Adsorption and nanowear properties of bovine submaxillary mucin films on solid surfaces: Influence of solution pH and substrate hydrophobicity

• BSM formed more stable films on hydrophobic surfaces than on hydrophilic ones.
• Stronger BSM films were formed at acidic than at neutral conditions.
• BSM diffuses laterally on hydrophobic surfaces but not on hydrophilic ones.

The adsorption and mechanical stability of bovine submaxillary mucins (BSM) films at solid–liquid interfaces were studied with respect to both substrate hydrophobicity and solution pH. Dynamic light scattering revealed a single peak distribution in neutral aqueous solution (pH 7.4) and a small fraction with enhanced aggregation was observed in acidic solution (pH 3.8). Both substrate hydrophobicity and solution pH were found to affect the spontaneous adsorption of BSM onto solid surfaces; BSM adsorbed more onto hydrophobic surfaces than hydrophilic ones, and adsorbed more at pH 3.8 than at pH 7.4. Thus, the highest “dry” adsorbed mass was observed for hydrophobic surfaces in pH 3.8 solution. However, a highest “wet” adsorbed mass, i.e. which includes the solvent coupled to the film, was observed for hydrophobic surfaces at pH 7.4. The mechanical stability of the films was studied at the nanoscale with an atomic force microscope operated in the friction force spectroscopy mode. Results revealed that BSM films formed on hydrophobic substrates were stronger than those formed on hydrophilic ones. Moreover, the film stability also depended on the ambient pH and stronger films were formed at acidic conditions, i.e. close to the BSM isoelectric point.

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