Semi-open surface structures dramatically enhance the lubrication performance of in-situ grown hydrogel coatings

The lubrication properties of hydrogel coatings depend on their surface hydrated dangling chains and network structures. These properties are strongly influenced by the gelation environment, resulting in orders of magnitude variations in wettability and friction coefficient even within the same hydrogel system. Developing a suitable fabrication strategy and gelation environment to create surfaces with dense dangling chains and gradient network structures for hydrogel coating can enhance surface hydration and stress dissipation, thus significantly improving lubrication performance. In our research, we utilized the catechol-based interface catalytic initiation to in-situ grow hydrogel coatings (IGHC) for enhancing lubrication. The semi-open gelation environment during the in-situ growth system generated high density surface dangling chains, while the interfacial reaction-diffusion enabled gradient networks, resulting in a semi-open surface structure. Load-dependent ATR-FTIR, LF-NMR, Nanoindentation and SEM were applied to confirm these structures. Compared the wettability and friction coefficient to the conventional bulk polymerized hydrogel coatings (BPHC), prepared by one-pot gelation with crosslinked and uniform network structure, the IGHC exhibited excellent hydrophilicity, a 10-fold increase in load-bearing capacity, and a 10-fold reduction in friction coefficient, respectively. Furthermore, IGHC also exhibited superior rehydration, anti-fouling, drag reduction as well as shape adaptability than BPHC due to this semi-open structure. This work systematically demonstrated excellent lubricity and mechanism in hydrogel coatings prepared by in-situ growth. It highlights the advantages of this in-situ strategy for designing lubricating hydrogel coatings, significantly advancing their potential applications.