Water as a glue: Elasticity-enhanced wet attachment of biomimetic microcup structures

Octopus, clingfish, and larva use soft cups to attach to surfaces under water. Recently, various bioinspired cups have been engineered. However, the mechanisms of their attachment and detachment remain elusive. Using a novel microcup, fabricated by two-photon lithography, coupled with in situ pressure sensor and observation cameras, we reveal the detailed nature of its attachment/detachment under water. It involves elasticity-enhanced hydrodynamics generating self-sealing and high suction at the cup-substrate interface, converting water into glue. Detachment is mediated by seal breaking. Three distinct mechanisms of breaking are identified, including elastic buckling of the cup rim. A mathematical model describes the interplay between the attachment/detachment process, geometry, elasto-hydrodynamics, and cup retraction speed. If the speed is too slow, then the octopus cannot attach; if the tide is too gentle for the larva, then water cannot serve as a glue. The concept of water glue can innovate underwater transport and manufacturing strategies.

Automated summary

This study uses a novel microcup to reveal the mechanisms of its attachment and detachment underwater. The cup utilizes elasticity-enhanced hydrodynamics to generate self-sealing and high suction, effectively turning water into glue. The study also identifies three mechanisms of cup breaking and develops a mathematical model to describe the interplay between attachment and detachment.