Material systems used in 4D printing

Compared to creating static objects with 3D printing, 4D printing systems add time as the fourth dimension to 3D printing: 4D printing allows a 3D printed structure to change its configuration or function with time in response to external stimuli such as temperature, light, water, pH, etc.

4D printing, still in its infancy (the term was first introduced in 2013 in a TED talk), has become an exciting branch of additive manufacturing and attracts enormous interest from academia and industry of different disciplines.

The basic idea is to manipulate materials at nano and micro levels in order to produce, via 3D printing, materials that can modify their structures over time at the macro level.