Vertical Anisotropic Microfibers for a Gecko-Inspired Adhesive

Abstract

Geckos are able to adhere strongly and release easily from surfaces because the structurally anisotropic fibers on their toes naturally exhibit force anisotropy based on the direction of articulation. Here, semicircular fibers, with varying amounts of contact area on the two faces, are investigated to ascertain whether fiber shape can be used to gain anisotropy in shear and shear adhesion forces. Testing of 10-μm-diameter polydimethylsiloxane (PDMS) fibers against a 4-mm-diameter flat glass puck show that shear and shear adhesion forces were two to five times greater when in-plane movement caused the flat face, rather than the curved face, of the fiber to come in contact with the glass puck. The directional adhesion and shear force anisotropy results are close to theoretical approximations using the Kendall peel model and clearly demonstrate how fiber shape may be used to influence the properties of the adhesive. This result has broad applicability, and by combining the results shown here with other current vertical and angled designs, synthetic adhesives can be further improved to behave more like their natural counterparts.

Bioinspired dry adhesive: Poly(dimethylsiloxane) grafted with poly(2-ethylhexyl acrylate) brushes

“…The adhesion was found to increase with increasing the pre-indentation depth (Fig. 4B), which is in agreement with the previously published literature [7,38]. The adhesion was also found to be dependent on the speed of the tip retraction, with the adhesion reaching a maximum value around retraction rate of 35 nm/s (Fig.…”

“…Over the last decade, a variety of approaches have been used in attempts to fabricate fibrillar Gecko-like adhesives based on synthetic materials [1,6]. Among other materials, PDMS has shown great potential due to its low elastic modulus, availability and ability to micro mould [7][8][9][10][11]. Many micro-and nano-sized fibrillar http://dx.doi.org/10.1016/j.eurpolymj.2015.05.016 0014-3057/Ó 2015 Elsevier Ltd. All rights reserved.…”

Optimal articulation strategy for a microfabricated gecko-inspired controllable adhesive

“…The synthetic adhesive, shown in Figure 1, is created using a combination of vertical etching and molding techniques previously described in [7]. Using a silicon wafer to create a negative image of the fibers, the lateral geometry is first defined in a layer of photoresist.…”

Articulation of angled semicircular microfibers for a gecko-inspired anisotropic adhesive

“…Adhesive testing was performed using a previously MEMS 2013, Taipei, Taiwan, January 20 -24, 2013 978-1-4673-5655-8/13/$31.00 ©2013 IEEE reported flat-on-flat testing geometry with a custom-built microtribometer in which careful relative alignment of the two surfaces before testing is possible with manual goniometer and tilt stages [2]. After alignment, a 4-mm diameter flat glass puck is brought into contact (test contact area = 12.6 mm 2 ) with the adhesive at a vertical speed of 1 µm/s (puck motion in the -z direction as defined in Figure 1) until a specified preload is reached.…”

“…Although a variety of vertical [2], angled [3][4], or hierarchical [5][6] fibrillar materials have been developed to create gecko-inspired adhesives, a combination of tilt angle and anisotropic microfiber shape has not been investigated for its effect on the anisotropy of adhesion and friction forces. Durability is also a very important concern for synthetic adhesives in most practical applications.…”