High performance high-density polyethylene/hydroxyapatite nanocomposites for load-bearing bone substitute: fabrication, in vitro and in vivo biocompatibility evaluation

In this study, a strong and tough high-density polyethylene (HDPE)/hydroxyapatite (HA) nanocomposites with bone-analogues structure was successfully prepared via a simple dynamic-oscillation-shear processing method for biomedical application as bone substitute materials. Dynamic-oscillation-shear flow field was applied by self-made loop oscillatory push-pull molding (LOPPM) equipment. The LOPPM-processed HDPE/HA composites exhibited tremendous increase of tensile strength, modulus and toughness up to 95.1 MPa, 4.2 GPa, 58.4 kJ/m(2), respectively, which could be attributed to better dispersion of HA in HDPE matrix and highly ordered shishkebab structure as evident from DSC, SEM, WAXD and SAXS studies. Meanwhile, the formed hierarchical structure not only showed bone-like structure, but also endowed composites with high strength, modulus and toughness, even close to the human cortical bone. Moreover, in vitro cell culture study was performed on NIH-3T3 fibroblast cells to evaluate the biocompatibility of the composites. The results showed that the produced bone substitutes exhibit good biocompatibility. Besides, using a rabbit calvarial defect model, in vivo testing has shown that a strong and stable interface is developed between the composites and the host bone. Overall, we present a facile and green strategy to generate polymer composites with high strength and toughness and the produced LOPPM-processed HDPE/HA polymer nanocomposites have a great potential for use as load-bearing bone substitute in biomedical application.