Just as everyone was getting their head around "3D Printing", along comes "4D Printing" jumping on the same meme.
Just as "3D Printing" is in reality a set of over twenty diverse manufacturing processes sharing little but the concept of layer-by-layer construction, "4D Printing" is an equally meaningless term, even if the idea is intriguing.
Researchers postulate that very soon we will be able to print objects in 3D, that then evolve, morph, merge with other objects, or otherwise assemble themselves, over time. And as Dr Who knows all too well, Time really is the 4th Dimension!
Take a look at this vision for the future of 4D manufacturing: