The effects of soft and rough substrates on suction-based adhesion

Abstract

The Northern clingfish (Gobiesox maeandricus) has a suction-based adhesive disc that can stick to incredibly rough surfaces, a challenge for stiff commercial suction cups. Both clingfish discs and bioinspired suction cups have stiff cores but flexible edges that can deform to overcome surface irregularities. Compliant surfaces are common in nature and technical settings, but performance data for fish and commercial cups is gathered from stiff surfaces. We quantified the interaction between substrate compliance, surface roughness, and suction performance for the Northern clingfish, commercial suction cups, and three biomimetic suction cups with disc rims of varying compliance. We found that all cups stick better on stiffer substrates and worse on more compliant ones, as indicated by peak stress values. On compliant substrates, surface roughness had little effect on adhesion, even for commercial cups that normally fail on hard, rough surfaces. We propose that suction performance on compliant substrates can be explained in part by effective elastic modulus, the combined elastic modulus from a cup-substrate interaction. Of all the tested cups, the biomimetic cups performed the best on compliant surfaces, highlighting their potential to be used in medical and marine geotechnical fields. Lastly, we discuss the overmolding technique used to generate the bioinspired cups and how it is an important tool for studying biology.

Stickiness in shear: stiffness, shape, and sealing in bioinspired suction cups affect shear performance on diverse surfaces

“…On smooth surfaces, we observed a significant decrease in performance when a soft rim was added to the designs. This was not unexpected, as previous work has shown that stiff single material cups often outperform soft rim cups on rigid, smooth surfaces [4,13,15,25]. While these studies were performed under normal loading, the conditions that induce 'slippage' of the cup's contact margins are likely similar in shear.…”

“…For the rigid, smooth surface, an acrylic sheet was simply used. For the compliant surfaces, the silicone rubber was cast onto the appropriate surface to acquire roughness, degassed, and allowed to cure, as in [25]. All epoxy and silicone surfaces were then adhered to a mounting plate to secure it in the custom water tank.…”

“…Once the seal breaks, the pressure differential between the suction chamber and the external environment is lost [4,15]. Therefore there is a tradeoff-having sufficient compliance in the cup wall for increased ability to conform to the surface and maintain a seal, though not too much compliance which will limit the cup's ability to resist deformation and slipping to failure [21,25,29]. In terms of shape, previous work by Palecek et al [21] did test an oval-shaped design under normal loading conditions.…”

“…Palacek, et al embedded 3D-printed pelvic girdles from gobies within silicone cups to test performance under normal pull conditions [21]. Huie, et al tested stiff suction cups with soft rims on various compliant surfaces to evaluate sealing on these substrates [25]. Each study produced relevant models that tested particular aspects of adhesive disc performance, validating the ability to test biologicallyrelevant designs through the use of engineering-based methods.…”

A self-loading suction cup driven by a resonant dielectric elastomer actuator

“…To achieve the reliable performance of passive suction cups, ensuring effective sealing is crucial for generating a pressure differential between the inside and outside of the suction cup. Numerous novel bio-inspired suction cups have been proposed to enhance the sealing performance, particularly on rough substrates [20][21][22][23][24][25][26][27][28]. For instance, inspired by the suction disc of northern clingfish, Sandoval et al designed an artificial suction disc that is capable of adhering to rough surfaces and nonplanar objects [20].…”