Researchers have designed materials that can control and mold a balloon into pre-programmed shapes. The system uses kirigami sheets — thin sheets of material with periodic cuts — embedded into an inflatable device. As the balloon expands, the cuts in the kirigami sheet guide the growth, permitting expansion in some places and constricting it in others. The researchers were able to control the expansion not only globally to make large-scale shapes but locally to generate small features. The team also developed an inverse design strategy, an algorithm that finds the optimum design for the kirigami inflatable device that will mimic a target shape upon inflation.
An individual cut on a kirigami sheet contributes to the larger shape of the balloon like a pixel helps form an image on a 2D surface. By tuning the geometric parameters of these cuts, the team could control and embed complex shapes such as bends, twists, and expansions. Using these parameters, the researchers developed an inverse algorithm that could mix and match pixels of different width and height, or delete certain pixels altogether, to achieve the desired shape. By manipulating the parameters of individual pixels, they were able to tune shapes at a significantly smaller scale.
To demonstrate this, the team programmed a balloon to mimic the shape of a squash, complete with the characteristic bumps and ridges along the side. By controlling the expansion at every level of the kirigami balloon, a variety of target shapes can be reproduced.