Starting from now I am only using Blender for 3D figures. This software seems promising for scientific illustrations. 

It is the first time that I have used Affinity Designer to illustrate a 3D system. The metallic effect is quite good and I tried my best to do some shadowing. This figure is good enough to be published but I was not really satisfied with the light effects, which seem unnatural to me. After that, I switched to Blender to do this kind of figure.