Reversible Elastomer-Fluid Transitions for Metamorphosic Robots

Abstract Endowing robots with reversible phase transition ability, especially between elastomer and fluid states, can significantly broaden their functionality and applicability. Limited attempts have been made to realize the reversible elastomer-fluid transition. Existing phase transition materials in robotics have over-hard (~4 GPa) or over-soft (~4 kPa) stiffness in the solid states, which should be further investigated to perform more compliant motions. Advanced reversible phase transitions for metamorphosic robots demand sufficient elasticity in the elastomer state, rapidity and reversibility of the transition state, and controllable fluidity in the fluid state. To address these challenges, we present a reversible elastomer-fluid transition mechanism for metamorphosic robots enabled by magnetically induced hot melt materials (MIMMs). The transition principle is explained by material analysis, and material characterizations are conducted to understand the reversible elastomer-fluid transition. MIMMs-based metamorphosic robots endow self-metamorphosing abilities, such as self-healing, spatial self-growing, self-division/assembly, and additive manufacturability. When interacting with external environments, MIMMs-based robots can perform further multifunctional abilities, such as collaborations for structure repairs, swimming by symbiosis with external objects, flowing through a narrow terrain by transiting to fluid, and working with elastomeric structures for stiffness-variable fluid soft actuators. Biomedical applications were demonstrated to present the multi-functionality of MIMMs-based robots. The proposed elastomer-fluid transitions may open a new path for robots to generate more flexible and metamorphosic motions, thereby addressing the cross-phase transformation challenges that soft robots face.