Lignin-based hydrogel coatings with robust lubricity and strong interfacial toughness enabled by facile soaking strategy

Hydrogel coating is an effective solution to realize the high lubricity of solid material. However, conventional hydrogel coatings face challenges of weak interfacial adhesion, insufficient mechanical strength, often requiring complex preparation processes. Herein, a robust, easily prepared PDMA/lignin/PVP physical hydrogel coating is developed by soaking a pre-formed PDMA/lignin dry coating in a polyvinylpyrrolidone (PVP) solution. The interaction between PVP and lignin enhanced the diffusion-in and prevented the diffusion-out of PVP from the coating. The long PVP chains penetrate the coating, forming hydrogen bonds with lignin and leaving dangling chains on the surface that enhances the toughness of the coating film and significantly improves lubricity (friction coefficient of around 0.03 against stainless steel). Furthermore, PVP's ability to form strong ionic interactions with metal ions results in a highly improved interfacial interaction of the coating on metal substrates with the high interfacial energy up to 1210 J m −2 . This easy to prepare, high-performance hydrogel coating shows promising application prospects, especially in the biomedical field.