If you forgot what is 4d printing here is a new overview. Hint: fourth dimension is the time.
Good people from MIT made this robotic forms that move in preassigned forms when exposed to heat. They are also working on self-folding laser-cut materials and present designs for resistors, inductors, and capacitors, as well as sensors and actuators - the electromechanical “muscles” that enable robots’ movements.
http://newsoffice.mit.edu/2014/bake-your-own-robot-0530
More related 4d stuff:
http://diy3dprinting.blogspot.com/2013/09/skylar-tibbids-talks-about-4d-printing.html