Researchers from the Massachusetts Institute of Technology (MIT), in collaboration with industry partners Stratasys and Autodesk, have used 3D printing technology to create objects that can self-assemble into new structures when desired. The process is called 4D printing because its designs involve not just the three physical dimensions but also planned changes over time. The research was led by Skylar Tibbits, director of the Self-Assembly Lab at MIT. Stratasys provided the 3D printer and materials, and Autodesk provided the software for self-assembly and folding design.

In 4D printing, a combination of rigid static materials (such as polymers, rubber, and wood) and active materials (also called smart materials, which have changeable properties) is precisely configured by a printer. The printed structure embodies a geometric code for a final assembled design that is based on understanding of how the various materials will respond to surrounding conditions: When activated by stress, heat, light, water, or some other change in the environment, the structure changes shape predictably. See also: 3D printing of multiple materials; Active materials and smart structures; Computer-aided design and manufacturing; Polymer; Rubber; Stimuli-responsive polymers; Wood properties

In demonstrations of the technology, one-dimensional strands, flat pieces of material, and 3D structures have all shown that they can reconfigure themselves into different 3D shapes. To date, the active material in the printed objects that drives these changes has been a hydrophilic polymer that swells to 150 percent of its original volume when it absorbs water. When the printed object is immersed in water, its swelling hydrophilic polymers force certain rigid polymers to bend in desired directions until other deliberately placed rigid polymers, called angle limiters, force the bending to stop. The full program for controlling the printed object’s shape change is encoded in the specifications of the original printer file.

The current 4D printing research is still far removed from making devices with practical uses. Nevertheless, it is easy to conceive of printing a flat object that, when activated, would assemble into a table or chair, for example, with a built-in capability to self-repair if damaged. At the end of the product’s lifetime, it could be deactivated to self-disassemble for reuse or recycling. New types of intelligent construction materials or medical products are also among the many possible applications of 4D printing. See also: Recycling technology