Corrosion products on biomedical magnesium alloy soaked in simulated body fluids
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Kaifu Huo Department of Physics and Materials Science, City University of Hong Kong, Kowloon, Hong Kong, China; and Hubei Province Key Laboratory of Refractories and Ceramics, College of Materials and Metallurgy, Wuhan University of Science and Technology, Wuhan 430081, China
Tao Hu Department of Physics and Materials Science, City University of Hong Kong, Kowloon, Hong Kong, China
Guoyi Tanga) Advanced Materials Institute, Tsinghua University, Shenzhen Graduate School, Shenzhen 518055, China
Paul K. Chub) Department of Physics and Materials Science, City University of Hong Kong, Kowloon, Hong Kong, China (Received 3 November 2008; accepted 4 February 2009)
Magnesium alloys are potential materials in biodegradable hard tissue implants. Their degradation products in the physiological environment not only affect the degradation process but also influence the biological response of bone tissues. In the work reported here, the composition and structure of the corrosion product layer on AZ91 magnesium alloy soaked in a simulated physiological environment, namely simulated body fluids (SBFs), are systematically investigated using secondary electron microscopy (SEM), Fourier transform infrared (FTIR) spectroscopy, x-ray photoelectron spectroscopy (XPS), x-ray diffraction (XRD), and in situ monitoring of the corrosion morphology. Our results show that the corrosion product layer comprises mainly amorphous magnesium (calcium) phosphates, magnesium (calcium) carbonates, magnesium oxide/hydroxide, and aluminum oxide/hydroxide. The magnesium phosphates preferentially precipitate at obvious corrosion sites and are present uniformly in the corrosion product layer, whereas calcium phosphates nucleate at passive sites first and tend to accumulate at isolated and localized sites. According to the cross sectional views, the corrosion product layer possesses a uniform structure with thick regions several tens of micrometers as well as thin areas of several micrometers in some areas. Localized corrosion is the main reason for the nonuniform structure as indicated by the pan and cross-sectional views. The results provide valuable information on the cytotoxicity of magnesium alloys and a better understanding on the degradation mechanism of magnesium alloys in a physiological environment. I. INTRODUCTION
Because of their unique mechanical properties and biodegradability, Mg-based alloys are potential biodegradable hard tissue implants. Good biocompatibility has been observed in earlier clinical studies and in many in vivo and in vitro experiments.1–3 Some studies have also shown that dissolved magnesium ions may promote Address all correspondence to these authors. a) e-mail: [email protected] b) e-mail: [email protected] DOI: 10.1557/JMR.2009.0323 J. Mater. Res., Vol. 24, No. 8, Aug 2009
bone tissue growth.4–7 However, attacks by aggressive ions in body fluids such as chlorides, hydrocarbonates, and sulfates lead to fast surface corrosion on Mg-based biomedical implants.8–11 Many in vivo experiments have been carri
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