Nature‐Inspired Directional Microneedle Structures for Reversible Gripping on Skin and Fibrous Materials

Abstract

Plants such as Galium aparine show directional gripping to various surfaces because of their microscale hook structures. A bio‐inspired artificial version of microhooks holds potential as a bidirectional, reversible, and reusable dry adhesive for soft, wet, or fibrous substrates such as skin or textiles. However, current methods for fabricating 3D structures are often costly, time‐consuming, or require precise alignment steps. Herein, a facile, cost‐effective, scalable, and unconventional microfabrication technique is proposed using tilted photolithography on a rotary stage and shear molding to fabricate a soft polydimethylsiloxane polymer mold containing the inverse replica of directional microneedle structures. To demonstrate the proof‐of‐concept, polyurethane is then added to the mold to obtain directional microneedles, referred to as microhooks. Friction force measurements using a nanotribometer show anisotropic performance (strong attachment in one direction and easy detachment in the opposite direction over multiple cycles) similar to the natural microhooks. Tribological characterization of the microhooks shows a gripping force 2.25 times greater than the sliding force. The fabricated microhook structures also provide an adhesion force of ≈0.62 N cm−2 to artificial skin. This biomimetic approach promises precise adhesion control and material versatility for attaching wearable devices and patches to the skin in biomedical applications.