A triple‐layered hybrid coating with self‐organized microporous polymer film on magnesium for biodegradable implant applications

In this study, a triple‐layered hybrid coating with self‐organized microporous polymer film was developed on pure magnesium for biodegradable implant applications. Firstly, plasma electrolytic oxidation (PEO) technique was used to form a highly adherent but porous coating on magnesium metal. Secondly, the pores in the PEO coating were sealed by electrochemically depositing calcium phosphate (CaP). Finally, a self‐organized microporous biodegradable polymer, poly( l ‐lactide acid) PLLA, was formed as a top coat on the material using spin coating method. The degradation resistance of the triple‐layer coated magnesium was evaluated using electrochemical techniques in simulated body fluid (SBF). The triple‐layered hybrid coating reduced the corrosion current density ( i corr ) of pure magnesium from 28.79 to 0.24 μA/cm 2 . Similarly, the electrochemical impedance spectroscopy (EIS) results showed that the triple‐layered hybrid coating increased the polarization resistance ( R p ) of pure magnesium more than three orders of magnitude after 2 hr exposure to SBF (pure Mg: 4.76 × 10 +2  Ω cm 2 ; triple‐layer coating: 8.67 × 10 +5  Ω cm 2 ). Although the R p of the triple‐layer coated magnesium decreased with increase of immersion time in SBF (8 hr = 4.27 × 10 +5  Ω cm 2 ; 24 hr = 1.57 × 10 +5  Ω cm 2 ; 48 hr = 6.5 × 10 +4  Ω cm 2 ; 72 hr = 3.5 × 10 +4  Ω cm 2 ), it was noted that the R p of the triple‐layer coated magnesium was two orders of magnitude greater than pure magnesium even after 72 hr exposure to SBF, which shows the robust nature of the coating. Further, the architecture and the dissolution mechanism of the triple‐layer coating suggest that the coating has a great potential for tailoring the degradation rate of magnesium for targeted implant applications.