Imagine a time in the future when you could 3D-print a full robot or flexible electronic medical equipment with the push of a button, saving you hours of arduous manual assembly. Thanks to a significant development in 3D printing technology led by experts at the University of Colorado Boulder, that option might be more feasible than ever.
The team describes a method in a new paper for using already-accessible printers to make materials that combine solid and liquid components, a difficult task if you don’t want your robot to fall over.
“I think there’s a future where we could, for example, fabricate a complete system like a robot using this process,” said Robert MacCurdy, senior author of the study and assistant professor in the Paul M. Rady Department of Mechanical Engineering.
The findings were published by MacCurdy, doctorate students Brandon Hayes and Travis Hainsworth, and the journal Additive Manufacturing on April 14.
For a long time, 3D printers were only used by lab workers and enthusiasts. They do a decent job of producing plastic dinosaurs and individual joints and gears for machinery. But according to MacCurdy, they are capable of much more: by combining solids and liquids, 3D printers might produce objects that are more adaptable, dynamic, and perhaps even more useful.
They can be replicas that approximate the squishiness of actual human organs or wearable electronic gadgets with liquid wires enclosed within solid substrates. The engineer contrasts the development with conventional color printers, which also print in black and white.
“Color printers combine a small number of primary colors to create a rich range of images,” MaCurdy said. “The same is true with materials. If you have a printer that can use multiple kinds of materials, you can combine them in new ways and create a much broader range of mechanical properties.”
Empty space
It helps to compare 3D printers to the regular printers in your business in order to comprehend those characteristics. Thousands of flat pixels are covered in liquid inks by paper printers to produce a picture. Contrarily, inkjet 3D printers employ a printhead to dispense small liquid beads known as “voxels” (a combination of the words “volume” and “pixel”) one on top of the other.
Color printers combine a small number of primary colors to create a rich range of images. The same is true with materials. If you have a printer that can use multiple kinds of materials, you can combine them in new ways and create a much broader range of mechanical properties.
Robert MacCurdy
“Very soon after those droplets are deposited, they are exposed to a bright, ultraviolet light,” MacCurdy said. “The curable liquids convert into solids within a second or less.”
But there are many situations, he continued, where you might wish those substances to remain liquid. For instance, some engineers make microscopic channels within their solid materials using liquids or waxes, which they then empty later. Similar to how a few drops of water can sculpt a cavern beneath the ground.
These types of empty gaps can be created in 3D-printed parts thanks to engineering innovations, but cleaning them usually requires a lot of time and work. The channels must also continue to be quite straightforward.
MacCurdy and his colleagues made the decision to develop a workaround for these restrictions by learning more about the circumstances that would enable engineers to print both solid and liquid materials simultaneously.
Liquid courage
The scientists first created a number of computer simulations to investigate the physics of printing various materials next to one another. One of the big problems, MacCurdy said is:
“How can you keep your droplets of solid materials from mixing into the liquid materials, even when the droplets of solid material are printed directly on top of the liquid droplets?”
“We found that the surface tension of a liquid can be used to support solid material, but it is helpful to pick a liquid material that is more dense than the solid material the same physics that allow oil to float on top of water,” Hayes said.
The researchers next conducted experiments in the lab using a real 3D printer. They filled the printer with a regular cleaning solution and a curable polymer, or plastic (the solid).
They were able to 3D-print intricate networks of channels that resembled the branching paths of a human lung, as well as twisted loops of liquid.
“Both structures would have been nearly impossible to make through previous approaches,” Hainsworth said.
MacCurdy most recently became a member of a group of scientists from the CU Anschutz Medical Campus and CU Boulder who are exploring techniques to 3D-print accurate replicas of human tissue. These models could be used by medical professionals to practice procedures and make diagnoses. Among other techniques, the research will use MacCurdy’s liquid-solid methodology.
“We hope that our results will make multimaterial inkjet 3D printing using liquids and solids more accessible to researchers and enthusiasts around the world,” he said.
