Graphene 3D Lab is one of the leading companies that aim to develop graphene-based materials for functional 3D printing - so you could print strong graphene based devices, and also print conductors, etc.

We posted an interview with the company's founder and COO. They aim to have the first graphene 3D material as a commercial product in 6 months:

http://www.graphene-info.com/graphene-3d-lab-aims-have-commercial-graphene-based-3d-printing-materials-6-months