Biomechanics of underwater adhesion by suction

Wei-Ting Yueh¹, Yu-Tze Hung¹, Tien-Yun Lin¹, Ming-Chih Shih¹, Kai-Jung Chi^1,2,3*

¹Department of Physics, National Chung Hsing University, Taichung, Taiwan
²Department of Life Sciences, National Chung Hsing University, Taichung, Taiwan
³The iEGG and Animal Biotechnology Center, National Chung Hsing University, Taichung, Taiwan

* Presenter:Kai-Jung Chi, email:kjchi@phys.nchu.edu.tw

Attachment is important for many aspects of life. Diverse attachment devices have evolved independently and are classified according to their morphology and force involved. Some animals manage to attach dynamically onto irregular surfaces in water by suction, which remains a challenge for human technology. Most biological suckers (e.g., octopus, remora fish) actively contract muscles to generate pressure difference. In this talk, I will present two passive systems of distant lineages and explain their functioning mechanisms. In cuttlefish, the muscular suckers on the tentacle clubs are used to capture fast-moving preys. The sucker stalk and ring, not found in octopus, are critical for suction. Their compliant contact surface allows self-sealing with rough substrates when pressure differential is generated across the sucker. In male diving beetles, specialized adhesive setae (hairs), in spatula or circular form, are used to mount onto female elytra during underwater courtship. The circular setae provide long-term adhesion; while the spatula setae found only in male Cybister beetles perform velocity-dependent, tunable adhesion. To decipher the physical principles of this unusual velocity-dependent adhesion, we construct a conceptual “water-leaking model” incorporating measurements of seta’s surface geometry, material property, as well as the sucker and stalk deformation. Results suggest that the spatula setae combine suction and viscous resistance for adhesion through three mechanisms: (i) water flowing through microfluidic channels leads to velocity-dependent adhesion; (ii) stalk-pulling increases pressure difference to compress the channel wall, triggering seal-off of the micro-channels; (iii) stalk elasticity provides buffer for energy storage, further increasing the adhesion capacity. Unlike artificial ones, these bio-suckers perform well on rough, curved, or even soft substrates. The design principles abstracted from these passive sucker systems can provide insights for making bio-inspired underwater attachment devices that require less energetic cost.

Keywords: Underwater attachment, Suction, Viscous resistance, Biomechanics