Bionic layered hydrogel with high strength for excellent lubrication and load capacity.

Traditional hydrogels with soft and wet features often show poor mechanical properties due to their single cross‐linked network and amorphous structure. Hence, there are still great challenges in the preparation of strong and elastic hydrogels with superior lubrication performance for broader applications. Inspired by the biphasic structure of natural cartilage, the tough layered P(AM‐AA)‐Fe3+ (poly(acrylamide‐co‐acrylic acid)‐Fe3+) hydrogels are prepared via a sodium citrate treatment‐induced surface dissociation approach. The top lubricating layer with porous structure and high water content can achieve ultra‐low friction (friction coefficient [COF] ~ 0.010 at 5 N load), whereas the bottom stiff layer with compact structure demonstrates excellent load‐bearing capacity. The layered structure could provide hydrogels with excellent physical functions such as high strength (~7.1 MPa), superior lubrication (COF ~ 0.018, 10 N), and wear resistance (COF < 0.05, 5 N, 18,000 cycles), thereby expanding the application of hydrogel in the field of bioinspired lubrication materials. [ABSTRACT FROM AUTHOR]