The Japanese art form inspires a new engineering technique

Paper snowflakes, pop-up children’s books and intricate paper cards are of interest not only to artisans. A team of engineers at Northwestern University uses ideas taken from the practice of folding paper to create a sophisticated alternative to three-dimensional printing.

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

The research, published in 2015, showed promise in the model of making kirigami “pop-ups”. In this iteration, the ribbon-like structures created by the cuts were of open shapes, with limited ability to achieve closed shapes. Other research based on the same inspiration generally shows that kirigami can be applied on a macro scale with simple materials like paper.

But a new study was published today (December 22) in a journal Advanced materials the process progresses a step further.

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

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

Researchers begin by creating two-dimensional structures using state-of-the-art semiconductor manufacturing methods and carefully placed “kirigami cuts” on ultrathin films. Structural instabilities caused by residual stresses in films then create well-defined 3-D structures. Constructed kirigami structures can be used in a number of applications, from micro-scale catchers (e.g., cell selection) to spatial light modulators to control the flow in aircraft wings. These capabilities position the technique for potential applications in biomedical devices, energy collection, and aviation.

Typically, there is a limit to the number of shapes that can be created by a single kirigami motif. But using variations of the cuts, the team was able to demonstrate the bending and twisting of the film resulting in a number of shapes – including symmetrical and asymmetrical configurations. Researchers have demonstrated for the first time that structures on micro scales, using a film thickness of a few tens of nanometers, can achieve unusual three-dimensional shapes and present wider functionality.

For example, electrostatic micropincers close, which can be rough on soft samples. In contrast, kirigami-based tweezers can be designed to precisely control the gripping force by adjusting the size of the stretch. In this and other applications, the ability to design cut locations and predict structural behavior based on computer simulations removes trial and error, saving money and time in the process.

As their research progresses, Espinosa says his team plans to explore a large space of kirigami designs, including array configurations, to achieve more possible functionality. Another area for future research is the installation of distributed actuators for setting up and controlling kirigami. By further studying the technique, the team believes that kirigami may have implications for architecture, aviation, and environmental engineering.