Kirigami technology: special paper folds itself when heated

Kirigami is a variant of the Japanese origami paper folding technique. 

Kirigami Technique Special Paper folds itself with heat.
Kirigami Technique Special Paper folds itself with heat.

Material scientists use the principle to design self-folding structures.

With the help of heat, a special paper can be folded into a three-dimensional structure. When developing the material, the scientists led by Jie Yin from North Carolina State University in Raleigh (USA) were inspired by the Japanese Kirigami cutting and folding technique.

Thermal kirigami gripper.

Among other things, they used the technology to design a gripper and to develop a soft robot that has a kirigami body and pneumatic legs. The researchers present their work in the journal "Proceedings of the National Academy of Sciences" (PNAS).

Kirigami-based turning soft robot.

Kirigami patterns become three-dimensional structures autonomously

This is the first case known to us in which 2-D Kirigami patterns autonomously transform into different 3-D structures without mechanical use, This is made possible by a three-layered sheet, the outer layers of which are made of paper or similar materials; in any case, they do not change with heat. The inner layer consists of a plastic that contracts above a certain temperature.

With the help of computer simulations, Yin and colleagues created cutting and folding patterns, which they applied to the special paper by laser cutting or etching. 

In some places, they cut completely through all three layers, so that the paper can open there when it is folded. In other places, they cut only the top or bottom layer, so that the paper folds at this point when the plastic contracts in the middle. The width of the cuts determines the angle of the fold.

Special paper with four "fingers

Among other things, the researchers designed an long piece of special paper with four "fingers". When they raised the room temperature, the plastic in the middle shrank and the "fingers" bent to form a gripper. The scientists also applied the Kirigami principle to a soft robot whose "legs" are operated by compressed air. 

In the middle, two slits are cross-shaped. If compressed air is now used to open one slot, which was previously closed, the other slot closes and the robot changes the orientation of its legs by 90 degrees. It can thus make a quarter turn on the spot with the fold.

They used a temperature-sensitive polymer for this work, there is no reason to believe that other stimulus-responsive polymer materials - such as photoactive liquid crystals - do not work as well.