Rectangle-capped and tilted micropillar array for enhanced anisotropic anti-shearing in biomimetic adhesion

Abstract

Dry adhesion observed in the feet of various small creatures has attracted considerable attention owing to the unique advantages such as self-cleaning, adaptability to rough surfaces along with repeatable and reversible adhesiveness. Among these advantages, for practical applications, proper detachability is critical for dry adhesives with artificial microstructures. In this study, we present a microstructured array consisting of both asymmetric rectangle-capped tip and tilted shafts, which produce an orthogonal anisotropy of the shearing strength along the long and short dimensions of the tip, with a maximum anti-shearing in the two directions along the longer dimension. Meanwhile, the tilt feature can enhance anisotropic shearing adhesion by increasing shearing strength in the forward shearing direction and decreasing strength in the reverse shearing direction along the short dimension of the tip, leading to a minimum antishearing in only one of the two directions along the shorter dimension of the rectangular tip. Such a microstructured adhesive with only one weak shearing direction, leading to well-controlled attachment and detachment of the adhesive, is created in our experiment by conventional double-sided exposure of a photoresist followed by a moulding process.

Spatially variant microstructured adhesive with one-way friction

“…The uniform microstructure performs nearly symmetrically, while the uniform microstructure with added roughness shows a slightly higher ratio of 3.1 (95% CI: 2.0-6.0). This is in line with typical friction ratios reported in the literature for uniform microstructured adhesive materials [4][5][6][7][8]12,24,27], with asymmetric friction ratios below 10 : 1. By contrast, the spatially variant microstructure has a friction ratio of 100 (95% CI: 96 -110), an improvement of 100Â over the uniform microstructure and an order of magnitude better than previously published soft-polymer friction ratios.…”

Process, Design and Materials for Unidirectionally Tilted Polymeric Micro/Nanohairs and Their Adhesion Characteristics

“…In general, the molds with micro/nano hole arrays are prepared by photolithography, where tilted exposures are required under a patterned shadow mask to create an angled structure. Here, the desired angle can be calculated by Snell’s law and by reactive ion etching (RIE), in which the holder should be tilted to the certain angle followed by subsequent etching [ 38 , 39 , 40 ].…”

Forcing the issue: testing gecko-inspired adhesives

“…While many studies use a very stiff force sensor (e.g. [32], [33]), others use single or dual-axis cantilevers with comparatively low stiffness in comparison to a positioning stage [1], [27], [38], [41], [47], [48], [53]. While not all publications specify the cantilever stiffness, those that do often employ cantilevers that are stiffer than the adhesive itself, so that adhesive behavior remains dependent on the applied displacement trajectory.…”

“…Testing against flat surfaces makes sample alignment more challenging but makes extraction of a limit curve in terms of pressure relatively easy. Previous approaches have included passive compliant approaches [35], [40], [45], [46], and precision rotation stages to perform sample alignment [8], [9], [41], [48], [51], [56]. The resulting limit curve represents an upper bound limit on adhesive performance, and is a starting point for analyzing more complex loading geometries [55], [57].…”