It was created (designed by Armin Stachiewicz) in a new way (I keep checking it out, please give me feedback if you know any similar solution).
It is not a 3d print thing ;)
The method is extremely cheap. You can easily repeat entire process in your own garage or even in kitchen...
In general, this is metal composite. The specific gravity of below object is lower than if solid metal was used (now about 70% but this can be freely changed). Ultimately, I want to add a "shell" with a higher density so as to obtain the bone-like structure.