3D printing is a universal process in the sense that pretty much any part that can be drawn up in a CAD program can be printed, at least within a certain resolution. Machining a part on a mill or lathe, while having the advantage of greater accuracy and material options, is a slightly less universal process in that many possible designs that exist in theory could never be machined. A hollow sphere can easily be printed, but a ball could never be milled as a single part into a hollow sphere—unless you happen to have a milling machine tiny enough to fit inside the ball. But what about biological parts, and whole animals? How universal, from a design perspective, is growth?