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The biodegradation behaviors and cytocompatibility of the as-cast Mg-5Zn-xSr alloys (≤ 1.0%) are carefully characterized by immersion testing, electrochemical measurement and cell proliferation and adhesion testing. The biodegradation rates increase in the order of Mg-5Zn-0.2Sr, Mg-5Zn-1Sr, Mg-5Zn-0.6Sr and Mg-5Zn in both 0.9%NaCl and Hank's solution. The as-cast Mg-5Zn-0.2Sr alloy is the most corrosion resistant, which can be attributed to the finest grain size, the lower volume fraction of secondary phases and the higher stability of corrosion layer. Filiform corrosion along grain boundaries is dominant in the Mg-5Zn-0.2Sr alloy at the initial stage, and the cyclic polarization scans show that it has the highest pitting corrosion resistance. Grain size effect on corrosion is not as obvious as that of the secondary phases for the as-cast Mg-Zn-Sr alloys. The 0.2%Sr addition can reduce the biodegradation rate, promote the cell growth and improve the cell adhesion ability of the as-cast Mg-5Zn alloy, which is attractive for biomedical applications. [ABSTRACT FROM AUTHOR]

Tetracyanoethylene (TCNE), with its strong electron-accepting ability, was used to dope graphene as a metal-free electrocatalyst for the oxygen reduction reaction (ORR). The charge transfer process was observed from graphene to TCNE by x-ray photoelectron spectroscopy and Raman characterizations. Our density functional theory calculations found that the charge transfer behavior led to an enhancement of the electrocatalytic activity for the ORR. [ABSTRACT FROM AUTHOR]