Properties and in vitro assessment of ZrO2-based coatings obtained by atmospheric plasma jet spraying on biodegradable Mg-Ca and Mg-Ca-Zr alloys

Magnesium (Mg)-based biodegradable alloys have gained a major interest in the biomedical field. The advantages of Mg alloys are depicted by their high biocompatibility, easy biodegradation and satisfactory mechanical properties. However, one major disadvantage of these alloys is represented by their low corrosion resistance in physiological environment. Coatings are considered to be a viable alternative used to improve corrosion, mechanical and cell viability properties of Mg- based metallic alloys. In this paper, two types of ceramic coating materials ZrO₂-Y₂O₃ and ZrO₂-CaO were deposited on Mg-Ca and Mg-Ca-Zr substrates by the atmospheric plasma jet technique. The two types of the deposited coatings exhibit similar Young modulus and a hardness in the range of 0.2–0.4 GPa. Values of the elastic modulus for the layers were measured to be in the range of 11–27 GPa for ZrO₂-Y₂O₃ and of 16–31 GPa for ZrO₂-CaO. The corrosion rate for the ZrO₂-CaO coating has superior values than that for the ZrO₂-Y₂O₃ one. The ZrO₂-CaO coated samples present a better adhesion to the substrate. The MTT colorimetric tests (3-(4,5-dimethyl-thiazol–2-yl)-2,5-diphenyl tetrazolium bromide) did not reveal significant differences in cytocompatibility between the two types of coatings, presenting a moderate cell viability.