Describing a material as “strong” is woefully ambiguous, because there are many different kinds of strength. Concrete, for example, has amazing compressive strength, which is why it is ideal for foundations that support heavy structures. But it has pretty terrible tensile strength, which is a material’s ability to resist pulling forces. That is why concrete is often reinforced with high-tensile material such as steel rebar. The resulting reinforced concrete combines the strengths of both materials. Similarly, this “4D printing” nozzle can morph into new shapes to embed fibers into 3D-printed objects in order to increase their strength or introduce shape-changing capabilities.
This special 3D printer nozzle was developed by a team from the University of Maryland’s A. James Clark School of Engineering. Its purpose is to orient fibers that are embedded into the 3D-printed material during the extrusion process. The nozzle is made of a flexible material and has inflatable bladders on its sides. By inflating those bladders, fibers can be oriented in the desired direction within the extruded material. While fiber-filled 3D printer filament does already exist, those fibers have to be relatively short and are oriented somewhat unpredictably. This nozzle lets designers orient the fibers in a manner that increases the 3D-printed parts strength in whatever manner is required, just like the rebar that is used to reinforce a concrete building.
The ability to orient fibers at will also facilitates 4D printing. While still largely experimental, 4D printing refers to 3D-printed objects that change shape after the printing process has been completed. Usually, 4D-printed objects morph when exposed to specific environmental conditions like heat. In this case, the parts change shape when submerged in water. This works by using fibers that swell when wet and by orienting those fibers to create either anisotropic regions or isotropic regions. The former will swell more in one direction than the other, while the later will swell uniformly in all directions. Like a bimetallic strip in a thermostat, the combination of anisotropic and isotropic regions forces the part to expand and bend from one shape to another. It is unclear what the specific applications would be for this technology, but the team is in talks with Department of Defense labs to determine if it could be useful for defense. They also believe that it would be practical for biomedical devices that reshape themselves in the body.