RESEARCH ARTICLE Influence of dicalcium phosphate dihydrate coating on the in vitro degradation of Mg-Zn alloy Shao-Xiang ZHANG 1 , Jia-Nan LI 1 , Yang SONG 1 , Chang-Li ZHAO 1 , Xiao-Nong ZHANG (✉) 1,2 1 State Key Laboratory of Metal Matrix Composites, School of Materials Science and Engineering, Shanghai Jiao Tong University, Shanghai 200240, China 2 Key Laboratory of Special Inorganic Coating, Shanghai Institute of Ceramics, Chinese Academy of Sciences, Shanghai 200050, China © Higher Education Press and Springer-Verlag Berlin Heidelberg 2010 Abstract To reduce the degradation rate and further to improve the biocompatibility of magnesium alloy, dical- cium phosphate dihydrate (CaHPO 4 %2H 2 O, DCPD) has been fabricated on a kind of magnesium-zinc alloy by way of electrodeposition method. The experimental results of XRD, SEM and EDS showed that the electrodeposited coating on the Mg-Zn alloy mainly contains the flake-like DCPD, along with some octacalcium phosphate (Ca 8 (H- PO 4 ) 2 (PO 4 ) 4 %4H 2 O, OCP). After the in vitro degradation of the coated alloy in modified-simulated body fluid (m- SBF), it was proved that the coating could reduce the degradation rate effectively, and the samples were covered by calcium phosphate salts with a higher Ca/P ratio. Therefore, it indicates that compared with the bare alloy, the DCPD coating rendered a more biocompatible surface, and is a promising coating candidate for biomedical magnesium materials. Keywords biodegradable, magnesium, corrosion, coat- ing, DCPD 1 Introduction Magnesium alloy is becoming a kind of potential absorbable metallic biomaterials [1–3]. To reduce the possibility of damages to the human body caused by toxic elements, some new magnesium alloys have been deve- loped as biomedical materials, such as Mg-Ca, Mg-Zn, and Mg-Mn-Zn alloys [4–6], the biocompatibilities of which have also been proven to be good. However, the degradation rates of these bioabsorbable magnesium alloys still need to be improved. Therefore, surface modification methods have been applied to adjust the degradation rates of Mg alloys [7–9]. The calcium phosphate salts (Ca-P) that have the similar element constitutions to the human bone minerals are the promising coatings for orthopedic applications. The crystallized hydroxyapatite (c-HAp) seems difficult to be directly precipitated on magnesium substrate in solutions [10,11]. Besides, the transformation of precursor to HA will cause a remarkable mass loss, and thus, many micro holes and the loose structure will be formed in the coating, leading to a vulnerable surface. Dicalcium phosphate dihydrate (CaHPO 4 %2H 2 O, DCPD), which can be formed on magnesium easily and stably, is an important precursor of HA and owns good biocompatibility [12]. Therefore, it is proposed that the DCPD is an appropriate coating candidate for the modification of biomedical magnesium alloys. The electrodeposition technique is a convenient way to prepare surface coating. It is easy to control the morphology and composition of coating by adjusting the current density and other parameters. Therefore, in the present work, a DCPD coating was fabricated on Mg-Zn, an alloy without toxic or controversial elements for biomedical applications [4] through electrodeposition method, and the in vitro degradation behavior was studied. 2 Experimental 2.1 Sample preparation The solid-solution treated Mg-Zn alloy was used as the substrate material, and the Mg-Zn was cut into small plates with a diameter of 11.3 and 2 mm in height, then ground up to 1000 grit SiC paper to secure suitable roughness, and followed by ultrasonic rinse in ethanol for 15 min. Received February 3, 2010; accepted March 2, 2010 E-mail: xnzhang@sjtu.edu.cn Front. Mater. Sci. China 2010, 4(2): 116–119 DOI 10.1007/s11706-010-0026-z