Microstructure and in vitro degradation performance of Mg\u2013Zn\u2013Mn alloys for biomedical application

Manganese and zinc were selected as alloying elements to develop a Mg-based ternary alloy for biomedical applications, taking into account the good biocompatibility of these metals. The microstructures of Mg\u2013Zn\u2013Mn alloys containing 0.5 or 1.0 mass% of manganese and 1.0 or 1.5 mass% of zinc were investigated by scanning electron microscopy coupled with energy dispersive X-ray spectroscopy. Their corrosion properties were assessed by means of potentiodynamic polarization and electrochemical impedance spectroscopy measurements performed in Ringer's physiological solution that simulates bodily fluids. All tested samples are two-phase alloys formed by a Mg-based matrix, consisting of a Mg\u2013Zn\u2013Mn solid solution, and a Mg\u2013Zn binary phase. The electrochemical results show an improvement of the corrosion behavior of the investigated alloys with increasing Zn and Mn content. This is attributed to the formation of a partially protective Mg(OH)2 surface film whose protective capabilities are increased by the alloying elements. The reduced influence of the Mg\u2013Zn intermetallic compound on the corrosion rate of Mg\u2013Zn\u2013Mn alloys in the presence of a partially protective surface layer can be ascribed to an increasing resistance between the Mg\u2013Zn\u2013Mn solid solution and the second phase, thereby decreasing the effective driving force for microgalvanic corrosion. Owing to its highest corrosion protective ability, the Mg\u20131.5Zn\u20131Mn alloy is a promising candidate for the development of degradable implants, such as screws, plates, and rod