Variable Stiffness Soft Eversion Growing Robot via Temperature Control of Low-Melting Point Alloy Pressurised Medium

This paper presents, for the first time, a low melting point alloy (LMPA)-based variable stiffness soft eversion growing robot. Eversion robots can extend into difficult-to-access pathways, such as anatomical structures, by means of pressure-induced apical extension. The proposed system combines the benefits of soft-robot compliance with temperature-based stiffening to enable navigation of such robot within the human body whilst permitting high force exertion. The system uses a LMPA as both, the actuation and stiffening medium, with emphasis on miniaturisation and adaptability. The temperature of the LMPA is controlled to alternate between the stiff, solid state and the compliant, liquid state. The robot architecture follows our previous work, achieving steerability through a tendon-driven catheter embedded in its lumen. As a proof-of-concept, the proposed system has a maximum eversion length of 6 cm, It is capable of sharp bends when steered and can apply shear forces of 2.9 N vs 0.16 N in its solid vs soft states at maximum deflection. This implies a stiffness ratio of 21.9 between the two states, which is 3–9 times higher than what has been previously reported for jamming-based stiffening approaches.