Spherical polyelectrolyte brushes facilitate cartilage repair

Polymelectrolyte brushes have garnered extensive attention for their outstanding lubrication capabilities. The typical structure of brushes with chains stretched in the normal direction tends to suppress interpenetration of opposing brushes and so creates a fluid-like cushioning layer on surfaces, may slide with low friction. However, the lubrication contributions and mechanism behind of polymer structures underexplored. This study aims to evaluate the lubrication performance where various monomers are used. Especially, we utilized 2-methacryloyloxyethyl phosphorylcholine (MPC) and 2-acrylamide-2-methylpropanesulfonic acid sodium salt (AMPS) as monomers, polymerized from the surface of spherical gelatin-based nanoparticles. Our findings reveal that mixing monomers is favorable; the mixture of brushes, and in particular the copolymer brush provides significantly lower friction coefficients than the corresponding homopolymers. We then show, both experimentally and theoretically, that these findings can be explained by the lower Van der Waals attraction between chemically dissimilar monomers. Finally, our results show that superior lubrication also leads to spontaneous repair of damaged biological tissues such as arthritic cartilage and tendon. Such insights should help to development novel and better biomimetic lubrication materials.