A microfabricated gecko-inspired controllable and reusable dry adhesive

Abstract

Geckos utilize a robust reversible adhesive to repeatedly attach and detach from a variety of vertical and inverted surfaces, using structurally anisotropic micro- and nano-scale fibrillar structures. These fibers, when suitably articulated, are able to control the real area of contact and thereby generate high-to-low van der Waals forces. Key characteristics of the natural system include highly anisotropic adhesion and shear forces for controllable attachment, a high adhesion to initial preload force ratio (μ′) of 8–16, lack of inter-fiber self-adhesion, and operation over more than 30 000 cycles without loss of adhesion performance. A highly reusable synthetic adhesive has been developed using tilted polydimethylsiloxane (PDMS) half-cylinder micron-scale fibers, retaining up to 77% of the initial value over 10 000 repeated test cycles against a flat glass puck. In comparison with other gecko-inspired adhesives tested over 10 000 cycles or more thus far, this paper reports the highest value of μ′, along with a large shear force of ∼78 kPa, approaching the 88–226 kPa range of gecko toes. The anisotropic adhesion forces are close to theoretical estimates from the Kendall peel model, quantitatively showing how lateral shearing articulation in a manner similar to the gecko may be used to obtain adhesion anisotropy with synthetic fibers using a combination of tilt angle and anisotropic fiber geometry.

Switchable Adhesives for Multifunctional Interfaces

“…Often breaking the symmetry of a material or interfacial property enables much greater contrast in the two different failure mechanisms. A prominent approach in this area is to create angled microstructures including angled pillars, [83,117,[129][130][131][132][133][134][135][136][137] angled "flap" features, [83,[138][139][140][141][142][143][144] and hierarchical structures. [145][146][147][148][149][150] The directional microstructure provides strong adhesion in one direction while the opposite direction is used for release.…”

Benefit of Backing‐Layer Compliance in Fibrillar Adhesive Patches—Resistance to Peel Propagation in the Presence of Interfacial Misalignment

“…Since developing an understanding of the underlying principles of fibrillar adhesive systems in nature, careful attention has been paid to the design and fabrication of synthetic fibrils for both strength and reversibility . Efforts addressing the former have primarily focused on controlling the fibril‐substrate interfacial stress distribution through modification of the tip geometry.…”

Funnel‐Shaped Microstructures for Strong Reversible Adhesion

“…[1][2][3][4] The improved understanding has triggered the desire to mimic the natural principles by creating synthetic, reusable polymer adhesives that show high potential for emerging applications. [5][6][7][8][9][10][11][12] The key is an optimized surface pattern tailored to the application that can be manufactured by techniques such as lithography, nanoimprint, or self-organization. [7,[13][14][15][16] Patterned surfaces can exhibit better adhesion compared to nonpatterned counterparts, e.g., due to a higher compliance and, therefore, reduced elastic strain energy penalties and a higher conformability to various substrate topographies; these benefits have been termed the "contact splitting" effect.…”