Surface Engineering of Magnesium Alloys for the Next Generation of Biodegradable Device

Although the biocompatibility and good mechanical properties make the magnesium and its alloys excellent candidates for biomedical applications, the high corrosion rate, involving hydrogen release and the alkalization of the physiological environment, limit their clinical use. However, this constrain could be exploited for the realization of biodegradable devices. In this regard, it is necessary to ensure a degradation rate comparable to the rate of growth of the hosting tissues, avoiding side effects, premature failures, and adverse reactions. The surface engineering approaches which involve the use of a coating made of single or multiple layers represent a possible method to tailor the deterioration rate. The poor adhesion strength between layers could be an important drawback of this approach. In the present research, a multilayer coating composed of an oxide layer, a bio-inspired polydopamine (PDA)-based one and a biodegradable polymer film, made of polylactic acid (PLA) has been realized on magnesium alloys substrates. The first layer was obtained by a plasma electrolytic oxidation (PEO) treatment to increase the corrosion resistance. Then, the polydopamine layer has been applied by the dip-coating method to improve the adhesion between the oxide layer and the polylactic acid film. Each layer and their combinations were characterized by using morphological examinations, and electrochemical test by means of potentiodynamic polarization (PD) and electrochemical impedance spectroscopy (EIS) methods. The use of a multilayer coating has demonstrated to be a promising strategy to control the degradation rate of the magnesium alloys to produce biodegradable device.