Degradation of biodegradable implants: The influence of microstructure and composition of Mg-Zn-Ca alloys

This work reports on the degradation of two (Zn-poor and Zn-rich) Mg-Zn-Ca crystalline alloys produced by mold casting yielding different kinds of microstructures with several scales. The dependence of corrosion properties and hydrogen evolution with alloy compositions, sizes and kinds of microstructure was exhaustively analyzed. The results were compared with amorphous alloys of same compositions. Zn-rich composition with average grain sizes of less than 500 nm presented marginal and an acceptable level of hydrogen, which was lower than for larger grains or Zn-poor composition. This behavior was explained by the reduction of the intrinsic metallic surface reactivity and the higher stability of the oxide film, which reduce the corrosion rate and, consequently, the hydrogen evolution. Mg-Zn-Ca crystalline alloys with Zn-alloying threshold and homogeneous grain size (<500 nm) appear hence to be of great potential for use in biodegradable implants. (C)2018 Elsevier B.V. All rights reserved.