Anticorrosive and Antibacterial Properties of Chitosan Coating on AZ91D Magnesium Alloy

LOPERENA, A.P.; LEHR, I.L.; SAIDMAN, S.B.

Congreso; 34th Topical Meeting of the International Society of Electrochemistry; 2023

Magnesium and its alloys are promising materials for biomedical applications. They have properties such as biodegradability, biocompatibility and mechanical properties similar to those of the human bone, making them excellent materials for bone repair and stent applications [1]. However, these clinical applications are significantly hindered by the rapid degradation of magnesium materials in physiological environments and the risk of infection after implantation [2]. To overcome the degradation problem, the generation of coatings onto the material surface is most commonly used because they do not alter the inherent properties of the magnesium substrate [3]. On the other hand, combining anticorrosive coatings with antibacterial properties is also a great alternative to improve the properties of magnesium-based materials for biomedical applications [2]. Chitosan (Ch) is a biopolymer known for its excellent biocompatibility and antibacterial properties [4]. In addition, chitosan is attractive because its chemical stability and chelating ability with metal ions [5]. According to the literature, when chitosan is dissolved in acetic acid solution, it forms a protonated cationic polyelectrolyte [6]. When the magnesium-based substrate is immersed in the polyelectrolyte, the Mg(OH)2 surface film dissolves in the acidic media and forms the Mg-Chi complex [5,6]. This complex leads to good adhesion between the substrate surface and the chitosan film. On the other hand, the corrosion inhibiting effect of cerium compounds has been demonstrated for magnesium alloys [6]. In this work, an attempt was made to investigate the generation of chitosan-based film onto AZ91D Mg alloy in order to enhance the corrosion resistance of the substrate in simulated physiological fluid (Ringer solution) and to impart antibacterial properties to the substrate. Mg electrodes were firstly pre-treated in NaOH solution. Then, EPD process was employed to generate the coatings from a solution containing chitosan biopolymer and stearic acid (SA) using a mixture of acetic acid and ethanol as solvents. The addition of cerium compounds in the formation solution was evaluated in order to improve the anticorrosive properties of the films. The characterization of the films was performed by electrochemical and surface analysis techniques such as SEM, EDS, FTIR and X-ray photoelectron spectroscopy (XPS). The degree of corrosion protection achieved was evaluated in Ringer solution by monitoring the open circuit potential, polarization techniques and electrochemical impedance spectroscopy (EIS). The antibacterial activity against the Gram-negative bacteria Escherichia coli was evaluated by a modified Kirby-Bauer technique. Results indicated that the Ch-SA coated AZ91D Mg alloy substrate with compact morphology and lower corrosion current density leads to a lower Mg degradation in Ringer solution. Also the incorporation of cerium compounds allows to form a dense composite film on the surface of the Mg alloy in one step, thereby improving the corrosion resistance of the Ch-SA coating. The bacterial studies proved that Ch-SA /Ce coating possessed inherent antibacterial activity.