Novel 3D Printer Uses Light to Transform Liquids into Complex Solid Objects

An innovative 3D printer converts sticky liquids into intricate solid objects in just a matter of minutes using light.

Inventors have dubbed this 3D printer the “replicator”, after the famous Star Trek device that can produce any kind of object on demand. The printer can produce smoother, more complex, and more flexible objects than what is possible with conventional 3D printers. Through this 3D printer, an already existing object can be covered with new types of materials—for example, a handle can be added to a metal screwdriver shaft, which would be difficult to do with present-day printers.

According to the researchers, the novel technology has the ability to change the way products—from eyeglass lenses to prosthetics—are designed and manufactured.

I think this is a route to being able to mass-customize objects even more, whether they are prosthetics or running shoes.

Hayden Taylor, Study Senior Author and Assistant Professor, Department of Mechanical Engineering, University of California, Berkeley.

The study describing the 3D printer has been reported in the journal Science on January 31^st, 2019.

“The fact that you could take a metallic component or something from another manufacturing process and add on customizable geometry, I think that may change the way products are designed,” stated Taylor.

3D objects are built up layer by layer by a majority of 3D printers, including other light-based methods. This results in a “stair-step” effect along the edges. Such printers also find it difficult to produce flexible objects because flexible materials can distort easily at the time of the printing process, and, moreover, supports are needed for printing objects of specific shapes, for example, arches.

The latest 3D printer depends on a viscous liquid, which upon exposure to a specific threshold of light, reacts to create a solid. When meticulously crafted patterns of light—fundamentally “movies”—are projected onto a rotating cylinder of liquid, the preferred shape is solidified “all at once.”

Basically, you’ve got an off-the-shelf video projector, which I literally brought in from home, and then you plug it into a laptop and use it to project a series of computed images, while a motor turns a cylinder that has a 3D printing resin in it. Obviously there are a lot of subtleties to it—how you formulate the resin, and, above all, how you compute the images that are going to be projected, but the barrier to creating a very simple version of this tool is not that high.

Hayden Taylor, Study Senior Author and Assistant Professor, Department of Mechanical Engineering, University of California, Berkeley.

The printer was used by Taylor and the team to produce an array of objects, ranging from a modified jawbone model to a small model of Rodin’s “The Thinker” statue. Presently, up to 4” diameter–objects can be created.

“This is the first case where we don’t need to build up custom 3D parts layer by layer,” stated Brett Kelly, the paper’s co-first author who completed the analysis while as a graduate student working jointly at Lawrence Livermore National Laboratory and UC Berkeley. “It makes 3D printing truly three-dimensional.”

A CT scan—in reverse

The researchers developed the novel printer by taking a cue from the computed tomography (CT) scans that assist physicians to detect fractures and tumors inside the body. CT scans can project electromagnetic radiation, including X-rays, into the body from various angles. Examining the transmitted energy patterns reveals the object’s geometry.

“Essentially we reversed that principle,” stated Taylor. “We are trying to create an object rather than measure an object, but actually a lot of the underlying theory that enables us to do this can be translated from the theory that underlies computed tomography.”

For light patterning, complicated calculations have to be made to get the right kind of intensities and shapes. In addition to this, the researchers faced another major difficulty on how to create a material that remains liquid upon exposure to a small amount of light but reacts easily to form a solid upon exposure to plenty of light.

“The liquid that you don’t want to cure is certainly having rays of light pass through it, so there needs to be a threshold of light exposure for this transition from liquid to solid,” stated Taylor.

The 3D-printing resin contains liquid polymers combined with dissolved oxygen and photosensitive molecules. Light stimulates the oxygen-depleting photosensitive compound. The polymers form the “cross-links” only in those 3D areas where the entire oxygen has been used up; this changes the resin from a liquid state to a solid one. Taylor added that the unused resin can be recycled by heating it up in atmospheric oxygen.

“Our technique generates almost no material waste and the uncured material is 100 percent reusable,” stated Hossein Heidari, co-first author of the study and graduate student in Taylor’s lab at UC Berkeley. “This is another advantage that comes with support-free 3D printing.”

Moreover, the objects do not necessarily have to be transparent. The investigators printed objects that seem to be opaque with the help of a dye that absorbs most of the other wavelengths yet conveys light at the curing wavelength.

This is particularly satisfying for me, because it creates a new framework of volumetric or ‘all-at-once’ 3D printing that we have begun to establish over the recent years. We hope this will open the way for many other researchers to explore this exciting technology area.

Maxim Shusteff, Staff Engineer, Lawrence Livermore National Laboratory.

UC Berkeley’s Indrasen Bhattacharya is the study’s co-first author. Christopher M. Spadaccini of Lawrence Livermore National Laboratory is the other author.

The study was supported by UC Berkeley faculty startup funds and by Laboratory-Directed Research and Development funds from Lawrence Livermore National Laboratory. A patent application has been filed on the technique.

A new 3D printer developed by researchers at the University of California, Berkeley, uses light patterns to transform viscous liquids into custom objects. (Video credit: UC Berkeley video by Roxanne Makasdjian and Stephen McNally)