Saturday , February 27 2021

Research: The technology has potential to transform how prosthetics products for eyeglass lenses are designed and manufactured –

A new 3D printer uses light to turn sticky liquids into complex solid objects in a matter of minutes.

Dubbed "replicator" by inventors – after the Star Trek device that can materialize any object on demand – the 3D printer can create softer, more flexible, and more complex objects than traditional 3D printers do. It can also involve an existing object with new materials – for example, by adding a handle to a metal screwdriver shaft – that current printers struggle to make.

The technology has the potential to transform the way prosthesis products for eyeglass lenses are designed and manufactured, say researchers.

"I think this is a way to be able to customize mass objects even more, be they prostheses or sneakers," said Hayden Taylor, assistant professor of mechanical engineering at the University of California, Berkeley, and senior author of an article. describing the printer, which appears online today (January 31) in the magazine Science.

"The fact that you can pick up a metal component or something from another manufacturing process and add a customizable geometry, I think this can change the way the products are designed," said Taylor.

Most 3D printers, including other light-based techniques, create 3D objects layer by layer. This leads to a "step" effect along the edges. They also have difficulty creating flexible objects because collapsible materials may deform during the printing process, and supports are required to print objects of certain shapes, such as arches.

The new printer depends on a viscous liquid that reacts to form a solid when exposed to a certain threshold of light. Projecting carefully created light patterns – essentially "films" – into a rotating liquid cylinder solidifies the desired shape "all at once."

"Basically, you have a shelf video projector, which I literally brought from home, and then you plug it into a laptop and use it to design a series of computed images, while a motor rotates a cylinder that has a printing resin 3D on it, "said Taylor. "Obviously there are many subtleties to it – how you formulate the resin and, most of all, how you calculate the images that will be projected, but the barrier to creating a very simple version of that tool is not that high. .

Taylor and the team used the printer to create a series of objects, from a tiny model of Rodin's "The Thinker" statue to a custom jasmine model. Currently, they can create objects up to four inches in diameter.

"This is the first case where we do not need to create custom 3D layers layer by layer," said Brett Kelly, co-author of the article that completed the work, while a graduate student works together at UC Berkeley and Lawrence Livermore. National Laboratory. "This makes 3D printing truly three-dimensional."

A CT scan – in reverse

The new printer was inspired by computerized tomography (CT) scans that can help doctors find tumors and fractures in the body.

CT scans design X-rays or other types of electromagnetic radiation in the body from all different angles. By analyzing the transmitted energy patterns, the geometry of the object is revealed.

"We essentially reverse this principle," Taylor said. "We are trying to create an object instead of measuring an object, but in fact much of the underlying theory that allows us to do this can be translated from the underlying theory of computed tomography."

In addition to standardizing light, which requires complex calculations to obtain correct shapes and intensities, the other major challenge faced by researchers was how to formulate a material that remains liquid when exposed to light but reacts to form a solid. when exposed to a lot of light.

"The liquid you do not want to heal is certainly having rays of light passing through it, so there needs to be a threshold of light exposure for this transition from liquid to solid," Taylor said.

The 3D printing resin is composed of liquid polymers mixed with photosensitive molecules and dissolved oxygen. The light activates the photosensitive compound that depletes oxygen. Only in those 3D regions where all oxygen was used, the polymers form the "cross-links" that transform the resin from a liquid to a solid. Unused resin can be recycled by heating it in an oxygen atmosphere, Taylor said.

"Our technique generates almost no material waste and uncured material is 100% reusable," said Hossein Heidari, a graduate student at Taylor's lab at UC Berkeley and co-lead author of the paper. "This is another advantage that comes with unsupported 3D printing."

Objects also do not have to be transparent. Researchers have printed objects that look opaque using a dye that transmits light at the curing wavelength, but absorbs most other wavelengths.

"This is particularly gratifying to me because it creates a new volumetric or" one-time "3D printing structure that we have begun to establish in the last few years," said Maxim Shusteff, a team engineer at Livermore Laboratory. "We hope this opens the way for many other researchers to explore this exciting area of ​​technology."

Indrasen Bhattacharya of UC Berkeley is co-first author of the paper. Other authors include Christopher M. Spadaccini of the Lawrence Livermore National Laboratory.

This work was supported by UC Berkeley faculty start-up funds and funds from Research and Development Directed by the Lawrence Livermore Laboratory National Laboratory. The team filed a patent application on the technique.

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