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

Abstract

The interaction of porcine gastric mucin (PGM) with polycations possessing amine functional groups,including polyallylamine hydrochloride (PAH), poly-l-lysine (PLL) and polyethylenimine (PEI), wasexamined from a tribological standpoint at a self-mated polydimethylsiloxane (PDMS) interface. In allcases, PGM interacted with the cationic polymers, leading to a smaller size of the aggregates compared toPGM, surface charge compensation, and distortion of the PGM protein conformation. But, a synergisticlubrication effect was clearly observed only from the 1/1 (w/w) mixture of PGM with branched PEI (BPEI)where the friction coefficient was reduced by two orders of magnitude compared to neat PGM or BPEIin the speed range of 0.25e100 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 complexationwith PGM, fast surface adsorption, and continuous reformation of the lubricating layer under cyclictribostress in pin-on-disc tribometry