Enhanced corrosion resistance of magnesium alloy via surface transfer of microwave-synthesized, non-toxic, and ultra-smooth nitrogen-doped amorphous carbon thin film

Magnesium (Mg) alloys are increasingly recognized as a promising material for the next generation of implants due to their biocompatibility, favourable mechanical strength, and ability to biodegrade effectively in physio-logical environments. However, their clinical utility is hindered by rapid corrosion. This study introduces and investigates the application of an ultrathin, ultra-smooth, and corrosion-resistant nitrogen-doped amorphous
carbon (a-C:N) thin film on a magnesium alloy (Mg-0.5Zn-0.2Ca) for the first time. The a-C:N film was synthesized using a polymer composite based on branched polyethyleneimine and subsequently applied to the magnesium alloy surface to enhance its corrosion resistance. Comprehensive characterization using advanced techniques confirmed the amorphous nature of the synthesized film, revealing the presence of sp2-C, sp3-C, and
C-N bonds. AFM analyses and electrochemical corrosion tests demonstrated that the synthesized a-C:N film exhibits excellent corrosion resistance and reduces the corrosion rate of the substrate. Additionally, cytotoxicity
tests indicated that the film is non-toxic and compatible for orthopaedic implant applications, thereby expanding the potential clinical use of Mg-based implants. Carbon, being a biocompatible and inert nonmetallic element, makes it a suitable choice for enhancing the biocompatibility and corrosion resistance of Mg-based implants.