I love 3D printing. My first book was about 3D printing and I've owned dozens of 3D printers over the years. But it isn't perfect for every scenario because it has one massive drawback: print time is directly correlated with the size of the object. For FDM/FFF printing, the correlation is with volume. For MSLA resin printing, the correlation is with height. In both cases, print time increases along with the size of the object. But researchers from the University of Tokyo have developed new 4D printing technology that almost eliminates that correlation.
The term "3D printing" is, of course, referencing the fact that it allows for three-dimensional fabrication. 4D printing adds a fourth dimension. In this case, that fourth dimension is self-folding after printing. The object prints as a flat model. Then after the print completes, the user can submerge the model in hot water and it will morph into an origami-like 3D object. This is similar to common sheet metal fabrication techniques in which objects are cut from flat sheets, then bent to into 3D forms. But this 4D printing technology doesn't require any special tools or labor for that second step — just a container of hot water.
This technology relies almost entirely on thermodynamics and the differentials between different materials. This requires two material types in particular: a special plastic sheet and standard inkjet 3D printer material. That plastic sheet shrinks when exposed to heat (like hot water). But the structures printed onto the sheet control the contraction, forcing the object to fold into the desired shape. The researchers created software that converts any standard 3D model into a flat model with seams in the proper places to allow for the controlled contraction. Because this works with inkjet 3D printers, it can produce full-color models.
The obvious benefit here is time. It takes much less time to print a flat model a few millimeters thick than it does to print a full 3D model. The flat model might only take a few minutes to print, while the equivalent 3D model could take several hours.
However, the folded model can't come close to matching the quality of a standard 3D model. Like origami, it will have obvious seams, folds, and flat faces. For that reason, this 4D printing technology has very few applications. It might be suitable for artistic models that benefit from the origami-like appearance or for very rough initial prototypes, but it won't replace more conventional 3D printing.