Sticky bio-inspired micropillars: finding the best shape.

Very recently, both experimental and theoretical investigations have shown that micro-structured surfaces covered with mushroom shaped micropillars present strongly enhanced adhesive properties if compared to standard flat surfaces made of the same material. However, different geometries lead to different adhesive performance, and finding the optimal solution has become of utmost importance. In this paper we show on which physical ground the optimal mushroom pillar shape should be sought, and provide a relatively simple methodology to achieve this result. Our calculations demonstrate that the adhesive performance of the pillar strongly depends on the geometry of the terminal plate. We find that the best performance is achieved when the ratio s/Ri between the plate thickness and the pillar internal radius is close to 0.3, and the ratio Re/Ri larger than 2, where Re is the external radius of the plate