Properties of Interfacial Proteinaceous Films with Emphasis on Oral Systems

Sammanfattning: The present thesis addresses three issues related to proteinaceous films at solid/liquid interfaces: adsorption, lubrication and enzymatic interactions. Most of the work has been devoted to oral systems. In addition, gelatin has been investigated as a model protein. Salivary protein adsorption from human whole saliva (HWS) onto hydroxyapatite (HA) and silica has been characterised using ellipsometry. The shapes of the adsorption isotherms at HA and silica were similar, indicating similar surface affinities for the two substrates. Desorption, as induced by the addition of sodium dodecyl sulphate (SDS) to the salivary pellicles, was found to occur in the same SDS concentration range at both surfaces, although a residual layer was observed at HA. Normal and lateral forces between surfaces bearing adsorbed salivary films have been investigated by colloidal probe atomic force microscopy. The presence of salivary pellicles, adsorbed from HWS, largely reduced the friction between hard surfaces. The normal forces acting between such salivary films were found to be purely repulsive. Further investigation of three pellicle key proteins (human acidic proline-rich protein 1 (PRP-1), human statherin and mucin (bovine submaxillary mucin, BSM)) revealed lubricating capacities in the order PRP-1 > BSM > statherin. Investigations of enzymatic degradation of proteinaceous films of oral origin indicated that the observed removal of dental plaque by krillase may partly be due to a degradation of the salivary pellicle. The results obtained demonstrate the potential of krillase for plaque control. Interactions upon exposure of adsorbed gelatin layers to the proteolytic enzymes trypsin and krillase have been studied using ellipsometry and total internal reflectance fluorescence spectroscopy. In brief, the behaviour at hydrophobic substrates was to a large extent determined by proteolytic degradation, although interfacial exchange processes could not be disregarded. At hydrophilic substrates, the balance between interfacial degradation and exchange was reversed. Furthermore, temperature effects were noted on the enzyme-induced desorption rates and the residual adsorbed amounts.