FlexiStiff: A Variable Tensile Stiffness Element for Modulating the Behavior of Tensegrity Structures

Soft and tensegrity structures are two configurations that have appeared as robots continue to draw inspiration from nature and diversify beyond rigid machines toward compliant systems. One artificial manifestation of a biological attribute that is an active research topic is the body's capacity to calibrate its stiffness for adapting its behavior to a given task. This study brings together these designs spaces and presents a soft tensile element named FlexiStiff for tensegrity structures to enable transitioning between flexible and stiff states for variable load-bearing capability and compliance. The device's tensile stiffness constant can be increased by 4400% with a change in pressure. It can provide a high blocking force of 535.5 N and can endure elongation up to 184%. It is assembled using four commercially available materials and a two-step fabrication method consisting of 3D printing and elastomer curing. As opposed to classical tensegrities for which shape change is inexpensive in terms of energy, this work betokens a new stage in their design wherein the arrangement can radically alter the magnitude of its demand for external energy for shape morphing, a crucial characteristic for operation in partially mapped environments that present diverse terrains and disturbances of varying intensities prompting adaptability. This article presents a device that changes its tensile stiffness constant by 4400% when it is vacuumed. At atmospheric pressure it is highly deformable. Upon application of vacuum, its semirigid toothed inner units interlock and resist tensile force. It is fabricated using only four commercially available materials in two steps.image (c) 2024 WILEY-VCH GmbH