Green-synthesized MXenes enable low-friction, cytocompatible PVA-chitosan hydrogels

Soft, hydrated biomaterials for cartilage-facing interfaces must combine high hydration, low friction, and cytocompatibility, yet achieving all of these properties within a single hydrogel system remains challenging. Here, we develop poly(vinyl alcohol)-chitosan (PVA-CS) hydrogels reinforced with HF-free, green-synthesized Ti₃C₂T_x MXene flakes, further modulated through a sodium-citrate salting-out process. The mild synthesis route produced mainly O-terminated, multilayered MXenes that were incorporated effectively into the polymer network. The resulting hydrogels reveal an excellent cytocompatibility as assays showed that MXenes did not impair fibroblast viability and also supported human chondrocyte viability, addressing an area scarcely available for MXene-reinforced hydrogels. In terms of physical and mechanical properties, MXene addition increased equilibrium swelling (from 198% to 221%) and maintained high water content (WC) (>89%), while still enhancing compressive and viscoelastic responses. Salting-out yielded a denser network, but at the expense of thermal sensitivity near physiological temperatures. MXene reinforcement decreased friction by ∼15% relative to PVA-CS and by ∼70-80% compared to a titanium alloy benchmark, demonstrating a clear lubrication advantage across the tested conditions. These results identify green MXene-reinforced hydrogels as safe, highly hydrated, and low-friction soft biomaterials, offering promising potential for cartilage-related and other load-bearing interfaces where reduced friction is beneficial.