This is one in a series presenting news on technology and innovation, made possible with generous support from the Lemelson Foundation.
Unlike their rigid 3-D cousins, 4-D-printed objects can flex. Some can totally reconfigure their shapes. People usually design these to respond to some sort of facet of the environment. They might open or transform when exposed to heat, for instance, or when dropped in water. Until now, however, there were only a few ways they could move.
Scientists at the Georgia Institute of Technology in Atlanta have now developed a novel “ink.” When combined with a new method of printing, it opens up hundreds of new options for movement.
The Georgia Tech team showed it off March 21 at the spring national meeting of the American Chemical Society in New Orleans, La.
Epoxy is a strong and versatile material used in many applications. H. Jerry Qi and his team had been developing an epoxy resin to use in printing. But to harden, Qi notes, the resin has to be exposed to heat for many hours. That’s just too long when each 3-D printed layer must fully harden before the next can be laid down.
Qi, a materials scientist, invented a way around that hurdle. His innovation: Mix the resin with another material that could be cured — turned into a solid — using light. Now each layer can be set with light, then fully hardened later with heat. This two-stage process really sped up the printing rate.
While testing different ways to cure resins with light, Qi’s group also found that the light‘s intensity (how bright it was) could affect how hard a resin became. They could vary the lighting to make some parts of a printed object harder and more rigid, while others stayed soft and flexible. That prompted them to apply this to the printing process. Their goal was to create an object where parts of it might be hard, while other parts were soft enough to serve as movable joints.
And it worked.
Qi showed that he could print objects that would bend and flex in a range of different ways. Some joints were stiffer, others looser.
Still, it needed tweaking. The hardest part of the printed object could be only some 20 times harder than the softest part. While good, that was not good enough for Qi’s group. It wanted to be able to have access to a broader range of stiffness and flexibility while designing an object.
The researchers’ inspiration — or “aha” moment — came when they tried combining their two innovations. By varying the light intensities as their new epoxy resin printed, they were able to get a much greater range of softness. Now, the stiffest part of a printed object can be 600 times harder than its softest part.
The Georgia Tech team developed the process together with scientists at the Singapore University of Technology.
Printing objects with several materials
Many 3-D printers today can make objects from plastic. Or metal. Or living cells. Even from cheese. But Qi introduced a new 3-D printer at the same meeting that could build objects from a range of different materials at the same time.
One example was a plastic ribbon that has electrical wires running through it. “Each layer you print can have multiple materials,” he explains. This, he says, makes it “a powerful manufacturing tool.”
Consider objects used in electronics. They contain multiple materials that sit side by side, such as the metal wire surrounded by insulating rubber that might be embedded into a plastic structure. Most 3-D printers can now print those different materials only as separate layers. But Qi’s new printer can lay them down, side by side, all within the same layer. Objects that today must be assembled piece by piece in a factory, might one day be printed out as needed, layer after layer.
That’s an important step for 3-D printing, says Geoffrey Spinks. He’s a materials engineer in Australia at the University of Wollongong. Right now, the range of materials that can be printed together is limited, he says. “If you want to have plastic and metal printed together,” he says, “you can’t do that.” But he says that what they have already shown, “in my opinion, is a step toward that goal.”
Qi hopes one day to combine technologies again. He’d like to use the variable-light hardener in a multi-material printer. It would give his new device another unique trait — the ability to print multi-material objects with a wider range of motion.
3-D printing The creation of a three-dimensional object with a machine that follows instructions from a computer program. The computer tells the printer where to lay down successive layers of some raw material, which can be plastic, metals, food or even living cells. 3-D printing is also called additive manufacturing.
4-D An adjective that refers to being able to define something in terms of four dimensions: height, width, depth and time.
4-D printing The process of printing a three-dimensional object that is also able to move and transform over time or in response to stimuli.
application A particular use or function of something.
chemical A substance formed from two or more atoms that unite (bond) in a fixed proportion and structure. For example, water is a chemical made when two hydrogen atoms bond to one oxygen atom. Its chemical formula is H2O. Chemical also can be an adjective to describe properties of materials that are the result of various reactions between different compounds.
cure (in manufacturing and chemistry) The process of finalizing some chemical process that makes a product or surface strong and useful. For instance, cement and paint may feel dry to the touch within an hour or two, but will not really be strong until they have fully cured (a process that may take another one or more days).
engineer A person who uses science to solve problems. As a verb, to engineer means to design a device, material or process that will solve some problem or unmet need.
environment The sum of all of the things that exist around some organism or the process and the condition those things create. Environment may refer to the weather and ecosystem in which some animal lives, or, perhaps, the temperature and humidity (or even the placement of components in some electronics system or product).
epoxy An adhesive resin made from synthetic polymers.
flex To bend without breaking. A material with this property is described as flexible.
innovation (v. to innovate; adj. innovative) An adaptation or improvement to an existing idea, process or product that is new, clever, more effective or more practical.
manufacturing The making of things, usually on a large scale.
materials science The study of how the atomic and molecular structure of a material is related to its overall properties. Materials scientists can design new materials or analyze existing ones. Their analyses of a material’s overall properties (such as density, strength and melting point) can help engineers and other researchers select materials that are best suited to a new application. A scientist who works in this field is known as a materials scientist.
metal Something that conducts electricity well, tends to be shiny (reflective) and malleable (meaning it can be reshaped with heat and not too much force or pressure).
plastic Any of a series of materials that are easily deformable; or synthetic materials that have been made from polymers (long strings of some building-block molecule) that tend to be lightweight, inexpensive and resistant to degradation.
resin A sticky, sometimes aromatic substance, often secreted by plants. It may also be the viscous starting ingredient for some plastics that will harden when heated or treated with light.
Singapore An island nation located just off the tip of Malaysia in southeast Asia. Formerly an English colony, it became an independent nation in 1965. Its roughly 55 islands (the largest is Singapore) comprise some 687 square kilometers (265 square miles) of land, and are home to more than 5.3 million people.
technology The application of scientific knowledge for practical purposes, especially in industry — or the devices, processes and systems that result from those efforts.