How synergistic aqueous lubrication is mediated by natural and synthetic molecular aggregates

Abstract

Nature lubricates in aqueous environment, and thus the example of a human synovial joint with its seamless function has been a fascination for scientists since the times of the birth of modern science. Here, inspired by nature, we investigate the mechanistic function of three different types of synergistic molecular aggregates. Firstly, we show how simple phospholipids lubricate hydrophilic model surfaces of silica and how this lubrication is facilitated further by the presence of an anionic polysaccharide, hyaluronan, due to the enhanced surface build-up of lubricant material. Next, we mimic natural polylectrolytesurfactant aggregation by employing a highly positively charged polyelectrolyte and anionic surfactant that strongly associate both in the bulk and at the surfaces by building structured aggregates that lubricate due to hydration lubrication. This occurs despite of the presence of strong attraction between the lubricated surfaces. This is an example of synergistic lubrication due to particular internal structural arrangement of the aggregates. Finally, we investigate the case of synergistic lubrication due to preferential surface ordering of two biological polyelectrolytes, cartilage oligomeric matrix protein and lubricin, that leads to favourable lubrication.