Microstructures that mimic the very grippy surface of the aptly named clingfish, could lead to a new type of suction cup that might not only save your suckered shower caddy from flopping off the wall but could be used in more exacting engineering roles.
On the rocky shores of Washington State, the northern clingfish (Gobiesox maeandricus) maneuvers over rocks to prey on limpets and other invertebrates, but hunting on those rocks means keeping a tight grip of the rock itself in heavy seas while it preys on the limpet and prizes them off. Evolution's answer was to modify pelvic and pectoral fins to give the clingfish a big sucker on its belly to allow it to get a grip. Petra Ditsche and Adam Summers of the University of Washington and colleagues have taken inspiration from the clingfish to create prototype suction cups that are capable of adhering to rough, wet surfaces.
Importantly, unlike a typical manufactured plastic or rubber suction cup, the clingfish sucker is not completely smooth. Indeed, the edges are irregular and resemble the surface of a tongue. On closer inspection, you can see that the individual papillae, which cover the disk margin, are themselves not smooth and branch out into tiny, hair-like, projections, which are again divided into tiny filaments on their tips, forming a hierarchical structure. It is the resulting fractal-like surface that allows sealing to irregular surfaces and maximizes the frictional forces between clingfish and rough rock at the same time. In the ocean, where clingfish are endlessly buffeted by crashing waves, their hierarchical suction disc allows them to remain in place even when they experience forces equivalent to 150-250 times their body weight.
Ditsche and her colleagues are attempting to mimic biology with their approach, which requires a clear understanding of the underlying mechanisms being exploited by nature so that technology can use a simplified analog of the biology. Initial tests with their biomimetic models of the clingfish suction reveal it to have a grip equivalent to 70000 Pascals of pressure even on a rough surface.
Applications of such suction might be in grabbing hold of tissue during surgery without the risk of cutting or puncturing the tissue as is always a possibility with metal clamps and other surgical instruments. The same technology might be used to design new equipment to allow a climber to scale a wet surface, for instance, or a research to clamber more safely over slimy rocks on the seashore.
"We are developing our suction cup prototype for specific applications," Ditsche told Materials Today. "One possible application is their application for whale tagging." A more permanent sucker tag would be much less invasive than the usual metal barb fired into the dorsal fin of the animal. The suction cups might also have use in surgery. "They can strongly attach to wet, slimy surfaces of different surface texture," adds Ditsche. "Like clingfish our suction cups attach reversibly. They do not only attach strongly, but can be easily detached, which should be important."
David Bradley blogs at Sciencebase Science Blog and tweets @sciencebase, he is author of the popular science book "Deceived Wisdom".