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.
It’s the “arching” or “ bridging” problem when dealing with other “ink” types when 3d’ing. With PLA or ABS you can solve it with print speed, thickness and how fast the printed material drys. With tissue deposition, there might be a reason to have bio-dissolvable arches to support the cells while they adhere to each other and form vessicles that transport blood in and out. After the structure solidifies, the temporary scaffolding could be removed. Just not sure what works as the scaffolding. Yeah, I 3d, but not tissue.