Gecko-Inspired Biomimetic Surfaces with Annular Wedge Structures Fabricated by Ultraprecision Machining and Replica Molding

Abstract

The current research on gecko-inspired dry adhesives is focused on micropillar arrays with different terminal shapes, such as flat, spherical, mushroom, and spatula tips. The corresponding processing methods are mostly chemical methods, including lithography, etching, and deposition, which not only are complex, expensive, and environmentally unfriendly, but also cannot completely ensure microstructural integrity or performance stability. The present study demonstrates a high-precision, high-efficiency, and green method for the fabrication of a gecko-inspired surface, which can promote its application in dexterous robot hands and mechanical grippers. Based on the bendable lamellar structures of the gecko, annular wedge adhesive surfaces that stick to the finger surfaces of dexterous robot hands to improve their load capacity are proposed and fabricated via a suitable combined processing method of ultraprecision machining and replica molding. The greater the width, the higher the replication integrity, and when the minimum width is 20 μm, the replication error is less than 5.5% due to the superior processing performance of the nickel–phosphorus (Ni–P) plating of the master mold. The fabricated annular wedge structures with an optimized width of 20 μm not only exhibit a strong friction force of up to 35.48 mN under a preload of 20 mN in the GCr15/poly(dimethylsiloxane) (PDMS) friction pair but also demonstrate an obviously improved anisotropic friction characteristic of up to λ = 1.36, as the molecular force exhibits a stronger increase as compared to the decrease of the mechanical force of the structure with a small width.

Gecko-Inspired Controllable Adhesive: Structure, Fabrication, and Application

“…However, the metal molds were more durable than the wax molds, did not require the molds to be sprayed with a release agent, and were easy to clean. Since aluminum is prone to thermal deformation during ultraprecision cutting, which affects the machining accuracy of the wedge structure, Zhou et al plated Ni-P on the surface of tungsten carbide and used it as a mold to fabricate an annular wedge structure (as shown in Figure 7c) with an anisotropy ratio of each of the shear adhesion forces of 1.36 [68]. The several above-mentioned controllable adhesives with wedge structures are only a collection of arrays of wedge structures with a single size feature, and some researchers have mentioned that there are also shorter bristles located closer to the thin plate and longer bristles located farther away from the thin plate in the gecko's adhesion system [69,70].…”

“…However, the metal molds were more durable than the wax molds, did not require the molds to be sprayed with a release agent, and were easy to clean. Since aluminum is prone to thermal deformation during ultraprecision cutting, which affects the machining accuracy of the wedge structure, Zhou et al plated Ni-P on the surface of tungsten carbide and used it as a mold to fabricate an annular wedge structure (as shown in Figure 7 c) with an anisotropy ratio of each of the shear adhesion forces of 1.36 [ 68 ].…”

Recent Progress on the Use of Stimulus-Responsive Materials for Dry Adhesive Applications

“…PDMS is then cast on the mold to obtain microwedge shaped structures. Zhou et al 44 used ultraprecision machining method to produce gecko inspired adhesive. They fabricated wedge shaped structures on tungsten carbide material by using a diamond tool.…”

Preparation and Hydrophobicity of Bionic Structures Based on Composite Infiltration Model

“…In the experiment, ultra-precision machine tools were used to process different sizes of microstructures on Ni-P coating molds, as shown in Figure 10. By observing the inclined surface with microstructures of different widths under laser scanning confocal microscope (LEXT OLS5000, Olympus, Japan), the average surface roughness was 20 nm, which has high processing quality and facilitates the flow of PDMS during injection and the separation of PDMS during demolding [19]. removed from the mold from the edge to the middle.…”