Fiber-reinforced, polycarbonate-based polyurethane composites for enhanced long-term fatigue resistance in orthopedic applications

Orthopedic implants demand materials that combine long-term biocompatibility with robust mechanical durability to ensure sustained load-bearing performance and reliable tissue integration. However, conventional implant materials often exhibit inadequate dimensional stability and limited fatigue resistance over prolonged use. In this study, three medical-grade polycarbonate-based polyurethanes (PCUs) and their fiber-reinforced composites (totalling five material models) were systematically evaluated for mechanical and biological performance; of these, PU-3585 was identified as an optimal base material. To further enhance functionality, PU-3585 was reinforced with either aramid or ultra-high-molecular-weight polyethylene (UHMWPE) fibers. Compared to unreinforced PU-3585, UHMWPE fiber reinforcement led to a 1.2-fold increase in tensile strength. Notably, aramid fiber reinforcement resulted in a 2.7-fold improvement in tensile strength and a 7.56-fold enhancement in stress retention under 30% strain during stress relaxation testing. Creep displacement under a 40 N load was significantly suppressed to approximately 0.88%, and the creep rate was reduced from 0.73%/min to 0.0045%/min. These findings highlight the superior mechanical resilience imparted by fiber reinforcement, particularly with aramid fibers, positioning these PCU composites as promising candidates for durable, long-term orthopedic implant applications.