Eye cells as 3D printing material.
http://m.smh.com.au/technology/sci-tech/eye-cells-3dprinted-for-first-time-20131219-2zm75.html
Given that the eyes are the fastest repairing part of the body, I can see why they’re concentrating on this. 
eyes and livers. Those are two different 3D printed parts now. For the livers, I would still like to see if an a printed liver piece could be incorporated into a natural liver and what its effectiveness is then. The natural liver may actually be able to complete the printed liver part. Afterall, just how good are we at keeping organs alive in a jar?
I think that currently 3D printing is entering a stage that the materials used are becoming most important in pushing the boundaries of this industry.
@jenia_zelikman I think how we think about the materials to be used is equally important. Is there a time when a material can or cannot be used? What causes undesired affects? How can we change the situations and material behaviours to match our needs? Is there a time when a supposed flaw can be a benefit? Non traditional thinking and an open mind can really change so many things and 3D printing is surely no exception.