Supplementary material from "HDPE/UHMWPE hybrid nanocomposites with surface functionalized graphene oxide towards improved strength and cytocompatibility"

High-density polyethylene (HDPE)-based and ultra-high molecular weight polyethylene (UHMWPE)-based composites with carbonaceous reinforcements are being widely investigated for biomedical applications. The enhancement of material properties critically depends on the nature, amount and compatibility of the reinforcement with the polymeric matrix. To this end, this study demonstrates the efficacy of a ‘dual’ hybrid approach of incorporating modified inorganic nanofiller into an optimized polyethylene blend. In particular, a unique synthesis strategy was adopted to design a covalently bonded maleated polyethylene (mPE) grafted modified graphene oxide (mGO) hybrid nanocomposite. In this scheme, polyethyleneimine (PEI) was initially attached onto GO to synthesize amine functionalized GO (GO–PEI). This is followed by mPE grafting, resulting in mGO. Melt-extrusion together with injection moulding of a polymer mix (60% HDPE–40% UHMWPE) with different proportions (less than or equal to 3 wt%) of surface functionalized GO was conducted to develop nanocomposites of different sizes and shapes. The nanocomposites with 1 wt% mGO resulted in an increased ultimate tensile strength by 120% (up to 65 MPa) and elastic modulus by 40% (up to 908 MPa), when compared with the neat blend. The uniform dispersion of modified GO nanofillers, confirmed using X-ray micro-computed tomography and transmission electron microscopy, facilitated effective interfacial adhesion and compatibility with the hybrid polymer matrix. The variation in mechanical properties with GO/mGO addition to PE blend was critically discussed in reference to the structural modification of GO, crystallinity and nature of dispersion of fillers. The nanocomposites also support the attachment and proliferation of C2C12 murine myoblast cells over 3 days in culture in statistically insignificant manner with respect to polymer blends without any nanofiller. Taken together, the experimental results suggest that this innovative approach of tailored addition of surface functionalized GO to HDPE/UHMWPE blend has unique potential for enhancement in the mechanical properties with desired cytocompatibility, making it a promising candidate for bone tissue engineering applications.