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New 3D printer lets object appear using light

Researchers at the University of Berkeley developed a new method to 3D print objects, by turning gooey liquids into solid objects in a matter of minutes using light.

The 3D printer is nicknamed the ‘Replicator’ by the inventors, named after the device from Star Trek that can materialise any object on demand. Rather than layer by layer, as most 3D printers create objects, the objects are formed in one piece, which makes them smoother. The new technique allows for more flexible and complex designs as well.

The printer relies on a viscous liquid that turns solid when exposed to a certain threshold of light. By projecting carefully crafted patterns of light, basically a movie, onto a rotating cylinder of liquid, the material solidifies in the desired shape at once.

The researchers created a variety of objects, from a replica of Rodin’s ‘The Thinker’ to a customised model of a jawbone. The technique can also be used to encase other objects with new materials, like creating a handle to a metal screwdriver shaft.

The new printer was inspired by CT scans that help doctors locate tumors and fractures in the body. This type of scan project X-rays or other types of electromagnetic radiations into the body from all different angles. Analysing the patterns of energy reveals the geometry of the object. Essentially, the team reversed that principle.

The main complication in this type of printing is patterning the light, which requires complex calculations to get the exact shapes and intensities right. Another challenge was how to formulate a material that stays liquid when exposed to a little bit of light, but turns solid when exposed to a lot of it. The resulting resin is composed of liquid polymers mixed with photosensitive molecules and dissolved oxygen. Light activates the photosensitive compound, which depletes the oxygen. Only in these parts where all oxygen has been used up do the polymers form crosslinks, turning the material solid. Unused resin can be recycled by hearing it up in an oxygen rich atmosphere. This means the technique generates almost no material waste.

Photos: Stephen McNally / Hayden Taylor / UC Berkeley

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