Magnesium alloys have long been recognized as promising degradable biomaterials, however, bacterial infection, poor mechanical and corrosion properties limit its clinical application. In this study, controlled aging of forged Mg-Mn-Gd alloy leads to the development of nano Mg₅Gd precipitate, which improved mechanical, corrosion and antibacterial performance without deteriorating cytocompatibility. High resolution transmission electron microscopy (HRTEM) observations confirmed nano-scale Mg₅Gd precipitates and their subsequent coarsening during transition from peak-aging to overaging. The nature of dislocation-precipitate interaction, size, fraction, and coherency-dependent characteristics of nano-scale Mg₅Gd precipitates are accountable for strengthening in aged specimens. The precipitation-dislocation interaction governed by precipitate-shearing mechanism contributes to pronounced strengthening in peak-aged specimen. The reduced volta potential difference between the galvanic couples (α-Mg and Mg₅Gd), residual strain removal, strengthened basal texture and fine semi-coherent Mg₅Gd precipitate of peak-aged specimen significantly improved the corrosion resistance. All the investigated specimens exhibit strong antibacterial performance against gram-negative Escherichia coli (DH5α) bacteria, primarily attributed to the release of Mg and Gd ions. The applied thermal treatment to the forged specimen exhibited no signs of cytotoxicity, rather promoted cell proliferation and osteogenic differentiation against MC3T3-E1 cells. Micro-CT and hard tissue histology by Masson’s trichome staining demonstrated highest bone-implant integration and active callus formation across the peak-aged implant in rabbit femur. Furthermore, the peak-aged specimen was well tolerated by all the vital organs without any histological abnormalities. Overall study demonstrated that the thermomechanical process optimization can effectively tailor the Mg-Mn-Gd alloy for successful internal fracture fixation application.

Surface modification is found to be an effective way to control the initial degradation of Mg based biomedical alloys. The present study focuses on the modulation of in vitro and in vivo degradation behavior of Mg-Ce alloy through a stearic acid-treated polypyrrole coating, which developed superhydrophobic surface (contact angle ~ 153°) that drastically enhanced the corrosion resistance (more than 85% efficacy). Cerium addition to Mg alloy results basal texture strengthening and grain refinement, resulting in improved mechanical properties. All the specimens exhibited excellent antibacterial performance against gram-negative E. Coli (DH5α) and gram positive S. aureus bacteria. The oligodynamic effect of polypyrrole coating leads to complete bacterial mitigation. Non-toxic nature of the specimens was studied by MC3T3-E1 cell proliferation and differentiation in indirect cell culture method. Improved corrosion resistance of the coated specimen leads to enhanced cell proliferation and osteogenic differentiation. Hard tissue histology and micro-CT analysis exhibited higher fraction of newly formed callus tissues and highest bone-implant integration across the coated specimen, when implanted in rabbit femur. Efficacy of the material in fracture healing was evaluated by implanting bone plate and screw in a clinically fractured goat tibia. At 3 months, complete fracture healed with no vital organ toxicity was observed for the coated specimen. The present results suggest that Ce addition and polypyrrole coating are effective ways to modulate the corrosion and biocompatibility behavior making it a potential candidate for fracture fixation applications.