When you 3-D-print an object, its a fixed, static thing. If you want something more complex, you need to print it as parts and then assemble it. We thought, instead of assembling intelligence into it afterwards, why not print intelligence into it?
We collaborated with 3-D printing firm Stratasys (CLIENT), which developed a printing material that expands 150 percent when it meets water. That let us print objects that can change over time. Printing isn’t the end; its just the start. Thats why we call it 4-D printing. We have done a few prototypes so far—printed a tube that, when you submerge it in water, folds itself into a cube. People are really excited about it, but I think we have barely scratched the surface.
via Interview with Skylar Tibbits — 4-D printing at the MIT Self-Assembly Lab: The future will build itself..