Interactions between mucin and surfactants at solid-liquid interfaces

The association between mucin and surfactants at the solid-liquid interface has been investigated employing reflectometry. The study is particularly aimed at understanding the removal of preadsorbed mucin layers by surfactant addition. To this end we investigated the effect of three different surfactants, one anionic surfactant, sodium dodecylsulfate (SDS), and two nonionic ones, penta(oxy ethylene) dodecyl ether (C12E5) and n-dodecyl beta-D-maltopyranoside (C-12-mal), All three surfactants were found to be potent in removing mucin from hydrophobic surfaces. On the otherhand, C-12-mal was found to have a very limited effect on mucin adsorbed to hydrophilic negatively charged surfaces, whereas the mucin layer was removed by SDS and C12E5. The association between mucin and the three different surfactants was also investigated by means of dynamic light scattering and surface tension measurements. It was concluded that SDS associates readily with mucin above a critical surfactant concentration, about 0.2 cmc, whereas the nonionic surfactants associate with mucin to a very limited degree. The results obtained with the different techniques allow us to propose that C12E5 removes mucin from silica surfaces by competitive adsorption, whereas the removal of mucin by SDS is due to formation of mucin/SDS complexes that have reduced surface affinity and increased water solubility compared to mucin alone.