The effect of polylactic acid ordering on the long-term corrosion protection capacity of biodegradable magnesium alloys

The polylactic acid (PLA) coatings of different crystallinity were prepared on biodegradable Mg-2.2Zn-0.3Ca alloy wires to improve the long-term anti-corrosion properties. The composition characteristics and microstructure of the samples were investigated by differential scanning calorimetry (DSC), Fourier transform infrared spectroscope (FTIR), wide angle X-ray diffraction (WAXD) and scanning electron microscope (SEM). The corrosion resistance of all samples was investigated by immersion tests and electrochemical techniques in vitro simulated body fluid (SBF). The results indicated heat treatment improved the crystallinity of PLA coating and heated-coating performed protective behaviors in the short and long-term immersion. The corrosion rate of heated samples was lower than that of unheated samples and exhibited superior long term protective effect for Mg alloy wires. The lifetime of heated sample (H2) increased significantly from 33 to 55 days. The initial electrochemical performance of unheated coating was better than heated coating, but it declined more rapidly during the long-term immersion. These results indicated that PLA coating could not ignore the effect of its crystallinity to anti-corrosion ability, and only the suit heat treatment makes PLA coating more ordering and achieves higher corrosion resistance in vitro immersion. Therefore, it has promising potential by controlling effectively the PLA ordering for surgical implant applications.