Wet versus dry adhesion of biomimetic mushroom-shaped microstructures

Currently, biomimetic geometry-controlled adhesives are based mostly on dry adhesion, whereas the majority of adhesive systems in biology involve fluids. Here, we assess the influence of the presence of oil on a pull-off force measured in a flat-on-flat contact between a mushroom-shaped microstructured adhesive and chemically identical smooth and rough substrates. A microstructured surface has stronger adhesion compared to a smooth control on both smooth and rough substrates in both dry and oiled contacts. In the presence of oil, the microstructured surface has stronger adhesion on both smooth and rough substrates compared to the dry contact. We found that, after detachment from the substrate, a microstructured surface retains fluid more effectively compared to the smooth control. The study demonstrates that covering an adhesive microstructure with an oil film may expand its application range, showing that this method is potentially attractive for the creation of new biomimetic adhesives.