Though 3D printers have become well-known in public, 4D printers might be put to practical use in near feature.
Another element added to 3D is heat, moisture, time and so on.
For example, you confined drugs in a box made by 4D printers, you are able to break the box by adding heat where you want to make the medicine effective. (Nikkei Sangyo Shimbun)
You confine fish’s feeds in a membrane made by 4D printers and the membrane will open after 1day, 2days, 3days later in the aquarium.
This is a good help for travelers, isn’t it?