoreticmobility of the latex after controlled fibrinogen adsorption was systematicallymeasured. A monotonic decrease in the electrophoretic mobility offibrinogen-covered latex was observed for all ionic strengths. Theresults of these experiments were interpreted according to the three-dimensionalelectrokinetic model. It was also determined using the concentrationdepletion method that fibrinogen adsorption was irreversible and themaximum coverage was equal to 0.6 mg m–2for ionicstrength 10–3M and 1.3 mg m–2for ionic strength 0.15 M. The increase of the maximum coveragewas confirmed by theoretical modeling based on the random sequentialadsorption approach. Paradoxically, the maximum coverage of fibrinogenon positively charged latex particles was more than two times lowerthan the maximum coverage obtained for negative latex particles (3.2mg m–2) at pH 7.4 and ionic strength of 0.15 M.This was interpreted as a result of the side-on adsorption of fibrinogenmolecules with their negatively charged core attached to the positivelycharged latex surface. The stability and acid base properties of fibrinogenmonolayers on latex were also determined in pH cycling experimentswhere it was observed that there were no irreversible conformationalchanges in the fibrinogen monolayers. Additionally, the zeta potentialof monolayers was more positive than the zeta potential of fibrinogenin the bulk, which proves a heterogeneous charge distribution. Theseexperimental data reveal a new, side-on adsorption mechanism of fibrinogenon positively charged surfaces and confirmed the decisive role ofelectrostatic interactions in this process. [ABSTRACT FROM AUTHOR]