Biodegradable polymer for sealing porous PEO layer on pure magnesium: An in vitro degradation study

An attempt was made to seal the porous silicate-based plasma electrolytic oxidation (PEO) layer on pure magnesium (Mg) with a biodegradable polymer, poly(L-lactide) (PLLA), to delay the localized degradation of magnesium-based implants in body fluid for better in-service mechanical integrity. Firstly, a silicate-based PEO coating on pure magnesium was performed using a pulsed constant current method. In order to seal the pores in the PEO layer, PLLA was coated using a two-step spin coating method. The performance of the PEO-PLLA Mg was evaluated using electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization. The EIS results showed that the polarization resistance (R-p) of the PEO-PLLA Mg was close to two orders of magnitude higher than that of the PEO Mg. While the corrosion current density (i(corr)) of the pure Mg was reduced by 65% with the PEO coating, the PEO-PLLA coating reduced the i(corr) by almost 100%. As expected, the R-p of the PEO-PLLA Mg decreased with increase in exposure time. However, it was noted that the R-p of the PEO-PLLA Mg even after 100 h was six times higher than that of the PEO Mg after 48 h exposure, and did not show any visible localized attack. (C) 2014 Elsevier B.V. All rights reserved.