Tailoring degradation behavior of CNT- and GNS-reinforced AZ61 and AZ91 magnesium matrix biodegradable nanocomposites for biomedical applications: The effect of reinforcement content

Magnesium alloys are promising candidates for biodegradable implants due to their biocompatibility and mechanical properties comparable to natural bone. However, their rapid corrosion in physiological environments limits their clinical application. This study comparatively evaluates the electrochemical corrosion behavior of carbon nanotube (CNT)- and graphene nanosheet (GNS)-reinforced AZ61 and AZ91 composites in Hank’s solution. The composites were fabricated via powder metallurgy with reinforcement contents of 0.1, 0.2, and 0.5 wt.%. Potentiodynamic polarization (PDP) and electrochemical impedance spectroscopy (EIS) tests were carried out under in-vitro conditions at body temperature (37 °C). In addition, SEM/EDS, XRD and X-ray photoelectron spectroscopy (XPS) analyses were performed to investigate the morphology and chemical nature of the corrosion products formed after immersion in Hank’s solution. The results reveal that low reinforcement contents significantly improve corrosion resistance compared to unreinforced alloys, except for specific higher/intermediate reinforcement contents, demonstrating a clear dependence on reinforcement type, content, and matrix composition. In particular, the highest corrosion resistance was achieved in AZ61 and AZ91 alloys containing 0.1 wt.% CNT, owing to uniform dispersion and formation of a stable surface layer. In contrast, GNS-reinforced composites showed a non-linear behavior, with improved performance at 0.5 wt.% GNS compared with 0.2 wt.% GNS in both AZ61- and AZ91-based composites, due to nanosheet redistribution and barrier effects. XPS analyses confirmed that the corrosion layers mainly consisted of Mg(OH) 2 /MgO-based surface products enriched with Ca-containing deposits formed during immersion. While CNTs promoted more continuous Ca–P deposition indicating enhanced bioactivity and biomineralization potential, GNSs mainly improved corrosion resistance through physical protection mechanisms and surface stabilization effects.