Just as an octopus can change colours and contort its body, materials built by a 3D printer can now alter their hues and bend into new shapes.
The process known as 4D printing adds the dimension of time to 3D printing, creating objects that can reshape themselves. Qingping Liu at Jilin University in Changchun, China, Lei Ren at the University of Manchester, UK, and their team added the ability to change colour as well.
The researchers created a material that can simultaneously change shape and color by mixing a shape-memory polymer and thermochromic pigments: when bent into a particular configuration above a certain temperature and then cooled, it will return to its original shape when heated again. Along withshape change, the materials change when heated from, for example, orange to yellow then back to orange when cooled.
By controlling process parameters such as the layer thickness or printing temperature, the researchers could determine the pace of the shape and colour changes. The authors created a dark green and orange flower bud that opened into a yellow blossom, as well as an octopus with tentacles that changed colour as they unfurled.
Compared with current 4D printing research,the proposed shape–color double-responsive 4D printing strategypushes the envelope of 4d printing, and is expected to be helpful for understanding and exploring the full potential of 4D printing.