Starfish-inspired tube feet for temporary and switchable underwater adhesion and transportation

Abstract

Temporary and reversible underwater adhesion is important for a number of robotic applications, including picking up objects, facilitating locomotion in confined environments, and attaching to surfaces during periods of observation. Here, we present a starfish-inspired tube foot composed of a soft hydrogel mouth and a rigid stem, fabricated by integrating two serially bonded cylindrical components with distinct mechanical properties. Upon swelling, the initially straight hydrogel cylinder undergoes a selective shape transformation into a soft, cupped pad that deforms to stretch and spread upon contact, enabling effective adhesion to target surfaces. During detachment, a vacuum is formed within the tube, leading to strong underwater adhesion. The artificial tube feet show high adhesion hysteresis, autonomous release by external stimuli, and immediate detachment by pneumatic actuation with integrated system. The temporary underwater adhesive inspired by the tube feet of starfish enables functionality in underwater robotics and is demonstrated through underwater manipulation of rocks.