Interaction of porcine gastric mucin with various polycations and its influence on the boundary lubrication properties

The interaction of porcine gastric mucin (PGM) with polycations possessing amine functional groups, including polyallylamine hydrochloride (PAH), poly-l-lysine (PLL) and polyethylenimine (PEI), was examined from a tribological standpoint at a self-mated polydimethylsiloxane (PDMS) interface. In all cases, PGM interacted with the cationic polymers, leading to a smaller size of the aggregates compared to PGM, surface charge compensation, and distortion of the PGM protein conformation. But, a synergistic lubrication effect was clearly observed only from the 1/1 (w/w) mixture of PGM with branched PEI (B-PEI) where the friction coefficient was reduced by two orders of magnitude compared to neat PGM or B-PEI in the speed range of 0.25-100 mm/s. This was attributed to the smallest hydrodynamic size and "sphere-like" conformation of B-PEI due to high degree of branching, which favors tenacious complexation with PGM, fast surface adsorption, and continuous reformation of the lubricating layer under cyclic tribostress in pin-on-disc tribometry. (C) 2016 Elsevier Ltd. All rights reserved.