Performance Of A New Silane Coating For Corrosion Protection Of AZ31 Magnesium Alloy In Hank's Solution

摘要

In recent years a new domain of research on metallic biomaterials is focused on new biodegradable implants which dissolve in biological environment after a certain time of functional use. The application of such resorbable implants avoids medium/long time problems associated with the use of conventional metallic biomaterials, namely the need of implant removal surgeries. In this frame, magnesium alloys are emerging as a good alternative for biodegradable implant materials. In comparison to other temporary materials, like polymers, magnesium alloys exhibit superior mechanical properties, with high tensile and compressive strength and a Young's modulus similar to cortical bone. Another advantage that leads to the choice of these alloys is the fact that degradation of magnesium releases Mg~(2+) ions which are a vital element involved in many metabolisms and biological mechanisms. Obviously, the use of resorbable implants requires that the degradation rate should be consistent with the rate of healing of the affected tissue, and that the release of the degradation products should be within the body's acceptable absorption levels. One limitation of the use of magnesium alloys in such applications is related with these requirements, as these materials present high electrochemical activity. Consequently, problems such as in vivo resorption being too rapid, too localized and unpredictable and the fact that magnesium corrosion produces hydrogen gas which may accumulate adjacent to the implant in the body still need to be overcome. It is therefore crucial to develop strategies to reduce the corrosion degradation of these alloys to acceptable levels. Biocompatible silane coatings are envisaged as suitable strategies for retarding the corrosion process of magnesium alloys. In this work, a new glycidoxypropyltrimethoxysilane (GPTMS) based coating was tested on AZ31 magnesium substrates, submitted to different surface conditioning prior to coating deposition. The protective performance of the coating was assessed by electrochemical impedance spectroscopy (EIS) and a new equivalent circuit was proposed to interpret the results. It was shown that the surface conditioning plays a key role in the effectiveness of the silane coating.