This is honestly not a late April Fools joke.  TED Fellow Skylar Tibbits gave a TED talk to describe the research and development partnerships his MIT lab is making to develop 4D printing.  What is 4D printing?  Well, you should watch his TED talk below, but basically, the first 3 dimensions are the normal ones for 3D printing (X, Y, Z for Cartesians among us), while the fourth represents an automatic change in the object that is built into it while printing but takes place later.  So you might say the dynamics or flexibility of the object causing the object to re-form over time suggests time is the fourth dimension here.

The idea of printing something with the constraints of the 3D printing process that could later deform and form into a target configuration has great opportunities.  However, the software tools are in their infancy in this area, needing much work to be done by hand and there are relatively few printers that can use multiple materials in the process.