4D Printing is Taking a Big Step Forward

Printing in 4D was invented in 2013 by Skylar Tibbits who currently runs the Self-Assembly Lab at the Massachusetts Institute of Technology. With this technology it is possible to print shape-changing structures made of programmable materials. Their color or texture can also change in response to external stimuli. Printing in 4D also creates self-assembling objects since the reaction of materials can be predefined. The fourth dimension therefore is a reference to time as the objects created are modified without relying on another manufacturing step. Manufacturers have not been that attracted to the technology because integrating other materials and components in programmable materials is a delicate and expensive operation.

A team at the Georgia Institute of Technology in Atlanta has developed a new generation of 4D printers that addresses these restrictions. Functions have been added to create objects and electronic components faster and using a simpler process. In fact, this innovation is interesting for both civil and military applications, and aerospace.

Researchers presented this technology at the 255th national meeting and exhibition of the American Chemical Society (ACS) held March 18 to 22, in New Orleans.

Presenting the technology at the ACS event

In addition to simplifying the configuration of existing printing machines, this technology makes it possible to create objects made from several materials and to incorporate electrical components at the same time.

Previously, the team was able to optimize the printing technique of programmable materials. This step was carried out in another project, in collaboration with researchers from the Singapore University of Technology and Design in 2017. Again, objects based on programmable materials change shape when excited by heat, moisture, light or other stimuli. To make a flower that opens and closes, a dome from a star and a retractable grid, the researchers used a commercial 3D printing machine, a heat source and an acrylic-epoxy-based polymer. The team was able to increase the reaction rate of the material by 90% by integrating the mechanical programming steps directly into the 3D printing process.

In addition, the new technology promises to produce even more complex shapes and structures.

A Combination of Technologies

The machine is multifunctional, using four distinct printing technologies, namely:

1. Molten material deposition
2. Inkjet
3. Aerosol jet printing
4. Direct writing

Combining these functions was made possible thanks to the development of an integrated thermomechanical programming that does not alter the materials during the different heat treatments.

While commercial 4D printers can only print one material, this technology simultaneously prints a wide range of rigid and flexible materials, including hydrogels, silver nanoparticle-based conductive inks, liquid crystal elastomers, and shape memory polymers, etc.

The device has a component that projects lights in various shades of gray on different parts of the printed object to determine the areas that must harden and those that must soften depending on the desired outcome. A light shade can produce a hard part, while a dark shade can produce a softer part. This way, an object or a part of this object can have its own structure, which can bend or stretch.

Using the inkjet feature, the printer can manufacture an electrical wire. The procedure involves spraying ink containing silver nanoparticles onto the target surface. Under the action of the pulsed lights, the ink evaporates and the metal layers harden, forming the wire. Then the printer constructs the plastic coating that surrounds the wire.

The team is working with Children’s Healthcare of Atlanta (CHOA) to print prosthetics for children born with deformed arms.

The study was funded by HP-Inc, the National Science Foundation, the US Air Force Office of Scientific Research and Northrop Grumman.