Japanese art form inspires new engineering technique

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

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

Research, published in 2015, showed promise in the kirigami “pop-up” 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 that builds on the same inspiration especially shows that kirigami can be applied on a macro scale with simple materials such as paper.

But new research published today (Dec. 22) in the journal Advanced materials takes the process a step further.

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

“By combining nanofabrication, in situ microscopy experiments and computer modeling, we have unraveled the rich behavior of kirigami structures and identified conditions for their use in practical applications,” said Espinosa.

The researchers will start by creating 2D structures using state-of-the-art semiconductor fabrication methods and carefully placed “kirigami cuts” on ultra-thin films. Structural instabilities caused by residual stresses in the films then create well-defined 3D structures. The constructed kirigami structures could be used in a number of applications, ranging from microscale grippers (eg, cell picking) to spatial light modulators to wing power control. These capabilities position the technique for potential applications in biomedical devices, energy harvesting and space travel.

Usually there is a limit to the number of shapes that can be made with a single kirigami motif. But by using variations in the cuts, the team was able to demonstrate the bending and twisting of the film that result in a wider variety of shapes – including both symmetrical and asymmetrical configurations. The researchers showed for the first time that microscale structures, using film thicknesses of several tens of nanometers, can achieve unusual 3D shapes and offer broader functionality.

For example, electrostatic micro tweezers snap shut, which can be harsh on soft samples. Kirigami based tweezers, on the other hand, can be designed to precisely control the gripping force by adjusting the amount of stretching. In these and other applications, the ability to design cutout locations and predict structural behavior based on computer simulations takes trial and error, saving money and time in the process.

As their research progresses, Espinosa says his team plans to explore the vast space of kirigami designs, including array configurations, to achieve a wider range of possible functionalities. Another area for future research is the embedding of distributed actuators for the deployment and control of kirigami. By further investigating the technique, the team believes that kirigami could have implications for architecture, space and environmental engineering.