Self-lubricating and wet-adhesive bilayer UPG-PAN elastomeric cartilage substitute enabled by glycerol surface migration and PEGS/Gly-modulated fatigue resistance

UPG-PAN integrates self-lubrication, wet adhesion, and fatigue resistance. • UPG-2 achieved 3.22 MPa strength and 92.5% fatigue resistance. • Glycerol migration lowered contact angle to 28° and friction to 0.035. • PAN-2 provided 27.53 kPa wet adhesion to subchondral bone. • UPG-PAN showed good cytocompatibility and milder early tissue response. Articular cartilage remains a significant clinical challenge. The ideal implant would support joint loads, resist fatigue, reduce friction, adhere to wet subchondral bone and demonstrate good biocompatibility. Although hydrogels have a hydration profile similar to that of cartilage, many lack long-term durability under load. Elastomers have higher mechanical strength, but they often show poor surface lubrication and weak wet-tissue adhesion. In this study, we developed a biomimetic bilayer elastomeric cartilage substitute, named UPG-PAN. It contains a self-lubricating upper elastomer layer, UPG, and a wet-adhesive lower hydrogel layer, PAN. In the UPG layer, thermoplastic polyurethane (TPU) forms the elastic load-bearing framework. Poly(ethylene glycol)-modified poly(glycerol sebacate) (PEGS) and glycerol (Gly) regulate chain entanglement, reversible hydrogen bonding, surface hydration, and energy dissipation. The UPG-2 elastomers maintained MPa-level compressive strength (∼3.22 MPa), tunable modulus (∼1.58 MPa), stable cyclic compression behavior, and good fatigue resistance (∼92.5%). Gly migrated toward the material surface during formation and drying. This migration formed an OH-rich hydrated lubricating layer. The layer improved surface wettability and helped maintain low friction during reciprocating sliding (∼0.035 COF). The PAN layer was prepared by photocuring PEGS-Ac, PEGS-NH 2 , and acrylic acid (AAc). This layer formed a continuous UPG-PAN interface and strong wet adhesion to bone (∼27.53 kPa). The adhesion was related to interfacial chain interpenetration, hydrogen bonding, crosslinking, and electrostatic interactions. L929 cell culture and rat subcutaneous implantation showed good biological safety. Compared with TPU-PAN, UPG-PAN showed improved cytocompatibility and a milder early inflammatory response. Overall, UPG-PAN combines fatigue-resistant mechanical support, self-lubrication, wet fixation, and biocompatibility. This bilayer design may help slow local cartilage degeneration and delay invasive joint replacement in patients with focal cartilage defects.