  3D printers based on the Fused Decomposition Modeling create objects
layer-by-layer dropping fused material. As a consequence, strong overhangs
cannot be printed because the new-come material does not find a suitable
support over the last deposed layer. In these cases, one can add some support
structures (scaffolds) which make the object printable, to be removed at the
end. In this paper we propose a level set method to create object-dependent
support structures, specifically conceived to reduce both the amount of
additional material and the printing time. We also review some open problems
about 3D printing which can be of interests for the mathematical community.
