As the science of 3D printing progresses, it was only a matter of time before research brought it to the next level. “Four-dimensional” (“4D”) printing is a term that was recently defined to describe the integration of existing 3D printing technology and active material science to create printed components that can change their configuration with environmental stimulus such as temperature or humidity. For some researches, it means getting a step closer to being able to incorporate the mechanical programming post-processing step directly into the 3-D printing process, saving time and materials.
A team of researchers from Georgia Institute of Technology, Singapore University of Technology, and Design (SUTD) and Xi'an Jiaotong University in China recently developed a new 3-D printing method to create objects that can permanently change their shape in response to heat. Using a Stratasys multimaterial Objet 3D printer, the team laid down layers of shape memory polymers, with each layer designed to respond differently when exposed to heat.
Smart shape memory polymers (SMPs) are materials with the ability to “remember” one shape and change to another programmed shape when uniform heat is applied. For the purpose of the research, the team created a model of a daisy with petals that bent in a similar manner to a real flower with exposure to sunlight, and a lattice-shaped object that could be expanded by nearly eight times its original size.
A lattice created by a multi-material 3-D printer at Georgia Institute of Technology that can permanently expand to eight times its original width after exposure to heat. Image source: Georgia Tech
Jerry Qi, a professor at the George W. Woodruff School of Mechanical Engineering at Georgia Tech, told Design News that the new process will save significant time and materials in the additive manufacturing process while eliminating time-consuming mechanical programming from the design and manufacturing workflow. High-resolution 3D printed components can be designed by computer simulation, 3D printed, and then directly and rapidly transformed into new permanent configurations by simple heating.
“A typical process requires 1) heating the polymer; 2) mechanically deforming the polymer into the second shape; 3) lowering the temperature; 4) removing external load,” he said. “The polymer stays in the deformed shape (we call it “programmed shape”). To recover, one just needs to heat the polymer again; the polymer will return to its original (permanent) shape. In our new approach, one just needs to heat the printed structure (no need to mechanically deform it), and it will change into a new shape.”
Using the new process, the new shape remains stable, and will not change upon further heating or cooling. More interestingly, according to the team, this new material can have the shape memory effects, but it will take the new shape as its permanent shape.
A process that allows for high-resolution complex 3D reprogrammable structures would enable a wide variety of applications across domains, including aerospace, medical technology and consumer products. It may even allow for a new paradigm in product design, where components can be simultaneously designed to inhabit multiple configurations during service.
Dr. Qi told Design News that for design engineers, the method would be an ideal way to design thin, flexible structures.
“Here, the shape change is due to the placement of different materials, which was not part of consideration in the traditional design methodology,” he said. “Also, since the new shape (the shape after heating) is the permanent shape, the design will need to consider both 3D and 4D printed shape; this is also new. Our new method can provide a significant amount of savings in terms of printing time and materials.”
The precise numbers depend on the structures, according to the team, but on average, the process can save between 60 and 70 percent printing time and printing materials. It could also offer compelling benefits to the packing and shipping process: thin, flat items could be packed flat, delivered, then heated to change to a larger structure of more complex shape. The medical applications are also compelling: a biomedical stent, for example.
“We can print the structure into a tube using our expanding lattice design,” said Dr. Qi. “After delivering that tube into a blood vessel, we can use either body temperature or some external heating to deploy it. The tube will expand significantly and stay in the expanded shape.”
Going forward, the research team hopes to gain a more fundamental understanding of how different materials can provide different (either better or worse) responses. They’re also planning to experiment with different designs and look for industrial collaborators to take the process further.
The research was published in the journal Science Advances, a publication of the American Association for the Advancement of Science. It was funded by the U.S. Air Force Office of Scientific Research, the U.S. National Science Foundation and the Singapore National Research Foundation.