All sorts of interesting blue-sky possibilities here:
1. Print-a-kidney, in which the dialysis membranes are manufactured by depositing the various types of kidney cells on the collagen membrane surface (ideal would be two-sided printing, endothelial cells on one side, kidney cells on the other side, kidney-specific mix of matrix proteins as the "paper"). Blood flows through chamber in contact with endothelial side, filtrate comes out through the kidney cell side. Current machine dialysis involves size filtration through inert membranes, plus extraction of excess salts or replacement of salts by diffusion to/from various chambers with specific salt concentrations.
2. neuronal migration and connection requirements in vitro. Lay down gradient of growth factors on one axis, gradient of cell density on other axis. Print-a-neuronal-circuit?
I haven't really thought out much of this, but the engineers and nanoscientists and biologists are also making biodetection apparati using specially engineered organisms (bacteria, mammalian cells in culture, even entire zebrafish). If there is a need for a specific 2-d relationship between cell type#1 and a cooperating cell type #2, printing could be a good way to provide reproducibility, and also relative immobility (instead of gloss optimizer, just apply an extra few layers of collagen gel to make a little cage for the cell group).
