Researchers at North Carolina State University have designed and created 2-D materials that are remotely controlled so that specific folds can be triggered at any time and in any order to form 3-D structures, according to a report on the university website.
An object folds into a 3-D structure because of the reaction of ink with blue light. (YouTube)
This new development, inspired by origami, builds on previous work by the researchers that showed a pre-stressed plastic sheet could have bold, black lines printed on it by standard inkjet printers and when placed under an infrared lamp fold into 3-D shapes.
This worked because the black ink absorbed more energy than the rest of the material causing the plastic to contract and form hinges for it to bend and fold. Varying the width of the lines affected how quickly and how much the hinges folded.
This new breakthrough builds on this process by incorporating different colored inks that each absorb different wavelengths of light. Using specific combinations of lights will provide an order to the folds.
The article explained, “For example, if one hinge is printed in yellow and another hinge is printed in blue, the researchers can make the yellow hinge fold by exposing it to blue light. The blue hinge won’t fold, because blue ink doesn’t absorb blue light. The researchers can then make the blue hinge fold by exposing the sheet to red light.”
It may even be possible to manipulate the colors of the ink to get hinges to fold sequentially because certain colors are able to absorb wavelengths of light more efficiently.
The work was recently published in Science Advances. The abstract stated:
“Shape plays an important role in defining the function of materials, particularly those found in Nature. Several strategies exist to program materials to change from one shape to another; however, few can control the shape temporally and spatially.
“Programming the sequence of shape transformation with temporal control has been driven by the desire to generate complex shapes with high yield and to create multiple shapes from the same starting material. This paper demonstrates a remarkably simple strategy for programmed self-folding 2-D polymer sheets into 3-D objects in a sequential manner using external light.
“Printed ink on the surface of the polymer sheets absorbs light discriminately based on the wavelength of the light and the color of the ink that defines the hinge about which the sheet folds. The absorbed light heats the underlying polymer gradually across the thickness of the sheet, which causes relief of strain to induce folding.
“These color patterns can be designed to absorb only specific wavelengths of light (or to absorb differently at the same wavelength using color hues), thereby providing control of sheet folding with respect to time and space.
“This type of shape programming may find numerous applications including reconfigurable electronics, actuators, sensors, implantable devices, smart packaging, and deployable structures.”
Watch the 2-D material fold into a 3-D structure in the video below: