Insights of stearic acid/polypyrrole superhydrophobic coating on controlling corrosion, antibacterial and cytocompatibility of biodegradable Mg alloy and its implication on fracture fixation

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.