A Biomimetic Suction Cup with a V-Notch Structure Inspired by the Net-Winged Midge Larvae

Net-winged midge larvae (genus Liponeura) can achieve robust attachment and crawl on the slippery surface in the fast stream. This remarkable capability is endowed by the rapid and reversible adhesive suckers on their abdomen. Previous studies reveal that two components play essential roles for adhesion: the V-shaped gap of the ring structure on the outer sucker surface (V-notch) and the cylinder-like structure (Piston) located at the central cavity. However, their conjoint movement mechanism and the directional adhesion of the midge larvae' suckers are still less understood. To reveal this mechanism, we designed a biomimetic sucker and performed systematic force experiments. A hydraulic cavity circuit and a piston circuit integrated with the biomimetic sucker are utilized to actuate V-notch opening and closing in conjunction with the Piston upwards and downwards. We found that the Piston's downward movement triggers the V-notch structure to open; the liquid inside the sucker is ejected out of the chamber. The Piston's upward movement triggers the V-notch structure to close and forms a pressure differential for the attachment. We also investigated the effect of the morphological parameters of the V-notch, including V-notch angle (α), V-notch depth (β). Ink particles are applied to track the water flow, and the FTIR(Frustrated Total Internal Reflection) experiment shows surface contact during the attaching and detaching process. Our experimental results show that the adhesive force of the sucker is very sensitive to the values of α and β within a specific range (α: 3-9 β: 0.33-0.38), which is consistent with the results of biological observation (α: 9.36 ± 1,08;β: 0.33 ±0.027). Also, the results suggest that the V-notch structure can control the gap during the sucker's detaching process, thus adjusting the mechanical anisotropy of the sucker in the circumferential directions. This study may pave the way for designing biomimetic underwater robots with directional adhesion in the future.