# Microstructural, Electrochemical and In Vitro Analysis of Mg-0.5 Ca-xGd Biodegradable Alloys
## 4 Conclusions  
In this article, five experimental biodegradable Mg-based alloys (Mg-0.5 Ca-0.5 Gd, Mg-0.5 Ca-1 Gd, Mg-0.5 Ca-1.5 Gd, Mg-0.5 Ca-2 Gd and Mg-0.5 Ca-3 Gd) were analyzed. In summary, the authors highlighted the influence of Gd in a Mg-0.5 Ca system from the point of view of microstructure, corrosion resistance and cell viability. Microstructural characterization results from optical and scanning electron microscopy and XRD analysis highlighted patterns of a refined polyhedral shape of Mg grains, with cubic crystalline structures, due to Gd addition. The morphological aspects of Gd particles (Mg\({}_{5}\)Gd--white compounds) seem to have an acicular or round aspect and at the Mg grains' limit, the Mg\({}_{2}\)Ca eutectic compound is formed due to Ca addition. The results on the degradation rate performed in a simulated body fluid solution highlighted low values and showed an area slightly affected by corrosion. The best results of electro-corrosion resistance were achieved by the Mg-0.5 Ca-3 Gd, which showed a degradation rate of 0.28 mm/yr. Decreasing the Gd concentration led to increasing the corrosion rate up to 4.2 mm/yr (0.5 wt.%). The presented experimental samples highlighted very good cell viability at 3 days (73-80% range) and at 5 days (77-100% range). Some low viability results were obtained for the experimental alloys (0.5 wt.%-2 wt.% Gd) after 24 h, a fact which should be attributed to the samples' reactivity leading to ion release from the alloys, pH and osmolarity increasing, and salt precipitation with toxic or inhibitory effects. Cell viability after 5 days was not significantly different for alloys with a Gd amount of 1.5%, 2% and 3% (\(p>0.05\)) compared with the MgCa control alloy, so increasing the Gd alloying amount also improved the cytocompatibility of these alloys (as a consequence of improving the  
Figure 8: Fibroblastic cells’ morphology evaluated by fluorescence microscopy after 1 and 5 days of co-incubation with the studied samples. Viable cells are stained in green as a result of calcein fluorescent dye’s presence inside the cells. Bar: 200 μm.  
alloys' stability). The study will continue with in vivo analysis, in order to see the exact behavior of the experimental alloys implanted within laboratory animals.  
Conceptualization, B.I., C.M., N.C. and M.D.V.; methodology, C.M., R.C. and M.D.V.; software, B.I. and M.D.V.; validation, C.M., R.C., N.C. and M.D.V.; formal analysis, O.D.P.; investigation, B.I., R.C. and M.D.V.; resources, C.M. and N.C.; data curation, B.I. and M.D.V.; writing--original draft preparation, B.I., R.C. and M.D.V.; writing--review and editing, C.M., R.C. and M.D.V.; visualization, N.C.; supervision, C.M. and N.C. project administration, C.M.; funding acquisition, C.M. All authors have read and agreed to the published version of the manuscript.  
This work was supported by a grant from the Romanian Ministery of Research and Innovation, CCCDI--UEFISCDI, project number PN-III-P1-1.2-PCCDI-2017-0239/60 FCCDI 2018, within PNCDI III.  
Not applicable.  
The authors declare no conflict of interest.