A University of Penn researcher has used a RepRap to "print up"
a sugar based cell matrix, to spec.  This is a major breakthrough
toward creating custom replacement organs out of a user's own cells.  

Up to now the big problem in organ synthesis has been creating
the complicated micro-vasculature to supply internally located
cells with blood, to keep the cells alive.  

It appears that the printed sugar matrix solves this. By creating
a custom "vasculature" matrix out of sugar, then adding cells in
a gel, the matrix supports and spaces out the layered cells.  
Once the added cell-gel mix has hardened, the sugar is dissolved
away, leaving the vascular spaces needed for blood flow.

IMO it's a darn innovative medical app for a RR, and could be a game-changer..

If you can drive the RR with the proper fractal based math to
generate the proper input and output vacular tree geometries,
add the right stem cell lines derived from the patient (stimulated
to produce the desired cell type), and figure out how to package
the organ and connect normal vessels to it, then you're well on
your way toward making custom 3D printed rejection-free organs
of many kinds.

- Keith Mc.