Development of Multifunctional Mg-3Zn-0.5Mn/0.5GNP Nanocomposites Modified with Rare-Earth Oxide Addition and Hot Rolling for Biodegradable Orthopaedic Implants

Although magnesium-based biomaterials are promising for biodegradable implants owing to their bone-matching mechanical properties, their clinical adoption is hindered by insufficient strength, rapid degradation, and limited biocompatibility. Graphene nanoplatelets (GNPs) hold the potential to enhance mechanical performance and corrosion resistance when well dispersed at low concentrations but may compromise long-term biocompatibility. Moreover, hybridising GNPs with nano CeO2 (n-CeO2), which is largely unexplored, can improve cytocompatibility, and hot rolling can further strengthen this by refining the grain size beyond what is achieved by incorporating reinforcement alone. In the current investigation, Mg–3Zn–0.5Mn/0.5GNP nanocomposites, with and without bone-friendly n-CeO2, were fabricated by stir casting, followed by hot rolling at 350 °C, and were comprehensively investigated for their microstructure, mechanical properties, in vitro corrosion, and biocompatibility. The incorporation of GNPs alone enhanced yield strength by 72.4% and elongation at fracture by 8.63% compared to pure Mg, and the lowest hydrogen evolution rate among all fabricated composites. Hybridising GNPs with n-CeO2 further improved yield strength and elongation at fracture by 118.9% and 10.78%, respectively, enhanced MG-63 cell viability, and increased initial degradation resistance, but a less stable protective layer led to higher degradation during prolonged PBS immersion. The hot-rolled, hybrid GNP/n-CeO2 composite exhibited the highest strength improvements, with increases of 185% in yield and 90.6% ultimate strength, owing to further grain refinement and a strong basal texture. Thus, the developed nanocomposites are promising, and the investigation presents a cost-effective and scalable approach to tailoring the mechanical, degradation, and biocompatibility of biodegradable biomaterials.