Chameleon properties inspire 3D-printed objects

In a new paper, they present colourFab, a method for repeatedly changing the colours of 3D printed objects, after fabrication. Using their own 3D printable ink that changes colour when exposed to ultraviolet light, the team can recolour a multicoloured object in just over 20 minutes — and they say they expect that number to decrease significantly with future improvements.

While the project is currently focused on plastics and other common 3D printing materials, the researchers say that eventually people could instantly change the colour of their clothes and other items.

“Largely speaking, people are consuming a lot more now than 20 years ago, and they’re creating a lot of waste,” says Stefanie Mueller, the X-Consortium Career Development Assistant Professor in the departments of Electrical Engineering and Computer Science and Mechanical Engineering. “By changing an object’s colour, you don’t have to create a whole new object every time.”

Mueller co-authored the paper with postdoc Parinya Punpongsanon, undergraduate Xin Wen, and researcher David Kim. It has been accepted to the ACM CHI Conference on Human Factors in Computing Systems, which takes place in April in Montreal. 

Previous colour-changing systems have been somewhat limited in their capabilities, using single colours and 2D designs, for example.

To move beyond single-colour systems, the team developed a simple hardware/software workflow. First, using the colourFab interface, users upload their 3D model, pick their desired colour patterns, and then print their fully coloured object.

After printing, changing the multicoloured objects involves using ultraviolet light to activate desired colours and visible light to deactivate others. Specifically, the team uses an ultraviolet light to change the pixels on an object from transparent to coloured, and a regular office projector to turn them from coloured to transparent.

The team’s custom ink is made of a base dye, a photoinitiator, and light-adaptable dyes. The light-adaptable (photochromic) dyes bring out the colour in the base dye, and the photoinitiator lets the base dye harden during 3D printing.

“Appearance adaptivity in general is always a superior feature to have, and we’ve seen many other kinds of adaptivity enabled with manufactured objects,” says Changxi Zheng, an associate professor at Columbia University who co-directs Columbia’s Computer Graphics Group. “This work is a true breakthrough in being able to change the colour of objects without repainting them.”

The team tested colourFab on three criteria: recolouring time, precision, and how quickly the colour decayed. A full recolouring process took 23 minutes. However, the researchers note that they could speed up the process by using a more powerful light or adding more light-adaptable dye to the ink.

They also found the colours to be a bit grainy, which they hope to improve on by activating colours closer together on an object. For example, activating blue and red might show purple, while activating red and green would show yellow.

Mueller says that the goal is for people to be able to rapidly match their accessories to their outfits in an efficient, less wasteful way. Another idea is for retail stores to be able to customise products in real-time, if, for example, a shopper wants to try on an article of clothing or accessory in a different colour.

“This is the first 3D-printable photochromic system that has a complete printing and recolouring process that’s relatively easy for users,” Punpongsanon says. “It’s a big step for 3D printing to be able to dynamically update the printed object after fabrication in a cost-effective manner.”

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Image credit: MIT.