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.