Simple and Reliable Fabrication of Bioinspired Mushroom-Shaped Micropillars with Precisely Controlled Tip Geometries

We present a simple yet scalable method with detailed process protocols for fabricating dry adhesives with mushroom-shaped micropillars of controlled tip geometries. The method involves using photo-lithography with a bilayer stack combining SU-8 and lift-off resist, and subsequent replica molding process. This approach utilizes widely used and commercially available materials and can thus be used to generate mushroom-shaped micropillars with precisely controlled tip diameters and thicknesses in a simple, reproducible, and cost-effective manner. The fabricated mushroom-shaped micropillar arrays exhibited highly different tendencies in adhesion strength and repeatability depending on tip geometries, such as tip diameter and thickness, thereby demonstrating the importance of precise tunability of tip geometry of micropillars. The fabricated dry adhesives with optimized tip geometries not only exhibited strong pull-off strength of up to ∼34.8 N cm^-2 on the Si surface but also showed high durability. By contrast, dry adhesives with nonoptimized tips displayed low pull-off strength of ∼3.6 N cm^-2 and poor durability.