How to design 3D Voronoi lattice structure?

Hi,

I have already made some voronoi patterns with Meshmixer, but it's all only a lattice on the surface of the model.
Next thing I want to design and print is a 3 dimensional voronoi lattice like in this or this example.

1) It looks like it's only possible with Rhino + Grasshopper. Maybe I can try it with the 90-days trial-version. But I haven't found a description how to make it with these programs. Is it all I need or is there more needed, I read something about qhull and grasshopper?

2) I also found this tutorial for Blender, but it doesn't look like real voronoi lattice, more like triangles.

3) Here is a programm Voro++ and there are these pictures of 3D-voronoi lattices, but the description on the website looks quite complicated and I have no idea how to get out a stl from this program.


So, in general: how to design these lattice structures and get a stl for printing?