Development of graphene-reinforced magnesium metal matrix composites for biodegradable bone implants

Author(s): Yuncang Li

Despite the promising prospects of magnesium (Mg) alloys over conventional metallic biomaterials, there are still several challenges for bone implants such as the insufficient mechanical strength and ductility of Mg alloys and its rapid degradation in the physiological environment before adequate bone healing. Nano-sized reinforcements have the potential to enhance the mechanical properties of metal matrices by Orowan strengthening and load-transfer strengthening mechanisms. In this study, powder metallurgy (PM) fabrication routes was used to fabricated new magnesium (Mg) metal matrix composites (MMCs) reinforced with graphene nanoplatelets (GNPs) for biomedical applications. GNPs (0.1, 0.2, 0.3 wt.%) with variable layer thicknesses and sizes were dispersed into Mg powder using high-energy ball-milling (BM) processes. The microstructure of the fabricated composites was characterized using transmission electron microscopy (TEM), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), optical microscopy (OM), X-ray diffraction (XRD), and Raman spectroscopy (RS). The mechanical properties were evaluated by compression tests. The corrosion resistance was investigated by electrochemical tests and hydrogen evolution measurements. The cytotoxicity was assessed using osteoblast-like cells. The results indicate that GNPs are excellent candidates as reinforcements in Mg matrices for the manufacture of biodegradable Mg implants. GNP addition improved the mechanical properties of Mg via synergetic strengthening modes including grain-refinement strengthening, thermal-mismatch strengthening, dispersion strengthening, and load-transfer strengthening. Moreover, retaining the structural integrity of dispersed GNPs improved the ductility, compressive strength, and corrosion resistance of the Mg–GNP composites. Cytotoxicity assessments did not reveal any significant adverse effects on biocompatibility with the addition of GNPs to Mg matrices. Mg–xGNPs with x < 0.3 wt.% may constitute promising biodegradable implant materials for load-bearing applications.