Abstract
Magnesium alloys have been recently recognized as a biodegradable material for bone substitute application. Degradation rates of Mg alloys in the physiological environment, mechanical properties and cytocompatibility are interesting research topics up to now as their combination limits most clinical applications. At least the first two properties are in a direct connection with structure and microstructure of proposed materials. Two variants of the commercial WE-type alloy (Mg-Y-Nd-Zr) modified by Mn addition and Zr absence and alloyed with either Sc or Zn were studied in the as cast as well as in the T5 condition in this work. Yield tensile stress and ultimate tensile stress values at room temperature for both alloys studied after the T5 temper are comparable with those in the T6 treated commercial WE43 alloy. Hardening is caused by precipitation of prismatic plates non-uniformly distributed in matrices of both alloys. Ductility of both alloys regardless the treatment increases essentially compared to the WE43 alloy. Thin coherent hexagonal plates containing Zn and Y in a high number density and with a very high aspect ratio developed parallel to matrix basal planes during the T5 temper in the as cast Mg-Y-Nd-Zn-Mn alloy. The extracts of the studied alloys in EMEM prepared according to the ISO 10993-5 are cytotoxic for human osteosarcoma MG63 cells. The worst result was obtained for the T5 treated Mg-Y-Nd-Zn-Mn alloy and can be ascribed to the enhanced corrosion connected with the observed microstructure. The viability of Mg63 cells improves considerably in the ten times diluted extract, which is more realistic for a comparison with in vivo testing due to dynamic effects.

Key words
degradable Mg alloys, mechanical properties, corrosion, cytocompatibility

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