Biorobotic adhesion in water using suction cups

Area of Science:

• Biomimetics
• Adhesion Science
• Robotics

Background:

• Underwater adhesion is crucial for many marine organisms, including echeneid fish, limpets, and octopi.
• Echeneid fish exhibit remarkable suction-based adhesion to sharks, raising questions about their low-energy, persistent, and leak-free contact on rough surfaces.

Purpose of the Study:

• To explore the design features of echeneid fish suckers in a biorobotic context for underwater adhesion on rough surfaces.
• To compare the adhesion performance of man-made suction cups with natural examples.

Main Methods:

• Experimental comparison of release force and tenacity between man-made and natural suction cups.
• Analysis of factors influencing adhesion, including cup size/type, surface roughness/curvature, and liquid surface tension.
• Characterization of water flow in sharkskin-like roughness.

Main Results:

• Man-made cups achieved an average tenacity of 5.28 N cm⁻² in the sub-ambient pressure range (14.6–49.0 kPa) under monotonically increasing force.
• Tenacity decreased with harmonically oscillating release forces, highlighting dynamic structural interactions.
• Biorobotic sealed contact on rough surfaces is feasible when the suction cup negatively replicates the host surface topology.

Conclusions:

• Achieving persistent, leak-free suction on rough surfaces, like echeneid fish on sharks, may require active maintenance of the negative surface topology.
• Protracted adhesion might not be energetically free for echeneid fish, suggesting active mechanisms are involved.
• Further research is needed on the efficiency of natural actuators for leak-proof contact and their biorobotic replication.