Formation and In vitro evaluation of a deep eutectic solvent conversion film on biodegradable magnesium alloy.

The chemical conversion films from deep eutectic solvents (DESs) have recently been shown to reduce the corrosion rate of magnesium alloys, which are recognized as a kind of promising materials applied in the human body. However, the biocompatibility of the conversion film has not been investigated. This study proposes an uncommon DES system composed by lithium chloride and urea to fabricate the chemical conversion films on Mg and its alloy. The fabrication process of the conversion film is facile, which is performed by the heat-treatment of substrate in the DES at about 200 oC for 30 min. It is found that the thermal decomposition of DES can release hydrogen, which diffuses into the Mg substrate to form the MgH2 based conversion films. The DES conversion film possesses a porous structure on the pure Mg, while it becomes dense on the alloy with some cracks. X-ray photoelectron spectroscopy shows that MgCO3 and oxides also exist in the DES conversion films, which depends on the substrate. Electrochemical corrosion test and in vitro biocompatibility tests, including hemolysis, cytotoxicity, antibacterial and cytoskeleton staining experiment are performed in simulated body environment, which shows that the corrosion resistance and biocompatibility of the substrates have been improved significantly. We expect that DES heat-treatment method will be applied to the fabrication of corrosion resistant and biocompatible surfaces for biodegradable Mg alloys.