The Japanese art form inspires a new engineering technique

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

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

The research, published in 2015, showed promise in the “pop-up” kirigami manufacturing model. In this iteration, the ribbon-like structures created by the cuts were open shapes, with limited ability to achieve closed shapes. Other research based on the same inspiration mainly demonstrates that kirigami can be applied to a macroscale with simple materials such as paper.

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

Horacio Espinosa, a professor of mechanical engineering 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 Professor James N. and Nancy J. Farley in Production and Entrepreneurship.

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

Researchers begin by creating 2-D structures using state-of-the-art methods in semiconductor fabrication and carefully placing “kirigami cuts” on ultra-thin films. The structural instabilities induced by the residual stresses in the films then create well-defined 3D structures. The designed kirigami structures could be used in a number of applications, from microscopic scale attachments (eg cell sampling) to spatial light modulators to flow control in aircraft wings. These capabilities position the technique for potential applications in biomedical, energy harvesting and aerospace devices.

Usually, there was a limit to the number of shapes that could be created for a single kirigami motif. But using variations in cuts, the team was able to demonstrate the bending and twisting of the film, which resulted in a wider variety of shapes – including symmetrical and asymmetrical configurations. Researchers have shown for the first time that microscale structures, using film thicknesses of several tens of nanometers, can achieve unusual 3-D shapes and have wider functionalities.

For example, electrostatic microtypes close quickly, which can be harsh for soft samples. Instead, kirigami-based tweezers can be designed to precisely control the gripping force by adjusting the amount of stretching. In this and other applications, the ability to design truncated locations and predict structural behavior based on computer simulations eliminates trial and error, saving money and time in the process.

As their research progresses, Espinosa says his team intends to explore the large space of kirigami projects, including array configurations, to get as many functionalities as possible. Another area for future research is the incorporation of distributed actuators for the deployment and control of kirigami. Further analyzing the technique, the team believes that kirigami may have implications for architecture, aerospace and environmental engineering.