Mucin layers on hydrophobic surfaces studied with ellipsometry and surface force measurements

• The forces acting between layers of gastric mucins from rat (RGM) and pig (PGM) adsorbed on to hydrophobized mica surfaces were investigated by using the surface force technique, whereas information on the kinetics and the reversibility of the adsorption process was obtained with ellipsometry. From the surface force measurements, we found that the amount adsorbed from a 0.1 mg/ml RGM solution was 3.5±1.5 mg/m2 at adsorption equilibrium, within experimental error equal to that (about 3 mg/m2) found with ellipsometry. The forces obtained with RGM were purely repulsive, whereas those displayed by PGM were partially attractive. Dilution of the bulk solution caused only minor desorption and the interaction force between the RGM layers was only weakly dependent on the excess electrolyte concentration. Hence, steric forces predominate the interaction in the RGM system. Both RGM and PGM adsorb in a flat conformation, with compressed adsorbed layer thicknesses of 10-20 nm and 3-4 nm, respectively. The interaction force was essentially reversible on approach and separation for RGM, whereas 'relaxation effects' were prominent for PGM layers.

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