Effect of Fluoride Coatings on the Corrosion Behavior of Mg–Zn–Ca–Mn Alloys for Medical Application

Abstract

The most critical shortcoming of magnesium alloys from the point of view of medical devices is the high corrosion rate, which is not well-correlated with clinical needs. It is well- known that rapid degradation occurs when an implant made of Mg-based alloys is placed inside the human body. Consequently, the implant loses its mechanical properties and failure can occur even if it is not completely degraded. The corrosion products that appear after Mg-based alloy degradation, such as H2 and OH− can have an essential role in decreasing biocompatibility due to the H2 accumulation process in the tissues near the implant. In order to control the degradation process of the Mg-based alloys, different coatings could be applied. The aim of the current paper is to evaluate the effect of fluoride coatings on the corrosion behavior of magnesium alloys from the system Mg–Zn–Ca–Mn potentially used for orthopedic trauma implants. The main functional properties required for the magnesium alloys to be used as implant materials, such as surface properties and corrosion behavior, were studied before and after surface modifications by fluoride conversion, with and without preliminary sandblasting, of two magnesium alloys from the system Mg–Zn–Ca–Mn. The experimental results showed that chemical conversion treatment with hydrofluoric acid is useful as a method of increasing corrosion resistance for the experimental magnesium alloys from the Mg–Zn–Ca–Mn system. Also, high surface free energy values obtained for the alloys treated with hydrofluoric acid correlated with wettability lead to the conclusion that there is an increased chance for biological factor adsorption and cell proliferation. Chemical conversion treatment with hydrofluoric acid is useful as a method of increasing corrosion resistance for the experimental Mg–Zn–Ca–Mn alloys.