Programmable balloons pave the way for new shape-morphing devices

Balloon shaping isn't just for kids anymore. Materials have been designed that can control and mold a balloon into pre-programmed shapes, research shows.

Massachusetts: A team of researchers from the Harvard John A. Paulson School of Engineering and Applied Sciences (SEAS) developed a system that uses kirigami sheets -- thin sheets of material with periodic cuts -- embedded into an inflatable device.

Based on the expansion and constricting properties of the material, inverse design strategy, an algorithm developed by the researchers helps to give the ballons a target shape(small to big) upon inflation. The cuts in the kirigami sheet guide the growth as and when the balloon expands.

"This work provides a new platform for shape-morphing devices that could support the design of innovative medical tools, actuators, and reconfigurable structures," said Katia Bertoldi, William and Ami Kuan Danoff Professor of Applied Mechanics at SEAS and senior author of the study.

The research is published in Advanced Materials.

An individual cut on a kirigami sheet contributes to the larger shape of the balloon-like a pixel that helps form an image on a 2D surface. The researchers found that by tuning the geometric parameters of these cuts, they could control and embed complex shapes.

The parameters of the pixel if changed in terms of width, height, or deletion of certain parts of pixels, the desired shape ( any simple to crazy shapes, big to small ) of the kirigami ballons can be obtained, with all twists, bends, and expansion.

To demonstrate this, they programmed a balloon to mimic the shape of squash (the experiments took place around Halloween) complete with the characteristic bumps and ridges along the side.

Even shapes of calabash gourds, hooks and vases were tried

Antonio Elia Forte, a postdoctoral fellow at SEAS and co-first author of the study. "Our strategy allows us to automatically design a morphable balloon starting from the shape that you need. It's a bottom-up approach that for the first time harnesses the elasticity of the material, not only kinematic."

Next, the researches aim to use these kirigami balloons as shape-changing actuators for soft robots. The work lays a foundation for the design of structures at multiple scales: from micro minimally-invasive surgical devices to macro structures for space exploration.