Novel biocompatible magnesium alloys design with nutrient alloying elements Si, Ca and Sr: Structure and properties characterization

Magnesium has been widely studied as a biodegradable material, where its mechanical property and biocompatibility make it preferred candidate for orthopedic implant. Proper alloying can further improve the properties of Mg. First and foremost, to guarantee the biosafety for biomedical application, the alloying element should be toxic free. To address this point, nutrient elements including Si, Sr and Ca were selected due to their biological functions in human body, especially in bone regeneration and repair. In this study, 0.5-1.0 wt% Sr and Ca were used to refine and modify the morphology of coarse Mg2Si in Mg-1.38wt% Si to obtain an uniform microstructure. Microstructure, mechanical and degradation properties of as-cast and homogenizing-annealed quaternary Mg-1.38Si-xSr-yCa (x,y = 0.5-1 wt%) alloys were investigated by optical microscopy, scanning electronic microscopy, X-ray diffraction, tensile and electrochemical measurement. Addition of Sr and Ca element cause a morphological change in Mg2Si particles from coarse Chinese script shape to small polygonal type. The presences of intermetallic phases, such as Mg2Si, CaMgSi and Mg17Sr2, were confirmed in quaternary alloys, of which content was applied to interpret the results for the quaternary system. Compared with the as-cast state, fewer, finer and homogenized microstructure were observed after an anneal heat treatment under 500 degrees C. The mechanical properties were improved with increase of Ca and Sr additions, which was related to the evolution of the microstructure and second phases, however, also causing an increase of corrosion rate due to the galvanic-corrosion at the same time. The cytocompatibility results revealed that the Mg-Si-Sr-Ca alloys promote the proliferation of preosteoblasts and exhibit cytotoxicity of Grade 0-1, indicating their acceptable biosafety and potential for the orthopedic applications. (C) 2016 Elsevier B.V. All rights reserved.