Design and tribological study of cartilage-inspired biphasic hydrogel-containing composites

Boundary lubrication under harsh working conditions results in severe wear of water-lubricated bearing materials, e.g., a tail bearing in a ship. Inspired by cartilage lubrication, we prepare a smart hydrogel with balanced hydration and load-bearing properties through the construction of polyvinyl alcohol (PVA)-chitosan/sodium alginate (CS/SA) double networks and the introduction of aramid nanofibers. The hydrogels are blended with ultrahigh molecular weight polyethylene (UHMWPE) particles into new bionic biphasic hydrogel-containing composites. Thorough assessments (chemical, thermal, surface, and bulk mechanical properties) of the hydrogels and composites revealed that the high hydrophilicity of the hydrogel particles encapsulated in bulk UHMWPE facilitates water absorption, leading to improved friction performance under the boundary lubrication mode, e.g., at startup. The stripped hydrogel pits and induced microtextures between the friction interfaces as the hydration layer play a role in separating the friction interface, effectively reducing the friction contact. Under a 40 N load, the friction coefficient and wear rate of one composite are 28.7% and 14% lower than those of the plain UHMWPE composite, respectively. After soaking in seawater for 28 days and holding at 50 °C for 1 h, the mechanical properties of the composite material are still better than those of plain UHMWPE. Taken together, the smart biphasic hydrogel-containing composites were able to improve the lubrication state according to the operating conditions.