Employing the colloidal probe AFM technique we have investigated normal and friction forces between flat mica surfaces and silica particles coated with mucin and combined mucin-chitosan layers in presence and absence of anionic surfactant, SDS, in 30 mM NaCl solution. We have shown that the normal interactions between mucin coated mica and silica surfaces are dominated by long-range steric repulsion on both compression and decompression. Friction forces between such mucin layers are characterized by a low effective friction coefficient, mu(eff) = 0.03 +/- 0.02, which is lower than the value of 0.13 +/- 0.02 observed when chitosan layers were adsorbed. Forces between combined mucin-chitosan layers have Adsorption of chitosan on mucin results in considerable compaction of the layer, also been measured. and development of attractive forces detectable on separation. Friction between mucin-chitosan layers in 30 mM NaCl solution is high, with mu(eff) approximate to 0.4. Adsorption of additional mucin to this layer results in no improvement with respect to lubrication as compared to the mucin-chitosan layer, and mu(eff) approximate to 0.4 is We argue that the layers containing both mucin and chitosan are not strictly layered but rather observed. As a result attractive interactions between oppositely charged moieties of sialic acid strongly entangled. residues from mucin and amine groups from chitosan residing on the opposing surfaces contribute to the increased friction. The effects of SDS on normal and friction forces between combined mucin-chitosan layers were also investigated. The relation between surface interactions and friction properties is discussed. (c) 2008 Elsevier Inc. All rights reserved.