3D printed objects that can move and change shape are technically 4D printed – the fourth dimension comes in the object’s ability to change shape when exposed to environmental stimuli like heat, humidity, and/or light, and then revert back to its original form. At this week’s National Meeting & Exposition of the American Chemical Society (ACS), the largest scientific society in the world, a team of researchers is presenting research on their powerful new 4D printer.
This emerging technology is challenging, as lengthy, complex post-processing steps are usually needed to mechanically program each component. Aside from this, most commercial systems are only able to print 4D structures in one material only.
The 4D printer that this research team created, with funding from HP Inc., the National Science Foundation, the US Air Force Office of Scientific Research, and Northrop Grumman, could be used to streamline the creation of structures that can self-assemble and change shape, using multiple materials.
“We are on the cusp of creating a new generation of devices that could vastly expand the practical applications for 3-D and 4-D printing. Our prototype printer integrates many features that appear to simplify and expedite the processes used in traditional 3-D printing,” explained H. Jerry Qi, PhD, a professor in the George W. Woodruff School of Mechanical Engineering at the Georgia Institute of Technology (Georgia Tech). “As a result, we can use a variety of materials to create hard and soft components at the same time, incorporate conductive wiring directly into shape-changing structures, and ultimately set the stage for the development of a host of 4-D products that could reshape our world.”
Previously, Qi and his Georgia Tech research team, working with researchers from Xi’an Jiaotong University and the Singapore University of Technology and Design, have 4D printed objects, like a flower that can close its petals, using a heat source, a commercial 3D printer, and a composite made from an acrylic and an epoxy. We have heard Qi discuss his work, pointing toward potential real-world applications.
Because the scientists added the time-consuming mechanical programming steps right into the 3D printing process, the objects were able to transform their shapes up to 90% faster than was currently thought possible. The team presenting at the ACS meeting this week built on this work in order to develop an all-in-one printer to address additional 4D printing challenges. The researchers published their findings in a paper, titled “Multimaterial 3D Printing for Shape Changing Devices and 4D Printing.”
The abstract reads, “To date, hydrogels and shape memory polymers (SMPs) are the two main active polymers used in 4D printing. SMPs have been used in 4D printing with both commercial and research printing technologies based on photopolymer inkjetting and projection micro stereolithography. However, 4D printing with SMPs generally requires a series of steps, including synthesis/processing by 3D printing, heating, mechanical loading, cooling, and removing the load. Thermomechanical programming often requires special jigs and fixtures to apply mechanical loads and a well-controlled thermal environment. In this paper, we propose a new direct 4D printing approach with shape memory polymers (SMPs) where we integrate the programming steps into the 3D printing process. As a result, the 3D printed component can directly change its shape rapidly upon heating. This second shape largely remains stable in later variations in temperature, such as cooling back to room temperature. Furthermore, a third shape can be programmed by thermomechanical loading, and the material will always recover back to the permanent (second) stable shape upon heating. We also created a theoretical model that incorporates the key elements, including the material behaviors during the processing/programming and deployment phases and 3D printing processing parameters. The model was then used to guide to design complicated shape changes.”
The new 4D printer combines aerosol, inkjet, direct ink write, and an extrusion-based printing technique, and can handle multiple elastic and stiff materials, including hydrogels, liquid crystal elastomers, silver nanoparticle-based conductive inks, and SMPs. This last is the most common substance when it comes to 4D printing, as it can be programmed to ‘remember’ certain shapes and transform into them once heated.
Thanks to the team’s new technology, they will be able to print higher-quality SMPs capable of making more intricate shape changes, which could introduce new functional 4D applications. The researchers can also project a range of white, gray, or black shades of light to form and cure a component into a solid. Depending on the grayscale of shade shining on the component, the lighting triggers a crosslinking reaction that can change the object’s behavior. Darker light shades produce softer parts, while brighter shades create harder ones, meaning that the components will stretch or bend differently than the other 4D structure parts they’re surrounded by.
The 4D printer can also use a direct ink write method to produce silver nanoparticle ink, which means it can create electrical wiring for direct printing onto electrical devices like sensors or antennae; the plastic coating surrounding the wire is created by the printer’s ink-jet component.
Qi and his team are also partnering with Children’s Healthcare of Atlanta to see if the new 4D printing technology can be used to produce prosthetic hands for children who were born with malformed arms.
“Only a small group of children have this condition, so there isn’t a lot of commercial interest in it and most insurance does not cover the expense. But these children have a lot of challenges in their daily lives, and we hope our new 4-D printer will help them overcome some of these difficulties,” Qi said.
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