Inspired by the polygonal arrays on the toe pads of tree frogs and newts, micro hexagonal pillars were fabricated on a cast polyurethane elastomer (CPUE) surface so that a network of interconnected channels was formed. To investigate the effect of channel sizes, adhesion experiments were carried out with a flat polymethyl methacrylate (PMMA) probe and the patterned surface of CPUE samples under wet conditions. It was found that single factors alone, such as channel width ( W ), length ( L ), and height ( H ) have a slight effect on wet adhesion force. Comparatively, the values of width-to-length ( W / L ), height-to-length ( H / L ), and height-to-width ( H / W ) determine the wet adhesion force significantly. Actually, the wet adhesion force is reduced with increasing W / L values. Furthermore, optimal ranges of H / L and H / W values clearly enhance the wet adhesion force, even considering the reduction with the increasing W / L values.

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