A bilayer composite hydrogel with simultaneous high load bearing and superior lubrication by dopamine modified nano-hydroxyapatite

Zwitterionic polymer is an ideal material with excellent biocompatibility and hydrophilicity for biomimetic soft tissue. Inspired by the structure of natural cartilage, a bilayer structural model was designed. By using dopamine to modify nano-hydroxyapatite as an additive, we prepared a bilayer nanocomposite hydrogel with excellent surface lubrication and high bottom load-bearing. The porous structure on the top layer could interact with water molecules to form a lubrication film for lower friction (CoF∼0.01) while the bottom layer provides sufficient compressive strength, arriving at approximately 14.55 MPa. The outstanding tribological behavior was mainly attributed to the biphasic and hydration lubrication of the hydrogel. This study provides a new design idea for the optimization of hydrogel lubrication performance.