(686a) The Influence of Geometry on the Mechanical Properties of Kirigami-Inspired Thin Films

Kirigami, the Japanese art of cutting shapes into sheets of paper, has found utility in materials science as a method to engineer a material’s mechanical properties. By creating precise geometric cuts, kirigami-inspired films can be imbued with properties such as enhanced stretchability and conformability. Structural designs can be integrated with functional materials to form biodevices and surfaces for health monitoring. Computational methods to understand how kirigami patterns influence mechanics can be used for in-silico design of multifunctional materials with specific properties.

This study explores how cut geometries impact the stretching behavior of a thin film. A slit geometry was investigated to impart stretchability. The slits are modeled using an open-source kirigami design simulator GamIan. Finite-element analysis is used to visualize stretching behavior under strain. Various cut/slit parameters were studied using polyimide as a model substrate -e.g. cut width, cut length and cut spacing (by varying the number of cuts on the sheet). A 3D mesh of the designed thin films was simulated via a simple tensile test fixing one edge of the sheet, and pulling the other end over a number of steps. The elastic behavior is recorded via a stress-strain curve. The influence of each parameter was quantified individually and in combination. The stretch could also be visualized to better understand how the films behave under stress (Figure 1).

For instance, increasing the cut widths and decreasing cut spacings result in a steadily increasing and controlled elongation. Wider edges to the cuts, or minimizing the cut spacing allows the sheet to elongate without accumulating excessive stress in the structure. Instead, increasing stress is evenly distributed among the opening slits as the film is elongated. Thus, when designing a film device, decreasing cut spacing can be prioritized over increasing cut width to preserve material and ease of microfabrication. Polyimide films are widely used in thin film electronics as substrates for wearable devices. Our work further explored a silk fibroin biomaterial to show how this technique can be used for bio interfacing applications. This technique can be broadly applied to design complex geometries to induce specific properties for applications in healthcare and electronics.