3D printing of octopi-inspired hydrogel suckers with underwater adaptation for reversible adhesion

Biological structures with reversible adhesion can be widely observed in nature. The current biomimetic adhesion system has attracted extensive interest yet remains the fundamental challenge in the reversible high-adhesion with good environment compatibility, especially underwater. Herein, inspired with octopus, we propose the hydrogel-based suckers with favorable mechanical performance achieved readily by digital light processing 3D printing of the Zr4+-coordinated hydrogels, leading to the excellent underwater adaptation due to the water permeability. In this case, hydrogel, as the typical soft material infilled with water, can effectively enhance the adhesion and stability by the interfacial water sealing in comparison with the traditional hydrophobic and dry materials. The optimized hydrogel sucker with the radius of 5 mm, inclination of 30°, and wall thickness of 1 mm exhibits the highest adhesive strength of 48.46 ± 3.93 kPa in air, and 57.19 ± 1.93 kPa under water by experimental and numerical demonstration. The hydrogel suckers also display good adhesion versatility to different materials, including metal, ceramic, plastic and tissue etc. Finally, a pneumatic hydrogel gripper integrated with the bioinspired suckers can efficiently capture objects under water and in air. This research provides a novel path to develop the intelligent adhesion systems and mobile devices/robots.