I was playing around with origami when I had the idea for this inflatable twisting actuator. In my last two weeks with the Gat Research Group at the Technion I had the idea, did some back-of-the-napkin math to show it could work, and rapidly prototyped with Ezra Ben-Abu to develop and test a working model. I returned to my studies at Cornell, but the lab developed the idea for the next two years and published a paper on the device in 2024. They found that the simple design allowed the actuator to be made very, very small. With an inner radius of just 44 µm it is the smallest inflatable multistable actuator ever made, and is being developed for use in a catheter for robotic surgery!

Abstract

The study of multistable structures, particularly those that can twist, has attracted significant attention in recent years. This ability to transition between multiple stable geometries of these structures has paved the way for advances in diverse applications, such as morphing structures and robot actuation mechanisms. Conventional methods of designing and fabricating these structures often involve complex and resource-intensive fabrication processes, which restrict their widespread adoption and limit their miniaturization. Here, we present a novel inflatable multistable twisting structure, based on helical folds of an elastic tube. Our fabrication approach utilizes directed mechanical instability as a method for a rapid fabrication, which is readily imple mented at various length scales. We developed a theoretical model for the deformation of the bistable helical elements comprising the twisting structure, and compared it to experimental data. Furthermore, we demonstrate our fabrication methodology using a variety of polymers, including medical grade polymers, as well as various inner radii ranging from5mm to44 µm and thicknesses of the tubes’ walls ranging from250 µm to 19 µm.

Full Paper

Directed instability as a mechanism for fabricating multistable twisting micro-structure