MEAM/MSE Special Seminar: “Starfish-Inspired Tubefeet for Temporary Underwater Adhesion”

Temporary and switchable underwater adhesion plays an important role in robotic underwater locomotion and transportation. The physical features of the suction cups of octopuses have been mimicked, where the vacuum chamber formed by the deformation of these cups enable strong adhesion. However, the works mainly focused on the strength of the underwater adhesion. For the underwater locomotion and transportation of objects in aqueous environment, rapid and autonomous detachment following strong adhesion should be accomplished. To address this challenge, we turned to the starfish and its tube feet for inspiration. Starfish possess hundreds of tube feet beneath their arms, each comprising a thin cylindrical tube. At the end of these tube feet lies the cupped pad, which resembles a conically shaped frustum with recessed dimples that widen outward. During movement, when a starfish steps on a surface, the foot pushes the mouth downward, causing it to spread along the underlying surface and secure attachment. Moreover, when digging, starfish employ their tube feet to carry sand grains. Taking inspiration from starfish tube feet, three strategies have been proposed to achieve temporary adhesion. Firstly, high adhesion hysteresis, characterized by a high ratio of normal to shear adhesion force, is observed when the aspect ratio is high. This implies that detaching the tube foot from an object becomes easier by simply tilting it. Secondly, autonomous detachment is facilitated by utilizing stimuli-responsive hydrogels within the supple mouth of the tube foot. When exposed to stimuli such as heat or light, the hydrogel undergoes shrinkage, rapidly reducing the adhesion force. Lastly, immediate detachment can be achieved by integrating the tube foot with an external syringe. By manipulating the syringe, the water-filled cylinder of the tube foot can apply pressure swiftly, leading to rapid detachment. These strategies can provide efficient and versatile solutions for temporary adhesion and detachment in underwater locomotion and transportation.