Hexagonal Microstructure Bioinspired by the Toe Pad of a Tree Frog For Increasing Adhesive Force in Shear Direction

Tree frogs are able to grasp and climb on various materials such as glass and plastic by using their pads on toes. Bioinspired by the toe pad of a tree frog, the microstructure consisting of hexagonal channels was fabricated on a PDMS (polydimethylsiloxane) pad. It adhered to a surface even if it is vertical, for example, which is useful for robotic gripper. The mechanism of that the adhesive force increases thanks to the microstructure was experimentally investigated. It was proven that the flexibility due to microchannels is effective for increasing the adhesive force, no matter whether its microscopic adhesion principle may be Van der Waals force, mechanical interlock, or hydrophobic/hydrophilic effect.