This is why every time I look at our highway system, I think of blood carrying nutrients through the body. It's the same repeating pattern at a different scale.
Funny you should say that. Highways are artificial of course but their layout is governed by a planning process which seeks the path of least resistance. Which is to say, which will cost the least. Cost is the constraining factor being worked against, whereas in the case of blood vessels it's metabolic cost, and in the case of crystallization, it's temperature.
https://trid.trb.org/view/689139
http://ieeexplore.ieee.org/document/881008/
http://www.sciencedirect.com/science/article/pii/S0898122107001897
Optimizing process (freeway planning) working against constraints (cost) equals fractal patterns. It's spooky how universally this seems to apply.