Japanese art form inspires new technology

Paper snowflakes, pop-up children’s books and elaborate paper cards are of interest to more than just artisans. A team of Northwestern University engineers use ideas drawn from paper folding to create a sophisticated alternative to 3D printing.

Kirigami comes from the Japanese words “kiru” (to cut) and “kami” (paper) and is a traditional art form in which paper is precisely cut and transformed into a 3-D object. Using thin films of material and software to select exact geometric cuts, engineers can create a wide range of complex structures by taking inspiration from practice.

Research published in 2015 showed promise in kirigami’s “pop-up” manufacturing model. In this iteration, the band-like structures created by the cuts were open shapes with limited ability to achieve closed shapes. Other research based on the same inspiration shows primarily that kirigami can be used on a macro scale with simple materials such as paper.

But new research published today (December 22) in the journal Advanced materials promotes the process one step further.

Horacio Espinosa, a mechanical engineering professor at the McCormick School of Engineering, said his team was able to apply design and kirigami concepts to nanostructures. Espinosa led the research and is James N. and Nancy J. Farley Professor of Manufacturing and Entrepreneurship.

“By combining nanoproduction, in situ microscopy experimentation, and computational modeling, we revealed the rich behavior of kirigami structures and identified conditions for their use in practical applications,” Espinosa said.

The researchers start by creating 2-D structures using advanced methods of making semiconductors and carefully placed “kirigami cuts” on ultra-thin films. Structural instabilities induced by residual stresses in the films then create well-defined 3D structures. The constructed kirigami structures could be used in a variety of applications ranging from microscale grippers (e.g., cell picking) to spatial light modulators for flow control in flight wings. These possibilities place the technique for potential applications in biomedical devices, energy harvesting and aerospace.

There has typically been a limit to the number of shapes that can be created by a single kirigami motif. However, using variations in the cutouts, the team was able to demonstrate film bending and twisting, resulting in a wider range of shapes – including both symmetrical and asymmetrical configurations. The researchers demonstrated for the first time that structures in microscales using film thicknesses of a few dozen nanometers can achieve unusual 3D shapes and present wider functionality.

For example, electrostatic micro-trends click closely, which can be hard on soft samples. In contrast, kirigami-based tweezers can be designed to precisely control the gripping force by setting the amount of stretch. In this and other applications, the ability to design swath locations and predict structural behaviors based on computer simulations takes tests and errors, saving money and time in the process.

As their research progresses, Espinosa says his team plans to explore the vast space with kirigami designs, including array configurations, to achieve a greater number of possible features. Another area for future research is the embedding of distributed actuators for the implementation and control of kirigami. By examining the technique further, the team believes that kirigami can have implications for architecture, aviation and environmental engineering.