(542e) Biomimetic Microhooks for Directional Adhesion

Plants (for e.g., Dolichandra unguis-cati and Galium aparine) show directional attachment and detachment to various surfaces because of mechanical gripping of microhook structures. A bio-inspired artificial version of such microhook structures can potentially be used as a directional, reversible, and reusable dry adhesive to attach to soft or fibrous substrates such as skin or textiles. Researchers have suggested many different methods for fabricating 3D structures on surfaces. Some of these techniques are expensive, time consuming, or need precise alignment steps (such as laser-based technique). In this study, using novel unconventional microfabrication techniques including tilted photolithography on a rotary stage and shear molding, a polymer mold containing the inverse replica of microhook structures is fabricated. The resulting mold is then used to create the microhook structures with Polyurethane. The proposed technique is feasible, easy, cost-effective, can be applied to a wide range of materials and can be scaled-up. Various sizes of microhooks (approximately 100-300 μm in height, 50-100 μm in base diameter, 300-500 μm in spacing) with sharp tips (tip diameter of less than 10 μm) are fabricated using this technique. The friction forces of the fabricated surfaces are then measured by a nanotribometer. Similar to the behavior of the microhook structures in natural plants, depending on the direction of the applied shear force, the biomimetic surface show strong attachment in one direction but easy detachment from surfaces in the opposite direction over multiple attachment/detachment cycles. Tribological characterization of the microhook structures show a gripping force 2.5 times greater than the sliding force. The fabricated microhook structures also provide an adhesion force of 0.006 N/mm² to artificial skin. This biomimetic approach can potentially be used to attach wearable devices and patches to the skin in biomedical applications, with good control over the size and material.

The figure shows the schematic of the proposed fabrication technique.