Creating polysaccharide-protein complexes to control aqueous lubrication

An emerging understanding of natural biolubricants such as saliva and synovial fluid reveals that they rely on synergistic interactions between biomacromolecules in aqueous media, wherein one polymeric component promotes adsorption to biological substrates while another facilitates hydration lubrication. We hypothesize that this phenomenon can be achieved by combining the strong adsorption characteristics of proteins with the hydration of polysaccharides. To confirm this hypothesis, hydrated soluble complexes were formed through electrostatic interactions between positively-charged lysozyme molecules and anionic residues on pectic polysaccharides extracted from Plantago ovata seed mucilage. Boundary friction was measured between smooth hydrophobic polydimethylsiloxane (PDMS) surfaces using a ball-and-disk tribometer, while adsorption was assessed using a combination of the quartz-crystal microbalance with dissipation monitoring technique and ellipsometry. The results indicate that complexation between polysaccharides and proteins leads to improved adsorption on hydrophobic PDMS surfaces, which in turn decreases boundary friction in sliding contact. By comparing the adsorption behaviour of the complexes and individual components, we conclude that pectic polymers maintain the film's hydration while lysozyme improves surface adsorption, thereby providing new evidence that physical complexes can be utilised to design bi-functional surface layers. Our findings open up a range of opportunities for application in food and oral healthcare products, particularly in the use of food-compatible ingredients to control aqueous lubrication.