Abstract

From large space antennas to medical balloon catheters, we rely on the deployability of rod-shaped structures. Deployable rod structures enable designs that can be compactly assembled into a cylindrical form for transport and then rapidly deployed to achieve the desired shape transformation. For example, in robotic-assisted surgeries, concentric tube continuum robots are designed to provide precise shape transformations, which make it possible to perform intricate maneuvers and complex procedures with greater accuracy. However, the deformations achieved by currently existing compliant mechanisms are highly susceptible to environmental disturbances, particularly in fluid-filled confined spaces. Attaining and maintaining a desired shape requires a triggering mechanism, which takes space, and a constant force, which consumes energy under real-time control. Current rod concepts are less suitable for complex tasks like soft robot motions.
Recent efforts have produced Bi-stable meta-structures with morphing functionalities by mimicking the snap-through mechanism of the Venus Flytrap in nature. This work presents a new class of Bi-stable metastructures named “Meta-rod.” Meta-rod structures can transform their shapes from a rod-shaped stable stage to a desired deployed stable stage, realizing linear, bending, twisting, radial, and volumetric changes, or combinations of them. The desired deformation can be programmed into the layout of the Bi-stable structures. Designing different deformation modes, like translation and twisting, involves studying how building block symmetry relates to possible deformations. The Bi-stable concept enables accurate programmed motion and deployment at the second stable stage, freeing space and energy for shape locking.
Via a combination of numerical simulations and physical experiments, this study developed prototypes that demonstrated effective deformation in a range of shape-reconfigurations. The proposed Meta-rod can achieve linear deformation of 60% of its original length, 45° in bending, and 18° of twisting via one unit cell. An umbrella-like areal model and a balloon-like volumetric structure, both stabilized by a locking mechanism, were developed and tested. Their stability and adaptability were validated through static and dynamic loading, including a left ventricle duplicator that mimics physiological conditions.