Macromolecular Coatings Enhance the Tribological Performance of Polymer-Based Lubricants

In many biomedical settings, hard surfaces cause friction and wear at interfaces. Surface coatings have been introduced to reduce tribological stress—especially at slow sliding velocities where boundary friction dominates. Here, the ability of coatings generated from differently charged macromolecules, i.e., poly(ethylene glycol) (uncharged), mucin (polyanionic), and poly-l-lysine (polycationic), to synergistically interact with polymer-based lubricants is studied as they are also present in almost every body fluid. It is demonstrated that, in combination with solutions containing either poly(ethylene glycol) or hyaluronic acid, these surface-bound macromolecules significantly reduce boundary friction and, in addition, protect the surfaces from wear formation. This is attributed to entanglement effects between surface-bound and solubilized macromolecules, which are most efficient in the absence of repulsive electrostatic forces. The synergetic effects described here could help optimizing medical devices such as catheters, endotracheal tubes, stents, or contact lenses to reduce patient discomfort and prevent inflammatory reactions arising from tribological stress.