The hard part will be keeping the capillaries open. This is a common problem with any organ transplant, or reattaching things like fingers or ears, you get massive clotting in the capillaries and tissue death sets in.
Often leeches are used to drain excess blood from such sites to prevent large clots. Yes, leeches.
I’d think that a printing process could in principle create a perfectly orderly grid of capillaries and arterioles/venules, ready to hook right up. It might even be set up to match up with whatever the patient already has, if we have the luxury of doing the printing real time. No leeches needed.
I can see that in harvested organs but in a printed organ why would there be any blood in a capillary?