Enhancing the corrosion resistance and surface bioactivity of a calcium-phosphate coating on a biodegradable AZ60 magnesium alloy via a simple fluorine post-treatment method

Abstract

Biocompatible coatings, such as calcium phosphate (CaP), have been applied on biodegradable magnesium and its alloy to control their rapid degradation rates. This paper reports a further enhancement to the CaP coating performance by applying a simple fluorine post-treatment on a CaP coating to form an F–CaP composite coating. The CaP coating was first deposited on AZ60 magnesium alloy samples via a phosphating method, then subjected to different post-treatment solutions to obtain F–CaP composite coatings. The effects of pH and post-treatment time were analyzed and the optimal corrosion resistance was obtained at pH 12 for 2 h. The F–CaP coating consisted of mainly fluoridated hydroxyapatite, tricalcium phosphate and magnesium fluoride. An electrochemical corrosion measurement in simulated body fluid revealed that the polarization resistance of the F–CaP coating is about 3 and 26 times higher than those of the HA and CaP coatings, respectively, due to its denser coating structure and smoother surface. During immersion tests, the F–CaP coating also exhibited an improved corrosion resistance with more active biomineralization than the CaP and HA coatings. This fluorine post-treatment offers a novel practical approach in improving the biodegradation behavior of CaP coatings on biodegradable magnesium implants.