Bone grafts used to repair weight-bearing tibial plateau fractures often experience cyclic loading, and there is a need for bone graft substitutes that prevent failure of fixation and subsequent morbidity. However, the specific mechanical properties required for resorbable grafts to optimize structural compatibility with native bone have yet to be established. While quasi-static tests are utilized to assess weight-bearing ability, compressive strength alone is a poor indicator of in vivo performance. In the present study, we investigated the effects of interfacial bonding on material properties under conditions that re-capitulate the cyclic loading associated with weight-bearing fractures. Dynamic compressive fatigue properties of polyurethane (PUR) composites made with either unmodified (U-) or polycaprolactone surface-modified (PCL-) 45S5 bioactive glass (BG) particles were compared to a commercially available calcium sulfate and phosphate-based (CaS/P) bone cement at physiologically relevant stresses (5–30 MPa). Fatigue resistance of PCL-BG/polymer composite was superior to that of U-BG and CaS/P at higher stress levels for each of fatigue failure criteria, related to modulus, creep, and maximum displacement, and was comparable to human trabecular bone. Steady statecreep and damage accumulation occurred during the fatigue life of the PCL-BG/PURand CaS/P cement, whereas creep of U-BG/PUR primarily occurred at a low numberof loading cycles. From crack propagation testing, fracture toughness orresistance to crack growth was significantly higher for the PCL-BG compositethan for the other materials. Finally, the fatigue and fracture toughnessproperties were intermediate between those of trabecular and cortical bone.These findings highlight the potential of PCL-BG/polyurethane composites asweight-bearing bone grafts.
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