Proposal of a three-stage hair structure imitating the sole of gecko foot and its fabrication by UV nanoimprinting

In order to apply UV nanoimprinting method to fabricating fine hairs, which imitates those on sole of a gecko's foot, the shape of hair was designed as straight, making it easy to be released from the mold. The length of hairs which branch off at the tip was designed to be short, preventing them from aggregating. Under these restrictions, considering the asperities due to roughness of objective surface, a three-stage hair structure comprising a root hair, intermediate hairs, and tip hairs was proposed instead of the two-stage hair structure comprising a seta and spatulae of the gecko, so that the tip hairs can easily come into contact with the surface of asperities. A high-precision 3D stereo-lithography was used to fabricate a master consisting of a base and the hairs. A polydimethylsiloxane (PDMS) mold was obtained by transferring this master to PDMS. By performing UV nanoimprinting using this mold, we succeeded in fabricating fine hairs made of photo-curable resin. This method has the advantage that the three-stage hairs can be fabricated by single nanoimprint due to 3D lithography capable of realizing the master of complicated structure with high aspect ratio, i.e., it is not necessary to nanoimprint twice on the root and the tip separately. It was confirmed that the fine hair fabricated by UV nanoimprinting showed the adhesive force.