Robust Super-Lubricity for Novel Cartilage Prototype Inspired by Scallion Leaf Architecture

The simultaneous achievement -under physiologically high contact pressures- of ultra-low friction, nearly zero surface wear, and long lifetime in the development of human cartilage prosthetics is still a big challenge. In this work, inspired by the unique lubrication mechanism of scallion leaves resulting from the synergy of oriented surface micro-topography and mucus hydration, a novel layered soft hydrogel as cartilage prototype is developed by chemically embedding thick hydrophilic polyelectrolyte brush chains into the sub-surface of a high strength anisotropic hydrogel bulk. It exhibits an anisotropic polymer network with unique mechanical properties (tensile strength: 8.3 to 23.7 MPa; elastic modulus 20.0 to 30.0 MPa), anisotropic hydrated surface texture, super-lubricity, and excellent wear resistance. Thydrogel architecture can exhibit low coefficient of friction (COF) less than approximate to 0.01 under a wide range of contact stresses (0.2 to 2.4 MPa) and maintain cartilage-like long-lasting (50k sliding cycles) robust super-lubricity (COF approximate to 0.006) and nearly-zero wear under high contact pressure (approximate to 2.4 MPa) condition. Theoretical underpinning reveals how multiscale surface anisotropy, mechanics, and hydration regulate super-low friction generation. This work provides a novel design paradigm for the fabrication of robust soft materials with extraordinary lubricity as implantable prototypes and coatings. A novel anisotropic layered lubrication hydrogel (ALLH) is engineered by mimicking the architecture and lubrication mechanism of natural scallion leaf (NSL). The ALLH exhibits low coefficient of friction (COF) less than approximate to 0.01 under a wide range of contact stresses and demonstrates long-lasting (50k sliding cycles) robust super-lubricity (COF approximate to 0.006) along with nearly-zero wear under high contact pressure (approximate to 2.4 MPa).image