When light meets liquid: the 3D printer replicating art. Replicate an image unto the beast.

Researchers in the US create detailed objects using video images and light-sensitive polymer

The Guardian. January 31, 2019

It is no rival for the replicator that whips up meals on demand on the USS Enterprise, but it can transform gloop into useful objects and even works of art, such as miniature versions of Rodin’s Thinker.

The real-world version of the replicator, nicknamed after the handy 24th-century appliance, churns out detailed 3D shapes and components by beaming images of them on to a rotating container filled with a gooey liquid that reacts to light.

Researchers used the new 3D printing process to make model jaws, little planes and bridges, and more complex structures such as a ball inside a cage. In footage from the scientists’ lab, objects emerge from the light-sensitive fluid fully formed in under two minutes.

Christopher Spadaccini, at the US government’s Lawrence Livermore National Lab, said he was surprised at how well the first objects turned out. “We all knew right away we had something pretty exciting.”

Traditional 3D printers build structures layer by layer, but this can leave tiny steps running up the sides of the printed objects. Another drawback is that certain shapes, such as arches, need supports to fill the gaps as the structure is built up. The new process, called computed axial lithography, produces objects with smooth surfaces and removes the need for supports.

To print an object, the scientists start with a 3D representation either from a scan or a drawing on a computer. This is converted into a sequence of video images that show what the object looks like from different angles. A projector then beams the images one after another on to the rotating container filled with thick, light-sensitive polymer. The images change thousands of times during a single revolution.

“As the container rotates, the pattern that’s projected changes, so over time the amount of light that each point receives can be controlled,” said Hayden Taylor at the University of California, Berkeley. Spots that receive a lot of light solidify, while those that do not remain liquid.

“The key thing is that the video being projected is perfectly synchronised with the rotation of the container,” said Indrasen Bhattacharya, also at Berkeley. “At every particular angle you choose a particular image to project.

In the lab it took less than a minute for the printer to create a 2cm-high figure of Rodin’s sculpture The Thinker. The largest item they have made is about 10cm with features as small as 0.3mm. The gloop left over from each print run is drained off and reused, said Hossein Heidari, a co-author on the study published in Science.

The researchers are now exploring what products they can make and how big. Beyond scale models for designers, dental implants and medical prostheses are on the cards. But the process can also print on top of existing objects, so could add customised ergonomic handles to tools and sports equipment, and in the future, perhaps even print clear, soft hydrogels around tiny electronic circuits to make smart contact lenses.

Ian Campbell, who works on computer-aided product design in the Additive Manufacturing Research Group at Loughborough University, said the idea of “volumetric 3D printing” has been around for some time, but this was the first system he had seen that used multi-angle projections to make complex objects.

“The key advantages are reduced time and no supports being required. However, the second of these advantages depends on the high viscosity of the resin material used,” he said. If the light-sensitive liquid is not thick enough, parts of the object that solidify first might simply sink to the bottom of the container.

The main limitation of the process is that photoreactive polymers can be expensive and are not generally used to manufacture actual products. “Nevertheless, these materials have proved very effective for prototype production and this new system could also fit into this segment of the 3D-printing market,” he said.

“The system would need to be scaled up to be of commercial benefit to most companies but could be of immediate use to companies requiring small models, such as in the dental and jewellery industries,” Campbell added.

Scientists have a habit of making little replicas of Rodin’s Thinker to show off their latest breakthroughs. More than a decade ago Korean researchers went a step further than Willard Wigan’s tiny copy, which could sit on a pinhead, with a version no taller than half the width of a human hair. It is not clear how many people saw it.