Characteristic of chitosan composite coatings deposited on magnesium alloys

Generally, Mg alloys exhibit attractive mechanical properties, low density and high strength-to-weight ratio. Therefore they are widely used as structural materials in the automotive and aerospace sectors. However, the low corrosion resistance of magnesium alloys significantly limits their application in the industry. In recent years, Mg alloys are considered as a new class of biodegradable implant materials. It has been revealed that magnesium alloys exhibit very good biocompatibility and their density is close to that of natural bones (1.8 - 2.1 g cm³). In vitro and in vivo studies have shown that magnesium alloys easily undergo resorption and do not cause allergic reactions. Magnesium alloys undergo active dissolution in physiological fluids. Such active corrosion is related with the presence of high concentration of chloride ions in the body fluids. In order to improve the corrosion resistance of Mg alloys and to hinder their dissolution in physiological fluids, it is necessary to perform surface treatment (coatings, laser treatment...).

In this work, the corrosion behaviour of several magnesium alloys (MgZn and MgZnCa) has been investigated in the Hank’s solution at 37 °C. These alloys can be used as biodegradable implants but they have very poor corrosion resistance in solutions containing Cl^- ions. Therefore, in order to improve their corrosion resistance, protective chitosan coatings were deposited by means of spin coater. The following types of coatings were deposited on the surface of Mg alloys: chitosan, chitosan containing TiO₂ nanoparticles and chitosan with addition of NaF and glass silica. The electrochemical performance of coated magnesium alloys was evaluated by linear sweep voltamperometry (LSV) and electrochemical impedance spectroscopy. The structure of coatings has been investigated by using Fourier – Transform Infrared (FTIR) spectroscopy. The corrosion tests have revealed that the chitosan coating improves the corrosion resistance of magnesium alloys in simulated body fluids. The highest corrosion resistance of Mg alloys was found when chitosan coatings containing NaF and Na₂SiO₃ salts were deposited on their surface.

Acknowledgements

The authors would like to thanks to European Commission for financial support in the frame of project H2020-MSCA-ITN-2017, grant agreement no. 764977 –mCBEEs.